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Article

Engineering and Durability Properties of Sustainable Bricks Incorporating Lime Kiln Dust, Ground Granulated Blast Furnace Slag, and Tyre Rubber Wastes

by
Joy Ayankop Oke
* and
Hossam Abuel-Naga
Civil Engineering Discipline, Department of Engineering, La Trobe University, Bundoora, Melbourne, VIC 3086, Australia
*
Author to whom correspondence should be addressed.
Buildings 2025, 15(12), 2079; https://doi.org/10.3390/buildings15122079
Submission received: 9 May 2025 / Revised: 11 June 2025 / Accepted: 15 June 2025 / Published: 17 June 2025
(This article belongs to the Section Building Materials, and Repair & Renovation)
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Versions Notes

Abstract

:
This study explores the potential of using sustainable materials in brick manufacturing by designing a novel brick mix in the laboratory, incorporating sand, lime kiln dust (LKD) waste, tyre rubber, and ground granulated blast furnace slag (GGBFS) waste. These cementless bricks blended LKD–GGBFS wastes as the binder agent and fine crumb rubber from waste tyres as a partial replacement for sand in measured increments of 0%, 5%, and 10% by volume of sand. Ordinary Portland cement (OPC) and fired clay bricks were sourced from the industry, and their properties were compared to those of the laboratory bricks. Tests performed on the industry and laboratory bricks included compressive strength (CS), freeze-thaw (F-T), and water absorption (WA) tests for comparison purposes. Additionally, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses were performed on the bricks to assess the morphological and mineralogical changes responsible for the observed strengths and durability. The CS and WA values of the engineered bricks were 12, 6, and 4 MPa, and 7, 12, and 15%, respectively, for 0, 5, and 10% crumb rubber replacements. The industry bricks’ average CS and WA values were 13 MPa and 8%, respectively. From the results obtained, the green laboratory bricks passed the minimum strength requirements for load-bearing and non-load-bearing bricks, which can be used to construct small houses. Lastly, the engineered bricks demonstrated strength and durability properties comparable to those of the industry-standard bricks, indicating their potential as a sustainable alternative to help divert waste from landfills, reduce the pressure on natural fine sand extraction, and support eco-conscious brick production for a sustainable environment.

1. Introduction

Bricks are construction units globally used in house construction due to their properties, which include strength, low cost, durability, satisfactory fire resistance, and acceptable tolerance against external conditions, including weathering, freeze-thaw, and their distinctive appearance. Additionally, the cost of producing bricks is relatively low, which is why they are widely accepted in many countries [1,2,3]. According to Jayasinghe and Mallawaarachchi [1], masonry can be categorised as alternative or conventional. The alternative type of masonry is compressed stabilized earth, consisting of interlocking pavers, solid bricks, solid blocks, rammed earth, and interlocking hollow blocks. In contrast, the conventional type of masonry consists of fired clay bricks or cement-sand blocks, with fired bricks being predominant in some countries, including Australia, India, Vietnam, Kenya, Iran, and Ukraine. Right from ancient times, dating back to 8000 BCE, clay earth material has always been an essential construction material for producing fired bricks among the Egyptians, Romans, and Mesopotamians [4,5] mainly due to their durability, higher compressive strength, adequate resistance to weathering, low thermal conductivity, fireproof, and low levels of sound transmission [2,3,6,7]. These properties have made them globally accepted in construction over the years [8,9,10,11]. Fired clay bricks produced from clays promote thermal mass, which results in buildings requiring less energy for cooling and heating. Hence, with proper building design, clay bricks can provide extended service life and offer liveable and healthy environments [9,12]. Additionally, clay bricks are ranked as the highest artificial construction bricks used on outdoor surfaces due to their vibrant and attractive colours, which are inexpensive to maintain. However, despite its attractive properties, its production results in substantial CO2 emissions, primarily due to the burning of fuels required for firing the bricks in the kilns. Research has shown that, on average, about 222 g of CO2 gas is emitted while firing 1 kg of clay brick [13]. Furthermore, the adverse effects of brick firing in kilns are causing health issues [14,15,16]. Hence, research into strengthening processes that utilize the emitted CO2 gas is necessary.
The construction industry is a major consumer of ordinary Portland cement (OPC) and contributes significantly to global carbon emissions [17,18,19]. Furthermore, OPC in construction and building activities accounts for about 36% of global use of energy and 40% of CO2 emissions, thus, ranking OPC as a construction cementitious material of great concern [20,21]. Additionally, it has been reported that in 2019, the cement industry was responsible for generating about 2.4 gigatonnes of CO2, contributing about 26% of the overall emissions from the industrial sector [22]. Furthermore, industries that produce ordinary Portland cement (OPC) have been reported to be primarily accountable for releasing carbon dioxide (CO2), which is a key driver of climate change [22,23]. With the rise in construction activities due to population increase associated with economic development [24], the urban global population has been projected to exceed 6 billion by 2045, implying increased construction activities in the future. Hence, there is a critical demand for supplementary cementitious building materials.
Naturally derived aggregates, such as natural sand, natural gravel, crushed stone, and manufactured sand, as well as recycled aggregates, expanded clay, slate or shale, crushed rock, slag aggregates, and glass aggregates, are commonly used in the construction industry [25]. Natural river sand, construction and demolition (C&D) wastes and manufactured sand are used as fine aggregates in manufacturing concrete blocks and bricks. However, geo-environmental consequences, including fluctuations in the riverbed structure caused by the widespread dredging of sand aggregates from rivers, have led to significant variations in the direction of river flow [24,26]. Additionally, the continued extraction of natural river sand needs to be addressed to prevent the erosion of riverbeds, alongside highlighting the importance of preserving sand as a natural filter for the groundwater process [27,28,29]. With the growing environmental restrictions on the exploitation of sand from riverbeds and the increase in construction activities attributed to population growth, urbanisation, and industrialisation, the constant search for alternatives to natural sand and manufactured sand is on the rise [24,26,27,29].
In contributing to addressing the challenge associated with the emission of CO2 gas throughout the brick firing process in kilns, Oke and Abuel-Naga [30] carried out research where captured and stored CO2 gas was utilised as a curing regimen for producing eco-friendly bricks. In their study, OPC was entirely replaced with a 60:40 blend ratio of LKD–GGBFS as an alternative cementitious material, and tyre rubber crumb obtained from waste tyres was used to replace sand in measured increments of 0%, 5%, and 10% of the sand volume. The samples were carbonated in CO2 gas for 30, 48, and 72 h. Thereafter, the samples were subjected to secondary hydration following carbonation to restore the water lost during the carbonation curing stage and to promote post-hydration of the unreacted hydraulic LKD–GGBFS binders. Results from the study highlighted carbonation curing as an environmentally safe and accelerated method, saving time while promoting a safer and cleaner environment.
In line with addressing the scepticism linked to brick manufacturing using OPC, Edike et al. [31] evaluated the performance of cementless polymer bricks made from plastic waste. In their study, melted polyethylene terephthalate (PET) waste bottle resin was mixed with sand, considering varying PET: sand mix ratios, ranging from 1:1 to 1:8 by mass. Their study concluded that the compressive strength of the cementless bricks increased with a reduction in the PET/sand ratio up to 1:4. Below this ratio, the compressive strength of the bricks reduced.
In line with addressing the challenges associated with dredging sand from riverbeds, Chin et al. [32] investigated agro-industrial waste used to develop eco-friendly cement bricks. Shell from oil palm was used to fully replace coarse aggregate, up to 20% of palm oil fuel ash (POFA) was used to replace cement, 20% of the limestone cement weight was considered admixture, and up to 50% of sand replaced quarry dust. According to the study, the green bricks developed exhibited better late strength development compared to conventional bricks made with cement, due to their POFA pozzolanic properties. Furthermore, they demonstrated that the cost of traditional bricks compared to green bricks was almost equivalent financially. Hence, the green bricks produced in the study were recommended for use in construction to enhance material sustainability and improve waste management.
With the challenges highlighted above, it is imperative to investigate alternative materials that can replace OPC and sand in brick production. This underscores the importance of researching LKD, GGBFS, and crumb rubber from waste tyres as potential alternative binders and aggregates for brick production. Furthermore, to compare the properties of the engineered bricks produced in this study with those of the industry, bricks were sourced from the Australian brick market, tested, and compared with the novel bricks produced in this study. Positive outcomes have been obtained, and the results are presented. Consequently, this study has contributed to environmental sustainability while suggesting an option to reduce the extraction pressure on natural fine aggregates.

