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Commercial sodium hydroxide (NaOH) and sodium silicate (SS) are commonly used as alkaline activators in geopolymer concrete production despite concerns about their availability and associated CO2 emissions. This study employs an alternative alkaline activator (AA) synthesized from a sodium silicate alternative (SSA) solution derived from rice husk ash (RHA) and a 10 M sodium hydroxide solution. The initial phase established an optimal water-to-binder (W/B) ratio of 0.50, balancing workability and structural performance. Subsequent investigations explored the influence of the alkali/precursor (A/P) ratio on geopolymer concrete properties. A control mix uses ordinary Portland cement (OPC), while ground granulated blast-furnace slag (GGBS)-based geopolymer concrete—GPC mixes (GPC1, GPC2, GPC3, GPC4) vary the A/P ratios (0.2, 0.4, 0.6, 0.8) with a 1:1 ratio of sodium silicate to sodium hydroxide (SS: SH). The engineering performance was evaluated through a slump test, and unconfined compressive strength (UCS) and tensile splitting (TS) tests in accordance with the appropriate standards. The geopolymer mixes, excluding GPC3, offer suitable workability; UCS and TS, though lower than the control mix, peak at an A/P ratio of 0.4. Despite lower mechanical strength than OPC, geopolymers’ environmental benefits make them a valuable alternative. GPC2, with a 0.4 A/P ratio and 0.5 W/B (water to binder) ratio, is recommended for balanced workability and structural performance. Future research should focus on enhancing the mechanical properties of geopolymer concrete for sustainable, high-performance mixtures.

The global demand for cement-based materials continues to rise, particularly in emerging economies where infrastructure and housing development are accelerating [...].The global demand for cement-based materials continues to rise, particularly in emerging economies where infrastructure and housing development are accelerating [...].

Sulfate soil stabilisation, while offering technical benefits for infrastructure, is a challenging process, complicated by the nucleation of ettringite, an expansive mineral that can cause soil deterioration. This study was undertaken to elucidate the synergistic effect of lime and metakaolin on the physico-mechanical performance of high-sulfate-bearing soil. The binder content in the stabilised specimens was fixed at 20 wt%, and metakaolin was used to partially substitute lime at different substitution levels. The physico-mechanical investigation revealed that supplementation of lime with metakaolin had a promotional effect on the unconfined compressive strength and swelling potential. The threshold of this effect was obtained by a binary blend of 7.5L–12.5MK, where the UCS was increased fourfold, while the swelling potential was reduced to a near-zero magnitude of 0.33%. This superior performance is due to the fineness and high reactivity of metakaolin, as both limit the nucleation of ettringite and promote the neoformation of further hydrated compounds, thus yielding a denser interlocked system and increasing its resistance to water soaking.

The utilisation of magnesium oxide-based binders (M) as an alternative to hydrated calcium silicate materials is a promising avenue for binding methodologies. However, the efficacy of using silica fume (S) as a co-binder with magnesium oxide in sulphate soil stabilisation, along with their ideal blending ratio, has yet to be unveiled. Therefore, an array of artificial sulphate soil specimens was fabricated, each featuring varying combinations of magnesium oxide and silica fume. These specimens were subsequently subjected to comprehensive testing, including unconfined compressive strength (UCS) test, linear expansion test, thermogravimetric analysis, and X-ray diffraction analysis. The outcomes demonstrated that the co-utilisation of silica fume and magnesium oxide significantly improves the compressive strength and linear expansion of sulphate soil, and such an improvement was more efficacious at a stoichiometric amount of 5% magnesium oxide and 5% silica fume (5M5S). This outperforming threshold, characterised by the highest UCS (1834 kN/m2) and minimal expansion (0.2%), occurred through the consumption of surplus brucite and the formation of further magnesium silicate hydrate.

