Search Results (214)

The construction industry plays a major role in the consumption of natural resources and the generation of waste. Construction and demolition waste (CDW) is produced in substantial volumes globally and is widely available. Its accumulation poses serious challenges related to storage and disposal, highlighting the need for effective strategies to mitigate the associated environmental impacts of the sector. This investigation intends to evaluate the influence of mixed CDW on the physical, mechanical, and durability properties of mortars with CDW partially replacing Portland cement, and allow performance comparisons with mortars produced with fly ash, a commonly used supplementary binder in cement-based materials. Thus, three mortar formulations were developed (reference mortar, mortar with 25% CDW, and mortars with 25% fly ash) and several characterization tests were carried out on the CDW powder and the developed mortars. The work’s principal findings revealed that through mechanical grinding processes, it was possible to obtain a CDW powder suitable for cement replacement and with good indicators of pozzolanic activity. The physical properties of the mortars revealed a decrease of about 10% in water absorption by immersion, which resulted in improved performance regarding durability, especially with regard to the lower carbonation depth (−1.1 mm), and a decrease of 51% in the chloride diffusion coefficient, even compared to mortars incorporating fly ash. However, the mechanical performance of the mortars incorporating CDW was reduced (25% in terms of flexural strength and 58% in terms of compressive strength), but their practical applicability was never compromised and their mechanical performance proved to be superior to that of mortars incorporating fly ash. Full article

This paper presents a comprehensive review of dealuminated metakaolin (DK), a hazardous industrial by-product generated by the aluminium sulphate (alum) industry and evaluates its potential as a component in cementitious systems for the partial or full replacement of Portland cement (PC). Positioned within the context of waste valorisation in concrete, the review aims to establish a critical understanding of DK formation, properties, and reactivity, particularly its pozzolanic potential, to assess its suitability for use as a supplementary cementitious material (SCM), or as a precursor in alkali-activated cement (AAC) systems for concrete. A systematic methodology is used to extract and synthesise relevant data from existing literature concerning DK and its potential applications in cement and concrete. The collected information is organised into thematic sections exploring key aspects of DK, beginning with its formation from kaolinite ores, followed by studies on its pozzolanic reactivity. Applications of DK are then reviewed, focusing on its integration into SCMs and alkali-activated cement (AAC) systems. The review consolidates existing knowledge related to DK, identifying scientific gaps and practical challenges that limit its broader adoption for cement and concrete applications, and outlines future research directions to provide a solid foundation for future studies. Overall, this review highlights the potential of DK as a low-carbon, circular-economy material and promotes its integration into efforts to enhance the sustainability of construction practices. The findings aim to support researchers’ and industry stakeholders’ strategies to reduce cement clinker content and mitigate the environmental footprint of concrete in a circular-economy context. Full article

This study investigates the feasibility of using volcanic lapillus as a supplementary cementitious material (SCM) in mortar production to improve the sustainability of the cement industry. Cement production is one of the main sources of CO₂ emissions, mainly due to clinker production. Replacing clinker with SCMs, such as volcanic lapillus, can reduce the environmental impact while maintaining adequate mechanical properties. Experiments were conducted to replace up to 20 wt% of limestone Portland cement with volcanic lapillus. Workability, compressive strength, microstructure, resistance to alkali-silica reaction (ASR), sulfate, and chloride penetration were analyzed. The results showed that up to 10% replacement had a minimal effect on mechanical properties, while higher percentages resulted in reduced strength but still improved some durability features. The control sample cured 28 days showed a compressive strength of 43.05 MPa compared with 36.89 MPa for the sample containing 10% lapillus. After 90 days the respective values for the above samples were 44.76 MPa and 44.57 MPa. Scanning electron microscopy (SEM) revealed good gel–aggregate adhesion, and thermogravimetric analysis (TGA) confirmed reduced calcium hydroxide content, indicating pozzolanic activity. Overall, volcanic lapillus shows promise as a sustainable SCM, offering CO₂ reduction and durability benefits, although higher replacement rates require further optimization. Full article

