Calcium Aluminum Silicate Hydrate Research Articles

The Atomic-Level Structure of Cementitious Calcium Aluminate Silicate Hydrate.

Despite use of blended cements containing significant amounts of aluminum for over 30 years, the structural nature of aluminum in the main hydration product, calcium aluminate silicate hydrate (C-A-S-H), remains elusive. Using first-principles calculations, we predict that aluminum is incorporated into the bridging sites of the linear silicate chains and that at high Ca:Si and H2O ratios, the stable coordination number of aluminum is six. Specifically, we predict that silicate-bridging [AlO2(OH)4]5- complexes are favored, stabilized by hydroxyl ligands and charge balancing calcium ions in the interlayer space. This structure is then confirmed experimentally by one- and two-dimensional dynamic nuclear polarization enhanced 27Al and 29Si solid-state NMR experiments. We notably assign a narrow 27Al NMR signal at 5 ppm to the silicate-bridging [AlO2(OH)4]5- sites and show that this signal correlates to 29Si NMR signals from silicates in C-A-S-H, conflicting with its conventional assignment to a "third aluminate hydrate" (TAH) phase. We therefore conclude that TAH does not exist. This resolves a long-standing dilemma about the location and nature of the six-fold-coordinated aluminum observed by 27Al NMR in C-A-S-H samples.

Early hydration of cementitious systems accelerated by aluminium sulphate: Effect of fine limestone

The early hydration of cementitious systems accelerated by an alkali-free aluminium sulphate based product was investigated in the presence and absence of fine limestone. The results show that the first seconds after the accelerator is added to the wet mix play a key role: Simultaneously to the massive ettringite formation, the Al2(SO4)3 accelerator favours the dissolution of the major cement clinker phase alite and thereby leads to an oversaturation of the pore solution with respect to calcium-aluminium-silicate-hydrates (C-A-S-H) and consequently the precipitation of nuclei of these phases. The surface of the limestone powder acts as an ideal substrate for these nuclei, which are the foundation for an outstanding early-strength-giving effect a few hours later.

Effect of Soda Residue Addition and Its Chemical Composition on Physical Properties and Hydration Products of Soda Residue-Activated Slag Cementitious Materials.

Soda residue (SR), the solid waste of Na2CO3 produced by ammonia soda process, pollutes water and soil, increasing environmental pressure. SR has high alkalinity, and its main components are Ca(OH)2, NaCl, CaCl2, CaSO4, and CaCO3, which accords with the requirements of being an alkali activator. The aim of this research is to investigate the best proportion of SR addition and the contribution of individual chemical components in SR to SR- activated ground granulated blast furnace slag (GGBS) cementitious materials. In this paper, GGBS pastes activated by SR, Ca(OH)2, Ca(OH)2 + NaCl, Ca(OH)2 + CaCl2, Ca(OH)2 + CaSO4, and Ca(OH)2 + CaCO3 were studied regarding setting time, compressive strength (1 d, 3 d, 7 d, 14 d, 28 d), hydration products, and microstructure. The results demonstrate that SR (24%)-activated GGBS pastes possess acceptable setting time and compressive strength (29.6 MPa, 28 d), and its hydration products are calcium silicate hydrate (CSH) gel, calcium aluminum silicate hydrates (CASH) gel and Friedel’s salt. CaCl2 in SR plays a main role in hydration products generation and high compressive strength of SR- activated GGBS pastes.

Immobilization of hazardous ferronickel slag treated using ternary limestone calcined clay cement

This study aims to develop the limestone calcined clay (LC3) as a low-carbon treatment to immobilize waste ferronickel slag (FNS) containing heavy metals. The results indicate that the ordinary portland cement (OPC) and limestone calcined clay cement (LC3) adequately immobilized the Chromium (Cr), with the leaching results of 0.10–0.30 mg/L. The LC3 cement provided superior Mn immobilization (lower than 5 mg/L) compared to OPC. Calcium aluminum silicate hydrate (C-A-S-H) and ettringite (AFt) were the two main hydrated products of LC3 that ensure the capacity to encapsulate metals. The LC3 specimens had the lower porosity between 50 and 10,000 nm compared to that of OPC. The Embodied Energy (EE) and Embodied Carbon Emissions (ECO2e) of per m3 LC3 remarkably decreased by 38.21% and 44.77%.