2. Experimental Methods

Experimental procedures were conducted to prepare the laboratory bricks and compare their physical and mechanical properties to those of the industry bricks. This section outlines the test samples, the materials used for laboratory brick production, and the methods for preparing and curing the laboratory brick samples.

2.1. Test Samples

One type of OPC brick and eight different clay brick types (T1, T2, T3, T4, T5, T6, T7, and T8) were sourced from brick manufacturers in Melbourne.
The OPC bricks tested in this study were manufactured with cement and fine aggregates and cured with water for 28 days. Each brick measured 230 mm × 105 mm × 70 mm (L × B × H) and had a frog groove on the top extending to one end of the brick.
T1, T2, T3, and T4 are clay bricks manufactured using traditional methods with carefully selected clays from Melbourne. These clays were moulded, pressed, and fired in high-temperature kilns at temperatures ranging from 900 °C to 1200 °C. These bricks are characterised by a fine-textured surface finish and vivid mineralogical pigmentation, resulting from the use of high-purity, iron-rich or kaolinitic clays in their fabrication, making them suitable for internal and external applications. Each brick measured 230 mm × 110 mm × 80 mm (L × B × H) and has a frog groove at the top.
T5, T6, T7, and T8 are fired clay bricks produced with high-purity clays from New South Wales (NSW) and fired at temperatures ranging from 900 °C to 1200 °C to achieve their distinct finish and strength. They are manufactured to enhance architectural expression through refined form, uniform colour saturation, and surface uniformity, contributing to the aesthetic coherence and visual articulation of both contemporary and traditional structures. They are mainly characterised by their defined sharp edges and rough finish, which makes them suitable for external applications. Each brick measured 230 mm × 110 mm × 80 mm (L × B × H) and has a frog groove at the top.
The 0% tyre rubber waste crumbs (TRWC) engineered bricks were produced in the laboratory by mixing 1.0 parts by weight of an LKD–GGBFS blend as the cementitious material, 3.0 parts by weight of sand as the fine aggregate and a water–binder (w/b) ratio of 0.45. To improve the workability of the mix, an average of 1.5% of a water-reducing agent (WRA) was added, determined based on the weight of the LKD–GGBFS blend. For the brick samples containing the TRWC, sand was replaced with TRWC in measured increments of 5%, 10%, 15%, and 20% by volume of sand. These green bricks were tested in two batches. The first batch was tested at 7, 14, and 28 days of moist curing [24,33]. The second batch, reported in this article, was kept outside for approximately 12 months before testing to simulate similar external conditions to which industry bricks are exposed. Each brick measured 230 mm × 110 mm × 80 mm (L × B × H) and was characterized by a levelled, flat surface and a grey colour.

