This article presents laboratory experiments examining the potential benefits of the synergistic effects of ground granulated blast furnace slag (GGBS) and metakaolin (MK) on lime (L) stabilisation of synthetic sulfate-bearing soil. The different soil–binder mixtures considered in this study were prepared by partially replacing lime with GGBS, metakaolin, or a combination of both, at substitution levels ranging from 25% to 75% by mass. The engineering performance of the mixtures was characterised through physico-mechanical analyses (unconfined compressive strength and linear expansion) and microstructural analyses (X-ray diffraction and scanning electron microscopy). Among the binary binders examined in this study, the GGBS-rich binder demonstrated the highest strength, while the metakaolin-rich binder exhibited the lowest swelling behaviour. This difference in performance was balanced by the ternary L–GGBS–MK blend, particularly at a blending ratio of 5L–12.5GGBS–2.5MK. This optimal blend produced a near-zero linear expansion of 0.04%, with only a negligible reduction in strength compared with the binary blend 5L–15GGBS. By replacing a substantial proportion of lime with industrial by-products, the proposed stabilisation strategy reduces reliance on high-carbon conventional binders, supporting the development of green, low-carbon, and resource-efficient construction materials. The findings demonstrate the potential of circular material utilisation to mitigate sulfate-induced heaving while enhancing the durability and sustainability of ground improvement practices. This innovative approach addresses geo-environmental challenges associated with lime stabilisation and aligns with the broader transition towards net-zero construction, promoting the beneficial reuse of industrial by-products, reducing embodied carbon, conserving natural resources, and advancing environmentally responsible geotechnical engineering solutions for sustainable infrastructure development.

Awareness of environmental sustainability is driving the shift from conventional Portland cement, a major contributor to carbon dioxide emissions, to more sustainable alternatives. This study focuses on developing a geopolymer concrete by optimizing geopolymer concrete mixtures with various ratios of Ground Granulated Blast Furnace Slag (GGBS) and pulverized fly ash (PFA) as precursors, aiming to find a mix that maximizes strength while minimizing environmental impacts. The precursor was activated using a laboratory-synthesized silica fume (SF)-derived sodium silicate solution in combination with NaOH at a molarity of 10M. This study aims to find the optimal geopolymer concrete mix with a 0.55 water-to-binder ratio, a 0.40 alkali-to-precursor ratio, and a 1:1 sodium silicate to sodium hydroxide ratio. Ordinary Portland cement was used as the control mix binder (C), while the geopolymer mixes included varying GGBS-PFA compositions [CL0 (50% GGBS-50% PFA), CL1 (60% GGBS-40% PFA), CL2 (70% GGBS-30% PFA), CL3 (80% GGBS-20% PFA), and CL4 (90% GGBS-10% PFA)]. The engineering performance of the mixtures was assessed using slump, unconfined compressive strength, split tensile, and flexural strength tests in accordance with their relevant standards. Observations showed that GPC specimens exhibited similar or slightly higher strength values than conventional concrete using PC. In addition to strength, geopolymers have a smaller environmental footprint, consuming less energy and reducing greenhouse gas emissions. These qualities make geopolymer concrete a sustainable construction option that aligns with global efforts to reduce carbon emissions and conserve resources.

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.

Geopolymer concrete (GPC) can be produced by the chemical activation of industrial by-products and processed natural minerals that contain aluminosilicates with the presence of an alkaline activator. Raw components are one of the critical parameters affecting geopolymer performance. On the other hand, the mixing procedure of geopolymer concrete is not any less important. Few demonstrative constructions have been built using GPC as a greener alternative to Portland cement concrete. Numerous variables affect GPC manufacture, such as raw material specification, activator type and dosage, and curing regimes. Despite the conventions of the building industry, the lack of proper mix design methods limits the wide acceptance of GPC in the industry. This report conducted experimental trials on GGBS-based GPC to optimize a mixing design procedure to achieve best mechanical strength and structural integrity. Geopolymer concrete properties were evaluated through slump and unconfined compressive strength tests. The laboratory trials in this report revealed that all geopolymer mixes, except SD0HV and 1W-SG, exhibited high workability values. Also, the presence of an alkaline activator was vital to attain satisfactory compressive strength values. The alkaline activator could be used when cooled and reached room temperature after two hours of preparation and was not necessary after 24 h. Mix G-(0.5W-S) with a 0.5A.A. (alkaline activator)/precursor (GGBS) ratio, SSA (sodium silicate alternative)/SH (sodium hydroxide with 10 M molarity) ratio of 1:1, and 0.55 W/B (water to binder) ratio is recommended to achieve best mechanical performance and structural integrity.