Clayey soils endure adverse changes in strength and volume due to seasonal changes in moisture content and temperature. It has been well recognised that high cement content has been successfully employed in improving the mechanical properties of clayey soils for geotechnical infrastructural purposes. However, the environmental setbacks regarding the use of high cement content in soil reinforcement have necessitated the need for a greener soil reinforcement technique by incorporating industrial by-product materials and synthetic fibres with a reduced amount of cement content in soil-cement mixtures. Therefore, this study presents an experimental study to investigate the mechanical performance of polypropylene and glass fibre-reinforced cement-clay mixtures blended with ground granulated blast slag (GGBS), lime and micro silica for different mix compositions and curing conditions. The unconfined compressive strength, linear expansion and microstructural analysis of the reinforced soils have been studied. The results show that an increase in polypropylene and glass fibre contents caused an increase in unconfined compressive strength but brought on the reduction of linear expansion of the investigated clay from 7.92% to 0.2% at fibre content up to 0.8% for cement-clay mixture reinforced with 5% Portland cement (PC). The use of 0.4–0.8% polypropylene and glass fibre contents in reinforcing cement-clay mixture at 5% cement content causes an increase in unconfined compressive strength (UCS) values above the minimum UCS target value according to American Society for Testing and Materials (ASTM) 4609 after 7 and 14 days curing at 20 °C to 50 °C temperature. Therefore, this new clean production of fibre-reinforced cement-clay mixture blended with industrial by-product materials has great potential for a wide range of applications in subgrade reinforcement.

The role of gypsum level on the long-term strength and expansion of soil stabilised with different lime contents is not well understood. This research, therefore, studied the effect of varying gypsum concentrations of 0, 3, 6, and 9 wt% (equivalent to the sulfate contents of 0, 1.4, 2.8, and 4.2%, respectively) on the performance of sulfate soil stabilised with two lime levels (4 and 6 wt%). This was carried out to establish the threshold level of gypsum/lime (G/L) at which the increase in G/L ratio does not affect the performance of lime-stabilised sulfate soil. Both unconfined compressive strength (UCS) and expansion, along with the derivative thermogravimetric (DTG) analysis, were adopted to accomplish the present objective. Accordingly, the result indicated that the strength and expansion were proportional to the lime and sulfate content, of which a G/L ratio of 1.5 was the optimum case scenario for UCS, and at the same time, the worst-case scenario for expansion. This discovery is vital, as it is anticipated to serve as a benchmark for future research related to the design of effective binders for suppressing the sulfate-induced expansion in lime-stabilised gypseous soil.

Expansion of soils has been found to produce significant negative economic and environmental impact on various civil engineering infrastructure. This impact is more deleterious in soils containing sulphates, when treated with calcium-based stabilizers such as Lime and/or Portland cement (PC). The reported study investigated the strength and swell characteristics of Kaolinite clay artificially induced with high levels of Gypsum (sulphate) contents after stabilization with CEM I (PC), which is a calcium-based stabilizer. An optimum stabilizer content/Gypsum dosage, aimed at investigating the maximum magnitude of expansion possible using high levels of 10, 15 and 20% Gypsum contents (4.7, 7 and 9.3 wt.% sulphate) stabilized with calcium-based content of 7, 8, 9 and 10 wt.%. This was expected to provide further understanding on the mechanisms behind high sulphate-bearing clay soils, and the impact of sulphate and calcium content on strength and swell characteristics. The research outcomes showed that the introduction of sulphate to a Kaolinite clay soil reduces the compressive strength of the stabilised product by a factor range of 6–47% at 28 days curing age, while the swell behaviour is mainly dependent on both the sulphate content and curing age. Furthermore, the observed result suggests an 8 wt.% binder content to produce maximum magnitude of expansion (swell) with a high Gypsum content of 10% by weight. This finding is of economic importance, as it is expected to serve as a benchmark for further research on the stabilized clay systems, at high sulphate levels using sustainable binder materials.