This study presents a cost-effective, carbon-negative construction material for affordable housing, developed entirely from locally available agricultural wastes: rice husk ash, wood ash, and rice straw—materials often problematic to dispose of in many African regions. Rice husk ash provides high amorphous silica, acting as a strong pozzolanic agent. Wood ash contributes calcium oxide and alkalis to serve as a reactive binder, while rice straw functions as a lightweight organic filler, enhancing thermal insulation and indoor climate comfort. These materials undergo natural pozzolanic reactions with water, eliminating the need for Portland cement—a major global source of anthropogenic CO₂ emissions (~900 kg CO₂/ton cement). This process is inherently carbon-negative, not only avoiding emissions from cement production but also capturing atmospheric CO₂ during lime carbonation in the hardening phase. Field trials in Kenya confirmed the composite’s sufficient structural strength for low-cost housing, with added benefits including termite resistance and suitability for unskilled laborers. In a collaboration between the University of Tartu and Kenyatta University, a semi-automatic mixing and casting system was developed, enabling fast, low-labor construction of full-scale houses. This innovation aligns with Kenya’s Big Four development agenda and supports sustainable rural development, post-disaster reconstruction, and climate mitigation through scalable, eco-friendly building solutions. Full article

The pursuit of sustainable alternatives to portland cement has become a global imperative within the construction sector, driven by the need to reduce carbon dioxide emissions and energy consumption. Among the promising alternatives, agricultural ashes have garnered attention for their potential as alternative supplementary cementitious materials (ASCMs), owing to their inherent pozzolanic properties when appropriately processed. However, the availability and utilization of these ashes have predominantly been concentrated in tropical and subtropical regions, where such biomass is more abundant. This review offers a comprehensive bibliometric analysis to identify and assess agricultural ashes (specifically switchgrass, barley, sunflower, and oat husks) that are cultivated in temperate and cold climates and exhibit potential for SCM application. The analysis aims to bridge the knowledge gap by systematically mapping the existing research landscape and highlighting underexplored resources suitable for cold-region implementation. Key processing parameters, including incineration temperature, retention duration, and post-combustion grinding techniques, are critically examined for their influence on the resulting ash’s physicochemical characteristics and pozzolanic reactivity. In addition, the effect on fresh, hardened, and durability properties was evaluated. Findings reveal that several crops grown in colder regions may produce ashes rich in reactive silica, thereby qualifying them as viable ASCM candidates and bioenergy sources. Notably, the ashes derived from switchgrass, barley, oats, and sunflowers demonstrate significant reactive silica content, reinforcing their potential in sustainable construction practices. Hence, this study underscores the multifaceted benefits of contributing to the decarbonization of the cement industry and circular economy, while addressing environmental challenges associated with biomass waste disposal and uncontrolled open-air combustion. Full article

The pressing need for sustainable construction materials has identified alkali-activated materials (AAMs) as eco-friendly alternatives to conventional Portland cement. This study explores the synergistic performance of alkaline-activated natural pozzolan and limestone powder (AANL) blends against sulfate attack, evaluating mortar specimens immersed in sodium sulfate, magnesium sulfate, and a combined sulfate solution over 12 months. The samples were synthesized using natural pozzolan (NP) and limestone powder (LSP) in three distinct binder combinations to evaluate the influence of varying precursor ratios on the material’s performance, as follows: NP: LSP = 40:60 (AN₄₀L₆₀), 50:50 (AN₅₀L₅₀), and 60:40 (AN₆₀L₄₀). At the same time, the alkaline activators of 10 M NaOH_(aq) and Na₂SiO_3(aq) were combined in a ratio of 1:1 and cured at 75 °C. The research examines the weight variations of the samples, their residual compressive strength, and microstructural characteristics under exposure to magnesium sulfate, sodium sulfate, and a combined sulfate solution. In terms of weight change, samples exposed to Na₂SO₄ gained weight slightly, with AN₄₀L₆₀ recording the highest gain (3.2%) due to the ingress of sulfate ions and pore filling. Under MgSO₄, AN₆₀L₄₀ had the lowest weight gain (29%), while AN₄₀L₆₀ reached 54%. In mixed sulfate, AN₆₀L₄₀ showed negligible weight gain (0.11%); whereas, AN₅₀L₅₀ and AN₄₀L₆₀ gained 2.43% and 1.81%, respectively. Compressive strength retention after one year indicated that mixes with higher NP content fared better. AN₆₀L₄₀ exhibited the highest residual strength across all solutions—16.12 MPa in Na₂SO₄, 12.5 MPa in MgSO₄, and 19.45 MPa in the mixed solution. Conversely, AN₄₀L₆₀ showed the highest strength degradation, losing 47.22%, 58.11%, and 55.89%, respectively. SEM-EDS and FTIR analyses confirm that LSP’s vulnerability to sulfate attack diminishes with increased NP incorporation, highlighting a synergistic interaction that mitigates degradation and retains structural integrity. The combination of 60% NP and 40% LSP demonstrated superior resistance to all sulfate environments, as evidenced by visual durability, minimized weight gain, and retained compressive strength. This study highlights the potential of tailored NP-LSP combinations in developing durable and sustainable AAMs, paving the way for innovative solutions in sulfate-prone environments, while reducing environmental impact and promoting economic efficiency. Full article

