Towards Eco-Friendly Construction: A Comprehensive Review of Agricultural and Industrial Waste in Sustainable Masonry Production

Abstract

The growing focus on environmental sustainability in construction has driven advancements in the design and production of masonry materials, including bricks and concrete blocks. A major development is the incorporation of agricultural and industrial waste, such as fly ash, rice straw ash, bagasse ash, and other by-products, to reduce dependence on non-renewable resources and lower the carbon footprint of traditional manufacturing processes. This systematic review examines the potential of waste materials in masonry unit production by analysing Scopus-indexed studies published between 2015 and 2025. After screening, 30 studies were selected, covering fired bricks, unfired bricks, and concrete blocks, with emphasis on physical, mechanical, thermal, and durability properties. The findings show that industrial wastes typically improve mechanical strength through pozzolanic reactions, while agricultural wastes contribute to lower density and improved thermal insulation. However, performance depends on waste type, replacement level, and production conditions. Optimal incorporation levels are generally below 20%. Despite promising results, challenges remain, including the absence of standardised testing methods, limited durability evaluations, and insufficient evidence for large-scale industrial adoption. This review highlights current research trends and future opportunities for integrating waste materials into sustainable construction products.

1. Introduction

Recent decades have witnessed a significant increase in the adoption of green concepts and environmental sustainability by many organisations, driven by several factors, including limited natural resources, environmental degradation, and the worsening phenomenon of global warming [1]. The construction sector is one of the most prominent contributors to carbon emissions, given its intensive reliance on energy and resources, as well as the carbon emissions generated throughout its entire life cycle [2]. Current estimates indicate that approximately 34–37% of energy-related carbon emissions are attributable to this sector and its associated construction activities [3,4]. Carbon dioxide is considered the most significant greenhouse gas in terms of its negative impact on the environment, with emissions from the use of non-renewable energy sources expected to increase by about 50% by 2050 [1,5]. Therefore, achieving carbon neutrality through effective policies in the construction sector has become an urgent necessity [6]. In this context, the goals of achieving carbon neutrality by 2050, limiting the rise in the average temperature of the Earth to below 1.5 °C, and committing to reducing carbon dioxide emissions by 45% in 2030 are among the most prominent goals emphasised to meet climate change mitigation targets [1,7].

When assessing a material’s suitability for use as a building material, its engineering properties are a fundamental consideration. These properties influence the material’s quality and durability and determine its potential applications in construction projects. Building materials are typically evaluated in terms of several categories, such as their mechanical, thermal, and physical properties. Physical properties refer to characteristics that can be observed, measured, or determined without altering the material’s identity or composition. In contrast, mechanical properties describe a material’s ability to withstand applied stresses or deformations. The capacity of a material to conduct and transfer heat is referred to as its thermal qualities, which are another important category of construction material properties [8,9]. The mechanical and thermal properties of building materials are particularly important in the design of sustainable structures. A building’s lifespan depends largely on the mechanical properties of the materials used in its construction, while the thermal properties of these materials directly impact energy efficiency, given their crucial role in providing thermal insulation or thermal inertia for the building [9,10].

Masonry construction has been utilised for centuries. The term “masonry” encompasses a wide range of materials, including natural stone and manufactured products such as clay bricks, concrete blocks, cast stone, clay construction tiles, terracotta, adobe, sand-lime units, and glass blocks. Bricks are a fundamental building material due to their high durability and compressive strength. They are widely used in the construction of buildings, bridges, tunnels, floors, walls, arches, chimneys, and fireplaces [11,12]. Brickmaking dates to around 7000 BCE, when bricks were produced as sun-dried clay blocks. Throughout history, bricks have been used in construction in two forms: unfired (sun-dried) and fired. In modern times, bricks are among the most sought-after and widely used building materials in various civil engineering projects. Traditional bricks are produced from clay by firing it in high-temperature kilns [12,13]. Global fired clay brick production is estimated at approximately 1.9–4.1 billion tonnes annually, equivalent to roughly 1.2–1.6 trillion bricks per year [14,15]. However, their production consumes significant amounts of natural resources and results in high carbon dioxide emissions [16]. Brick kilns contribute between 70 and 282 g of carbon dioxide emissions and consume between 0.54 and 3.14 megajoules of specific energy per kilogram of brick produced, depending on the type of kiln and the fuel used [17]. Furthermore, approximately 340 billion tons of clay are used annually [18]. Consequently, there is a clear need for alternatives to traditional fired clay bricks to promote sustainable and environmentally friendly building practices. Unfired earth bricks, also known as sun-dried or raw earth bricks, are structural elements produced by mixing soil (clay) with various additives that enhance its properties. After preparation, the mixture is placed in special moulds and left to dry in the sun to minimise shrinkage and increase durability [19,20]. Using unfired earth as a building material offers a sustainable option that helps reduce the environmental impact of fired bricks [17,21,22]. The most common construction methods include adobe bricks, rammed earth, and compressed earth blocks (CEB). Made from sun-dried clay, adobe bricks are inexpensive and suitable for arid climates, but they are less durable and water-resistant. Rammed earth construction involves compacting soil in layers to form cohesive, layered walls, making it versatile and highly durable, but it requires specialised equipment. Compacted earth blocks (CEBs) are a modern version of adobe bricks, where moist soil is statically compacted using manual or hydraulic presses, resulting in a density between 1700 and 2300 kg/m³ [23,24,25]. Cement is the most used stabilising agent to stabilise blocks due to its role in improving strength and durability under various conditions. Other stabilising agents, such as lime, have also shown effective results [26,27]. However, studies have shown that increasing the cement content leads to higher strength in these blocks, but using more than 10% cement by weight of the soil becomes economically unfeasible [17]. On the other hand, concrete or cement building blocks are used as load-bearing and non-load-bearing structural elements within building envelopes and interior partition walls. These blocks are manufactured from a mixture of cement and fine and coarse aggregates. Of the main types of concrete building blocks available on the market, hollow and solid concrete blocks are the most common options [28,29]. However, block production requires substantial quantities of resources, including aggregates and cement. Cement is a fundamental material in the construction sector, experiencing unprecedented demand due to the massive expansion of development and construction activities worldwide [30,31]. This, in turn, poses major environmental challenges, including ecosystem degradation, riverbank erosion, and depletion of sand and gravel reserves in coastal areas, highlighting the urgent need to develop more environmentally sustainable alternatives [32,33]. Conversely, millions of tons of agricultural and industrial waste are generated annually, and these quantities are expected to increase in the coming years due to population growth, expanding agricultural production, and industrial development [34,35,36]. Rapid urbanisation, limited landfill capacity, and improper disposal methods are making landfilling operations increasingly complex and challenging. The accumulation of agricultural and industrial waste leads to numerous environmental problems, including pollution, an increased need for landfill space, and associated health issues [37,38,39]. The situation is exacerbated by rising pollution levels resulting from inefficient waste disposal practices. Open dumping has become a pervasive problem, adversely impacting the aesthetic integrity of landscapes and posing public health risks [40,41]. Given the finite nature of many construction resources, it is vital to balance resource consumption with natural replenishment rates. With the global trend toward sustainability, efforts are growing to promote waste recycling and reduce the carbon footprint of the construction sector. Waste materials are often available in large quantities and at low cost, yet they can acquire significant economic value when processed and reused as recyclable resources. Integrating waste into recycling frameworks, such as using it as a partial replacement for natural aggregates or cement, not only contributes to environmental protection but also enhances the economic viability of construction processes [40,42,43]. The utilisation of various types of waste in the manufacture of bricks and building blocks is a promising option for reducing reliance on traditional building materials and promoting sustainability in the construction sector [44,45]. Consequently, efforts have been directed toward integrating waste into the production of bricks and building blocks [46].

Significance of Research

Although numerous review studies have examined the utilisation of waste materials in fired bricks, unfired bricks, and concrete masonry blocks [47,48,49,50,51,52], important gaps remain in the literature. To the best of the authors’ knowledge, few studies have provided a truly integrated assessment of masonry units produced from waste materials across different systems. Most existing reviews are system-specific, focusing independently on fired clay bricks, unfired earth blocks, or concrete masonry units, with limited attempts to synthesise and compare their behaviour across different masonry products. Consequently, similarities and differences in the performance of agricultural and industrial wastes, as well as the influence of manufacturing methods and waste characteristics, remain insufficiently understood. Therefore, this review aims to provide a comparative and comprehensive assessment of agricultural and industrial waste utilisation in fired clay bricks, unfired clay bricks, and concrete masonry blocks, with particular emphasis on their influence on key physical, mechanical, and thermal properties. It systematically synthesises existing research to identify performance trends while highlighting key research gaps and future directions for advancing waste valorisation in sustainable masonry construction. By incorporating recent developments in the field, this work provides researchers and practitioners with an integrated understanding of current trends, debates, and advancements in sustainable masonry materials. By doing this, this review provides a broader understanding of waste valorisation strategies for sustainable masonry construction.

2. Methods

2.1. Review Methodology

The systematic literature review is recognised as a significant type of literature review, offering researchers a comprehensive and transparent overview [53,54,55]. This study adheres to the methodology as depicted in Figure 1. The review followed the general principles of the Systematic Reviews methodology to improve transparency, reproducibility, and consistency throughout the identification, screening, eligibility assessment, and inclusion stages. The process of conducting the review encompasses several phases as follows:

1.

Definition of database and keywords: The focus was on articles related to the use of agricultural or industrial waste in fired and unfired brick and concrete block production. The Scopus database was selected as the primary source for literature retrieval due to its comprehensive and well-structured nature, broad multidisciplinary coverage, and comprehensive indexing of peer-reviewed publications and citation information, establishing it as a robust resource for intensive scientific inquiry [56,57]. Although databases such as Web of Science may contain additional relevant studies, Scopus was selected as the primary database to ensure a consistent and reproducible search strategy within the scope of this review. The research was conducted from December 2024 to May 2025, and included studies published from 2015 to 2025. The search was performed using the title, abstract, and keyword fields in Scopus. The following search terms were combined using Boolean operators:

TITLE-ABS-KEY

((“fired brick*” OR “unfired brick*” OR “unburnt brick*” OR “concrete block*”)

AND

(“waste” OR “agricultural waste*” OR “industrial waste*”)

This has resulted in more than 600 articles. Figure 2a shows the growth in publications regarding brick/block production with waste materials. Figure 2b indicates that most research has been conducted in India, with China and Malaysia coming in second and third, followed by Brazil and Egypt. Figure 2c shows the share of documents by their type, with articles accounting for about two-thirds of the databases.

2.

Redefining the research: The selection criteria were established before the screening process to ensure consistency and minimise subjective selection. Studies were included when they met the following conditions:

• Published between 2015 and 2025;
• Available in English;
• Published as research articles, conference papers, or books;

After reviewing the titles of the documents, studies containing the keywords “paving block”, “tiles”, and “geopolymer” were excluded, as they were considered beyond the scope of this review. The exclusion of paving blocks and geopolymer materials was based on the objective of maintaining a consistent comparison between conventional walling masonry units (bricks and blocks). Although these materials represent important sustainable construction applications, their manufacturing processes, binder systems, and performance requirements differ significantly from traditional masonry products and were therefore considered beyond the scope of this review. The searches were constrained to articles that contained at least one of the keywords in their title, abstract, or indexed keywords. This resulted in more than 250 documents.

3.

Screening: Articles relevant to the defined theme were identified through a stepwise screening process. Titles were first reviewed to remove clearly unrelated studies, followed by abstract screening to exclude those not closely aligned with the research focus. This yielded over 150 articles for full-text assessment.

4.

Subsequently, the full texts were assessed, allowing for the removal of irrelevant studies and resulting in the final set of articles included in the analysis. Each paper was carefully evaluated to ensure its relevance to the topic. Studies were included when they met the following conditions:

• Investigated fired bricks, unfired bricks, or concrete blocks;
• Incorporated agricultural or industrial waste as a constituent material or partial replacement;
• Reported experimental evaluation of one or more relevant performance parameters, including density, water absorption, porosity, compressive strength, thermal conductivity, shrinkage, durability, environmental impact, or economic performance.

Studies were excluded when they:

• Investigated waste characterisation without producing masonry units;
• Did not report measurable performance results;
• Lacked sufficient information regarding material composition, waste proportion, or testing conditions.
• Were review articles.

This has resulted in 47 studies. To maintain consistency across studies, inclusion was limited to those investigating masonry units incorporating up to 30% agricultural or industrial waste. Most studies reported waste incorporation levels below 20–30%, and where higher substitution levels were explored, the optimal performance was still typically observed at or below 30% [58,59,60,61,62,63]. Recent review studies report a clear distinction between laboratory-scale experimentation and industrial-scale feasibility [47,48]. Higher substitution levels are often material- and process-dependent. They may require additional validation before practical implementation. The waste incorporation limit of 30% was selected to maintain comparability among studies and to reflect replacement levels commonly investigated for practical masonry production. Therefore, studies exceeding 30% replacement were not excluded due to poor performance but were considered beyond the comparative scope of this review, which focuses on waste incorporation levels with potential relevance to conventional masonry manufacturing. Following eligibility assessment, the final dataset consisted of 30 studies that provided sufficient quantitative performance data and methodological details for comparative analysis among different masonry products. The included studies were distributed among fired bricks, unfired bricks, and concrete blocks to provide balanced coverage of the three masonry categories. This distribution was intended to facilitate comparison between masonry types and was not based on predetermined performance expectations. The included studies covered a broad range of agricultural and industrial waste without restriction to specific types, ensuring diverse representation of materials and applications.

5.

Analysis: The extracted information included waste type, waste content, manufacturing method, curing or firing conditions, and reported physical, mechanical, thermal, durability, environmental, and economic properties. The data collected were organised using Microsoft Excel for Microsoft 365 (Version 2607, Univeristy of Liverpool) and analysed through comparative tables and graphical interpretation. The analysis focused on identifying common trends, material-specific effects, reported optimum incorporation ranges, advantages, limitations, and research gaps associated with the use of agricultural and industrial waste in sustainable masonry production. Due to the variation in waste characteristics, mixture compositions, manufacturing processes, and testing conditions among the reviewed studies, the analysis focused on identifying qualitative performance trends and underlying mechanisms rather than establishing direct quantitative relationships between waste content and material properties.

Figure 2. Bibliometric analysis of data retrieved from the Scopus database (https://www.scopus.com/pages/search/publications?searchId=55947ee9-ca37-4468-86c1-dae2697348ed [64]; Accessed on 15 May 2026); the figure was drawn using Python (v3.11.14) through Jupyter Notebook (v7.5.0; Anaconda).

Figure 2. Bibliometric analysis of data retrieved from the Scopus database (https://www.scopus.com/pages/search/publications?searchId=55947ee9-ca37-4468-86c1-dae2697348ed [64]; Accessed on 15 May 2026); the figure was drawn using Python (v3.11.14) through Jupyter Notebook (v7.5.0; Anaconda).

2.2. Production of Masonry Units

Table 1. Summary of the methods for manufacturing fired bricks by previous researchers.