2.2. Materials

LKD: LKD, a powdered waste obtained from quicklime production, though high in calcium oxide content, is generally dumped in landfills [24,34]. Due to its high calcium content, its incorporation into brick manufacturing has been considered. A chemical analysis of the LKD identified it as an appropriate alternative to OPC due to the oxides present, which is why it was utilized in this research. The LKD waste powder in this research was collected from high-temperature rotary kilns after the production of quicklime from Cement Australia. Specific gravity (Gs) and specific surface area (SSA) values of 2.75 and 2608 m2/kg were obtained, respectively.
GGBFS: GGBFS is a supplementary cementitious material obtained from producing iron with a good proportion of CaO and SiO2. These compositions, in combination with the CaO, SiO2, Al2O3, Fe2O3, and MgO from the LKD, accounted for the strengths recorded in the bricks [30] due to the formation of Calcium-Silicate-Hydrate (C-S-H) gel type within the samples [30,35]. Respective values of 2.65 and 4272 m2/kg were obtained as Gs and SSA for the GGBFS sample.
The SSA values for both the LKD and GGBFS were obtained using data from a hydrometer test.
Table 1 below shows the principal chemical oxides in the LKD and GGBFS samples.
Sand: Sand can be defined by size, as being coarser than silt and finer than gravel [36]. It is one of the most essential aggregate materials for building constructions, primarily originating from rocks that have been broken down and weathered over time to form much smaller particles that are rich in silica [36]. In this study, river sand, also known as Builder’s sand, was sourced from a sand supplier in Melbourne. The sand’s Gs and fineness modulus (FM) values were 2.61 and 2.47, respectively.
TRWC: To obtain TRWC from waste tyres, the tyres are sliced into smaller sizes and placed in the granulator to release the steel from the rubber. After releasing the steel from the rubber, the wires and the rubber were separated using a magnetic separation process. Then, the crumbs were reduced to the desired sizes of aggregates. However, research has shown that the engineering applications of TRWC cause strength reduction in concretes due to its water-repellent nature and the variation in stiffness between the cementitious pastes and the crumb rubber particles [30,37,38]. This resulted in incomplete adhesion between the cementitious pastes and the rubber crumb, leading to the development of cracks when the samples were subjected to external loading. As an improvement on the hydrophilicity of the rubber, the TRWC was immersed in a sodium hydroxide (NaOH) 10% (w/v) solution for 24 h. After 24 h, the crumbs were rinsed in clean water and air-dried in the laboratory for 5 to 7 days. The treatment caused the rubber crumbs to have rough and porous surfaces (see Section 3.4), which facilitated bonding within the LKD–GGBFS–sand matrix. The WTRC was incorporated into the bricks to create lightweight masonry units, prevent brittle cracks, and improve the concrete ductility of the bricks [39]. The FM and Gs values for the TRWC were 2.96 and 0.77, respectively. Since the TRWC possessed similar grading properties to the sand and fell within limits as specified by codes [40,41], it was a suitable replacement for sand in the mix as presented in Figure 1.
WRA: Sika Plastiment®-45 was used as a water-reducing agent to improve the workability of the mix.

2.3. Preparation and Curing of Laboratory Samples

The laboratory bricks were designed to achieve a minimum compressive strength of 3 MPa, which would be suitable as non-load-bearing bricks per standards [42].
Considering the 1:3 mix design discussed in Section 2.1, trial mixes were performed to achieve an optimum blend. The optimum blend was selected based on a higher amount of LKD in the LKD–GGBFS blend matrix with a corresponding minimum compressive strength (CS) of 6 MPa after 28 days of hydration curing. In total, 63 bricks were cast considering the varying LKD–GGBFS blends as shown in Table 2.
From Table 2 above, the 70-30 blend ratio was considered the optimum blend with a CS of 6.17 MPa. This blend was used to produce the bricks in this study, as highlighted in Table 3.
The steps below were carried out to prepare and cure the laboratory samples.
  • The procedure for mixing was carried out per the codes [43]. When mixing was completed, the mix was placed in formworks coated with a releasing agent to aid a smooth demoulding process.
  • The mix was vibrated in three layers using a vibration table to establish consistency, repeatability across all the samples, and ensure complete removal of entrapped air within the voids of the sample. The first and second layers were vibrated for 40 s, respectively. For the third layer, which was also the final vibration of the samples, a duration of 120 s was used to ensure that the three layers acted monolithically without any discontinuities.
  • Following the vibration, the surplus mix above the formwork was struck off, and the remaining mix was levelled and smoothed.
  • The bricks remained in the formworks for 48 h due to the slow setting time of GGBFS, and thereafter de-moulded, subjected to water-curing immediately through spraying, wrapped in cling film, and kept in a humid environment having an average temperature and humidity of 19 °C (±5 °C) and 79% (±5%), respectively, to complement moist curing (Figure 2).
  • Sample spraying was performed every second day until the respective curing ages of 7, 14, and 28 days considered in the study had elapsed, after which the samples were unwrapped and tested.
The mix designs for producing the bricks, considering varying TRWC contents, are shown in Table 3.

3. Tests

The bricks investigated in this study (laboratory and industry) were tested for strength (compressive strength), durability (freeze-thaw, water absorption), changes in morphology (SEM), and elemental composition (EDS).