Sulfate-induced expansion resulting from the formation of ettringite in sulfate-bearing soil stabilised with calcium-based stabilisers is a problematic issue with technical and economic implications. Thus, this research examines the viability of the co-addition of lime (L) and silica fume (S) at varying binder dosages (4, 6, and 10 wt%), with a view of establishing the optimum blend of L–S for suppressing the ettringite-induced expansion of artificially high sulfate-dosed soil (kaolinite-K and gypsum-G). To do so, a series of laboratory specimens, designed using different gypsum and lime concentrations, were investigated using unconfined compression strength (UCS), linear expansion, and derivative thermo-gravimetric analysis (DTG) as the main criteria for the examination. The research outcomes indicated that the increasing substitution of L with S induces a gradual reduction on the UCS and linear expansion at binder levels of 4 and 6 wt%, while its usage in a high binder level (10 wt%), can yield an expansion reduction, with no compromise on the UCS performance. Therefore, silica fume has the potential for restricting ettringite formation and suppressing the expansion, of which 3L7S is the optimum blending ratio for suppressing the expansion.

Commercial sodium hydroxide (NaOH) and sodium silicate (SS) have remained two of the leading alkaline activators widely used in producing geopolymer concrete, despite some identified negatives regarding their availability and additional CO2 emissions relating to the overall manufacturing process. This study reports the viability of developing geopolymer concrete using a laboratory-synthesised silica fume (SF)-derived SS solution in combination with NaOH at a molarity of 10M as an alternative binary alkali-alkaline activator to Ground Granulated Blast Furnace slag (GGBS). The use of SF in the development of geoolymer activators will pave the way for the quality usage of other high-silica content by-products from nature, industry, and agriculture. In the currently reported proof of concept, four geopolymer concrete batches were produced using different alkaline activator/precursor-A/P ratios (0.5 and 0.9) and SS to NaOH-SS/SH volume ratios (0.8/1.2 and 1.2/0.8), to establish the impact on the engineering performance. Two controls were adopted for ordinary and geopolymer concrete mixes. The engineering performance was assessed using slump and compaction index (CI) tests, while the Unconfined Compressive Strength (UCS) and tensile splitting (TS) tests were measured at different curing ages in accordance with their appropriate standards. The results indicated a reduction in slump values as the A/P ratio decreased, while the CI values showed a reversal of the identified trend in slump. Consequently, mix GC2 attained the highest UCS strength gain (62.6 MPa), displaying the superiority of the alkali activation and polymerisation process over the CSH gel. Furthermore, the impact of A/P variation on the UCS was more pronounced than SS/SH due to its vital contribution to the overall geopolymerisation process.

Geopolymers are an environmentally sustainable class of low-calcium alkali-activated materials (AAMs), distinct from high-calcium C–A–S–H gel systems. Synthesized from aluminosilicate-rich precursors such as fly ash, metakaolin, slag, waste glass, and coal gasification fly ash (CGFA), geopolymers offer a significantly lower carbon footprint, valorize industrial by-products, and demonstrate superior durability in aggressive environments compared to Ordinary Portland Cement (OPC). Recent advances in thermodynamic modeling and phase chemistry, particularly in CaO–SiO2–Al2O3 systems, are improving precursor selection and mix design optimization, while Artificial Neural Network (ANN) and hybrid ML-thermodynamic approaches show promise for predictive performance assessment. This review critically evaluates geopolymer chemistry and composition, emphasizing precursor reactivity, Si/Al and other molar ratios, activator chemistry, curing regimes, and reaction mechanisms in relation to microstructure and performance. Comparative insights into alkali aluminosilicate (AAS) and aluminosilicate phosphate (ASP) systems, supported by SEM and XRD evidence, are discussed alongside durability challenges, including alkali–silica reaction (ASR) and shrinkage. Emerging applications ranging from advanced pavements and offshore scour protection to slow-release fertilizers and biomedical implants are reviewed within the framework of the United Nations Sustainable Development Goals (SDGs). Identified knowledge gaps include standardization of mix design, LCA-based evaluation of novel precursors, and variability management. Aligning geopolymer technology with circular economy principles, this review consolidates recent progress to guide sustainable construction, waste valorization, and infrastructure resilience.