Elaboration of geopolymers based on clays by-products from phosphate mines for construction applications

Yellow clays from Moroccan phosphate mines are extracted with other waste rocks lithologies and stored in large dumps within the mine site. The present paper investigates the use of this by-product as a new aluminosilicate source for geopolymers elaboration at the laboratory scale. Yellow clays studied are mainly composed of montmorillonite, dolomite and quartz as major phases. The Toxicity Characteristic Leaching Procedure (TCLP) showed no existence of contaminant. In order to reach thermal activation, the raw clays were first calcined at different temperatures between 500 and 900 °C. Raw and calcined clays were characterized using thermogravimetric analysis (TGA), X-Ray Diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy. For the synthesis of geopolymers, calcined powder was mixed with an alkaline solution presenting different NaOH/Na2SiO3 ratios. The compressive strength was measured at 7, 14 and 28 days and material porosity was determined using Mercury Intrusion Porosimetry method in order to explain the mechanical behavior. XRD, 27Al and 29Si Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy, Fourier transformed infrared and TGA have been used to investigate the gel structure.The thermal treatment at 900 °C allowed the destruction of crystalline structure of montmorillonite clays, as well as the formation of new phases such as periclase (MgO) and gehlenite (Ca2Al2SiO7). Furthermore, the 27Al - 29Si MAS-NMR and the XRD analysis of the elaborated materials confirmed the formation of two cementitious gels C-A-S-H (Calcium aluminum silicate hydrate) and N-A-S-H (Sodium aluminum silicate hydrate). The compressive strength was around 25 MPa at 28 days. The obtained results are promising; they have shown that elaborated materials can be adapted for construction applications. In this case, it is recommended that economic and commercial study be developed.

Ferrochrome ash – Its usage potential in alkali activated slag mortars

This study is an attempt to develop a sustainable construction material, i.e., alkali activated slag (AAS) in combination with ferrochrome ash (FCA) as a replacement to ordinary Portland cement (OPC). The effect of the various levels of FCA (0, 25, and 50%) replacing ground granulated blast furnace slag (GGBS) in AAS mortars with 4% of Na2O dosage is studied. Further, five levels of the modulus of silica (Ms = 0.75, 1.00, 1.25, 1.5, and 1.75) are chosen to achieve targeted compressive strength at 28 days under ambient temperature curing conditions. The compressive strength decreases with the increase in level of the FCA replacement. The targeted design compressive strength is achieved with 25% FCA replacement to GGBS in the AAS mortar system with Ms = 1.25. In addition, microstructure and mineralogical studies are undertaken to ascertain the formation of different hydration products with the aid of the scanning electron microscope (SEM) and the X-ray diffractometer (XRD). Gismondine and calcium aluminate silicate hydrate (C-A-S-H) are the major hydration products in the AAS mortar mixes. Sodium aluminate silicate hydrate phases (N-A-S-H) are also observed prominently as the FCA replacement level increases in the AAS mortar mixes. The Fourier-transform infrared spectroscopy (FTIR) confirms the presence of the Si–O-(Si or Al) functional group. The addition of FCA in the AAS system is of vital significance in the reduction of the embodied carbon dioxide (ECO2eq), embodied energy (EEeq) and cost.

Versatile Surface Modification of Ceramsite Via Honeycomb Calcium-aluminum-silicate-hydrate and Its Functionalization by 3-thiocyanatopropyltriethoxysilane for Enhanced Cadmium(II) Removal

A low-cost and efficient filter medium for Cd(II) removal was prepared by anchoring -SCN functional groups (by 3-thiocyanatopropyltriethoxysilane, TCPS) on ceramsite via the approach of synthesizing a honeycomb calciumaluminum-silicate-hydrate (C-A-S-H) layer as intermediate. The specific surface area of ceramsite was increased enormously by more than 50 times because of the modification of honeycomb layer. Moreover, the abundant Si-OH bonds existing in the structure of CAS-H can serve as active sites for TCPS. The combined effects ensure that the hybrid filter medium (named ceramsite/C-A-S-H/TCPS) demonstrated a high Cd(II) adsorption capacity of 18.27 mg·g1 for particle size of 0.1-0.6 mm, 12.63 mg·g−1 for 0.6-1.25 mm and 8.64 mg g−1 for 1.25-2.35 mm. The Cd(II) adsorption capacity per unit area of ceramsite/C-A-S-H/TCPS (0.1-0.6 mm) is up to 4.07 mg·m−2, which is much higher than that of many nano-adsorbents. In addition, ceramsite/C-AS- H/TCPS could maintain a high removal efficiency (> 85%) in a wide range of pH 3-11 and showed excellent selectivity in the presence of competing ions. Furthermore, Cd(II) could be desorbed from ceramsite/C-A-S-H/TCPS composites with nearly 100%, suggesting the potential application in recycling of heavy metal ions.