3.1. Compressive Strength (CS) Test

The CS test was conducted on laboratory and industry bricks to determine the peak stress that the samples could withstand. This was conducted using a Cyber-Plus Evolution automatic Matest compression test machine, with a capacity of 2000 kN. The samples were loaded at a constant rate of 1 kN/s, and the load at which failure occurred in the samples was recorded. The CS was calculated using Equation (1) below as recommended by the standard [44].
C S = K a ( 1000 P ) A
where
CS = Compressive strength (MPa);
Ka = Aspect ratio factor determined from the height-to-thickness ratio of the brick;
P = Load that caused the failure of the brick (kN);
A = Area of the loaded surface of the brick (mm2).

3.2. Freeze-Thaw (F-T) Test

F-T is one of the durability properties of bricks and is identified as a significant factor in brick degradation, hence its importance. Additionally, F-T has been reported to be a qualitative and direct method for assessing the durability of bricks [33,45,46]. Hence, an F-T test was conducted on the bricks to assess their resistance to deterioration and durability when exposed to repeated F-T cycles.
The bricks (industry and laboratory) were exposed to 10 cycles of F-T using the DW-861-28 Labec Low-Temperature Freezer. A cycle comprised 18 h of freezing and 6 h of thawing by immersing in water. Three bricks of each type were randomly selected and tested using a cooling chamber and a water tank for freezing and thawing purposes, respectively. Though the brick samples were subjected to lower temperatures than required in the codes [47], due to the available equipment, they did not lose structural integrity. The temperature was lowered from 22 °C to −43 °C (71.6 °F to −45.4 °F) in the cooling chamber and then increased back to 11–17 °C (51.8–62.6 °F) in the water tank within 24 h. After each successful cycle, the bricks were weighed, and the changes in their mass were determined. Furthermore, the bricks were assessed to see changes in their physical appearance at the end of the 10 cycles. Lastly, the bricks were subjected to a CS test to investigate the bricks’ resistance to F-T cycles. Figure 3 shows the laboratory bricks during the F-T test.

3.3. Water Absorption (WA) Test

The WA test is also a durability test that highlights the water absorption properties of the bricks, which determines their behaviour in weathering, quality, and degree of burning [33]. The laboratory and industry bricks were subjected to cold water immersion WA tests, and three bricks of each type were randomly selected and tested. The samples were heated using a Steridiun dry oven D300+200, and after 24 h, they were removed, allowed to cool, weighed, and then immersed in water tanks for another 24 h. It is expected that bricks with a WA value of less than 20% provide better resistance to damages caused by freezing and have a reasonable degree of compaction due to the reduced pore sizes, increasing their CS. The WA test was carried out per the codes [48], and the WA was calculated using Equation (2) below:
W A = ( M 2 − M 1 ) M 1 × 100 %
where
WA = Water absorption (%);
M1 = Mass of the brick after oven-drying for 24 h (g);
M2 = Mass of the brick after soaking in water for 24 h (g).

3.4. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS)

TRWC has been reported to be hydrophobic and chemically inert, hence its poor bonding and strength reduction when used for brick production [24]. To address this challenge, the TRWC was treated with a 10% (w/v) sodium hydroxide (NaOH) solution for 24 h to etch the rubber surface, thereby increasing its micro-roughness, improving the hydrophilicity of the rubber, and removing any residual contaminants, such as carbon black layers and surface oils. After the treatment, the hydrophilicity of the TRWC was improved, and the modified rough surface interacted better with the hydration products of the cementitious materials [calcium silicate hydrates: C-S-H and calcium hydroxides: Ca (OH)2] and contributed to the formation of ettringite needles. These processes enhanced the bonding between the rubber aggregate and the cementitious matrix, resulting in improved CS and durability properties, including minimal surface cracks, reduced water ingress, and increased resistance to freeze-thaw cycles. Figure 4 below shows the SEM of the TRWC before and after treatment with NaOH solution.
Additionally, SEM was employed to examine the microstructure of the brick samples, assess the type and distribution of the C-S-H compounds formed during the curing stage when the bricks were in contact with the cementitious materials (LKD–GGBFS and OPC), and identify potential weak zones and porosity within the bricks. This microscopic investigation was necessary to better understand the macro-properties of the bricks. It was used to gain insights into how the microstructure influenced the brick samples’ strength, durability, and shrinkage or cracking behaviours, which is the focus of this study. The equipment used for the SEM analysis was the Hitachi SU7000, manufactured at Hitachi High-Tech Corporation, Tokyo, Japan.
EDS, which is usually carried out with SEM, detects and analyses the X-rays emitted when SEM electron beams encounter the sample to identify the elemental composition of the tested sample. Its importance includes providing the qualitative and quantitative elemental composition, detecting contaminants that could affect the sample’s strength and durability, and confirming the chemical phases present in the sample. Understanding the EDS highlights the elemental distribution within the sample, which is directly related to the bonding, strength gain, and durability exhibited by the samples.