Ref.	Type of Waste	Content of Waste (%)	Type of Soil	Content of Other Materials	Size of Brick (mm)	Mixing Method	Firing Temperature (°C)	Manufacturing Method	Tests (Standards)
[65]	Cigarette butts	(0, 2.5, 5, 7, 5, 10 wt.% of soil) and 1% wt.% of soil	Brown silty clayey Sand	Optimum moisture content	cube (100 × 100 × 100 mm), beam (225 × 110 × 75 mm), and brick (300 × 100 × 50 mm)	a Hobart mechanical mixer	Thermolyne furnace at 1050 °C	Mixes were mixed for 5- 15 min and compacted manually with predetermined masses for maximum density. The specimens were dried at 105 °C for 24 h, removed from moulds, and fired.	Compressive strength, Modulus of rupture, water absorption, and density (AS/NZS 4456.1:2003), thermal conductivity model, Leachate analyses, estimated total emissions, saving firing energy
[66]	Activated alumina sludge	(0–15% wt. Clay)	Clay	Water suitable to achieve the desired workability	230 × 110 × 70 mm	Manual	A kiln at approximately 900 °C	The materials were mixed with water for 15 min, moulded under pressure, sun-dried for 3 days, and then fired for 21 days.	Structural, non-structural Properties, acid resistance, leachate test.
[67]	Rice husk or wood ash	Each 10–30 wt.% clay	Clay (30 wt.% red, 30 wt.% yellow and 40 wt.% black clay)	(7–10 wt.% Moisture)	30 × 10 × 60 mm		Laboratory furnace at 900 Or 1000 °C	Water was added during the semi-dry compression moulding under 54.5 MPa of pressure. Samples were fired for 4 h, at a heating rate of 3 °C/min, then cooled to room temperature by natural convection inside the furnace.	Water absorption, Open porosity, Bulk density (ASTM C373), compressive strength (UNE-EN 772-1), Thermal conductivity, leachate test.
[68]	Olive mill waste	5%, 10% wt. Of soil	Clay	Sprayed water up to 15% wt.	Cylindrical pellets of 20 mm diameter	mechanical mixer	Electrical furnace at 850 °C, 950 °C, and 1050 °C	The mixture was compressed into cylindrical pellets and dried at 40 °C for 12 h and 110 °C for 24 h. It was then fired at 2.5 °C/min to 600 °C and heated at 10 °C/min for 2 h.	Apparent porosity, water absorption, bulk density (ASTM Standard C20), Compressive Strength (TS EN 771-1), Thermal Conductivity Analyser,
[69]	Rice husk ash	0%, 2%, 4%, 6%, 8% and 10%, wt. Of brick	Clay	Water (until proper mixing was Reached)	195 × 95 × 50 mm	handmade	Brick kiln (600 and 850 °C)	The clay and water were mixed, and then rice husk ash (RHA) was added with additional water. The bricks were dried at 35 °C with 60% humidity, fired for two days, and cooled for a week.	Atterberg limit (ASTM D4318), Sieve analysis (ASTM C136), X-ray fluorescence, water absorption and compressive strength (ASTM 67-07), Thermal performance, Acoustic performance
[70]	Waste fly ash	0–25% wt. Of clay	Clay	Plasticity Water (20.8–18.7%)	225 × 112 × 75 mm	General hand mixing and moulding technique	800 °C.	Freshly prepared wet bricks were air-dried for 4–5 days, then fired for three days in the kiln. After 20 days, the burnt clay bricks were removed from the kiln.	Mechanical properties, water absorption, and efflorescence (ASTM C67)
[71]	Spent shea waste	5, 10, 15 and 20 wt.% of the clay	Clay	13.5 wt.% of plasticity water	100 × 35 × 30 mm	thoroughly homogenised in a blender for 10 min	Electrical kiln at 900 °C to 1200 °C	The granulates were soaked for one hour, sun-dried for a week, fired at 2 °C per minute, and cooled by natural convection after two-hour soakings at each sintering temperature.	Densities, compressive strength (ASTM C67), apparent Porosity, and water absorption (ASTM C20), shrinkage
[72]	Paper mill sludge (DPMS)	Paper mill sludge (0–30% wt. Soil)	Alluvial soil	Water (0.22 wt. of soil, 0.60 wt. of waste)	75 × 50 × 33 mm	Lump-free mixing for 30 min	Electrically operated muffle furnace (900 °C, 950 °C and 1000 °C)	The sludge and soil were oven-dried at 100 ± 2 °C for 2 h, mixed with water, air-dried for 24 h, and then oven-dried for another 24 h. The briquettes were fired at 2 °C/min, 4 °C/min, and 5 °C/min for 2 h, then cooled to room temperature in the furnace.	Water absorption (IS:3495), the efflorescence of specimens (IS 3495), the apparent porosity (ASTM C20), compressive strength (IS3495), thermal conductivity (ASTM 5334), firing shrinkage (IS:12979)
[73]	Pomegranate peel waste	0%, 5%, 7.5%, 10%, and 15%	Clay	Water (20%)	50 × 50 × 50 mm	Manual	900 °C	The pastes were moulded, compressed to remove air bubbles, air-dried for 24 h, dried at 120 °C for 6 h, and fired for 4 h with a 10 °C/min heating rate.	Compressive strength (ISO 9652), water absorption and Apparent Porosity (ISO 5017), Thermal conductivity (ASTM D5334), and environmental impacts
[74]	Rice straw ash	0, 2, 4, 6, 8 and 10% wt. Clay	Clay	Water to the right consistency	229 × 114 × 76 mm with a frog of depth 10 mm		1000 °C	Rice straw ash and clay were mixed with water, kneaded for 24 h, moulded, air-dried for 48 h, kiln-fired for 3–4 days, and cooled for 10 days before extraction.	Compressive Strength test, water absorption test, shape, size, soundness, and hardness

,

Table 2. Summary of the methods for manufacturing unfired bricks by previous researchers.

Ref.	Type of Brick	Type of Waste	Content of Waste (%)	Type of Soil	Content of Other Materials	Size of Bricks (mm)	Mixing Method	Manufacturing Method	Tests (Standards)
[75]	Compressed stabilised earth blocks	Granulated blast furnace slag	(20% and 25%) wt. Soil	Lithomargic Clay and Lateritic soil	Cement (6–12%)/(2–8%), water (as required)	305 × 143 × 105 mm	Manual	Potable water was added to form a cohesive ball; the mix was sprayed and turned for uniform wetting, compacted in a mould using a compression machine, and all samples were cured for 28 days.	Effect of GBFS on properties of soil, compression testing, and Water absorption (Indian Standard)
[76]	Compressed soil blocks	Coconut Husk, bagasse and oil palm fruit	0.25, 0.5, 0.75 and 1 wt.% fibre, with lengths of 50 mm, 80 mm, and 38 mm for the fibres respectively	Clay soil (Red and Brown)	Soil (100%), water (as required)	290 × 140 × 100 mm	Manual	The soil was spread on a platform and mixed with fibre until consistent. Water was added, and the mixture was combined. Blocks were formed using a hydraulic machine at 100 bars of pressure and then sun-dried for 21 days at 27 °C and 72% humidity.	Density (BS EN 771-1), Water absorption (BS EN 772-11) Compressive test (BS EN 771-1), tensile splitting test (BS EN 12390-6), linear shrinkage, wearing and erosion
[77]	Reinforced soil blocks	Alkali-resistant glass, polypropylene, Banana and jute fibre	Each (0.25%, 0.5%, 0.75% and 1%) wt. Soil, with lengths of 12 mm, 12 mm, 60–70 mm and 60–70 mm for the fibres respectively	Sandy dark brown soil	Water (10%)	215 × 105 × 65 mm	Manual	The soil and fibres were mixed by hand, spread in a mould, and pressed. The blocks were sunbaked for 21 days at 25 °C to 30 °C and covered with banana leaves or plastic sheets to maintain humidity. Before testing, the blocks were dusted to remove loose soil.	Density (BS EN 771-1), Water absorption (BS EN 772-11), compressive stress and indirect tensile stress (ASTM D559-0), modulus of rupture (ASTM C-67), linear shrinkage, wearing and erosion (ASTM D559-03, New Zealand Standard)
[78]	Adobe bricks	Straw or seagrass fibres	0.5, 1.5, and 3 wt.% at 1, 3 cm and long	Clay, sand And gravel	60 wt.% fine clay, 40 wt.% sand-gravel, and 20 wt.% Water	40 × 40 × 160 mm	Manual	Samples were made by mixing materials with water to form a paste, poured into standardised moulds, removed once set, and left to dry in laboratory conditions (21–23 °C, 40–50% relative humidity) for about 28 days until achieving a constant weight.	Tensile strength and water absorption of fibres, Dry density, flexural and compressive strength (EN 196-1), thermal conductivity, linear shrinkage
[79]	Adobe bricks	Fonio straw	0.2, 0.4, 0.6, 0.8 or 1%, with length of 1 cm	Reddish brown clayey soil	Water (24%)	40 × 40 × 160 mm	Manual	The mixture was moulded in two layers with manual compaction (30 shocks). The samples were dried in the shade at 30 ± 5 °C for 24 h, then were demoulded and dried for an additional 21 days before testing.	Water absorption, compressive and flexural strengths (XP P13–901), thermal conductivity, apparent density, porosity, spray test
[80]	Compressed stabilised earth block	Crushed brick waste	6%, 12%, 18% and 24% wt. of soil-sand (sand 20–100% + 30% soil)	Silty clay soil	Cement (10%) wt. Soil, water (10–12%)	290 × 140 × 100 mm	Manual	A hand-operated press with a compaction ratio of 1.85 was used to produce bricks. The mixture was moulded, manually compressed, ejected, weighed, and cured for 28 days under wet gunny bags, followed by 7 days of air drying.	Compression test, three-point flexural (HB 195), Water absorption (IS 3495), sulphate resistance, wetting–drying (IS 1725)
[81]	Compressed earth blocks	Rice husk ash	0–20% wt. Soil	Clay	Cement and soil at 1:15, resin adhesive (20 mL/kg cement)	300 × 150 × 100 mm		The blocks were compacted at 1.37 × 109 N/m2, sprinkled with water for 3 days, and cured under polyethylene covers for 25 days. Initial curing involved 24 h in a canopy before the extended curing process.	Dry and bulk densities, compressive strength (SLS standard 1382), water absorption, erosion and acid resistances
[82]	Cement stabilised soil blocks	Sugarcane bagasse ash	4%, 6%, And 8% wt. Soil	Locally available soil	Cement (4%, 10%), water (12%)	190 × 90 × 90 mm		The mould was lubricated, filled with thoroughly mixed wet material, and compressed to form uniform-density blocks. After removal, the blocks were moisture-cured for 28 days by sprinkling water and covering with plastic gunny bags.	Compressive strength, Water absorption and efflorescence tests (BIS specifications)
[83]	Earth bricks	Flax, hemp	Each (1%, 3%)	Cohesive soil	Gypsum (5%, 10%) and Cement (5%, 10%)	160 × 40 × 40 mm	Mechanical Mixer	Materials were dry-weighed and mixed mechanically with water until a dough-like consistency was achieved, ensuring homogeneity. The mixture was then poured into formwork and evenly distributed.	Compressive strength (EN 1015), bending tensile test, density
[84]	Stabilised and compressed earth soil bricks	Ground granulated blast furnace slag, cement Kiln dust, and quick lime	Ground granulated blast furnace slag (20%, 25%), cement Kiln dust or quick lime (5, 10%)	Clay	Sand (15%), cement (5%), and quick lime (0, 5, 10%), water (10%)	Cylinders of 20 mm in diameter and 40 mm in height	Manual and a laboratory mixer	Ingredients, except cement, were manually shaken, mixed with water, and rested for three days. Cement was then added, and the mix was compacted at 10.0 MPa, demoulded, and cured at 23 °C and 80% RH for 7, 14, 28, and 60 days.	Water absorption, bulk density, and compressive strength (ASTM standards)

and

Table 3. Summary of the methods for manufacturing concrete blocks by previous researchers.

Ref.	Type of Block	Type of Waste	Content of Waste (%)	Content of Other Materials	Size of Blocks (mm)	Mixing Method	Manufacturing Method	Conducted Tests
[85]	Hollow non-structural type	Sugarcane bagasse and coffee husk	2.5, 5.0, 7.5 and 10%, Partial replacement of crushed stone	Control mix in mass 20: 100: 170: 17.05 (cement: sand: crushed stone: water).	390 × 190 × 140 mm	Mechanically mixed by three vertical blades with 40 RPM rotation	The materials were mixed in a conveyor-powered mixer for 8 min, vibro-pressed into blocks, and cured at room temperature for 28 days.	The water absorption, bulk density (NBR 9778, NBR 13280, ASTM C140, and ASTM C129), compressive strength (NBR 6136 and ASTM C129), and thermal transmission.
[86]	Low-strength concrete for Concrete masonry units	Sawdust, wood ash, Lime mud	Sawdust (5, 10, 20%) by volume of sand, Each wood ash, lime mud (5, 10, 15%) by volume of cement,	Plasticiser (SP) was 1% (by weight of cement) and the W/C ratio was 0.4	100 × 100 × 100 mm, 150 × 150 × 150 mm		Aggregates were mixed dry for 30 s, cement was added and mixed for another 30 s, followed by a gradual introduction of water and superplasticisers, with specimens cured in water at room temperature (20 °C).	Absorption after Immersion (EN 83980), Oven-dried density, Voids, Compressive strength (EN 12390–3), Thermal conductivity (EN ISO 22007)
[29]	Lightweight hollow Block masonry	Expanded polystyrene wastes, Silica fume	Expanded polystyrene wastes (0%, 10%, 15%, 20%, and 26%) as a replacement for sand, Silica fume (9.8%) as a replacement for cement	Cement (455 kg/m3), Sand (1613–408 kg/m3), W/C (1.1–2.2%), High range water reducer (0–26.2 kg/m3), Welded steel wire mesh, Fibreglass mesh	blocks 200 × 200 × 400 mm with two cylindrical holes each of 125 mm in diameter	Planetary drum mixer	The mould and PVC pipes were secured; the mixer drum rotated for 3 to 5 min to create uniform mortar; EPS particles were added; the mould vibrated for 2 h; and the blocks were cured for 28 days, dried, and tested after 48 h.	Density and water absorption (ASTM C642), Compressive strength, and cyclic ponding.
[87]	Concrete masonry blocks	Rice husk ash, coconut fibre	Each (0–15%), as sand Replacement	Cement: Sand: Rice husk Ash (1:(10–8.5): (0–1.5)), Cement: Sand: coconut fibre (1: (10–8.5): (0–1.5)),	400 mm × 200 mm × 100 mm	Mechanical	The batch formulation was mixed for eight minutes until homogeneous, transported to an elevated hopper, compacted in the moulding machine, and the blocks were moved to the drying area, with samples cured for 7, 14, and 21 days.	Compressive strength (ASTM C140)
[88]	Cement-based solid masonry blocks	Rice husk ash	5, 10, 15%	Cement/sand (1:6) and W/C (0.45)	300 × 150 × 113 mm	-	Rice husk ash was mixed with cement, sand, and 15% water, moulded by hand, covered with a tarpaulin in the shade and cured by sprinkling water twice daily for seven days after 24 h.	Thermal transmittance (BS EN ISO 9869 and BS EN ISO 8990),
[89]	Concrete masonry blocks	Palm oil fuel ash	10%, 20%, 30%, Replacement of cement	Cement and sand (1:3), water/binder (0.5)	215 × 105 × 65 mm	Manual	Masonry blocks were manually produced by mixing OPC, fine sand, and POFA with water for 15–20 min, followed by compaction in iron moulds. The blocks were demoulded after 24 h and cured in dry and wet conditions for 28 days.	Compressive strength (ASTM C55), water absorption (BS EN 772), and density.
[90]	Cement blocks	Coco pith	4, 6 and 8% replacement of cement	Cement, river sand, water Aggregate to cement (1:6),	200 × 100 × 60 mm, 100 × 100 × 100 mm	Manual	Mortar cubes and beams were cast by manually blending cement, sand, and coco pith, adding water, and compacting the mix in layers with a tamping rod. The specimens were cured for 28 days in ambient conditions.	Density and water absorption (ASTM-C140), Compressive strength (ASTM-C109), Flexural tensile strength (ASTM-C348), Sorptivity test, drying tests (CSN-EN-16322), Wetting and drying resistance (ASTM-C138/C138M), Durability against chemicals (ASTM-C289, C1152/C1152M), Environmental impacts
[91]	Hollow concrete blocks	Crumb rubber, high-density polyethylene (HDPE), low-density polyethylene (LDPE)	20% of CR, 20% of HDPE, and 10% of LDPE as a replacement for coarse aggregates	W/C (0.495)	400 × 200 × 200 mm	400 × 200 × 200 mm	The aggregates were mixed with cement, water, and replacement materials, then compacted into blocks under 70 kPa pressure and cured for 28 days with water spraying and covers.	Compressive strength, density, and absorption (ASTM C140), Thermal conductivity (ASTM C518), Environmental impacts
[92]	Sustainable concrete blocks	Marble dust (MD), Silica fume (SF), Fine wood aggregates (FWA), fine Recycled Glass aggregates (FGA), Coarse concrete aggregate (CCA)	RW (5%), MD (15%), RG (20%), CCA (25%), FWA (5%), FGA (20%), CCA (25%), MD (20%), FWA (10%), FGA (25%), and CCA (30%), replacement of cement and aggregates	W/C ratio (0.38)	250 × 130 × 65 mm	A B-20 mixer (220 V, 20-L capacity, 100–360 RPM)	A mixer was used to mix dry ingredients for 2 min, followed by 3 min of mixing with tap water at 22 °C. The concrete was cast into steel moulds and cured by immersing the specimens in water for 28 days.	Density (ASTM C90), water absorption (ASTM C90), Porosity (ASTM C642), compressive strength (ASTM C1634), Thermal properties (ASTM C518), Sustainability performance assessment
[93]	Solid masonry blocks	Recycled aggregate concrete, Fine recycled concrete aggregates	Cement-to-aggregate ratio (1:6 to 1:24), replacement of cement and natural aggregates	W/C = 0.5	400 × 200 × 200 mm	Drum mixer	Recycled aggregates were saturated for an hour to minimise water absorption effects before mixing with OPC, and the uniform mix was cast into moulds, compacted, and cured for 28 days under standard conditions.	Density, water absorption (IS 2185), compressive strength (ASTM C90), flexural strength (IS 4860), environmental analysis

summarise the methodologies adopted in previous studies. The production of masonry units generally begins with the preparation of raw materials, including soil, sand, stabilisers, cement, aggregates, and waste materials. These materials are dried, treated where necessary, ground, and sieved to obtain the required particle size distribution. For brick production, the prepared materials are dry-mixed, followed by the addition of water to achieve the optimum moisture content and produce a homogeneous mixture through manual or mechanical mixing. The mixture is then shaped and compacted using manual, hydraulic, or semi-dry compression methods to obtain uniform density and geometry. Fired bricks are typically air-dried for 24–48 h or kiln-dried at 100–115 °C before firing at temperatures of 600–1200 °C, with heating rates of approximately 3–5 °C/min. Firing temperature is a critical processing parameter controlling densification, sintering, vitrification, pore development, shrinkage, mechanical strength, and thermal performance. Replacement levels varied depending on waste characteristics, processing requirements, and target performance. Manufacturing processes generally followed conventional fired-clay brick production, involving material preparation, mixing, moulding, drying, and firing, with methods ranging from manual mixing and hand moulding to mechanical mixing, blending, and semi-dry compression moulding. After firing, specimens were cooled and conditioned before testing, although conditioning procedures and testing ages were not consistently reported; where available, additional cooling periods included one week to ten days. Testing was conducted according to recognised masonry and material standards, including ASTM, EN, IS, ISO, and other reported methods.