Repair of ordinary Portland cement concrete using ambient-cured alkali-activated concrete: Interfacial behavior

In this paper, alkali-activated concrete (AAC) mixtures synthesized using five different class C fly ashes (FAs) were used as a repair material for structures constructed using conventional Portland cement concrete (CC). The bond strength between ambient-cured AAC and CC was evaluated using slant shear and pull-off tests. Three inclination angles of 45°, 33.75°, and 22.5° were examined during the slant shear test. For the pull-off test, no surface treatment, bonding adhesive treatment, or sandblasting surface treatment were applied to the CC substrate before applying the ACC repair. Full-height cylinders and full-depth beams were also tested as references for comparison purposes. Repairing CC using AAC yielded results similar to those of repairing CC with CC. Using the slant shear test at different angles, the average adhesion between the CC and AAC was found to be 5.8 MPa with a slight increase when increasing the calcium content in the precursor. The average coefficient of friction of the repaired specimens was approximately 0.64. The pull-off test results were sensitive to the surface treatment with sandblasting, which yielded the highest direct tensile strength. The direct and indirect tensile strengths were also analytically correlated to the adhesion from the slant shear test. The SEM results displayed new products such as calcium aluminate silicate hydrate (CASH) at the interface surface, and no sign of visible gap between the substrate and repair materials: i.e., CC and AAC, was observed.

Strength, microstructure, efflorescence behavior and environmental impacts of waste glass geopolymers cured at ambient temperature

Abstract In this study, waste glass powder (d50 = 15.4 μm) obtained by crushing soda lime glass bottles was investigated as a raw material for geopolymer cement. The waste glass (WG) powder and class C fly ash (FC) were mixed at varying ratios (100:0, 75:25, 50:50, 25:75, 0:100) and activated by sodium hydroxide solutions of different concentrations (0 M, 2.5 M, 5 M, 7.5 M, 10 M). The geopolymer pastes were cured at ambient temperature and the compressive strengths at increasing curing ages were tested. The mechanical properties were analyzed with respect to the kinetics and Si/Al ratio of the reaction system. The experimental results suggested that the WG mostly acted as an inert filler at early ages due to the slow reaction rate. However, the strength performance improved significantly after the curing age of 14 days, which was attributed to the reaction between WG and FC. The geopolymer made by mixing WG and FC at a ratio of 1:3 (Si/Al = 3.038) and 5 Mol NaOH solution achieved a compressive strength of 34.5 MPa. The microstructure and minerology of the geopolymers analyzed by the SEM-EDX and XRD suggested the coexistence of sodium aluminate silicate hydrate (N-A-S-H) gel and calcium aluminate silicate hydrate (C-A-S-H) gel in geopolymer matrix. The results of leaching tests indicated the potential environmental impact caused by the leaching of excessive alkali, which should be carefully managed during the mix design. The sustainability analysis including the embodied energy and carbon footprint confirmed the environmental friendliness of WG geopolymer. This study exhibited the feasibility of producing WG geopolymer concrete at ambient temperature and the potential synergy between the waste glass recycling and geopolymer industry.

Stabilization of silty sand using bentonite‑magnesium-alkalinization: Mechanical, physicochemical and microstructural characterization

This paper investigates the mechanical, physicochemical, and microstructural characterization of treated silty sand using a novel additive. The additive from a mixture of bentonite, magnesium chloride, and alkaline solution was introduced for stabilization of soil. Atterberg limits, compaction, pH, and unconfined compressive strength (UCS) tests were used to assess the mechanical and physicochemical properties of the stabilized soil. Further investigation results on the optimum designed sample are discussed based on microstructural analysis using X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). Two curing types: unheated and heated at 60 °C for 24 h, were observed at 7, 14, 28 and 60 days in ambient temperature. Overall, it was found that the chemical additive improved the compressive strength of the soil and the heated curing tests showed significant strength improvement. The mechanical and physicochemical results revealed an optimum mix to improve silty sand strength using the addition of 40% bentonite with an alkaline activator (SS/SH) ratio of 0.5, an alkaline activator-to-MgCl2 (L/S) ratio of 0.7, and 3% MgCl2 by dry weight of the soil under heat curing condition at 60 °C for 24 h. The microstructure analysis confirmed the formation of the cementitious products, such as calcium aluminium silicate hydrate (C-(A)-S-H) and magnesium silicate hydrate (M-S-H) in the treated sample.