4. Results

4.1. Compressive Strength (CS)

A CS test was carried out to determine the peak stress that the brick samples could withstand. The results of the CS test are shown in Figure 5. It can be observed from the results that the 0% TRWC and the OPC bricks had similar CS values of approximately 12 MPa. Additionally, T1, T2, T3, and T4 (all Melbourne clay bricks) had CS values ranging between 11 to 15 MPa, with T1 having the highest CS of about 15 MPa.
Bricks T5, T6, T7, and T8 (all NSW clay bricks) had higher CS than T2, T3, and T4, with strength values between 13 and 14 MPa. The higher strengths may be due to their design, which prioritizes both strength and aesthetics. Lastly, the laboratory brick samples containing 5 and 10% TRWC had the lowest CS of 6 and 4 MPa, respectively. Thus, the 0 and 5% TRWC laboratory bricks produced in this study can be used in structural applications as load-bearing bricks, while the 10% TRWC bricks are suitable for use as non-load-bearing bricks per code [42].
It is also important to note that the CS of the 0%, 5%, and 10% TRWC bricks increased from 6, 5, and 3 MPa at 28 days of curing, [24] to 12, 6, and 4 MPa, respectively, after almost a year, indicating a 100%, 20%, and 33.3% increase in strength. The improved strengths recorded are because the strength development process before 28 days in slag is slower compared to OPC, leading to a product whose strength gain continues gradually beyond 28 days, which for standard concretes does not apply [49].

4.2. Freeze-Thaw (F-T)

The durability criteria checked during and after the F-T test were changes in CS at the end of the 10 cycles, mass change at the end of each cycle, and visual inspection to identify crumbling, splitting, pitting, cavitations, cracks, or falloffs. Initially, the samples were soaked in water tanks for 4 h before freezing to investigate the effect of initial expansion on the microstructure of the bricks. There was a change in mass at the beginning of the experiment for all the brick types, with some being more significant than others. This shows the extent of water absorbed by the bricks, which is highly dependent on the brick material’s permeability and porosity, highlighting their durability.
Figure 6 shows the changes in mass recorded for the brick samples (T1, T2, T3, T4, OPC, and 0% TRWC), which were categorised together due to their strength and minimal pore spaces as observed upon crushing the samples. The minimal mass change was recorded for the samples due to the particle size of fines used for the brick production, which did not allow for the intrusion and retention of moisture, except for T1, which is assumed to have absorbed and retained water through some cracks that were evident at the bottom of the brick. However, due to the tightness of the pore sizes, the mass change stabilised from the 7th cycle onwards. Furthermore, upon a physical examination at the end of the 10th cycle, the surfaces of all the brick samples in this category experienced no changes in terms of crumbling, splitting, pitting, cavitations, or falloffs. Additionally, all the samples exhibited stability at the end of the cycle, which is evident in the curve pattern at the end of the 10th cycle. It can be concluded that the bricks in this category can be classed as frost-resistant bricks. Figure 7 shows the 0% TRWC, OPC, T3, and T4 brick samples for this category.
Figure 8 below shows the changes in mass recorded for the brick samples (T5, T6, T7, T8, 5% TRWC, and 10% TRWC), which are categorised together mainly because they are characterised by a rough finish and larger pore spaces, as observed upon crushing.
The bricks in this category exhibited similarities in mass change, as evident in the plots at different test phases. This can be attributed to bigger voids inside the brick types caused by the coarser aggregates used in producing the T5–T8 bricks and the presence of TRWC in the laboratory samples, thereby leading to an absorption and retention of water in the voids of the matrix. Furthermore, the presence of moisture in the pores when frozen due to the repeated F-T cycles caused pressure to be generated, leading to failure phenomena in the form of spalling, cracks, and falloffs for T5–T8 brick and rounding/abrasion defects on the 5 and 10% TRWC samples which were observed after the 8th cycle onwards. This explains the changes in the curve patterns at the end of the F-T test. Lastly, due to the presence of TRWC in the laboratory samples (5 and 10% TRWC samples), significant ingress and retention of water occurred, which caused an expansion at the surface of the samples, thus explaining the considerable mass change at the beginning of the experiment [33]. This retained moisture was responsible for the rounding defects observed in the bricks during the cycle. Since the bricks in this category exhibited rounds, cracks, or falloffs, they were assessed as non-resistant to F-T. It can be assumed that if the bricks in this category are subjected to temperatures higher than −43 °C, they could behave differently. Figure 9 shows the 5%, 10% TRWC, T7, and T8 brick samples in this category.

4.3. CS After F-T Cycles

A compression test was performed on all the bricks subjected to F-T cycles. This was performed to understand the effect of F-T on the CS of the bricks after 10 cycles, with each cycle lasting for 24 h. Figure 10 below compares the compressive strength (CS) of the bricks before and after the 10 F-T cycles.
As seen in Figure 10, the CS of the bricks that did not undergo F-T was higher compared to those that were subjected to F-T. However, despite the rounding, cracks, and falloffs during the F-T cycles, the bricks subjected to F-T cycles maintained a minimum compressive strength (CS) of 3 MPa, indicating that the bricks can withstand repeated cycles of water freezing and expanding within their pores without losing structural integrity.

4.4. Water Absorption (WA)

The results of the WA test for each brick type are shown in Figure 11 below. All the bricks tested in the study had WA, which did not exceed 20% [50]. The laboratory bricks produced with 0% TRWC and the industry OPC bricks had the same water absorption (WA) values of 7.3%. Furthermore, brick types T1, T2, T3, and T4 had WA values ranging from 5.1% to 6.7%, while T5, T6, T7, and T8 had higher WA values, ranging from 8.4% to 10.9%, due to the wider pores within the bricks. Additionally, though the samples produced with 5 and 10% TRWC had the highest WA values of 11.76 and 14.96%, respectively, they were still within the 12% and 15% maximum water absorption for light-weight and normal-weight load-bearing bricks, respectively [51]. The high WA is attributed to the presence of the TRWC, which created more pores within the brick’s matrix, thereby leading to more water absorption within the bricks. The results show that the laboratory bricks produced in this study have water absorption properties comparable to those of the industry bricks.