In contrast, unfired bricks are removed from moulds immediately or after approximately 24 h and cured by air drying for 7–14 days or until constant mass is achieved. The reviewed studies on unfired bricks investigated a range of earth-based masonry units, including compressed stabilised earth blocks (CSEBs), compressed earth blocks (CEBs), reinforced soil blocks, adobe bricks, earth bricks, and stabilised compressed earth bricks. The investigated materials incorporated different stabilisation or reinforcement approaches, including mineral additives, industrial by-products, agricultural wastes, and fibres. The soil matrices varied among studies and included lithomargic clay, lateritic soil, red and brown clay soils, sandy dark brown soil, silty clay soil, cohesive soil, and locally available clay soils, with additional materials such as sand, gravel, cement, gypsum, lime, and water incorporated depending on the targeted application. Manufacturing processes involved material preparation, mixing, moulding, compaction, drying, and curing, with mixing conducted manually or mechanically and shaping performed using moulds, hydraulic presses, or manual compaction methods. Compaction conditions varied from manual pressing to controlled mechanical compaction. Testing procedures followed various international and national standards, with standards applied according to the tested property and masonry type.

Concrete block production involves dry mixing of prepared cement, lime, aggregates, and waste materials, followed by the addition of water and chemical admixtures and mixing for approximately 5–10 min to achieve a uniform consistency. The mixture is then moulded and compacted using hand tools, vibrating tables, or vibro-compressors for 1–2 min, followed by demoulding after approximately 24 h and curing for 7–28 days using damp covering, plastic sheeting, or water immersion. The reviewed studies for concrete blocks investigated a range of sustainable cement-based masonry products, including hollow non-structural blocks, concrete masonry units (CMUs), lightweight hollow blocks, solid masonry blocks, cement blocks, and sustainable concrete blocks. The investigated waste materials were incorporated through different modification approaches, including partial replacement of natural aggregates, partial replacement of cementitious components, and the addition of lightweight or fibrous phases within cement-based matrices. Waste replacement levels varied depending on material type, intended function, and masonry application. Manufacturing processes generally involved material preparation, dry or mechanical mixing, moulding, compaction, and curing. Testing procedures followed recognised standards.

3. Results and Discussions

Due to the considerable variation in testing standards, specimen dimensions, manufacturing procedures, and processing conditions reported in the literature, direct comparison of absolute values between different studies was not considered reliable. Therefore, the comparative analysis focused on relative trends within each study, such as improvement or reduction compared with reference samples, rather than direct ranking between different waste materials or masonry systems. The influence of key processing parameters, including firing temperature, curing regime, replacement ratio, and manufacturing method, was considered when interpreting the observed trends.

3.1. Density

3.1.1. Fired Bricks

The influence of waste substitution on material density varies considerably depending on the type of material used. The reviewed studies indicate that incorporating agricultural and industrial waste generally reduced the density of fired bricks, unfired bricks, and concrete blocks compared with conventional masonry units. The results of fired bricks are shown in

Table 4. Summary of the results of fired bricks from various references.

Ref.	Type of Waste, Temp. (°C)	Density (kg/m3)	Porosity (%)	Water Absorption (%)	Compressive Strength (MPa)	Flexural Strength (MPa)	Thermal Conductivity (W/m·K)	Efflorescence
[65]	Cigarette butts, 1050 °C	2118–1482	–	5–18	25.65–3	2.79–1.24	1.08–0.45	–
[66]	Activated alumina sludge, 900 °C	1930–1690	31.9–40.6	12.92–23	18–5.4	3.2–1.5	0.26–0.19	Nil
[67]	Rice husk ash, 900 °C	1839–1394	31–45.5	16.9–32.9	53.4–13.5	–	–	–
[67]	Rice husk ash, 1000 °C	1865–1395	30–44.9	16.7–32.7	55.1–17.5	–	1.05–0.68	–
[67]	Wood ash, 900 °C	1839–1693	31–36.48	16.9–26.7–21.2	53.4–34.3	–	–	–
[67]	Wood ash, 1000 °C	1865–1708	30–34.5	16.7–26.6–21.1	55.1–43	–	1.05–0.753	–
[68]	Olive mill waste, 850 °C	1840–1450	31.4–46.7	17–32.2	33–9	–	0.595–0.462	–
[68]	Olive mill waste, 950 °C	1860–1450	30.8–47.0	16.6–32.5	37–10	–	0.638–0.436	–
[68]	Olive mill waste, 1050 °C	1920–1490	27.8–44.9	14.5–31.1	55–17	–	0.690–0.477	–
[69]	Rice husk ash, 850 °C	1421–1207	–	19–26.7	3.52–1.9	–	–	–
[70]	Waste fly ash, 800 °C	–	–	12–24	23.5–6.5	6–3	–	Slight
[71]	Spent shea waste, 900 °C	1610–1210	36–55	22.5–33	6–9/6	–	–	–
[71]	Spent shea waste, 1000 °C	1780–1590	19–51	10–17.8	4–8	–	–	–
[71]	Spent shea waste, 1100 °C	1770–1570	12–46	6.8–17	13–5/8	–	–	–
[71]	Spent shea waste, 1200 °C	2010–1652	10–41	3–12	7–9	–	–	–
[72]	Paper mill sludge, 900 °C	1771–1219	33.61–49.42	12.8–28.64	21.8–4.68	–	0.540–0.242	Moderate
[72]	Paper mill sludge, 950 °C	1821–1302	33.12–49.05	12.34–28.57	22.55–5.82	–	0.551–0.245	Moderate
[72]	Paper mill sludge, 1000 °C	1824–1309	32.84–48.28	12.36–28.92	22.7–6.07	–	0.555–0.245	Moderate
[73]	Pomegranate peel waste, 900 °C	1870–1348	13.5–19.8	13.8–20.2	18.5–4.6	–	0.72–0.25	–
[74]	Rice straw ash, 1000 °C	–	–	3.5–20	13.88–3.12	–	–	–

Shrinkage values for [65], [67], [71] and [72] range between 6.44 and 9.01%, 0.52 and 0.36%, 2 and 7.9%, and 2.67 and 3.67%, respectively. Note: Where numerical values were not explicitly provided in the referenced sources, they were very closely manually estimated from the corresponding results graphs with ±0.05–0.1 accuracy. Note: – represents unreported values.

and Figure 3. Agricultural wastes such as rice husk ash, spent shea waste, and pomegranate peel waste produced noticeable reductions in density because the combustion of organic constituents during firing generated additional pore spaces within the ceramic matrix [69,71,73]. For example, the density of rice husk ash [69] decreases from 1421 kg/m³ to 1207 kg/m³. At higher substitution levels, various industrial waste products exhibited notable decreases in density. For instance, cigarette butts [65] displayed a reduction from 2118 kg/m³ (0% substitution) to 1482 kg/m³ (10% substitution). Additionally, at a firing temperature of 1000 °C and a substitution level of 30%, the density of paper mill sludge [72] declined from 1824 kg/m³ at 0% to 1309 kg/m³. A comparable decrease was noted with pomegranate peel waste [73], where a 15% substitution resulted in a density reduction from 1870 kg/m³ to 1348 kg/m³. Certain materials, including activated alumina sludge [66], exhibited analogous trends; however, their relatively modest reductions suggest that they may preserve structural density more effectively.

3.1.2. Unfired Bricks

The results of unfired bricks are shown in

Table 5. Summary of the results of unfired bricks from various references.

Ref.	Type of Waste	Density (kg/m3)	Water Absorption (%)	Compressive Strength (MPa)	Tensile Strength (MPa)	Flexural Strength (MPa) or Modulus of Rupture (Pa)	Thermal Conductivity (W/m·K)	Efflorescence
[75]	Lithomargic Clay + GBFS + Cement	–	13.9–12.51	1.61–5.55	–	–	–	–
[75]	Lateritic soil + GBFS + Cement	–	12.9–10.9	2.13–5.25	–	–	–	–
[76]	Bagasse (red soil)	1951–1808	8.1–15.7	2.15–2.7/1.52	0.26–0.30/0.275	–	–	–
[76]	Coconut husk (red soil)	1951–1795	8.1–14.8	2.15–3.0/1.6	0.26–0.32/0.27	–	–	–
[76]	Oil palm fruit (red soil)	1951–1823	8.1–13.6	2.15–3.1/1.6	0.26–0.35/0.31	–	–	–
[76]	Bagasse (brown soil)	1909–1790	8.5–16.5	1.65–2.1/1.15	0.24–0.28/0.255	–	–	–
[76]	Coconut husk (brown soil)	1909–1772	8.5–15.3	1.65–2.65/1.1	0.24–0.31/0.265	–	–	–
[76]	Oil palm fruit (brown soil)	1909–1802	8.5–14.3	1.65–2.55/1.15	0.24–0.34/0.27	–	–	–
[77]	Banana fibre	2041–1893	20–19	3.5–13.59	1.92–7.46	0.498–0.551	–	–
[77]	Jute fibre	2041–1751	20–17	3.5–18.04	1.92–9.89	0.498–0.611	–	–
[77]	Alkali-resistant glass fibre	2041–1811	20–12.9/13.1	3.5–6.87/4.86	1.92–3.99/3.01	0.498–0.626	–	–
[77]	Polypropylene fibre	2041–1710	20–6/8	3.5–9.91	1.92–5.44	0.498–0.678	–	–
[78]	Straw fibres, 3 cm	1952–1825	–	1.676–2.824/1.803	–	0.411–0.472/0.388	0.83–0.62	–
[78]	Seagrass fibres, 3 cm	1952–1913	–	1.676–2.64/2.496	–	0.411–0.502/0.363	0.83–0.71	–
[79]	Fonio straw	–	–	2.6–2.9/2.3	–	1.1–1.3/0.8	1.08–0.35	–
[80]	Crushed brick waste	–	8.41–10.52	8.2–9.57	–	2.19–2.65	–	–
[81]	Rice husk ash	1812–1560	16–15/23	3.3–4/2	–	–	–	–
[82]	Sugarcane bagasse ash + 4% cement	–	6.59–6.89	2.52–2.49/2.95	–	–	–	Nil
[82]	Sugarcane bagasse ash + 10% cement	–	5.84–6.95	5.42–5.85	–	–	–	Nil
[83]	Flax	–	–	4.4–4.5	–	–	–	–
[83]	Hemp	–	–	4.4–3.5/3.7	–	–	–	–
[84]	GBFS + cement	1880	–	7.36	–	–	–	–
[84]	GBFS + Cement kiln dust + cement	1900–1950	11–11.5	17.16–19.61	–	–	–	–
[84]	GBFS + Quick lime + cement	2000–2100	12–14.7	21.08–24.52	–	–	–	–

Shrinkage values for [76], [77] and [78] range between 1.05 and 0.35%, 1.7 and 0.5%, and 5.7 and 3.4%, respectively. Note: Where numerical values were not explicitly provided in the referenced sources, they were very closely manually estimated from the corresponding results graphs with ±0.05–0.1 accuracy. Note: – represents unreported values.

and Figure 4. Densities for fibre-reinforced blocks typically decrease as the proportion of fibre increases. Specifically, when the fibre content increases from 0.25% to 1% by weight, bagasse fibre bricks [76] exhibit a density range of 1951 to 1808 kg/m³. Similarly, the incorporation of coconut husk [76] and oil palm fruit fibres [76] into red soil yields densities ranging from 1951 to 1795 kg/m³ and 1951 to 1823 kg/m³, respectively. Analogous trends are observed in brown soil, where the density diminishes from 1909 kg/m³ to 1790 kg/m³ with the addition of bagasse [76], and from 1909 kg/m³ to 1772 kg/m³ when coconut husk [76] is included. In contrast, materials such as banana fibre [77], jute fibre [77], alkali-resistant glass fibre [77], and polypropylene fibre demonstrate [77] a significant reduction in densities. Also, adobe bricks incorporating straw fibres [78] decrease in density from 1952 kg/m³ to 1825 kg/m³, while seagrass fibres [78] result in a more modest density range of 1952 to 1898 kg/m³. Conversely, systems using ground blast furnace slag (GBFS) with cement or quicklime exhibited relatively higher densities due to improved granular packing and increased cementitious reaction products [84].

3.1.3. Concrete Blocks

The results of concrete blocks are shown in

Table 6. Summary of the results of blocks from various references.

Ref.	Type of Waste	Density (g/cm3)	Water Absorption (%)	Porosity	Compressive Strength (MPa)	Flexural Strength (MPa)	Thermal Conductivity (W/m·K)
[85]	Sugarcane bagasse	2430–2110/2130	8.25–7.28/8.69	–	3.29–7.02/4.73	–	0.467–0.360/0.457
[85]	Coffee husk	2430–2020	8.25–9.18	–	3.29–5.92/4.88	–	0.467–0.434/0.489
[86]	Sawdust	1960–1380	11.5–24.4	19.1–47.1	5.92–0.83	–	1.12–0.55
[86]	Wood ash	1960–1930	11.5–17.24	19.1–25.1	5.92–3.92/4.87	–	1.12–0.91
[86]	Lime mud	1960–2080/2010	11.5–13.2/12.02	19.1–16.5/18.1	5.92–7.56/7.29	–	1.12–1.13/1.12
[29]	Expanded polystyrene wastes + silica fume	2119–956	0.47–4.61/3.32	–	9.5–2.4	–	–
[87]	Rice husk ash	–	–	–	4.57–4.53/4.80	–	–
[87]	Coconut fibre	–	–	–	4.6–4.39/4.89	–	–
[88]	Rice husk ash	1799–1735/1784	–	–	–	–	0.55–0.46
[89]	Palm oil fuel ash, dry curing	1995–2043/2011	6.29–7.49	–	23.2–24.9/22.3	–	–
[89]	Palm oil fuel ash, wet curing	1981–2168/2129	6.04–9.91/8.85	–	24.9–28/24.8	–	–
[90]	Coco pith	2045–1895	–	–	3.9–4.2/2.9	1.55–2.21/1.81	–
[91]	HDPE/LDPE/Crumb rubber	2.091, 1.756, 1.912, 1.825	8.56, 7.73, 6.75, 8.12	–	6.33, 6.55, 4.99, 2.79	–	0.344, 0.342, –, 0.343
[92]	0, RW (5%),	2186, 2069	6.54, 4.92	–	46.7, 29.97	–	1.655, 1.571
	MD (15%),	2107	6.23	–	37.4	–	1.613
	RG (20%),	2125	3.84	–	41.82	–	1.477
	CCA (25%),	2071	9.16	–	30.45	–	1.352
	FWA (5%), FGA (20%), CCA (25%),	1733	12.91	–	32.7	–	0.793
	MD (20%), FWA (10%), FGA (25%), AND CCA (30%)	1654	13.78	–	21.35	–	0.723
	MD (15%), FWA (5%), FGA (20%), CCA (25%)	1756	10.18	–	13.75	–	1.001
	MD (20%), FWA (10%), FGA (25%), and CCA (30%)	1684	11.11	–	15.05	–	0.859
[93]	Recycled aggregate concrete + fine recycled concrete aggregates	2215–1995	1.42–3.6	–	24.79–3.7	4.2–0.65	–

Note: Where numerical values were not explicitly provided in the referenced sources, they were very closely manually estimated from the corresponding results graphs with ±0.05–0.1 accuracy. Note: – represents unreported values.

and Figure 5. Materials such as sawdust [86], coffee husk [85], sugarcane bagasse [85], and expanded polystyrene (EPS) [29] are characterised by low specific gravity and high void content, resulting in notable reductions in density. Specifically, the density of sugarcane bagasse decreases from 2430 kg/m³ at 0% concentration to 2130 kg/m³ at 10% concentration, while coffee husk exhibits a decline from 2340 kg/m³ to 2020 kg/m³ at the same concentration level. EPS indicates a particularly dramatic density reduction, falling from 2119 g/m³ at 0% to 956 kg/m³ at 26%. Sawdust [86], due to its porosity, experiences a substantial decrease from 1960 kg/m³ at 0% to 1380 kg/m³ at 20%, rendering it ideal for lightweight applications. Conversely, certain waste materials exhibit moderate density reductions while maintaining structural integrity. These materials include recycled aggregates and blends of marble dust, silica fume, and recycled wood aggregates [92]. In contrast, lime mud [86], wood ash [86], and rice husk ash [88] maintain relatively stable or only slightly varying densities. Lime mud [86] initiates at 1960 kg/m³, increases to 2080 kg/m³ at 5%, and then slightly decreases to 2010 kg/m³ at 15%, thus enhancing packing density at lower levels while providing diminishing contributions at higher concentrations. Wood ash [86] remains stable across varying percentages, thereby ensuring structural viability. Palm oil ash [89] reveals increased densities in response to rising waste content, while rice husk ash [88] and coco pith [90] display moderate reductions, reflecting their distinctive compositions.