The effect of dried paper-mill sludge on cement hydration

In the paper, the impact of paper-mill sludge dried at 75 °C (PS) on cement hydration is being analysed. The used specimens were made of CEM I 42.5 R cement and the added PS replaced 0%, 5%, 10% and 15% by mass of cement. The results of calorimetric measurements of the mixtures and the compressive strength were analysed (W/(C + PS) = 0.35). SEM and XRD tests were carried out after 3, 14, 28 and 56 days of curing W/(C + PS) = 1. PS was found to extend the induction period of the cement hydration and delay the time of the secondary heat release effect, especially in specimens with the highest content of the PS. The total heat release (after 96 h) measurement results showed that the highest total heat evolved from specimens without the PS. The total liberated heat gradually increased with the increase in the PS content in the cement paste mixture. In the specimens with 15% of PS, the total heat release decreased by 20%, as compared to the control specimen without the additive. XRD test results revealed that the standard minerals listed below were formed in cement stone: ettringite, calcite, portlandite, and calcium aluminium silicate hydrate. SEM tests revealed significant changes in cement stone microstructure caused by the increase in the PS in cement paste. The compressive strength of specimens with PS waste was found to be considerably lower in the initial stage of hardening; however, when samples hardening time is increased up to 56 days, the difference between the values of compressive strength for specimens 5% of PS and the control specimens decreases.

Nutrient release from K-feldspar ore altered in hydrothermal conditions

The development of potash materials from local K-bearing resources such as aluminosilicate minerals is desirable to overcome reliance on imported fertilizers in tropical countries. However, the nutrient release from such materials follows a time-dependent profile that is not well-understood and that is significantly different if probed at agronomic or geological timescales. This work investigates the nutrient release from a calcium–aluminum–silicate-hydrate (C–A–S–H) material obtained via hydrothermal alteration of K-feldspar ore and CaO. The C–A–S–H hydrothermal material is subjected to sequential leaching cycles with diluted HNO3 (initial pH = 5), renewing the leaching solution at every cycle. X-Ray Powder Diffraction (XRD) is used to monitor changes in the material mineralogy as the leaching progresses, showing a relative increase of calcite (up to 7 wt%) and amorphous phase (up to 23 wt%). Inductively Coupled Plasma Mass Spectrometry (ICP-MS) of the leachates is used to monitor the release of K, Ca, Si and Al, and shows that the material releases K nutrient at every leaching cycle. The pH of the leachates shows that as the content of calcite in the material increases a buffering capacity at pH ≈ 9.6 is developed by the material. The mineralogy, nutrient release, and pH results presented in this study suggest a potential application of the material as a slow release fertilizer when compared to KCl. Experimental results also imply that kinetic parameters rather than solubility are more suited to describe the fertilizer value of silicate materials.

Characterization study on coconut shell concrete with partial replacement of cement by GGBS

Increasing demand and depletion of natural resources has brought a need for the replacement of conventional concrete. This study is conducted by completely replacing coarse aggregate with coconut shell (CS) an agricultural waste. Though it achieves the target strength the decrease in quality of coconut shell concrete (CSC) is enhanced by utilizing a pozzolanic material Ground Granulated Blast-furnace Slag (GGBS) and its optimum percentage of replacement with cement is found as 10% by conducting compressive strength for varying percentage of replacement say 0%, 5%, 10%, 15%, and 20%. For the optimum mix, the durability study and microstructural investigation, say SEM, XRD, EDX, FTIR, and IMM was examined. The result revealed that incorporating GGBS increases the strength of concrete to around 15%. The microstructural study has clearly exhibits that the hydration process has been improved to better formation of Calcium Silicate Hydrate (C–S–H) and Calcium Aluminium Silicate Hydrate (C-A-S-H) when GGBS is incorporated.