4.5. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS)

4.5.1. Scanning Electron Microscopy (SEM)

SEM and EDS were carried out on the laboratory bricks (0, 5, and 10% TRWC), the OPC brick, the T1, and the T6 bricks. The OPC brick was chosen because it yielded similar results to the 0% TRWC brick for all tests performed. Additionally, the T1 and T6 bricks were selected because, in the group of bricks produced with Melbourne clays (T1, T2, T3, and T4) and NSW clays (T5, T6, T7, and T8), the T1 and T6 bricks had the highest strengths and were selected as the representative bricks within these groups. Lastly, the 5 and 10% TRWC bricks were analysed to observe the changes and effect of the TRWC on the morphology and strength of the bricks.
Figure 12, Figure 13 and Figure 14 show the SEM images of the brick samples, while Figure 15, Figure 16, Figure 17, Figure 18, Figure 19 and Figure 20 display their EDS site spectra.
Figure 12 compares the SEM images of the OPC and 0% TRWC samples, as these two brick types exhibit similar properties. From the images, it can be observed that both samples had identical features, hence the similarity in properties. Fibrous structures are visible in both images, indicating the presence of Calcium-Silicate-Hydrate (C-S-H) gels, which are the main binding phase for strength gain formed during the hydration of the cementitious agent, in this case, the OPC, and the LKD–GGBFS blend [52]. Furthermore, Calcium Hydroxide (CH), which appeared as plate-like crystals with hexagonal shapes, was also observed. These are usually formed during the hydration of Tricalcium Silicate (C3S) and Dicalcium Silicate (C2S), with the former being responsible for early strength gain and the latter being responsible for the late strength gain, as exhibited by the OPC and LKD–GGBFS blend samples, respectively [53,54]. Additionally, aggregate particles with distinct edges were observed, and ettringite (Aft) needles in radiating forms, especially in the 0% TRWC sample, were visible. Ettringite needles were formed due to the presence and chemical reaction between the sulphates, calcium, and alumina oxides during the hydration of the cementitious agents, and also contributed to early strength development [53], which was more in the 0% TRWC sample, mainly because of the higher sulphates, calcium, and alumina oxides present in the LKD–GGBFS blend when compared to OPC alone, which has been reported to be about 2.40, 62.25, and 5.90%, respectively [30,55].
Figure 13a,b shows the SEM of the T1 and T6 clay brick samples, which are typically observed to reflect their raw materials as described in Section 2.1. The image of the T1 brick sample shows fine and densely packed clay particles within a uniform matrix, with smooth areas characterized by mostly closed or micro-pores. Isolated voids were also observed, however, the clay matrices between these voids are densely sintered, hence the load transfer remains effective. These features can be assumed to be the reason for the high strength and durability recorded in the T1 bricks. For the T6 sample, the SEM image reveals a rough surface with visible coarse grains. However, the contact points between these particles were sintered, thereby forming fused zones that increase their strength and durability. Additionally, dense regions were observed despite the pore size distribution, which strengthened the brick. Lastly, angular quartz grains were observed to be well embedded in the matrix [56], resisting deformation and acting as a reinforcement in the brick, which is why the high strength and durability were recorded.
Figure 14a,b shows the images of the 5% and 10% TRWC samples. Both images were observed to have densely packed but rough surfaces with visible pores, primarily due to the inclusion of the TRWC in the mix. Like the OPC and 0% TRWC samples, CH, in the form of plate-like crystals with hexagonal shapes, were observed, which are usually formed during the hydration of Dicalcium Silicate (C2S), being responsible for the continuous strength gain exhibited by the LKD–GGBFS blend samples after 12 months [53]. However, minimal fibrous structures were observed in these samples, in addition to poor interfacial bonding observed as roughness, which can be assumed to be the reason for the lower strengths observed in these samples compared to the 0% TRWC samples.

4.5.2. Energy Dispersive X-Ray Spectroscopy (EDS)

Figure 15, Figure 16, Figure 17 and Figure 18 show the EDS of the samples discussed, while Table 4 shows the elemental composition of the sites analysed in the EDS. It can be observed that in the Figures and Tables, the samples that were cured with water (OPC, 0, 5, and 10% TRWC) were all characterised by elevated Ca, O, and Si due to the formation of C-S-H gels, the main strength-giving phase in both the OPC and LKD–GGBFS systems [53,57]. Additionally, the presence of Ca (OH)2 due to high Ca and O, which presented as plate-like crystals in the SEM, and the CaO in the OPC and LKD were responsible for the elevated elements [52]. However, trace amounts of Al, Ma, S, Fe, and C were observed in the water-cured samples, mainly because they are not significant hydration components, and the C-S-H dominates the reaction.
For the T1 and T6 clay brick samples, the elemental distribution reflected the mineral composition of the respective soils used to produce them and thermal transformations during firing, as shown in Figure 19 and Figure 20, and Table 5. Si, O, and Al were observed to be elevated, as shown in the Figures and Tables, while Ca, Fe, K, and Mg were in trace amounts, in line with the research [58,59]. Si and O combine to form SiO2 (quartz), a significant component in clays that survive the firing process. Since quartz is present in these analysed bricks, it implies the bricks were fired at temperatures lower than 1000 °C [56]. Also, Al from clay minerals like kaolinite, illite, and montmorillonite dehydroxylate, turning into metakaolinite upon firing, then into glassy aluminosilicates. Hence, the Si-O-Al phase forms the structural framework of the bricks and dominates the EDS. The trace amount of Ca was due to its decomposition during firing. The Fe is usually diffused into the glassy phase and not concentrated enough to dominate the EDS. At the same time, other elements were low mainly because of their low concentrations in clay soils.