3.2. Porosity

3.2.1. Fired Bricks

Porosity is a significant characteristic that affects material performance and highlights the interaction between waste content and the void structure of composites. The results of fired bricks are shown in Table 4 and Figure 6. Spent shea waste exhibited the highest porosity levels, reaching 55% at a 20% replacement ratio [71], while paper mill sludge showed porosity ranging from 33% to 49% at 30% [72]. An increase in the firing temperature of waste material has been observed to significantly reduce porosity, likely due to the enhanced density achieved at elevated temperatures. Wood ash [67] demonstrates an increase in porosity from 30% at 900 °C to 36.48% at a 30% substitution level, while rice husk ash [67] shows an increase from 30% at 900 °C to 45.5% at the same substitution level [72]. While rice husk ash, wood ash, and olive mill waste increased porosity, the effect was partly mitigated at higher firing temperatures due to improved sintering and vitrification [67,68]. Other materials displaying similar trends include activated alumina sludge [66] and pomegranate peel waste [73]. Although the effects on the internal pore structure of these materials are less pronounced, their relatively moderate increase in porosity renders them suitable for applications requiring specific porosity levels.

3.2.2. Concrete Blocks

The results of concrete blocks are shown in Table 6 and Figure 7. Sawdust [86] exhibits the highest reported porosity among the materials surveyed, demonstrating a notable increase from 19.1% at 0% concentration to 47.1% at 20% concentration. This substantial rise can be attributed to sawdust’s hydrophilic and fibrous nature, which introduces numerous voids into the material matrix. Although this high porosity results in enhanced water absorption and decreased mechanical strength, it is unfavourable for structural applications. Conversely, it offers benefits for uses that require insulation and lightweight properties. The porosity of lime mud [86] shows a more gradual decrease, changing from 19.1% at 0% concentration to 18.1% at 15% concentration. This relatively minor variation suggests that lime mud contributes to a denser and more cohesive matrix compared to sawdust. Furthermore, wood ash [86] demonstrates a progressive increase in porosity commensurate with its concentration, commencing at 19.1% for 0% and gradually reaching 25.1% at 15%. This trend indicates that higher wood ash content produces a more porous matrix.

3.3. Water Absorption

3.3.1. Fired Bricks

Water absorption reveals significant trends influenced by the type and composition of materials from various waste sources. The results are shown in Table 4 and Figure 8. Pomegranate peel waste [73] generally increased water absorption, rising from 13.8% to 20.2% at a 15% substitution level. Spent shea waste [71] notably increased the absorption from 22.5% to 33% at a 20% substitution level. Industrial by-products, such as paper mill sludge [72], also exhibit a rise in absorption from 12.36% to 28.92% at a 30% content. Furthermore, cigarette butts [65] display one of the most substantial increases in porosity, starting at 5% at 0% substitution and reaching 18% at a 10% substitution level. Olive mill waste [68] similarly exhibits a significant upward trend, increasing from 14.5% to 31.1% with a 10% substitution level at 1050 °C, indicating its influence on the formation of a more porous matrix. On the other hand, rice husk ash [67] reflects parallel increases, where absorption increased from 16.9% to 32.9% at a 30% substitution level at a firing temperature of 900 °C. The elevation in firing temperature noticeably reduces water absorption across various waste materials. Generally, materials fired at temperatures between 1000 °C and 1200 °C yield water absorption values equal to or below 20% [67,71,74]. Therefore, it is critical to achieve a balance in waste incorporation to optimise material performance.

3.3.2. Unfired Bricks

The findings for unfired bricks are presented in Table 5 and Figure 9. The incorporation of lithomargic clay, granulated blast furnace slag, and cement in compressed stabilised earth blocks [75] demonstrates a reduction in water absorption as the cement content and soil proportion increase, achieving optimal absorption rates of 12.51% and 10.9% for mixtures containing 10% cement, 75% soil, and 25% GGBS, as well as 8% cement, 80% soil, and 20% GGBS, respectively. The inclusion of fibres [76] such as bagasse, coconut husk, and oil palm fibres generally increases water absorption in compacted soil blocks. For instance, the addition of 1% oil palm fibre to red soil elevates absorption from 8.1% to 13.6%. A comparable peak absorption rate of 16.5% is noted in brown soil containing 1% bagasse fibre. The integration of alkali-resistant glass, polypropylene, and banana fibres [77] reveals varying absorption rates in reinforced soil blocks. Furthermore, ash-based materials demonstrated diverse behaviours. Water absorption in compressed earth blocks significantly increases with the introduction of rice husk ash [81], reaching 23% at a 20% ash concentration. In cement-stabilised soil blocks containing sugarcane bagasse ash [82], water absorption ranges from 6.59% to 6.89% at varying cement levels, indicating consistent performance.

3.3.3. Concrete Blocks

The results of concrete blocks are shown in Table 6 and Figure 10. The findings regarding water absorption provide insights into the porosity and hydrophilic characteristics of various materials, which exhibit considerable variation among different waste types. Notably, materials such as coffee husk and sugarcane bagasse [85] demonstrate moderate water absorption levels, with increases from 8.25% to 8.69% and 9.18%, respectively, when the content increases to 10%. These modest changes reflect minor alterations in the porosity and biological structure of the materials. Palm oil fly ash [89] exhibits minimal fluctuations in absorption, varying from 6.29% to 7.49% at 30% in dry conditions, indicative of its stable and low-porosity characteristics. In contrast, sawdust [86] exhibits high water absorption, increasing from 11.5% at 0% content to a considerable 24.4% at 20%, thereby indicating its highly porous and hydrophilic nature. Wood ash [86] demonstrates a consistent increase in absorption, rising from 11.5% to 17.24% at 15%, attributed to its inherent porous structure.

Other materials illustrate diverse absorption properties attributable to their structural composition. Lime mud [86] reaches a peak absorption of 13.2% at 5% from 11.5% for the reference mix, which subsequently declines to 12.02% at 15%, reflecting improved packing and reduced porosity at higher concentrations. Polymers [91] are noteworthy for their low to moderate absorption levels, thereby enhancing durability and environmental resilience. Expanded polystyrene (EPS) [29] records the lowest absorption rate among all materials, underscoring its applicability for moisture-resistant uses. Additionally, crumb rubber and polymers such as high-density polyethylene (HDPE) and low-density polyethylene (LDPE) [91] maintain low to moderate absorption, emphasising their durability advantages. Blends incorporating marble dust [92] exhibit comparatively low absorption rates ranging from 3.84% to 13.78%, rendering them suitable for applications with minimal moisture absorption. These findings underscore the significance of material selection in effectively reconciling moisture resistance with structural and environmental considerations.

3.4. Mechanical Performance

3.4.1. Fired Bricks

When evaluating the load-bearing capacity of masonry blocks, compressive strength emerges as a critical characteristic. The compressive strength results for waste materials demonstrate varied trends contingent upon the type of material and the level of substitution employed. The results of fired bricks are shown in Table 4 and Figure 11. Overall, the increase in firing temperature positively influences compressive strength and mitigates strength loss. Ash-based materials, including rice straw ash [74], waste fly ash [70], and rice husk ash [67], exhibit notable reductions in compressive strength as the substitution level increases. For instance, rice husk ash [67] experiences a decline from 53.4 MPa at 0% substitution to 13.5 MPa at 30% substitution when fired at 900 °C. At a firing temperature of 1000 °C, rice husk ash demonstrates enhanced strength, ranging from 55.1 MPa at 0% to 17.5 MPa at 30%, indicating the beneficial effects of elevated firing temperatures. Conversely, wood ash [67] displays a markedly lower reduction in strength when incorporated and fired under conditions comparable to those of rice husk ash. The incorporation of rice husk ash at low temperatures [69] at low levels, specifically below 15%, results in a consistent decrease in compressive strength.

Additionally, other industrial by-products, such as cigarette butts [65], pomegranate peel waste [73], activated alumina sludge [66], paper mill sludge [72], and olive mill waste [68] exhibit significant declines in compressive strength with increased substitution. For example, olive mill waste [68] shows a decrease from 55 MPa at 0% substitution to 17 MPa at 10% substitution when fired at 1050 °C, reflecting its diminished load-bearing capacity. Similarly, the compressive strength of pomegranate peel waste [73] falls from 18.5 MPa to 4.6 MPa at 15% substitution, underscoring its limited structural viability at elevated concentrations. Also, strength reductions are observed in other agricultural by-products, such as spent shea waste [71], which decreases from 36 MPa at 0% substitution to 12 MPa at 20% when fired at 1200 °C. These trends suggest the need to optimise waste content and investigate hybrid compositions to enhance compressive strength while also achieving environmental benefits.

Flexural strength is a fundamental characteristic that signifies a material’s capability to withstand deformation when subjected to load. There remains a limited number of studies addressing this property, indicating a notable gap in the existing research. The results about the flexural strength of fired bricks are presented in Table 4. The data provided demonstrate clear patterns contingent upon the type of waste material and its concentration. For instance, the inclusion of cigarette butts [65] across varying substitution levels reveals a reduction in flexural strength from 2.79 MPa at 0% to 1.24 MPa at 10%, indicating diminished resistance as the waste content increases. A similar trend is observed with activated alumina sludge [66]. Furthermore, the incorporation of waste fly ash [70] results in a decrease in strength from 6 MPa at 0% to 3 MPa at 25%. These findings underscore the importance of optimising substitution levels to maintain acceptable flexural properties while also achieving environmental advantages. Given that flexural strength is critical for structural elements subjected to bending forces, future research should investigate treatments or additives that may enhance these properties.

3.4.2. Unfired Bricks

The results of unfired bricks are illustrated in Table 5 and Figure 12. The strength of compressed stabilised earth blocks [75] composed of 75% lithomargic clay and 25% granulated blast furnace slag demonstrates an upward trend with increasing cement content, peaking at 5.55 MPa with 12% cement and reaching a maximum of 5.15 MPa at 10% cement. Similarly, at 6% cement content, a mixture of 80% lateritic soil with 20% granulated blast furnace slag attains a peak compressive strength of 4.7 MPa. Fibre materials play a significant role in influencing the compressive strength of compressed soil blocks [76]. Among these, bagasse, coconut husk, and oil palm fibres [76] exhibit notable effects. The strength peaks at 2.7 MPa in red soil containing 0.5% bagasse fibre but declines to 1.52 MPa at 1% fibre concentration. Oil palm fibre reduces compressive strength to 1.6 MPa at 1%, whereas both coconut husk and oil palm fibres yield lower strength at higher percentages. In contrast, banana and jute fibres [77] demonstrate higher strengths in reinforced soil blocks, with banana fibre reaching 13.59 MPa at 1% content and jute fibre achieving 18.04 MPa, thus establishing jute as a superior reinforcing option. Seagrass and straw fibres [78] show modest strengths in adobe bricks, with values of 2.640 MPa and 2.824 MPa at 1.5%, respectively.

Diverse ash materials reveal different performance characteristics in unfired and stabilised earth bricks. Cement-stabilised soil blocks incorporating sugarcane bagasse ash [82] display strengths ranging from 2.59 MPa to 5.85 MPa, with performance improving at elevated binder content. Rice husk ash [81] contributes compressive strengths of 3.3 MPa to 4 MPa at 7.5%, decreasing to 2 MPa at 20%. Ground granulated blast furnace slag [84], when combined with quicklime or cement kiln dust, can achieve peak strengths of about 24.5 MPa and 19.6 MPa, respectively. When integrated with binders such as cement, stabilised mixtures present significant potential for improving compressive strength.

Most of the studies on unfired bricks with waste fibres have considered evaluating tensile strength behaviour. Tensile strength varies widely across different materials and mixtures. The results are shown in Table 5. Compressed soil blocks incorporating bagasse fibres in red soil [76] achieve a peak tensile strength of 0.8 MPa at a fibre content of 0.75%, which subsequently decreases to 0.73 MPa at 1% content. In comparison, fibres derived from coconut husk [76] and oil palm [76] exhibit lower tensile strengths, with coconut husk reaching a maximum tensile strength of 0.35 MPa. Reinforced soil blocks demonstrate significantly enhanced tensile performance [77], with jute fibre achieving an impressive 9.89 MPa and banana fibre, while comparatively lower, attaining 7.46 MPa at 1% fibre content. Alkali-resistant glass fibres [77] provide moderate reinforcement, peaking at 3.99 MPa, while polypropylene fibres [77] achieve a tensile strength of 5.44 MPa. Furthermore, adobe bricks reinforced with fonio straws [79] exhibit reduced flexural strength. Flexural strength and modulus of rupture provide additional insight into the bending behaviour of bricks. However, only a few studies have been performed. The results are shown in Table 5. Similarly, the modulus of rupture in reinforced soil blocks is significantly affected by the type and quantity of fibres employed [77]. Polypropylene fibres [77] exhibit the highest modulus of rupture among the examined fibres, with a peak value of 0.678 Pa at a concentration of 0.55%. At 0.5% concentration, alkali-resistant glass fibres [77] display a modulus of rupture of 0.626 Pa. Jute fibre [77] has a higher modulus than banana fibres, achieving a modulus of rupture of 0.611 Pa at 0.5% content, while banana fibres [77] yield a slightly lower modulus of rupture of 0.551 Pa. For adobe bricks [78], flexural strengths are relatively modest; straw fibres reach 0.472 MPa at a 1.5% fibre content, and seagrass fibres exhibit slightly superior performance at 0.502 MPa with a 3% fibre content. These findings emphasise the importance of selecting appropriate stabilisers and fibre types tailored to specific applications to optimise the structural integrity of bricks.

3.4.3. Concrete Blocks

The results of concrete blocks are shown in Table 6 and Figure 13. Agricultural wastes, such as coffee husk and sugarcane bagasse [85] demonstrate peak compressive strength at lower content levels. Specifically, at 5% content, sugarcane bagasse achieves a compressive strength of 7.02 MPa; however, this value decreases to 4.73 MPa at 10% content, likely due to an increase in voids. A similar pattern is observed for coffee husk, which reaches a maximum strength of 5.92 MPa at 5% content and subsequently declines to 3.8 MPa at 7.5%. Conversely, sawdust results [86] in a pronounced reduction in compressive strength, plummeting from 5.92 MPa at 0% content to just 0.83 MPa at 20% content, indicating its unsuitability for load-bearing applications. Specialised materials, such as EPS waste [29], display a significant reduction in strength, decreasing from 9.5 MPa at 0% content to 2.4 MPa at 26% content, indicating that these materials are primarily applicable for lightweight, non-structural purposes. Similarly, materials like crumb rubber and polymers [91] also reduce strength, positioning them for insulation or lightweight components. In contrast, the strength of lime mud [86] peaks at 7.56 MPa at 5% content and shows consistent performance, while palm oil ash [89] performs better in wet curing, peaking at 28 MPa at 20% content. Among the recovered materials, recycled aggregates [92,93] present the highest compressive strength, rendering them suitable for high-strength applications.