Effect of the fineness of copper slag on the early hydration properties of cement–copper slag binder

The early hydration heat and hydration process, hydration products and strength of binders containing 20% copper slag with different fineness has been studied. The ordinary Portland cement is taken as the comparison sample. Results show that the replacement of cement in the same proportion copper slag can prolong its induction period, reduce its early hydration heat and prolong the hydration process, which was caused by the dilution of cement clinker after adding 20% copper slag, the limited pozzolanic activity and the agglomeration effect of copper slag particles, as well as the chemical composition which contained heavy metal compounds. Adding copper slag can reduce both the compressive and flexural strength, while the reduction rate of flexural strength is slightly smaller than that of compressive strength. Copper slag with specific surface areas 503 m2 (kg)−1 has the optimal strength development. Hydration products of composite binders such as calcium hydroxide, calcium carbonate, calcium aluminum silicate hydrate are about the same with the comparison sample ordinary Portland cement, while calcium iron oxide content Fe is always exist. With the curing aging growing, especially for sample with the highest fineness copper slag, the hydration will be deeper and generate calcium aluminum oxide carbonate hydrate.

Properties of ceramic tile waste based alkali-activated mortars incorporating GBFS and fly ash

Abstract This paper presents the experimental findings of a study on the performance of waste ceramic powder (WCP) as binder on the mechanical and microstructure properties of alkali activated mortars (AAMs) containing ground blast furnace slag (GBFS) and fly ash (FA). In this study, the ternary blend was activated with low concentration of alkaline solution (4 M). WCP was kept with high content of 50%, 60% and 70% for the total binder. After casting operation, the specimens were cured at ambient temperature of 27 °C and tested at eight different ages of 1, 3, 7, 28, 56, 90, 180 and 360 days. Microstructure tests such as X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) were conducted to evaluate the effect of high content of WCP on the formulation of sodium aluminium silicate hydrate (N-A-S-H), calcium aluminium silicate hydrate (C-A-S-H) and calcium silicate hydrate (C-S-H) gels. Test results indicated that high volume WCP produced environmental friendly alkali activated mortars with compressive strength higher than 70 MPa at age of 28 days. The results also showed that the workability and setting time of alkali activated mortars enhanced with the increase in WCP content.

Efecto del residuo de mampostería en la hidratación de pastas de cemento Portland

En este artículo se presentan los resultados de un estudio experimental sobre el efecto de la incorporación del residuo de mampostería (RM)proveniente de residuos de construcción y demolición (RCD) en la hidratación de pastas de cemento. La cinética y las reacciones exotérmicas durante edades tempranas de hidratación fueron monitoreadas mediante calorimetría, y la presencia de productos de hidratación fue determinada mediante microscopia electrónica de barrido (SEM), análisis termogravimetrico (DTG), difracción de rayosX (XRD) y espectroscopia infrarroja por transformada de Fourier (FTIR). Los resultados muestran que la presencia de RM en las pastas hace decrecer el calor de hidratación en las primeras 48 horas. Por otra parte, las técnicas de SEM, DTG, XRD y FTIR indican que los principales productos de hidratación en las pastas adicionadas con RM son silicato de calcio hidratado (C-S-H), aluminato cálcico hidratado (CAH) y silico aluminato cálcico hidratado (CASH).

Removal of heavy metals (Co, Cr, and Zn) during calcium\u2013aluminium\u2013silicate\u2013hydrate and trioctahedral smectite formation

Hydrated aluminosilicates were synthesized with and without aqueous heavy metals (Me), such as cobalt (Co), chromium (Cr), and zinc (Zn), by a sol–gel process at different initial molar ratios of Ca/(Si + Al) (0.6–1.6) and Me/Si (0.0–2.0), and constant Al/Si ratio (0.05) using equilibrium-approaching experiments. The chemical composition of the reactive solutions during aluminosilicate precipitation and maturation was monitored by ICP-OES. The mineralogy, nanostructure, and chemical composition of the precipitates were studied by XRD and high-resolution TEM. At Me/Si ratios ≤ 0.2, calcium–aluminium–silicate–hydrates (C–A–S–H) with a defect 14 Å tobermorite-like structure formed, whereas at a Me/Si ratio of 2.0, either trioctahedral Co- and Zn-smectite or amorphous Cr gels precipitated, independent of the initial Ca/(Si + Al) ratio used for gel synthesis. The immobilization capacities for {text{Co}}^{2 + } , {text{Cr}}^{3 + } , and {text{Zn}}^{2 + } by C–A–S–H, Cr gel, and trioctahedral smectite are 3–40 mg/g, 30–152 mg/g, and 122–141 mg/g, respectively. The immobilization mechanism of heavy metals is based on a combination of isomorphous substitution, interlayer cation exchange, surface (ad)sorption, and surface precipitation. In engineered systems, such as underground concrete structures and nuclear waste disposal sites, hydrated aluminosilicates should exhibit a high detoxication potential for aqueous heavy metals.