5. Conclusions

The increasing accumulation of waste tyres, LKD, and the dredging of fine sand from rivers presents environmental challenges, prompting research into the viable reuse of waste tyres and LKD as construction materials to replace sand and OPC, respectively. From the study, the following conclusions can be made:
  • The 70:30 LKD–GGBFS blend ratio can be used to entirely replace OPC in combination with 5 and 10% TRWC replacement by volume of sand to produce green bricks. Including these recycled wastes in bricks has shown that these engineered bricks meet industry standards while contributing to environmental sustainability.
  • CS for the 0, 5, and 10% TRWC replacement bricks increased from 6, 5, and 3 MPa at 28 days of moist curing to 12, 6, and 4 MPa after almost one year of exposure to external environmental conditions, indicating 100, 20, and 33.33% increments in strength, respectively. The improved strengths recorded are in line with strength development in slag, which is slower before 28 days compared to OPC, leading to products whose strength gain continues gradually beyond 28 days [49]. Additionally, the CS recorded met the minimum requirements for load-bearing and non-load-bearing bricks.
  • F-T test performed on the laboratory bricks to understand the effect of F-T on the CS of the bricks after 10 cycles showed that despite the abrasions on the bricks that occurred during the F-T cycles, and notwithstanding the very low temperatures that the bricks were subjected to, they maintained a minimum CS of 3 MPa, indicating that the bricks can withstand repeated cycles of water freezing and expanding within their pores without losing structural integrity.
  • The SEM images highlighted the novel bricks as having elevated C-S-H compounds, which are the main binding phase for strength gain formed during the hydration of the cementitious agent. Also, CH compounds in the form of plate-like crystals with hexagonal shapes were observed, which are usually formed during the hydration of Dicalcium Silicate (C2S), being responsible for the continuous strength gain exhibited by the LKD–GGBFS blend. These formations have given a proper understanding of the bricks’ macro-properties, which can be used to gain insights into how the microstructure influences the strength and durability behaviours of the novel brick samples.
  • The EDS provided qualitative and quantitative elemental composition of the novel bricks, indicating elevated Calcium (Ca) and Oxygen (O) elements. The elevated Ca, which implies the presence of C-S-H due to rich calcium content in the LKD–GGBFS blend, and the O in correlation with the Ca to form hydrated products were responsible for strength development in the laboratory bricks, which is directly related to the bonding, strength gain, and durability exhibited by the samples.
  • All the bricks tested in the study had WA, which did not exceed 20% [50]. Though the samples produced with 5 and 10% TRWC had the highest WA values of 11.76 and 14.96%, respectively, they were still within the 12% and 15% maximum water absorption for light-weight and normal-weight load-bearing bricks, respectively [51].
  • It is recommended that the bricks produced in this study be subjected to milder conditions as indicated in the codes [47] to assess their physical changes. Additionally, it is recommended that the laboratory bricks be replicated on a larger scale to evaluate their properties and compare the results with the laboratory-scale bricks.

Author Contributions

J.A.O.: Formal Analysis; J.A.O. and H.A.-N.: Conceptualization, Methodology, and Writing—Original Draft; H.A.-N.: Supervision and Validation; J.A.O. and H.A.-N.: Writing—Review and Editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Tertiary Education Trust Fund (TETFund).

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to ethical restrictions.

Acknowledgments

The first author acknowledges the Tertiary Education Trust Fund (TETFund) for funding her studies at La Trobe University, Melbourne, Australia. Furthermore, the authors wish to express their earnest appreciation to Cement Australia for the free LKD waste and GGBFS samples, and Sika Australia Pty. Ltd., Melbourne, for the free WRA (Sika Plastiment-45) samples that were donated to support this research. Lastly, the authors acknowledge the La Trobe University Bioimaging Platform and thank Boyin Liu for microscopy support.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