Flexural strength is less frequently reported in Table 6 for concrete blocks. In the case of coco pith [90], the flexural strength peaks at 2.21 MPa at 4% content and declines to 1.81 MPa at 8%, suggesting that moderate additions enhance flexural properties, while larger content adversely affects them. Recycled aggregate concrete [93] achieves a maximum flexural strength of 4.2 MPa at a 1:6 ratio; however, a notable decline occurs as aggregate concentration rises, dropping to 0.65 MPa at a 1:24 ratio. These results underscore the necessity of careful material selection, as various wastes and recycled aggregates exhibit differing strengths contingent upon their intended applications.

3.5. Thermal Conductivity

3.5.1. Fired Bricks

The study investigates the thermal conductivity of various waste materials, offering valuable insights into their prospective applications in insulation and thermal storage. The findings reveal distinct patterns associated with material type and composition. Analysis of thermal conductivity data from various waste materials indicates considerable variability in their potential for insulation purposes. The results of fired bricks are illustrated in Table 4 and Figure 14. Ash-based waste materials demonstrate moderate reductions in thermal conductivity. Specifically, rice husk ash [67] exhibits a gradual decline in conductivity, decreasing from 1.05 (0%) to 0.68 (30%) at 1000 °C, indicating consistent insulating properties even at elevated temperatures. Wood ash [67] reflects a similar trend, with conductivity values decreasing from 1.05 (0%) to 0.753 (30%) at 1000 °C, although its insulating capacity is marginally inferior to that of rice husk ash. Some materials have been examined across various firing temperatures, yielding only slight increases in thermal conductivities. Paper mill sludge [72] reveals marked reductions in conductivity across various temperatures, with values diminishing from 0.54 (0%) to 0.242 (30%) at 900 °C, thereby demonstrating considerable insulating potential. In contrast, other waste materials, such as bottom ash and pumice, maintain relatively higher thermal conductivity values. Furthermore, olive mill waste [68], when integrated into the soil, progressively reduces conductivity across temperature ranges from 850 °C to 1050 °C, with values declining from 0.69 (0%) to 0.477 (10%) at 1050 °C, thus rendering it a strong insulating material. Cigarette butts [65] also demonstrate a substantial reduction in conductivity, from 1.08 (0%) to 0.45 (10%) at 1050 °C, underscoring their high insulating capability. The lowest conductivity resulted from the use of activated alumina sludge [66], though the decrease was marginal, while a notable reduction was obtained from the use of pomegranate peel waste [73]. These findings highlight the critical importance of material selection for tailored thermal applications.

3.5.2. Unfired Bricks

These findings for unfired bricks are detailed in Table 5 and illustrated in Figure 15. Adobe bricks incorporated with straw or seagrass fibres [78] exhibited enhanced thermal performance as the fibre content increased. For instance, incorporating straw decreased the thermal conductivity from 0.83 W/m·K to 0.62 W/m·K with an increase from 0% to 3% by weight. Similarly, the inclusion of sawdust and straw in adobe bricks significantly diminished thermal conductivity. The use of fonio straw in adobe bricks [79] also resulted in a notable reduction in conductivity, from 1.08 to 0.35 W/m·K at a 1% content level.

3.5.3. Concrete Blocks

The results of concrete blocks are shown in Table 6 and Figure 16. The thermal conductivity of sugarcane bagasse blocks [85] decreases with increasing waste content, changing from 0.467 W/m·K at 0% to approximately 0.360 W/m·K at 7.5%, followed by a slight increase beyond 10%. In contrast, coffee husk [85] demonstrates minimal variation in conductivity, with values fluctuating from 0.467 W/m·K at 0% to 0.489 W/m·K at 10%, and a minimum of 0.434 W/m·K observed at 7.5%. Sawdust [86] is noted for producing a significant decrease in thermal conductivity, with values declining from 1.12 W/m·K at 0% to 0.55 W/m·K at 20%. A more consistent reduction in conductivity is noted in materials such as wood ash [86], lime mud [86], rubber [91], and polymers [91] as the waste content increases. Blends of marble dust [92], particularly those combined with fine wood aggregates and recycled glass, yield further improvements in thermal performance, achieving a reduced conductivity as low as 0.723 W/m·K.

3.6. Shrinkage

3.6.1. Fired Bricks

The results of fired bricks are shown in Table 4 and Figure 17. Spent shea waste [71] incorporation in clay bricks had a negligible influence on shrinkage behaviour, while firing temperature was the dominant controlling factor. The results showed a marked increase in shrinkage up to 1000 °C due to vitrification processes, after which values stabilised, with all brick samples exhibiting shrinkage below 8%. Meanwhile, the increasing content of paper mill sludge [72] caused only a slight and statistically insignificant increase in shrinkage, with 15% content exhibiting a firing shrinkage of 2.95% at 950 °C, comparable to the control bricks of 2.74%. Similarly, cigarette butts [65] also increased the shrinkage, then decreased it, peaking at 9.01% at 5% content, though the variation is more pronounced, revealing the impact of various wastes. In contrast, the addition of rice husk ash [67] generally increased shrinkage at higher contents (>10 wt.%), while low additions caused slight expansion, whereas wood ash [67] slightly reduced expansion without a strong dosage-dependent effect; these behaviours are linked to earlier liquid phase formation and gas entrapment in closed pores during sintering.

3.6.2. Unfired Bricks

The results of unfired bricks are shown in Table 5 and Figure 18. Bagasse, coconut husk, and oil palm fruit fibres [76] reduced linear shrinkage in both soil types from about 1.05% (red soil) and 0.90% (brown soil) to minimum values of 0.35–0.42%, with oil palm fibres giving the greatest reduction. This improvement is attributed to fibre reinforcement limiting soil matrix deformation through friction and interlocking. Meanwhile, all fibre types [77] effectively reduce linear shrinkage, with jute fibre [77] and polypropylene fibre [77] providing greater control, while all measured values remained below 1.8%. In contrast, straw fibres [78] performed better than seagrass [78] due to improved fibre–soil bonding, while seagrass fibres led to greater internal void formation and reduced performance. Overall, the collected findings consistently demonstrate that shrinkage in earthen and masonry materials is primarily governed by material composition and content, while the incorporation of fibres effectively reduces shrinkage and improves dimensional stability, confirming their suitability for enhancing construction material performance.

3.7. Efflorescence

Efflorescence, indicating salt crystallisation on brick surfaces, varied depending on the waste material used. Efflorescence tests on various brick types reveal notable variations in performance. The results are shown in Table 4 and Table 5. For instance, burnt clay bricks without fly ash [70] exhibited slight efflorescence (7.4%), while bricks containing 20% and 25% fly ash showed reduced efflorescence levels (3.8% and 3.6%), likely due to fly ash’s ability to bind salts and free lime. Other studies found slight to moderate efflorescence in bricks with paper mill sludge [72] dosages ranging from 0% to 10%, while higher dosages (15% to 30%) showed moderate efflorescence but no powdering, flaking, or cracking. In addition, bricks made from activated alumina sludge-clay mixtures (0%, 5%, and 10%) [66] showed no efflorescence or aesthetic changes.

Few studies have considered the evaluation of the efflorescence of unfired bricks. Blocks made with crushed brick waste [80] showed no signs of efflorescence, while control bricks developed a fine layer of efflorescence on their surfaces. The efflorescence test on stabilised soil blocks [82] with sugarcane bagasse ash showed no evidence of efflorescence in any of the combinations. Additionally, surface efflorescence of concrete blocks with coco pith [90] was observed, with its severity gradually reducing as the coco pith content in the mortar increased.

3.8. Durability

3.8.1. Fired Bricks

For fired bricks, the results are shown in

Table 7. The impact of various wastes on the leachate of fired bricks.

Ref.	Waste Type	Waste Content/Condition	Key Leached Constituents (mg/L, Reported Range or Representative Value)	Regulatory Compliance/Trend
[65]	Cigarette butts	0–10 wt.% in clay bricks	As: 0.007–0.123; Zn: 0.115–1.145; Cu: 0.155–0.295; Pb: 0.004–1.941; Ba: ~0.27–0.30; Cr: 0.003–0.008; Ni: 0.002–0.004	All metals below typical TCLP limits; Pb, Zn show highest variability with CB content
[66]	Activated alumina sludge	0%, 5%, 10% sludge in bricks	Al: 0.9–3.0; Fe: 0.4–0.8; Cu: ~0.20; Na: 773–1122; Ca: 18–70; SO42−: 22–169; F−: 0–1	All measured values within standard limits; increasing sludge slightly increases sulphate, fluoride, and nitrate release
[67]	Rice husk ash & wood ash	Control vs. 30 wt.%	As: 0.022–0.153; Ba: 0.096–1.157; Cr: 0.115–0.554; Cu: 0.181–0.642; Ni: 0.007–0.088; Pb: 0.0001–0.0076; Zn: 0.004–0.058; Hg: ~0.00003–0.00007	All elements comply with USEPA and Spanish limits; higher firing temperature improves immobilisation efficiency.

. Mohajerani, Kadir and Larobina [65] evaluated the heavy metal leaching behaviour of bricks manufactured with cigarette butts. The results showed that all heavy metal concentrations were within the established regulatory limits, indicating that the bricks containing cigarette butts did not pose a significant environmental risk under the tested conditions. Furthermore, increasing the cigarette butt content in the mixture led to a slight increase in the concentrations of arsenic, zinc, and copper, while the concentrations of chromium and lead decreased significantly, indicating effective fixation of these elements within the ceramic matrix.

Pokhara, Ekamparam [66] evaluated the leaching properties and acid resistance of activated alumina sludge-clay bricks. The results showed that all measured elements in the leached effluent were within permissible regulatory limits determined using Indian drinking water standard limits, USEPA-TCLP technical assistance document, and Ontario Environmental Protection Act, indicating that these types of bricks are not classified as hazardous materials. It was also found that the burning process helped to stabilise pollutants within the brick structure, as the released anions such as fluoride, chloride, nitrate, and sulphate decreased significantly (by approximately 52, 38, 6, and 10 times, respectively) compared to their content in the original sludge, indicating a high effectiveness in trapping pollutants within the solid matrix. However, acid resistance tests showed that increasing the sludge content led to a deterioration in mechanical properties. The brick’s capacity gradually decreased from Class I in the reference brick (0% sludge) to Class II at 5%, while increasing the sludge content to 10% resulted in the brick failing to meet the requirements of Class II. Despite this, these materials remain suitable for use in low-load structural applications, such as in single-floor buildings, parapet walls or boundary walls, as they meet basic compressive strength requirements.

Eliche-Quesada, Felipe-Sesé [67] investigated the leaching capacity of heavy metals in clay bricks containing biomass ash. The results showed that heavy metal concentrations in the leaching were very low, indicating that the produced bricks are not classified as hazardous materials. Although arsenic (As) and mercury (Hg) are considered among the elements of greatest concern, their measured concentrations remained within inert and non-hazardous levels. The results also showed that increasing the firing temperature to 1000 °C improved stabilisation performance and reduced leaching. This is attributed to the increased vitrification, which reduces the movement of heavy metals within the ceramic structure, thus enhancing the efficiency of incorporating biomass ash into the bricks as an effective means of stabilising pollutants.

3.8.2. Unfired Bricks

The results of unfired bricks are shown in

Table 8. The impact of various wastes on the durability of unfired brick.

Ref.	Waste Type	Test Type	Key Quantitative Results	Main Observations/Interpretation
[76]	Oil palm, coconut, bagasse fibres	Wearing	Red Soil: 20–38% (wearing reduction); brown Soil: 47–50%	Coconut fibre showed highest performance; optimal at ~0.5 wt.%
	Oil palm, coconut, bagasse fibres	Erosion (spray test)	Red Soil: 50–70%; brown Soil: 44–50% reduction	Strong improvement due to fibre network binding soil particles
	All fibres	Correlation analysis	r = 0.955–0.997 (wearing vs. erosion)	Very strong correlation → tests are interchangeable
	All fibres	Mechanical–durability correlation	Weak correlation	Strength/density not reliable durability predictors
[77]	Jute fibre	Wearing (abrasion)	Up to ~95% reduction at 1% fibre	Best-performing natural fibre due to strong bonding
	AR glass fibre	Wearing (abrasion)	~39.2% reduction	Lowest abrasion resistance among fibres
	Jute fibre	Erosion resistance	~50% reduction	High resistance to rainfall-induced degradation
	AR glass fibre	Erosion resistance	~26% reduction	Limited erosion protection compared to natural fibres
	All fibres	General trend	Increasing fibre → decreasing wear/erosion	Performance improves with fibre dosage
[79]	Fonio straw fibre	Spray erosion (2 bar, 10 min, 30° tilt)	High erosion (control) → low erosion (reinforced)	Fibre significantly improves water resistance
	Fonio straw fibre	General durability trend	Weight loss decreases with fibre content	Improved cohesion reduces surface disintegration
[80]	Crushed brick waste	Wet–dry cycles	Compressive strength: +37–47%; flexural: +1.13–1.42×; mass loss up to ~4.72%	Microstructural densification via hydration/pozzolanic reaction. Higher waste content increases shrinkage/swelling effects.
	Crushed brick waste	Sulphate exposure (Na2SO4)	+29–35% strength increase	Ettringite/CSH formation improves durability
[81]	Rice husk ash	Water spray erosion	2.19–8.51 mm pitting depth	Within acceptable standards
	Rice husk ash	Acid resistance (pH 3–5)	Severe damage at pH 3; mild at pH 5	Acid attack on calcium phases causes cracking
	Rice husk ash	General trend	Higher RHA → reduced cracking	Pore filling improves resistance to acid damage

. Danso, Martinson [76] evaluated the durability properties of fibre-reinforced earth blocks by conducting abrasion (wetting-drying/wearing) and erosion tests. The results showed that the addition of fibres led to a significant improvement in erosion and weathering resistance. A rapid decrease in loss rates occurred up to a fibre content of approximately 0.5% by weight, after which the improvements stabilised, or their effect diminished slightly. Abrasion reductions of 20–38% were recorded in red soil and 47–50% in brown soil, while erosion resistance improvements ranged from 44–70%, demonstrating the effectiveness of fibres in stabilising soil particles and reducing their loss, while physical properties such as density and water absorption exhibited the opposite behaviour compared to materials stabilised with traditional binders. In general, the results indicate that the durability performance of these systems depends primarily on the interaction of the fibres with the soil and not on traditional mechanical properties.

Sujatha and Selsia Devi [77] evaluated the durability of the earth blocks using abrasion and erosion resistance tests under harsh operating conditions representing various environmental factors. The results showed that reinforcing the blocks with fibres significantly improved their abrasion and erosion resistance, with loss rates decreasing markedly as the fibre content increased. Jute fibres achieved the highest efficiency, with an erosion reduction of approximately 95%, while glass fibres performed the least, with a reduction of approximately 39.2% when 1% of the fibres were added. This reflects the effect of the strong bond between the fibres and the soil matrix.

The study by Ouedraogo, Dao [79] aimed to evaluate the behaviour of unreinforced adobe bricks reinforced with fonio straw fibres under humid conditions using a water spray test. The results showed that the addition of the straw resulted in a significant reduction in mass loss, reflecting improved resistance to water abrasion compared to unreinforced bricks, which experienced severe deterioration. This improvement is attributed to increased fibre cohesion with the clay matrix, thus limiting particle drift under the influence of water.

The durability of the compressed earth blocks with crushed brick waste was evaluated by Kasinikota and Tripura [80] through periodic wet-dry and sulphate resistance tests. The results showed that exposure to wetting-drying and sulphate cycles generally led to an increase in compressive and flexural strength rather than a decrease. This is attributed to accelerated hydration and pozzolanic reactions, as well as increased internal density. Blocks with higher proportions of crushed brick residue also exhibited the best mechanical performance after curing.

Meanwhile, Yatawara and Athukorala [81] assessed the erosion and acid resistance of compressed earth blocks with rice husk ash, measuring pitting depth and pitting rate using a controlled water spray system. The results showed that the blocks exhibited moderate to good resistance to water erosion, with pitting depths ranging from 2.19 to 8.51 mm and pitting rates from 0.038 to 0.147 mm/min. In contrast, exposure to an acidic environment, especially at a low pH (3), led to increased mass loss and the appearance of surface cracks, while the high ash content of rice husks contributed to reducing cracks by improving the porous structure and facilitating the deposition of salts within the pores, which improved the resistance of the masses to acidic environments.

3.8.3. Concrete Blocks

Compared with unfired bricks, fewer studies have investigated the durability performance of waste-based concrete blocks. The results of concrete blocks are shown in

Table 9. The impact of various wastes on the durability of concrete blocks.