The alkali–silica reaction (ASR) is a critical concern for concrete durability, yet its assessment remains challenging and directly impacts mixture design decisions. This review shows that the inconsistencies are more prevalent in mitigation evaluations compared to aggregate reactivity assessments, mainly due to the chemical variations in supplementary cementitious materials (SCMs). A validated framework is suggested to determine the optimal SCM replacement levels for ASR mitigation based on extensive field data, offering direct guidance for mix design decisions involving potentially reactive aggregates. The combination of the accelerated mortar bar test (AMBT) and the miniature concrete prism test (MCPT) is shown to be a reliable alternative for the concrete prism test (CPT) in aggregate reactivity. Also, their extended versions, AMBT (28-day) and MCPT (84-day), can be applied for SCMs mitigation evaluation. Given the slower reactivity of SCMs compared to ordinary Portland cement (OPC), the importance of incorporating indirect test methods, such as the modified R3 test and bulk resistivity is underscored. In addition, emerging sustainability shifts further complicate ASR assessment, including the adoption of Portland limestone cement (PLC), the use of seawater in concrete, and the declining availability of fly ash (FA) and slag. These changes call for updated ASR testing specifications and increased research into natural pozzolans (NPs) as promising SCMs for future ASR mitigation. Full article

This study investigates the effects of supplementary cementitious materials (SCMs) on the material performance of foamed concrete containing lightweight coarse aggregates, namely hydrophobically modified expanded perlite (EP). The EP aggregates were treated with a sodium methyl silicate solution to impart water-repellent properties prior to being incorporated into the foamed concrete mixtures. Ordinary Portland cement (OPC) was partially replaced with various SCMs, namely, silica fume (SF), mineral powder (MP), and metakaolin (MK) at substitution levels of 3%, 6%, and 9%. Key indicators to evaluate the material performance of foamed concrete included 28-day uniaxial compressive strength, thermal conductivity, mass loss rate under thermal cycling, volumetric water absorption, and shrinkage. The results noted that all three SCMs improved the uniaxial compressive strength of foamed concrete, with MP achieving the greatest improvement, approximately 97% at the 9% replacement level. Thermal conductivity increased slightly with the addition of SF or MP but decreased with MK, highlighting the superior insulation capability of MK. Both SF and MK reduced the mass loss rate under thermal cycling, with SF exhibiting the highest thermal stability. Furthermore, MK was most effective in minimizing water absorption and shrinkage, attributed to its high pozzolanic reactivity and the resulting refinement of the microstructures. Full article