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Figure 1. Particle size distribution curves for the sand and TRWC within the specified limits.
Figure 1. Particle size distribution curves for the sand and TRWC within the specified limits.
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Figure 2. Wrapped laboratory samples in a humid environment.
Figure 2. Wrapped laboratory samples in a humid environment.
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Figure 3. F-T test: (a) laboratory bricks in the freezer and (b) laboratory bricks thawing in a water tank.
Figure 3. F-T test: (a) laboratory bricks in the freezer and (b) laboratory bricks thawing in a water tank.
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Figure 4. (a) SEM images of non-treated TRWC (500 µm); (b) SEM images of treated TRC (50 µm).
Figure 4. (a) SEM images of non-treated TRWC (500 µm); (b) SEM images of treated TRC (50 µm).
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Figure 5. Compressive strength results for the tested industry and laboratory bricks.
Figure 5. Compressive strength results for the tested industry and laboratory bricks.
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Figure 6. Change in mass with corresponding F-T cycle.
Figure 6. Change in mass with corresponding F-T cycle.
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Figure 7. Frost-resistant brick samples: (a) 0% TRWC, (b) OPC, (c) T3, and (d) T4.
Figure 7. Frost-resistant brick samples: (a) 0% TRWC, (b) OPC, (c) T3, and (d) T4.
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Figure 8. Mass change with corresponding F-T cycle.
Figure 8. Mass change with corresponding F-T cycle.
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Figure 9. Non-frost-resistant brick samples: (a) 5% TRWC, (b) 10% TRWC, (c) T7, and (d) T8.
Figure 9. Non-frost-resistant brick samples: (a) 5% TRWC, (b) 10% TRWC, (c) T7, and (d) T8.
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Figure 10. Plots comparing CS before and after F-T cycles.
Figure 10. Plots comparing CS before and after F-T cycles.
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Figure 11. Plots showing the WA levels of each brick type.
Figure 11. Plots showing the WA levels of each brick type.
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Figure 12. (a) SEM of the OPC sample (100 µm), (b) SEM of the 0% sample (100 µm).
Figure 12. (a) SEM of the OPC sample (100 µm), (b) SEM of the 0% sample (100 µm).
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Figure 13. (a) SEM of the T1 sample (100 µm), (b) SEM of the T6 sample (100 µm).
Figure 13. (a) SEM of the T1 sample (100 µm), (b) SEM of the T6 sample (100 µm).
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Figure 14. (a) SEM of the 5% sample (100 µm), (b) SEM of the 10% sample (100 µm).
Figure 14. (a) SEM of the 5% sample (100 µm), (b) SEM of the 10% sample (100 µm).
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Figure 15. EDS spectrum of the OPC sample.
Figure 15. EDS spectrum of the OPC sample.
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Figure 16. EDS spectrum of the 0% sample.
Figure 16. EDS spectrum of the 0% sample.
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Figure 17. EDS spectrum of the 5% sample.
Figure 17. EDS spectrum of the 5% sample.
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Figure 18. EDS spectrum of the 10% sample.
Figure 18. EDS spectrum of the 10% sample.
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Figure 19. EDS spectrum of the T1 sample.
Figure 19. EDS spectrum of the T1 sample.
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Figure 20. EDS spectrum of the T6 sample.
Figure 20. EDS spectrum of the T6 sample.
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Table 1. Major chemical oxides present in the LKD and GGBFS samples.
Table 1. Major chemical oxides present in the LKD and GGBFS samples.
SampleCaOSiO2Al2O3Fe2O3MgOK2ONa2OSO3
LKD63.2420.044.903.491.110.350.432.35
GGBFS42.1033.1013.200.306.50-0.502.00
Table 2. LKD–GGBFS blend ratios and their corresponding compressive strengths for the trial mix design.
Table 2. LKD–GGBFS blend ratios and their corresponding compressive strengths for the trial mix design.
LKD–GGBFS Blend Ratio28-Day Compressive Strength (MPa)
30-7012.04
40-6011.94
50-508.71
60-4010.49
70-306.17
80-203.69
90-101.67
Table 3. Mix design and weights considered for the laboratory bricks mix using the 70-30 blending ratio.
Table 3. Mix design and weights considered for the laboratory bricks mix using the 70-30 blending ratio.
Mix DesignTRWC Content (%)LKD:GGBFS Blend (g)Sand (g)TRWC (g)
1:301260:54054000
1:2.91:0.0951260:5405230170
1:2.81:0.19101260:5405060340
1:2.72:0.28151260:5404890510
1:2.62:0.38201260:5404720680
Table 4. Elemental composition of OPC and 0%, 5%, and 10% TRWC samples.
Table 4. Elemental composition of OPC and 0%, 5%, and 10% TRWC samples.
ElementOPC Sample0% TRWC5% TRWC10% TRWC
Wt %Wt % SigmaWt %Wt % SigmaWt %Wt % SigmaWt %Wt % Sigma
C12.360.2813.330.266.660.1713.330.19
O46.660.2247.240.2240.970.2250.320.19
Mg0.880.030.720.030.040.030.880.03
Al4.200.052.720.042.030.042.440.04
Si12.540.089.730.072.600.044.110.04
S--1.230.031.810.041.450.03
K0.770.030.240.03----
Ca17.020.1123.990.1344.940.1926.930.13
Fe3.590.100.800.070.500.080.550.07
Na1.380.04--0.100.03--
Ti0.060.04------
Total100.00 100.00 100.00 100.00
Table 5. Elemental composition of T1 and T6 samples.
Table 5. Elemental composition of T1 and T6 samples.
T1 SampleT6 Sample
ElementWt %Wt % SigmaWt %Wt % Sigma
C5.560.37--
O46.820.2461.220.22
Mg0.520.03--
Al13.530.10--
Si26.980.1634.060.18
K4.200.060.530.06
Ti0.790.063.290.10
Fe1.600.100.060.13
Ca--0.290.06
Total100.00 100.00
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Oke, J.A.; Abuel-Naga, H. Engineering and Durability Properties of Sustainable Bricks Incorporating Lime Kiln Dust, Ground Granulated Blast Furnace Slag, and Tyre Rubber Wastes. Buildings 2025, 15, 2079. https://doi.org/10.3390/buildings15122079

AMA Style

Oke JA, Abuel-Naga H. Engineering and Durability Properties of Sustainable Bricks Incorporating Lime Kiln Dust, Ground Granulated Blast Furnace Slag, and Tyre Rubber Wastes. Buildings. 2025; 15(12):2079. https://doi.org/10.3390/buildings15122079

Chicago/Turabian Style

Oke, Joy Ayankop, and Hossam Abuel-Naga. 2025. "Engineering and Durability Properties of Sustainable Bricks Incorporating Lime Kiln Dust, Ground Granulated Blast Furnace Slag, and Tyre Rubber Wastes" Buildings 15, no. 12: 2079. https://doi.org/10.3390/buildings15122079

APA Style

Oke, J. A., & Abuel-Naga, H. (2025). Engineering and Durability Properties of Sustainable Bricks Incorporating Lime Kiln Dust, Ground Granulated Blast Furnace Slag, and Tyre Rubber Wastes. Buildings, 15(12), 2079. https://doi.org/10.3390/buildings15122079

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