Ref.	Waste/System	Waste Content	Test Types	Key Numerical Results (Ranges)	Observations/Mechanism
[29]	EPS hollow blocks	0–26% EPS	5% H2SO4 cyclic ponding (4 cycles); sulphate/chloride ponding; salt precipitation; compressive strength loss	Water absorption: 0.47–4.61%; Acid cyclic weight loss: 0.28–47.43%; Salt solution absorption: 0.26–4.71%; Salt precipitation: 0.00–2.85%; Compressive strength loss: 6.1–47.4%	Increases porosity but improves chemical resistance by blocking transport pathways; however, strength becomes variable due to changes in pore structure.
[90]	Coco pith (cement-sand block)	0–8%	Sorptivity, drying, wet–dry cycles, acid/salt/alkali exposure	Sorptivity: increases from baseline (good class ~0.77–1.94 mm/min½) to highest at 8%; Initial drying rate (D1): decreases at 4%, ~control at 6–8%; Second drying rate (D2): up to ~6.3% lower than control (8%); Drying index (Di): increases with content; Compressive strength loss (12 cycles): 25.5% (0%), 33.8–44.1% (4–8%); Acid strength loss (21 days): 6.4–13.1%; (42 days): 10.9–23.9%	Increases porosity and water uptake, reduces drying performance, and accelerates strength loss due to fibre–matrix debonding and acid-induced C–S–H degradation.

. Cyclical immersion tests in sulfuric acid (H₂SO₄) were conducted by Ali, Fahmy [29] to assess resistance to acidic environments. Additionally, immersion tests in high-concentration sodium chloride solution were performed to simulate the effects of saline environments. Repeated wetting and drying cycles were applied to measure changes in mass and mechanical strength. The results showed that in acidic environments, severe deterioration was observed in the reference samples, with the formation of gypsum and ettringite layers and reinforcement corrosion. In contrast, the EPS-containing blocks showed reduced mass loss and improved corrosion resistance due to reduced permeability to aggressive materials and their entrapment within the porous structure. The results also indicated that the EPS-containing blocks with reinforcement exhibited more ductile failure behaviour and a higher ability to maintain structural shape, retaining approximately 70–80% of their compressive strength. This demonstrates a clear improvement in performance under harsh environmental conditions, despite some continued deterioration related to salt crystallisation and gradual corrosion.

A drying test was conducted by Sathiparan, Anburuvel [90] according to a standard protocol after the samples were fully saturated. Mass loss was monitored over extended periods to determine the drying rates in the first and second stages, as well as the drying index. Wet-dry cycle resistance tests were performed on the mortar cubes by subjecting them to several repeated cycles of water immersion and thermal drying. The development of compressive strength was measured during the different test stages. The results showed that the addition of coco pith increased water permeability due to increased porosity. The drying tests also showed that the drying rates in the first stage were higher than in the second. Performance decreased relatively at lower fibre content and increased as fibre content increased, while the drying index increased with increasing fibre content. The wet and dry cycles showed that compressive strength decreased gradually with an increasing number of cycles, and the rate of decrease was higher in the samples containing fibres compared to the reference sample due to increased porosity and weaker internal bonds.

3.9. Environmental and Economic Impacts

Environmental and economic assessments were reported in only a limited number of studies, and the evaluation methods varied between investigations. Therefore, the following discussion summarises the reported environmental and economic benefits of waste incorporation within each masonry system rather than providing a direct quantitative comparison between fired bricks, unfired bricks, and concrete blocks.

Mohajerani, Kadir and Larobina [65] reported that the toxicity equivalents of gases from cigarette butt bricks showed a reduction pattern with varying heating rates, with most gases reaching their lowest values at a heating rate of 10 °C min⁻¹, except for HCN, which peaked at 0.7 °C min⁻¹. CO levels decreased by 81%, while CO₂, NO, and HCN also showed significant reductions. Emissions from cigarette butt bricks were higher than those from clay bricks at lower heating rates but declined at higher rates, especially for CO and CO₂. This decrease in emissions at elevated heating rates can be attributed to the reduced organic content from carbonised biomass and improved structural integrity of the pore network. Despite some peak values at high heating rates, overall emissions decreased significantly over time. The energy savings for cigarette butt bricks with 2.5% and 5% cigarette butt content were estimated at 31% and 58%, respectively. This suggests that organic matter in clay enhances the firing process. Integrating cigarette butts improves heat input in the firing furnace, reducing energy consumption. However, the estimates are preliminary and do not account for all variables, such as the role of organic content in clay.

The study by Ahmed, El Attar [73] highlights that bricks made from pomegranate peel waste (PPW) can significantly improve thermal performance, reduce energy consumption, and lower CO₂ emissions in buildings. PPW bricks, particularly the PPW-15% variant, can decrease annual CO₂ emissions by up to 24.53%, with lower percentages (PPW-5%, PPW-7.5%, PPW-10%) achieving reductions of 7.50–15.65%. The energy savings and CO₂ reduction are particularly notable in hot, dry environments like Aswan and Jazan, with PPW-15% saving 31.16% in energy and 23.14% in CO₂ emissions in Jazan. Moreover, using 15% PPW in bricks can cut energy consumption by 33.13%, making it an economical option for low-income housing in Aswan, Egypt. A cost analysis reveals that PPW-15% bricks have the shortest payback period (2.26 years), offering the best financial benefit compared to other brick samples. The study shows that PPW-15% bricks provide significant energy savings and a quick return on investment, making them a viable solution for reducing energy costs.

A cost comparison by Sujatha and Selsia Devi [77] between fired bricks with 1:6 cement mortar and reinforced soil blocks with the same mortar mix reveals that reinforced soil blocks offer significant economic benefits. Soil blocks reinforced with natural fibres (banana, jute) are approximately 43% cheaper than fired bricks. In contrast, synthetic fibre-reinforced soil blocks (alkali-resistant glass, polypropylene) cost Rs. 1202 due to higher manufacturing costs. Cost savings are more significant with natural fibres, which are cheaper due to their local abundance. When using synthetic fibres, the cost reduction is around 1.28%, while natural fibres lead to a 19.35% reduction. This highlights the economic advantages of using natural fibre-reinforced soil blocks.

The study by Sathiparan, Anburuvel [90] aimed to evaluate the economic and environmental feasibility of incorporating coco pith into the production of cement and sand blocks. The results showed that increasing the percentage of added material led to a gradual decrease in raw material costs, ranging from 4.3% to 9.3%, compared to the reference block. In terms of economic efficiency, mortar containing 4% coco pith performed best, with a reduction in strength costs of 11.6% compared to the reference sample, while mixes up to 6% remained more economically viable. Furthermore, the partial replacement of conventional materials with coco pith reduced embodied energy consumption by up to 9.4% and CO₂ emissions by up to 9.2% during production. The study attributed these improvements to reduced cement consumption and lower raw material transportation requirements. The results confirm that using coco pith in moderate proportions is a sustainable option that enhances economic efficiency and reduces the environmental impact of construction products.

Al-Tarbi, Baghabra Al-Amoudi [91] aimed to evaluate the economic and environmental performance of building walls using improved blocks incorporating recycled HDPE and LDPE plastic waste. The results showed that while the initial cost of these blocks was higher than that of conventional blocks due to the processing and recycling, their superior thermal resistance contributed to a reduction in energy consumption and annual air conditioning costs of up to 57%. HDPE blocks also achieved superior thermal performance compared to other types, positively impacting operational energy demand. Furthermore, improved thermal insulation led to a reduction in fuel consumption and CO₂ emissions ranging from 53% to 56%, depending on the block type and energy source. These findings underscore the viability of using blocks containing recycled plastic as a sustainable solution that combines long-term economic benefits with reduced environmental impact.

The study by Kuoribo, Shokry and Mahmoud [92] estimated CO₂ emissions of concrete blocks in terms of transportation, based on the distance travelled to deliver raw materials. The reference block had the highest emissions, exceeding 550 kgCO₂/m³. However, mixes with alternative materials reduced emissions by up to 30.04% compared to the standard mix. This underscores the environmental benefits of substituting cement and natural aggregates with recycled waste materials. Overall, reducing typical quantities of cement, fine, and coarse aggregates in concrete mixtures is vital for both cost efficiency and the mitigation of carbon emissions in concrete block production. Kuoribo, Shokry and Mahmoud [92] analysed the quantities of concrete ingredients and the total costs for producing 1000 solid concrete blocks (25 × 13 × 6 cm), incorporating transportation, equipment, labour, and material waste expenses. Notably, recycled waste materials, sourced at no additional cost, served as alternative raw materials. The findings revealed that standard concrete block mixes incurred the highest production costs, but significant cost savings were achieved when over 75% of conventional materials were replaced with alternatives. Specifically, the developed blocks saved EGP 715.00 ($23.14) per 1000 blocks compared to industry-standard blocks. Crushed marble, used as coarse aggregate, offered additional cost advantages due to local availability.

The study by Dafedar, Rao [93] explored CO₂ emissions (CO₂-e) of various concrete mix ratios, focusing on small- and medium-sized businesses (SMBs). Using the embodied carbon gate-to-gate methodology, the research quantified emissions for all mixed components based on one cubic metre of concrete and assessed these using the Engineering Environmental Index (EEI) and the Engineering Economic Index (EEI). The findings revealed that increasing aggregate proportion relative to cement (i.e., higher cement-to-aggregate (C: A) ratios) resulted in lower CO₂ emissions, with a 1:21 mix ratio achieving a 55.36% reduction compared to a 1:6 ratio, and a 1:13 mix achieving a 39.50% reduction. Dafedar, Rao [93] highlighted the cost-effectiveness and additional advantages of using recycled concrete aggregates (RCAs), which are approximately 1 INR per kilogram to produce33% cheaper than river sandand 28% cheaper than manufactured sand. Beyond their ability to reduce carbon emissions, RCAs offer significant cost savings, reinforcing their value in sustainable construction practices.

Overall, the reviewed studies indicate that waste incorporation can contribute to reduced environmental impacts through lower energy demand, reduced consumption of conventional raw materials, and improved thermal performance. However, the magnitude of these benefits remains highly dependent on the waste type, manufacturing process, system boundaries, and assessment methodology. Consequently, standardised life cycle assessment approaches are required to enable reliable comparison of environmental performance among different masonry systems. Future research should also adopt a unified economic assessment framework considering material costs, waste processing and transportation costs, manufacturing energy requirements, labour, durability, maintenance requirements, and potential operational energy savings. Such an approach would enable a more reliable comparison of the economic feasibility of waste-based masonry systems.

3.10. Optimum Content

The analysis of waste materials reveals the optimal content for each type, thereby enhancing their performance in terms of incorporation and potential applications. The results illustrate that most materials achieve their optimal performance at contents below 20%, although certain materials have more specific requirements. The optimum waste incorporation levels reported in this review represent the values identified within the individual studies under their specific experimental conditions. These values should not be interpreted as universal optimum contents, as they depend on the waste type, masonry unit, material composition, processing method (e.g., firing temperature or curing regime), and the performance criteria being evaluated.

3.10.1. Fired Bricks

The results of fired bricks are shown in

Table 10. Comparative summary of reported optimum waste materials in fired bricks.

Ref.	Waste Material	Reported Optimum Material/Content	Optimum Property Achieved	Reason for Optimum Selection
[65]	Cigarette butt	1%	48 million tonnes of CBs could be recycled every year	Incorporating only 1% CB into bricks could recycle cigarette waste globally
[66]	Activated alumina sludge	10%	Compressive strength 5.4 MPa; thermal conductivity 0.19 W/m·K; porosity 40.6%; density 1690 kg/m3	Optimum because it achieved maximum sludge utilisation while maintaining sufficient strength for low-end structural applications and improving insulation performance.
[67]	Rice husk ash	10 wt% at 1000 °C firing	Thermal conductivity 0.70 W/m·K; compressive strength 35.9 MPa	Selected because it achieved significant insulation improvement while maintaining acceptable mechanical properties; higher RHA levels increased porosity and reduced durability.
[67]	Wood ash	20 wt% at 1000 °C firing	Compressive strength 53.7 MPa; thermal conductivity reduction ≈ 15%	Chosen as the best WA condition because it maintained mechanical strength close to conventional bricks while improving insulation and reducing clay consumption.
[68]	Olive mill waste	10 wt% at 950 °C firing	Density 1450 kg/m3; thermal conductivity 0.436 W/m·K; compressive strength 10.26 MPa; porosity 47%	Optimum formulation because it provided the best balance between lightweight characteristics, thermal insulation, and sufficient structural strength.
[69]	Rice husk ash	4 wt%	Compressive strength 3.55 MPa; water absorption 19%; temperature reduction ≈6 °C	Optimum due to improved silica-based bonding, maximum strength enhancement, acceptable durability, and improved thermal/acoustic performance.
[70]	Fly ash	10%	Balanced compressive strength, durability, and weight reduction	Recommended as the practical optimum because it maintained construction suitability while reducing brick weight and improving sustainability. Higher FA levels reduced flexural strength and breaking load.
[72]	Paper mill sludge	15% at 950 °C firing	Compressive strength 10.39 MPa; thermal conductivity 0.345 W/m·K; water absorption 18.77%; porosity 39.05%	Optimum because it achieved the required mechanical strength while providing significant thermal insulation, density reduction, and waste recycling benefits.
[74]	Rice straw ash	2%	Compressive strength 11.10 MPa; brick weight 2.86 kg; water absorption < 15%	Optimum practical replacement because it maintained strength and durability close to conventional bricks while reducing weight and enabling agricultural waste recycling.

and Figure 19. Materials with relatively low optimal contents include cigarette butts [65] and rice straw ash [74], which perform best at 1% and 2%, respectively. These materials are particularly effective in applications where minimal incorporation is essential. Conversely, materials such as olive mill waste [68], waste fly ash [70], and activated alumina sludge [66] attain their optimal performance at 10%. This proportion facilitates a balanced integration of waste, preserving properties. Additionally, other materials, including paper mill sludge [72]. In contrast, wood ash [67] demonstrates efficacy at higher contents up to 20%. Rice husk ash [67,69] exhibits variability in optimal content and firing temperature across various studies, with reported values ranging from 4% to 10%. This variability may stem from the influence of firing temperatures on the material’s performance, particularly in applications such as brick production. This observation emphasises the importance of firing conditions in optimising the efficacy of waste-derived materials. It is crucial to note that many materials demonstrate their optimal content at different firing temperatures. Generally, firing temperatures below 850 °C led to diminished performance levels. Some materials, such as spent shea waste [71], have documented specific optimum firing temperatures. These findings highlight the essential nature of establishing the optimal content and processing conditions for each waste material.

3.10.2. Unfired Bricks

As illustrated in

Table 11. Comparative summary of reported optimum waste materials in unfired bricks.

Ref.	Waste Material	Reported Optimum Material/Content	Optimum Property Achieved	Reason for Optimum Selection
[75]	Lithomargic clay + GBFS + cement blocks	75% clay + 25% GBFS + 10% cement	5.15 MPa dry strength, 3.63 MPa wet strength, 12.96% absorption	Provided the highest strength and acceptable water absorption through the combined effects of slag reaction and cement hydration, making it suitable for load-bearing masonry.
[75]	Lateritic soil + GBFS + cement blocks	80% soil + 20% GBFS + 6% cement	4.70 MPa dry strength, 3.61 MPa wet strength, 11.7% absorption	Achieved the required mechanical performance while reducing cement consumption owing to the favourable grading of lateritic soil.
[76]	Coconut, oil palm, bagasse	0.5 wt.%	Maximum strength and durability improvement	Provided the greatest improvement in strength and durability while avoiding the increased porosity associated with higher fibre contents.
[77]	Jute fibre	1%	Compressive strength 18.04 MPa; tensile strength 9.89 MPa; modulus of rupture 0.611 MPa	Delivered the greatest overall improvement in mechanical strength and durability through strong fibre–soil bonding and effective crack control.
[77]	Banana fibre	1%	Compressive strength 13.59 MPa; tensile strength 7.46 MPa; modulus of rupture 0.551 MPa	Achieved substantial strength enhancement by improving fibre–soil interaction and limiting crack propagation.
[77]	Polypropylene fibre	1%	Maximum energy absorption of 16.3 kNmm	Provided the highest energy absorption by improving ductility and post-failure crack bridging.
[77]	AR glass fibre	0.75%	Optimum artificial fibre performance	Achieved the best reinforcement efficiency, whereas higher fibre contents caused fibre clustering and reduced performance.
[78]	Straw fibres	0.5%	Compressive strength 2.824 MPa; thermal conductivity 0.755 W/m·K	Achieved the highest compressive strength by providing effective bonding and crack control without creating excessive voids. Produced the greatest thermal insulation by increasing internal porosity and reducing heat transfer.
[78]	Seagrass fibres	1.5%	Compressive strength 2.672 MPa; thermal conductivity 0.73 W/m·K	Provided the best balance between mechanical strength and thermal insulation through improved fibre interlocking and stress transfer.
[79]	Fonio straw adobe (compressive performance)	0.4 wt.%	Maximum compressive strength of 2.9 MPa	Produced the highest compressive strength by improving fibre dispersion, stress transfer, and matrix stability.
[80]	Crushed brick waste (CBW) stabilised CSEB	24%	9.57 MPa dry strength and 8.43 MPa wet strength	Provided the highest dry and wet strengths through pozzolanic reactions, improved particle packing, and filler effects.
[82]	Sugarcane bagasse ash (SBA) + cement soil blocks	4% cement + 8% SBA	2.95 MPa compressive strength; Class 30 requirement achieved	Achieved the required compressive strength while reducing cement content through the secondary cementitious reactions of SBA.

and Figure 20 on unfired bricks, materials like bagasse [76], coconut husk [76], and oil palm fruit [76] consistently demonstrate low optimal content values, averaging around 0.5%. Likewise, fibres, including banana fibre [77], jute fibre [77], and polypropylene fibre [77], achieve optimal performance at 1%, reflecting their uniform behaviour across diverse applications. Straw wastes [78,79] also exhibit low optimal content values, ranging from 0.4% to 0.5%. Notably, among fibre-based materials, seagrass [78] distinguishes itself with a higher optimal content of 1.5%, which is the highest within this category. Brick stabilisation further highlights the significance of cement content; a mix comprising 75% soil, 25% GGBS, and cement [75] necessitates an optimal cement content of 10%, while a mixture of 80% soil, 20% GGBS, and cement [75] requires a slightly lower optimal cement content of 6%. The combination of varying percentages of sugarcane bagasse ash with up to 4% and 10% cement [82] yields an optimal content of 8% when combined with 4% cement. The use of crushed brick waste [80] shows the highest optimal content of 24%. The variability in optimal content reflects the distinct properties inherent to each waste material. This adaptability contributes significantly to the advancement of sustainable building materials while optimising the use of waste-derived resources.