A structure of composite cement with 15 wt.% thermally activated clay shales has been developed. The phase composition and properties of aluminosilicate rocks of the Kazakhstan deposits—Mynaral and Kuyuk—have been studied. It has been shown that aluminosilicates are related to clay shales by their composition. The regularities of thermal activation processes of aluminosilicates have been established, and it has been shown that pozzolanic activity increases for all compositions with an increase in the heat treatment temperature from 700 to 900 °C. The clay shale of the Mynaral deposit is characterized by the highest activity. The physicomechanical properties of the obtained composite cements–including Portland cement clinker, gypsum, and thermally activated clay shale—have been studied. It has been shown that when replacing up to 15 wt.% Portland cement clinker with thermally activated clay shales, there is no decrease in the strength properties of the composite cement. The obtained results allow us to consider heat-treated clay shales as active mineral additives. Full article

Over 2 million tonnes of ceramic waste are generated annually in South Africa, with the majority disposed of in landfills, contributing to environmental degradation. Meanwhile, researchers are actively seeking sustainable alternatives to Portland cement (PC), which is associated with significant environmental challenges. Ceramic waste powder (CWP) refers to finely milled ceramic waste and powder derived from the polishing and finishing stages of ceramic production. This review examines the potential of CWP as a partial replacement for PC in concrete, focusing on its effects on workability, mechanical durability, and microstructural properties. The findings indicate that moderate replacement levels (up to 20%) enhance the compressive and flexural strengths of concrete. However, these benefits are not consistently reported across all studies. Additionally, CWP improves the microstructural properties of the concrete. This is probably due to the pozzolanic reactions of CWP, which result in a denser concrete matrix and enhanced long-term durability. Notable durability benefits include reduced water absorption, increased resistance to chemical attacks, and improved thermal insulation. However, the performance of concrete with higher CWP replacement levels (above 30%) remains unclear. Some studies have reported strength reductions and increased susceptibility to durability loss at this level. Further studies should focus on clarifying its pozzolanic reactivity, durability in aggressive environments, and optimum replacement percentage. Full article

This study evaluates pistachio shell ash (PSA) as a sustainable cement substitute and investigates its effect on setting time, strength and microstructure. In this study, pistachio shell ash (PSA) obtained from the kiln flue gas filter of pistachio shells burnt at 300–350 °C in an industrial kiln was used. PSA was substituted for ordinary Portland cement (OPC) at 5, 10, 15, 20, 25 and 30%. PSA increased the SO₃ value in the cement mortars, so 5% PSA substitution delayed the cement setting time by up to 174%. However, it increased the water requirement of the cement mortar by about 2%. While it increased the early strength (22% on day 1, 15% on day 2, and 5% on day 7), the 28-day strength decreased slightly (about 4.5%) due to low pozzolanic activity. Microstructural analyses such as SEM-EDX and XRD showed that the calcite and gypsum phases of PSA provided early strength gains, but there were long-term losses. With a 5% replacement rate, PSA provides significant environmental benefits by reducing CO₂ emissions while maintaining optimum mechanical performance and supports the circular economy through the efficient use of agricultural waste. Full article

The global cement industry faces a critical challenge of reducing its substantial carbon footprint while maintaining material performance. Portland cement production significantly contributes to global CO₂ emissions, necessitating innovative sustainable alternatives. This study evaluates the transformative potential of calcined natural pozzolans as a strategic approach to developing low-carbon cement. By systematically investigating the effects of calcined natural pozzolans derived from kaolinite and pyroclastic rocks on cement paste properties, the research demonstrates a promising pathway to environmentally efficient cement formulations. Utilizing advanced characterization techniques including XRD, TGA, SEM-EDX, and gas adsorption porosimetry, this study provides insights into hydration kinetics, compressive strength development, microstructural evolution, and porosity refinement. The results reveal that calcined natural pozzolans strategically enhance cement performance by accelerating hydration processes, improving compressive strength, and sophisticating microstructural characteristics. Notably, pastes incorporating pyroclastic rock pozzolans exhibited superior mechanical properties, with 28-day compressive strengths exceeding ordinary Portland cement by 35.2%. These findings not only validate the technical feasibility of natural pozzolan-based low-carbon cement but also underscore their potential to meaningfully reduce the construction industry’s environmental impact. Full article