Influence of low calcium fly ash on compressive strength and hydration product of low energy super sulfated cement paste

This research aims to explore the effects of low calcium Class F fly ash (FFA) as an alumina supplier on the compressive strength and hydration products of an ecological super-sulfated cement (SSC) with fluidized bed combustion (CFBC) fly ash (CFA) as a crucial activator. Experimental results showed that partial replacement of ground granulated blast furnace slag (GGBFS/slag) by FFA in range of 10–30 wt% significantly improved the compressive strength of hardened eco-SSC paste. Microstructural examination using scanning electron microscope equipped with energy dispersive X-ray spectrometer (SEM/EDS), X-ray diffraction (XRD), thermogravimetric and derivative thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectroscopy obviously proved that the main hydration products of the hardened paste were ettringite/monosulfate (AFt/AFm) and calcium aluminum silicate hydrate (C-A-S-H). Increase in FFA resulted in higher degree of AFt/AFm precipitation and C-A-S-H with lower Ca:(Si + Al) ratio.

A Comparative Study on Hydraulic Properties and Cementitious Activity of Carbon Steel Slag and Stainless Steel Slag

Abstract This work aims to make a comparative study on high-fineness, basic-oxygen-furnace, carbon steel slag (CS) and electric-arc-furnace stainless steel slag (SS) with high fineness to assess the possibility of using them as hydraulic binders. Test results reveal that CS has higher early hydraulic properties than SS, which has a higher rate of activity at later ages than at early ages (but still lower than that of CS), confirmed by compressive strength and mercury intrusion porosimeter (MIP) test results. Calorimetric analysis showed exothermic reactions in both slags. X-ray diffraction (XRD), thermogravimetry/differential scanning calorimetry (TG/DSC), Fourier transform-infrared spectra (FTIR), and scanning electron microscopy (SEM) results indicated that the hydration products of CS were mainly calcium silicate hydrate (C-S-H), calcium aluminate hydrate (C-A-H), calcium aluminate silicate hydrate (C-A-S-H), aluminum hydroxide (Al(OH)3 [AH3]), and calcium hydroxide (Ca(OH)2 [CH]); however, C-S-H was the only hydration product of SS. The microchemical analysis showed that the average silicon/calcium atom ratios for the hydration products in 90-day hydrated CS and SS pastes were 0.31 and 0.52, respectively. Wavelength-dispersive X-ray spectroscopy (WDS) mapping at 90 days for both slags revealed that silicon and calcium are included in the hydrated matrix surrounding slag particles, with the addition of aluminum in CS.

Mechanical behaviour of waste powdered tiles and Portland cement treated soft clay

The main objective of this study is to evaluate and compare the efficiency of ordinary Portland cement (OPC) in enhancing the unconfined compressive strength of soft soil alone and soft soil mixed with recycled tiles. The recycled tiles have been used to treat soft soil in a previous research by Al-Bared et al. (2019) and the results showed significant improvement, but the improved strength value was for samples treated with low cement content (2%). Hence, OPC is added alone in this research in various proportions and together with the optimum value of recycled tiles in order to investigate the improvement in the strength. The results of the compaction tests of the soft soil treated with recycled tiles and 2, 4, and 6% OPC revealed an increment in the maximum dry density and a decrement in the optimum moisture content. The optimum value of OPC was found to be 6%, at which the strength was the highest for both samples treated with OPC alone and samples treated with OPC and 20% recycled tiles. Under similar curing time, the strength of samples treated with recycled tiles and OPC was higher than the treated soil with the same percentage of OPC alone. The stress-strain curves showed ductile plastic behaviour for the untreated soft clay and brittle behaviour for almost all treated samples with OPC alone and OPC with recycled tiles. The microstructural tests indicated the formation of new cementitious products that were responsible for the improvement of the strength, such as calcium aluminium silicate hydrate. This research promotes recycled tiles as a green stabiliser for soil stabilisation capable of reducing the amount of OPC required for ground improvement. The replacement of OPC with recycled tiles resulted in higher strength compared to the control mix and this achievement may results in reducing both OPC in soil stabilisation and the disposal of recycled tiles into landfills.