3.10.3. Concrete Blocks

The results of concrete blocks are shown in

Table 12. Comparative summary of reported optimum waste materials in concrete blocks.

Ref.	Waste Material	Reported Optimum Material/Content	Optimum Property Achieved	Reason for Optimum Selection
[85]	Bagasse	5%	Best balance of compressive strength, water absorption, density reduction, and thermal performance	5% bagasse improved particle packing, crack bridging, matrix bonding, and insulation while avoiding excessive porosity and weak interfaces
[86]	Wood ash	10% wood ash (structural)/10% (non-load bearing) 5% lime mud (strength)	Wood ash: acceptable load-bearing strength; Lime mud: maximum strength increase	Wood ash provided balance between strength and sustainability; lime mud improved hydration through CaCO3 and C-S-H formation.
[87]	Rice husk ash + coconut fibres	15%	Highest strength: coconut fibre 4.99 MPa; rice husk 4.90 MPa	Optimum fibre content improved crack bridging, reinforcement efficiency, and pozzolanic contribution without excessive porosity
[88]	Rice husk ash	15%	Lowest U-value (3.04 W/m2·K), conductivity (0.46 W/m·K), highest thermal resistance (0.33 m2·K/W)	Higher RHA increased pore volume and trapped insulating air, reducing heat transfer.
[89]	Palm oil fuel ash	20%	Highest strength: 28 MPa soaked (+12.4%)	Optimum pozzolanic reaction improved hydration and matrix development; >20% caused poor packing.
[90]	Coco pith	4%	Best strength, durability, cost, and environmental balance	Improved crack bridging (+8% compressive, +45% flexural strength) while limiting excessive absorption and porosity
[91]	HDPE, LDPE, rubber waste	20% HDPE	Highest strength (6.55 MPa), lowest conductivity (0.322 W/m·K)	HDPE provided lightweight behaviour, good particle stability, and improved insulation while maintaining strength
[93]	Recycled concrete aggregate (RCA)	1:21 C:A	Best sustainability: 55.36% CO2 reduction while meeting IS 2185 requirements	Provided maximum RCA replacement while maintaining acceptable load-bearing strength

and Figure 21. Specifically, waste materials such as sugarcane bagasse [85] and coco pith [90] demonstrate maximal effectiveness at lower concentrations; coco pith performs optimally at 4%, while sugarcane bagasse performs best at 5%. These concentrations reduce the weight of the blocks without compromising structural integrity.

Meanwhile, wood ash [86] demonstrates efficacy at 10% for load-bearing applications and can be increased up to 15% for non-load-bearing applications. Additionally, lime mud [86] was optimised at a concentration of 15%. Lime mud enhances the packing density of the mixture while coconut fibres serve as a reinforcement, thereby contributing to the stability of the material while maintaining strength. Lime mud can be increased up to 20% and still satisfy the requirements for load-bearing masonry. In contrast, rice husk ash [88] and palm oil fuel ash [89] yield better results at higher content levels, at 20% and 15%, respectively, in enhancing the resilience of masonry blocks under various conditions. It was recommended to use 1:21 as a cement-to-aggregate ratio with recycled aggregates as fine and coarse aggregates in concrete masonry walls [93].

3.11. Practical Applications

Agricultural waste incorporation in masonry materials raises concerns regarding long-term biological stability; however, direct studies on biological decay and decomposition remain limited. Studies have mainly examined the effects of agricultural residues on physical, thermal and mechanical properties. Although existing research provides insight into durability-related behaviour, the long-term biological degradation potential of agricultural waste in fired bricks, unfired bricks, and concrete blocks remains insufficiently investigated. Bio-based masonry materials containing agricultural wastes offer environmental benefits, but their long-term durability depends on resistance to moisture-induced biological degradation. Studies on hemp concrete and other lignocellulosic composites show that fungi and bacteria can develop under favourable humidity conditions, while factors such as alkalinity, fibre composition and moisture control influence biological resistance [94]. Wei and Meyer [95] reported that the main degradation mechanisms include dissolution of lignin and hemicellulose, alkaline hydrolysis of cellulose, and fibre mineralisation, which reduce fibre strength, flexibility and toughness over time in the cement matrix. Therefore, further research is required to evaluate the long-term biological stability of agricultural waste-based bricks and concrete blocks.

Beyond material performance, practical implementation also depends on the availability, consistency, and scalability of waste-based masonry production. Although waste-based masonry materials demonstrate promising laboratory-scale performance, their industrial application requires consideration of waste supply, processing, and manufacturing challenges. Agricultural residues may be affected by seasonal production, geographical availability, and variations in composition, while industrial wastes may depend on the stability of industrial processes. Large-scale application also requires reliable collection, transportation, storage, and preprocessing strategies to ensure consistent material quality. Manufacturing parameters, including mixing procedures, waste preparation, curing conditions, and firing requirements, must be validated under larger production conditions. Therefore, future studies should incorporate pilot-scale investigations, life-cycle assessments, economic evaluations, and supply-chain analysis to determine the feasibility of integrating waste-based masonry materials into conventional construction practices.

4. Integrated Assessment of Agricultural and Industrial Waste in Sustainable Masonry Production

Although the reviewed studies were classified according to masonry product type (fired bricks, unfired bricks, and concrete blocks) to provide a systematic assessment, an integrated evaluation highlights the common mechanisms controlling the influence of waste incorporation on masonry performance. The behaviour of waste-based materials is mainly governed by waste composition, particle structure, replacement level, manufacturing process, and interaction with the surrounding matrix. To provide an integrated comparison of the influence of different waste categories on masonry performance,

Table 13. Effect of waste characteristics and processing conditions on the performance of waste-based masonry materials.

Material System	Waste/Processing Category	Density (kg/m3)	Water Absorption (%)	Compressive Strength (MPa)	Thermal Conductivity (W/m.K)	Underlying Mechanism
Fired Brick	Agricultural waste incorporation (rice husk ash, sawdust, bagasse, fibres)	↓	↑	↓ (optimum content may maintain strength)	↓	Organic components burn during firing, generating pores that reduce density and conductivity but weaken the ceramic matrix at high contents
	Industrial waste incorporation (fly ash, sludge, ashes, brick waste)	↔/↓	Variable	Variable	↓	Mineral wastes influence packing, vitrification, and ceramic bonding; behaviour depends on chemical composition and firing conditions.
	Increased firing temperature	↑	↓	↑	↔/slight ↑	Higher temperature enhances sintering and densification, reducing pores and improving strength.
	Excessive waste replacement	↓	↑	↓	↓	Excessive pore formation disrupts matrix continuity and reduces mechanical performance.
Unfired Brick	Agricultural fibres and residues	↓	↑	↑ at optimum, ↓ at excessive content	↓	Fibres reduce density and improve crack resistance, but excessive additions increase voids and moisture sensitivity.
	Industrial by-products (GBFS, CKD, slag, ashes)	↔/↑	↓	↑	Variable	Pozzolanic reactions and improved particle packing increase matrix strength
	Binder and stabiliser optimisation	↑	↓	↑	↔	Increased hydration and cementitious product formation improve densification.
	Compaction and curing optimisation	↑	↓	↑	↔/↓	Improved packing and hydration reduce pore connectivity.
Concrete Blocks	Agricultural fibres and porous wastes	↓	↑	Variable (↑ at optimum, ↓ excessive)	↓	Low-density wastes improve insulation; fibre reinforcement may improve strength before porosity dominates
	Industrial/mineral wastes	↔/slight ↓	Variable	Variable/↑ at optimum	↓	Reactive materials improve packing and secondary reactions, while inert wastes may increase defects.
	Recycled aggregates	↓	↑	↓ at high replacement	↓	Weaker interfaces and increased porosity reduce mechanical performance.
	Processing optimisation	↑	↓	↑	↔/↓	Better curing and compaction improve matrix integrity.

Note: ↑ is an increasing trend, ↓ is a decreasing trend, and ↔ is approximately the same.

summarises the general trends observed across fired bricks, unfired bricks, and concrete blocks. The table highlights the relationship between waste characteristics, processing conditions, and the resulting changes in density, porosity, water absorption, compressive strength, and thermal conductivity. These trends represent the general behaviour reported in the reviewed studies; however, the magnitude and direction of changes depend on waste composition, replacement level, and manufacturing conditions. In general, lightweight and porous wastes reduce density and thermal conductivity by introducing additional air voids, while reactive mineral wastes can improve matrix development through pozzolanic or hydraulic reactions. Therefore, the effectiveness of waste incorporation depends on achieving a balance between reducing weight and improving insulation while maintaining sufficient strength and durability.

Across different masonry systems, density reduction was commonly observed when low-density agricultural residues, fibres, polymers, or porous recycled materials replaced conventional constituents. This reduction can improve handling, reduce structural dead load, and enhance thermal insulation. However, excessive pore formation may increase water absorption and weaken mechanical properties by reducing particle bonding and increasing internal defects. The effect of porosity depends on its structure, as controlled pores can improve insulation, whereas interconnected pores negatively affect strength and moisture resistance. The effect of incorporating waste on water absorption is not consistent or uniform across all materials, highlighting the importance of conducting individual assessments of each type of waste to ensure the necessary balance between the physical, thermal and mechanical properties and functional performance of sustainable building materials.

In fired bricks (

Table 14. Relative change in properties of fired brick compared with the corresponding control brick.

Ref.	Type of Waste	Density (kg/m3)	Porosity (%)	Water Absorption (%)	Compressive Strength (MPa)	Flexural Strength (MPa)	Thermal Conductivity (W/m·K)	Shrinkage (%)	General Trend	Reasoning
[65]	Cigarette butts	↓	–	↑	↓	↓	↓	↓Variable	Lightweighting and insulation improved, but strength decreased significantly at higher waste contents.	CB particles burn during firing, creating pores that reduce density and thermal conductivity but weaken the brick structure and increase water uptake.
[66]	Activated alumina sludge	↓	↑	↑	↓	↓	↓	–	Increased porosity and absorption with reduced mechanical performance.	Sludge decomposition constituents such as calcinate release gases and form internal pores; increased porosity lowers weight and conductivity but reduces mechanical strength.
[67]	Rice husk ash	↓	↑	↑	↓	–	↓	↑	Higher firing temperature improved strength retention, but porosity increased.	RHA initially improves bonding through reactive silica, but excessive addition creates pores and reduces strength; pores improve insulation.
[67]	Wood ash	↓	↑	↑	↓	–	↓	↓	Better shrinkage and mechanical stability than rice husk ash with moderate physical deterioration.	Ash particles promote pore formation and fluxing reactions; moderate levels maintain strength while decreasing insulation.
[68]	Olive mill waste	↓	↑	↑	↓	–	↓	–	Higher firing temperature improved overall performance and strength retention.	Organic waste burns out during firing, producing a porous lightweight structure with lower strength but improved thermal resistance.
[69]	Rice husk ash	↓	–	↑	↓Variable	–	–	↓	Performance depended on replacement level; optimum behaviour observed at moderate content.	Fine RHA particles improve silica reactions at low contents, reducing pores and improving strength; excessive RHA increases porosity and absorption.
[70]	Waste fly ash	–	–	↑	↓	↓	–	–	Increased water absorption and reduced mechanical strength.	Lower-density ash replaces clay and increases pore formation; higher porosity reduces strength but improves insulation and reduces weight.
[71]	Spent shea waste	↓	↑	↑	↑ Variable	–	–	↑	Strong dependence on firing temperature; properties improved at elevated temperatures while shrinkage increased.	Organic waste combustion creates voids, reducing density and improving insulation while weakening the ceramic matrix.
[72]	Paper mill sludge	↓	↑	↑	↓	–	↓	↑	Improved insulation but reduced strength with increased porosity and a small increase in shrinkage.	Organic sludge components burn away and generate pores, producing lighter bricks with improved insulation but lower strength.
[73]	Pomegranate peel waste	↓	↑	↑	↓	–	↓	–	Thermal insulation improvement with strength reduction.	PPW acts as a pore-forming agent during firing; increased pores lower density and conductivity but reduce mechanical performance.
[74]	Rice straw ash	–	–	↑	↓	–	–	–	Increased absorption and reduced compressive strength	Ash addition increases pore volume and reduces brick weight; excessive pores decrease strength and increase moisture absorption.

Note: ↑ is an increasing trend, ↓ is a decreasing trend, and – is an unreported value.

), waste materials primarily influenced ceramic reactions and pore development during firing. Organic wastes and biomass residues generally acted as pore-forming agents because their combustion generated additional voids, leading to reduced density and thermal conductivity but increased water absorption and lower strength. Conversely, mineral-based wastes such as fly ash, activated alumina sludge, and other ash residues showed improved compatibility with clay matrices, as their reactive components contributed to sintering, vitrification, and matrix stabilisation. The final properties were strongly dependent on firing temperature and waste content, where controlled additions provided improved insulation without significant deterioration in mechanical performance.

For unfired bricks (

Table 15. Relative change in properties of unfired brick compared with the corresponding control brick.