This paper reviews the performance of low-grade calcined clay as a partial substitute for Portland cement in concrete, emphasizing its potential to enhance sustainability in construction. Thermal treatment of naturally occurring clays at optimal temperatures produces amorphous siliceous materials with pozzolanic properties. Clays with substantial kaolinite content exhibit significant pozzolanic reactivity when calcined at temperatures between 700 and 850 °C, with effective firing possible up to 1000 °C. Research shows that replacing Portland cement with calcined clays improves the mechanical and durability properties of concrete, with replacement levels ranging from 10% to 60%, depending on factors such as chemical composition, mineralogy, and reactivity. This paper synthesizes recent findings on low-grade calcined clays with 60–80% purity, which are more abundant, cost-effective, and easier to produce, particularly in developing regions lacking the resources and technology to process high-purity clays (>95% purity). Key aspects explored include calcination methods, optimal firing temperatures, and their effects on particle size distribution and pozzolanic activity. This study also examines the impact of low-grade calcined clay on fresh and hardened concrete and the durability properties of concrete and mortar. By providing a comprehensive analysis, this review highlights the potential of low-grade calcined clays to contribute to more sustainable and durable concrete production, emphasizing the need to optimize calcination processes and fully harness their pozzolanic properties. Full article

Oil palm kernel shell ash (POFA), a byproduct of the highly cultivated agro-industrial sector in Colombia, has been widely used for its pozzolanic properties, which enhance the mechanical and durability characteristics of concrete. Six POFA samples were analyzed after undergoing drying, cutting, grinding, crushing, and calcination at temperatures ranging from 500 °C to 1000 °C. SEM-EDS/EDX analysis, X-ray fluorescence (XRF), and loss on ignition (LOI) tests were conducted to characterize its pozzolanic potential. The results revealed that the SiO₂ content increased with the calcination temperature, reaching a peak of 76.8% at 1000 °C. However, calcination at 600 °C was identified as the optimal temperature, as it balances impurity removal without inducing the formation of crystalline silica, which would negatively affect the material’s reactivity. Considering the optimal calcination temperature and the high initial LOI values, which exceeded 70% in the first calcination stage, a second calcination was performed on the 500 °C sample by increasing the temperature to 600 °C. This resulted in an LOI of 3.33%, according to ASTM C311 standards for natural pozzolans used in Portland cement concretes. Full article

With respect to sustainability, the material must maintain the quality and properties of concrete and be safe for human health, the environment, and long-time use. In recent times, the emission of CO₂ from cement production processes has lessened with the passage of time due to its effect on the environment. In order to lessen the emissions and reduce environmental waste, available by-products with pozzolanic properties are applied. With respect to Portland limestone cement (CEMI II-BL), i.e., cement with lower carbon dioxide emissions and better workability than CEM I, the two main materials applied in the study as substitutes are brick dust (BD) and waste glass powder (WGP) bottles. Waste glass powder and brick dust, in quantities varying from 5% to 10%, 15%, and 20%, with a water/cement ratio of 0.35 and a 1.5% superplasticizer, were utilized to observe the effectiveness of BD and WGP on the flowability, compressive strength, flexural strength, water absorption, density, drying shrinkage, and fire resistance of the specimen mortar. The output shows that a WGP of 20% increased flowability compared to the control, whereas the inclusion of brick dust decreased it. At the age of 28, glass powder of 20% increased the compressive strength, while 20% brick dust exhibited a reduction; 15% WGP with 5% BD displayed the lowest absorption of water; and the density of all the samples proved to be much lower than the traditional mix, with 20% BD being the lowest (hereby labeled as light mortar). The 10% WGP with 10% BD displayed better resistance to fire, and the drying shrinkage of the sample was relatively low after several days of air curing. The impact on the environment and cost were considered without accounting for the transportation and manufacturing energy. As to the outcome of this experiment, we concluded that the use of both brick dust and glass powder with CEM II for producing mortar has proven very promising in a variety of different respects, including the mechanical and fresh features of mortar, with the combination of 5% WGP and 15% BD exhibiting the most potential in all of the acquired parameters. Full article