Ref.	Type of Waste	Density (Kg/m3)	Water Absorption (%)	Compressive Strength (MPa)	Tensile/Flexural Strength (MPa)	Thermal Conductivity (W/m·K)	Shrinkage (%)	General Trend	Reasoning
[75]	Lithomargic Clay + GBFS + Cement	–	↓	↑	–	–	–	Stabilisation reduced water absorption and improved compressive strength.	GBFS provided pozzolanic reaction and cement hydration products, increasing bonding and reducing pore connectivity.
[75]	Lateritic soil + GBFS + Cement	–	↓	↑	–	–	–	GBFS and cement addition improved bonding and reduced moisture uptake.	GBFS improved strength through particle bonding and pozzolanic reactions, while the naturally better-graded and sand-rich structure of lateritic soil provided higher initial strength and allowed effective stabilisation with lower cement demand.
[76]	Bagasse	↓	↑	↑Variable	↑	–	↓	Fibre addition reduced density and increased absorption; improvement in compressive and tensile strength was observed.	Low-density fibres increased pore volume and water uptake, while fibre bridging improved strength.
[76]	Coconut husk	↓	↑	↑Variable	↑	–	↓	Lightweight fibre increased pore volume but improved mechanical resistance at optimum content.	Porous fibres increased absorption, while rough fibre surfaces enhanced soil–fibre bonding.
[76]	Oil palm fruit	↓	↑	↑Variable	↑	–	↓	Fibre incorporation reduced density while maintaining improved strength behaviour.	Fibre reinforcement reduced block density and improved crack resistance through bridging effects. But showed lower reinforcement efficiency than coconut and oil palm fibres because of weaker fibre–soil interaction and lower tensile contribution.
[77]	Banana fibre	↓	↑ Variable	↑	↑	↑	↓	Fibre bridging improved compressive and tensile strength while increasing water absorption.	Natural fibre bridging restricted crack propagation and improved stress distribution.
[77]	Jute fibre	↓	↑ Variable	↑	↑	↑	↓	Density reduction accompanied by mechanical improvement.	High tensile capacity and a rough surface provided strong fibre–soil bonding, crack resistance, and shrinkage resistance.
[77]	Alkali-resistant glass fibre	↓	↓ Variable	↑ Variable	↑ Variable	↑	↓	Glass fibre reduced absorption and provided the lowest improved strength through reinforcement.	Non-porous fibres limited water penetration and showed limited strength improvement because fibre clumping reduced uniform distribution and weakened reinforcement efficiency.
[77]	Polypropylene fibre	↓	↓ Variable	↑	↑	↑	↓	Strong reduction in density and absorption with improved mechanical performance.	Low-density fibres provided crack bridging and reduced pore water pathways and shrinkage.
[78]	Straw fibres, 3 cm	↓	–	↑Variable	↑Variable	↓	↓	Lightweight fibre improved flexural behaviour and reduced thermal conductivity.	Low-density fibres increased porosity, reducing heat transfer while controlling shrinkage cracks.
[78]	Seagrass fibres, 3 cm	↓	–	↑Variable	↑Variable	↓	↓	Slight density reduction with improved insulation and mechanical properties.	Flexible fibres improved interlocking and reduced thermal conductivity through increased internal pores.
[79]	Fonio straw	–	–	↑Variable	↑Variable	↓	–	Low fibre levels improved strength, while excessive addition reduced strength but enhanced insulation.	Optimum fibre dispersion enhanced bonding; excessive fibres caused clustering and increased porosity.
[80]	Crushed brick waste	–	↑	↑	↑	–	–	Waste aggregate improved strength through particle packing but slightly increased water absorption.	Brick particles improved packing and pozzolanic activity, while porous waste increased water uptake.
[81]	Rice husk ash	↓	↑Variable	↑Variable	–	–	–	Ash addition reduced density; moderate replacement improved strength before deterioration at higher content.	Silica-rich ash enhanced pozzolanic bonding, while high ash content increased porosity.
[82]	Sugarcane bagasse ash + 4% cement	–	≈/↑ slight	↑Variable	–	–	–	Limited strength change; absorption remained approximately stable or slightly increased.	Reactive silica from SBA improved secondary cementitious reactions and compensated for lower cement content.
[82]	Sugarcane bagasse ash + 10% cement	–	≈/↑ slight	↑Variable	–	–	–	Higher cement content enhanced strength through improved binder reaction.	Higher cement content reduced water absorption due to denser hydration products. Provided smaller strength benefits in 10% cement blocks because sufficient cement hydration products already controlled strength development
[83]	Flax	–	–	↑	–	–	–	Fibre addition slightly improved compressive strength.	Fibre reinforcement restricted deformation and delayed crack growth.
[83]	Hemp	–	–	↓	–	–	–	Strength depended on fibre content and interaction with the soil matrix.	Lower fibre strength and increased porosity reduced compression performance.
[84]	GBFS + Cement kiln dust + cement	↑	≈/↑ slight	↑	–	–	–	Strong densification and high strength improvement due to combined hydraulic reactions.	CKD increased alkalinity, activating slag reactions and forming cementitious products.
[84]	GBFS + Quick lime + cement	↑	↑	↑	–	–	–	Highest density and compressive strength due to enhanced cementitious reactions, although water absorption increased.	Quicklime enhanced CSH/CASH formation, although excess calcium increased water absorption slightly.

Note: ↑ is an increasing trend, ↓ is a decreasing trend, ≈ is approximately similar, and – is an unreported value.

), the effect of waste materials depended largely on their interaction with the soil–binder system. Natural fibres, including bagasse, coconut husk, oil palm fibres, and other lignocellulosic materials, mainly improved lightweight behaviour, crack resistance, and deformation control through fibre reinforcement and particle interlocking. However, their porous nature increased moisture sensitivity when used excessively. In contrast, industrial wastes such as slag, cement kiln dust, lime-based materials, and crushed brick waste improved strength and durability by enhancing particle packing and promoting additional cementitious reactions. These differences indicate that lightweight wastes mainly contribute to reinforcement and insulation, whereas reactive mineral wastes improve matrix strength and stability.

Concrete blocks (

Table 16. Relative change in properties of concrete blocks compared with the corresponding control brick.

Ref.	Type of Waste	Density (kg/m3)	Porosity (%)	Water Absorption (%)	Compressive Strength (MPa)	Flexural Strength (MPa)	Thermal Conductivity (W/m·K)	General Trend	Reasoning
[85]	Sugarcane bagasse	↓	↓Variable	–	↑Variable	–	↓	Lightweight addition reduced density and absorption while improving strength and thermal insulation at optimum content.	Low-density fibres reduce block weight; moderate addition improves packing, crack resistance and insulation, while excessive fibres increase pores, reduce hydration and weaken bonding.
[85]	Coffee husk	↓	↑	–	↑	–	↓Variable	Density reduction and insulation improvement occurred, but excessive addition increased water uptake and reduced strength.	Higher extractive content inhibits cement hydration, increases void formation and weakens fibre–matrix interaction. Generally performed less effectively than sugarcane bagasse.
[86]	Sawdust	↓	↑	↑	↓	–	↓	Highly porous organic particles caused major density reduction, absorption increase, strength loss, and strong insulation improvement.	Porous wood particles replace sand, increasing air voids and reducing bonding; however, trapped air improves insulation.
[86]	Wood ash	↓	↑	↑	↓	–	↓	Ash addition slightly reduced density while increasing porosity and absorption with moderate strength reduction.	Ash particles have lower density and increase pores; excessive ash acts mainly as filler and reduces strength.
[86]	Lime mud	↑Variable	↑	↓	↑	–	≈	Improved packing increased density and strength while maintaining stable thermal behaviour.	CaCO3 promotes hydration, C-S-H formation and pore refinement, improving strength and reducing permeability. Accelerating hydration reactions and producing additional cementitious compounds, resulting in a denser and stronger matrix
[29]	Expanded polystyrene wastes + silica fume	↓	↑	–	↓	–	–	EPS produced a major lightweight effect but reduced strength due to weak polymer–cement bonding.	EPS particles replace dense aggregates, reducing weight and conductivity but lowering stiffness and load capacity
[87]	Rice husk ash	–	–	–	↑ slight	–	–	Pozzolanic activity slightly improved compressive strength.	Cellulose network and lignin improve crack bridging and bonding; excessive fibres increase moisture sensitivity and voids.
[87]	Coconut fibre	–	–	–	↑ slight	–	–	Fibre reinforcement improved strength retention.	Fibres improve reinforcement and particle interaction; excessive replacement reduces aggregate stability.
[88]	Rice husk ash	↓Variable	–	–	–	–	↓	Ash addition reduced density and improved thermal insulation.	Porous ash particles trap air and reduce heat transfer; increased pore volume improves insulation.
[89]	Palm oil fuel ash	↑Variable	↑Variable	–	↑Variable	–	–	Moderate ash replacement improved strength, although water absorption increased.	Pozzolanic reaction improves strength at moderate replacement; excessive ash reduces particle packing and increases weak zones. Wet curing enhanced hydration and pozzolanic reactions, producing higher strength.
[90]	Coco pith	↓	–	–	↑Variable	↑Variable	–	Lightweight coco pith reduced density, while optimum addition improved compressive and flexural strength.	Moderate additions improved compressive and flexural strength through fibre crack-bridging and enhanced fibre–matrix interaction. In contrast, excessive contents increased porosity, fibre clustering, and weak bonding, resulting in lower strength and greater moisture sensitivity.
[91]	HDPE/LDPE/Crumb rubber	↓	↓Variable	–	↓	–	↓Slight	Rubber particles reduced density and improved insulation but weakened mechanical performance.	Plastic particles reduce water absorption but provide weaker mechanical interaction with cement. Hydrophobic rubber reduces cement adhesion, traps air and creates weak interfaces.
[92]	Mixed recycled construction wastes (silica fume, marble dust, fine glass, wood waste, and recycled aggregates)	↓	↓ Or ↑	–	↓	–	↓	Reduced density and provided variable behaviour on water absorption while lowering strength and conductivity.	Increasing waste content generally increased porosity and water absorption, which reduced compressive strength because of weaker particle–cement bonding and lower packing efficiency. Silica fume and fine glass helped offset these effects by refining the pore structure, improving matrix densification, and enhancing bonding, resulting in better mechanical performance and lower water absorption than other waste mixtures.
[93]	Recycled aggregate concrete + fine recycled concrete aggregates	↓	↑	–	↓	↓	–	Increasing recycled aggregate content significantly reduced compressive and flexural strength and increased water absorption.	High replacement of conventional materials reduces production cost and emissions but decreases mechanical performance due to lower cement content, weaker aggregate–cement bonding, and increased porosity.

Note: ↑ is an increasing trend, ↓ is a decreasing trend, ≈ is approximately similar, and – is an unreported value.

) showed similar relationships between waste characteristics and performance. Agricultural fibres and porous organic wastes improved lightweight properties and thermal behaviour, while optimum additions could enhance strength through crack bridging and improved stress distribution. Nevertheless, excessive fibre content increased void formation and weakened cement–waste bonding. Ash-based wastes, including rice husk ash and palm oil fuel ash, provided strength improvements when sufficient reactive material was available to promote pozzolanic reactions, whereas high replacement levels reduced packing efficiency. Polymer wastes such as EPS, HDPE, LDPE, and crumb rubber produced significant weight and thermal reductions due to their low density; however, weak interfacial bonding with cement limited mechanical performance. Recycled aggregates and mixed construction wastes reduced environmental impacts and material consumption but generally decreased strength at high replacement ratios due to increased porosity and weaker interfaces. However, reactive additives such as silica fume and fine glass improved pore refinement and bonding.

Waste characteristics similarly influenced durability performance. Several studies demonstrated that fired bricks containing sludge, ashes, or cigarette butts remained within acceptable leaching limits due to pollutant immobilisation during firing. Fibre-reinforced unfired bricks showed improved erosion and abrasion resistance because fibres enhanced particle cohesion. However, long-term biological durability of agricultural waste-based materials remains insufficiently investigated, particularly under prolonged moisture exposure and biological attack conditions. Therefore, further research is required to assess fungal degradation, fibre mineralisation, and long-term service performance.

Environmental and economic assessments indicate that waste incorporation can provide substantial sustainability benefits beyond material performance. Reported studies demonstrated reductions in energy consumption, carbon emissions, and production costs through reduced use of conventional raw materials. For example, agricultural waste incorporation improved thermal performance and reduced operational energy demand, while recycled industrial materials reduced embodied carbon by replacing cement, aggregates, and virgin resources. However, economic benefits remain dependent on local waste availability, transportation requirements, processing methods, and manufacturing scale.

A comparison of the reviewed studies further indicates that optimum waste contents generally fall within moderate replacement levels. For fired bricks, optimum replacement levels commonly ranged from approximately 5–20%, depending on the waste material and firing temperature. Fibre-reinforced unfired bricks typically achieved optimum performance at relatively low fibre contents (approximately 0.5–2%), whereas higher percentages often resulted in significant strength reductions. For concrete and masonry blocks, optimum replacement levels for agricultural and industrial wastes were generally between 5% and 20%. However, certain industrial by-products, such as GBFS and recycled aggregates, could be incorporated at substantially higher proportions when combined with suitable binder systems.

Overall, the reviewed studies demonstrate that waste incorporation can enhance the sustainability of masonry materials by reducing the demand for conventional resources, lowering density, and improving insulation. However, the benefits of waste addition are highly dependent on material type and dosage. Organic wastes are generally effective for lightweight and thermal applications, fibres improve crack resistance and deformation behaviour, and mineral wastes contribute to strength development through chemical reactions. Therefore, optimised waste content and appropriate combinations of waste materials with reactive additives are essential to achieve masonry products with balanced mechanical performance, durability, and environmental benefits.

5. Conclusions

This study aimed to evaluate the impact of incorporating agricultural and industrial waste into the manufacturing of various building units, focusing on key properties such as density, water absorption, compressive strength, thermal conductivity, shrinkage, durability and environmental impacts. The findings showed that all types of waste studied contributed, to varying degrees, to improving certain properties of the building units. The reviewed studies confirm that waste materials have significant potential for improving the sustainability of masonry production by reducing reliance on conventional raw materials and promoting waste valorisation.

The reviewed studies also reveal that waste materials can serve different functional roles in masonry production. Some wastes act mainly as lightweight fillers, improving thermal efficiency and reducing material weight, while others contribute through chemical reactions, reinforcement effects, or improved particle packing. This highlights the importance of selecting waste materials according to their intended function within the masonry system.

The findings demonstrate that waste type, replacement level, processing conditions, and the characteristics of the masonry system strongly influence the performance of waste-based masonry products. Waste incorporation commonly reduced density and thermal conductivity; however, excessive additions often increased porosity and water absorption, resulting in reduced mechanical performance. Therefore, optimum waste contents are required to balance thermal efficiency, strength, and durability. Overall, waste incorporation provides a realistic pathway towards more resource-efficient masonry production. The transition from laboratory studies to practical construction applications will depend on developing optimised formulations, demonstrating long-term reliability, and integrating environmental and economic assessments into material design decisions.

6. Limitations, Recommendations, and Future Research

Analysis of previous studies identified several research gaps that warrant further attention. Important properties, such as flexural strength, efflorescence, shrinkage, durability, and thermal conductivity, were not consistently evaluated for all waste types, limiting comprehensive assessment of their suitability. Furthermore, although many studies followed recognised testing standards, direct comparison of results remains challenging due to variations in manufacturing conditions, firing temperatures, curing regimes, replacement ratios, replacement basis, and the range of evaluated properties. Therefore, future research should adopt a more consistent reporting framework to improve comparability and facilitate the assessment of waste-based masonry materials. Moreover, most studies focused on using only one type of waste at a time, while hybrid systems combining multiple waste types received insufficient attention, despite their potential to achieve synergistic effects that could improve the overall performance of building units. Furthermore, the industrial scaling and commercial application of these materials still require further research, particularly regarding production costs, energy consumption, market acceptance, and economic viability. It is also noteworthy that studies addressing carbon dioxide emissions, life cycle analysis, and the economic costs associated with producing waste-based building units are limited. Addressing these research gaps will enhance the scientific and technical understanding of these materials and accelerate their adoption on a practical and industrial scale, thus supporting the transition to more sustainable and efficient building practices within the framework of a circular economy. Addressing these research gaps can lead to significant strides toward improving the technical performance of waste-based bricks/blocks, expanding their applications, and ensuring their practical feasibility for large-scale use in sustainable construction. Furthermore, the diversity of waste materials and manufacturing approaches limits direct comparison between studies; therefore, the reported trends should be considered indicative of material behaviour rather than universal performance predictions.

Based on the identified methodological variations, a general reporting framework is recommended for future investigations of waste-based masonry materials. This framework should include: (i) detailed characterisation of waste materials, including their physical and chemical properties; (ii) clear reporting of mixture composition, replacement basis, and manufacturing conditions, including curing or firing parameters where applicable; (iii) systematic evaluation of fundamental properties, including density, water absorption, porosity, compressive strength, thermal conductivity, and durability-related performance where relevant; (iv) reporting of testing standards and specimen preparation procedures; and (v) assessment of suitable waste incorporation levels based on a balanced evaluation of mechanical, physical, thermal, environmental, and economic performance rather than a single property. Adoption of such a framework would improve reproducibility and facilitate meaningful comparison between different masonry systems and waste materials.

The analysis of the gaps was instrumental for the authors in their ongoing studies, which formed the basis of their current research. The future research directions proposed in this review are derived from the identified limitations and methodological inconsistencies observed across the analysed studies rather than from general recommendations reported in previous literature. The following are some recommendations for future directions on the subject, and most of them are being investigated by the authors:

• Future studies should aim to evaluate a wider range of properties for waste-based bricks/blocks, including porosity, flexural strength, efflorescence, and thermal conductivity, which are critical for determining the overall performance and suitability of these materials.
• A more complete dataset will allow for more informed decision-making regarding the potential of waste-based bricks/blocks in various construction applications.
• There is an opportunity for greater exploration of hybrid materials made from a combination of waste products.
• Research should focus on the potential synergistic effects of combining different types of waste, such as industrial by-products and organic materials, to enhance the mechanical and thermal properties of bricks/blocks.
• More comprehensive studies should focus on the environmental impact and life cycle assessment of bricks/blocks, considering not only cost but also carbon emissions, energy consumption, raw material sourcing, and long-term performance.
• Development of AI-based predictive models to determine the optimal performance of waste-containing building units.
• Studying durability performance under harsh environmental conditions (fire, freezing, chemical erosion).