This study investigates the feasibility of utilizing recycled plastic waste as a partial substitute for sand in concrete production. Reprocessing used plastic items or materials involves collecting, cleaning, shredding, and melting, resulting in reprocessed plastic particles. Incorporating these recycled plastic particles into concrete addresses environmental concerns related to plastic disposal and the growing scarcity and increasing cost of natural sand. To evaluate the sand replacement capacity of recycled plastic, four types of mixtures were created with varying levels of recycled plastic replacement (5%, 10%, 15%, and 20%). All mixtures maintained a water-to-binding ratio of 0.55 and were tested at 7, 28, and 56 days. The testing regimen encompassed determining the slump value, density, compressive strength, tensile strength, and resistance to freezing and thawing. The findings revealed that replacing sand in the concrete mix with recycled plastic enhanced workability, which was attributed to the hydrophobic nature of the plastic particles. However, both compressive and tensile strength exhibited a declining trend. Additionally, after undergoing multiple freezing and thawing cycles, the concrete mix exhibited poor durability properties and brittleness. These issues may arise due to factors such as incompatibility, non-uniformity, reduced cohesion, and the lower density of plastic particles.

The effective use of waste materials is one of the key drivers in ensuring sustainability within the construction industry. This paper investigates the viability and efficacy of sustainably incorporating a polylactic acid-type plastic (WP) as a 10 mm natural coarse aggregate (NA) replacement in geopolymer concrete. Two types of concrete (ordinary Portland cement—OPC and geopolymer) were produced for completeness using a concrete formulation ratio of 1:2:3. The ordinary concrete binder control was prepared using 100% OPC at a water/binder ratio of 0.55, while the geopolymer concrete control used an optimum alkaline activator/precursor—A/P ratio (0.5) and sodium silicate to sodium hydroxide—SS/SH volume ratio (1.2/0.8). Using the same binder quantity as the control, four concrete batches were developed by replacing 10 mm NA with WP at 30 and 70 wt% for ordinary and geopolymer concrete. The mechanical performance of the developed concrete was assessed according to their appropriate standards, while a microstructural investigation was employed after 28 days of curing to identify any morphological changes and hydrated phases. The results illustrate the viability of incorporating WP in geopolymer concrete production at up to 70 wt% replacement despite some negative impacts on concrete performance. From a mechanical perspective, geopolymer concrete indicated a 46.7–58.3% strength development superiority over ordinary concrete with or without WP. The sample composition and texture quantified using automated scanning electron microscopy indicated that adding WP reduced the presence of pores within the microstructure of both concrete types. However, this was detrimental to the ordinary concrete due to the low interfacial zone (ITZ) between calcium silicate hydrate (CSH) gel and WP, resulting in the formation of cracks.

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.

A geopolymer is an inorganic amorphous cementitious material, emerging as an alternative sustainable binder for greener concrete production over Ordinary Portland Cement (OPC). Geopolymer concrete production promotes waste reuse since the applicable precursor materials include agricultural and industrial waste that requires disposal, helping to reduce waste in landfills and ensuring sustainable environmental protection. This study investigates the development of an environmentally friendly sodium silicate alternative (SSA) derived from pumice powder (PP) in place of a commercial Na2SiO3 solution at a 10 M concentration. Six concrete batches were produced at alkaline/precursor (A/P) ratios of 0.1, 0.2, 0.3, 0.4, and 0.5. The geopolymer mix AF4, with an A/P ratio of 0.4, became the optimum geopolymer concrete design; however, it recorded lower compressive, tensile splitting, and flexural strengths, respectively, against the control OPC concrete. The geopolymer formulations, however, obtained 28-day-hardened concrete densities comparable to the control concrete. The 28-day compressive strength of the OPC concrete was 29.4 MPa, higher than the 18.8 MPa recorded for AF4. However, the 56-day strength of AF4 improved to 22.4 MPa, an around 19% increase compared to the 30.8 MPa achieved by the control mix on day 56, having experienced only a 5% strength increase. The low mechanical performances of the geopolymer formulation could be attributed to extra water added to the original geopolymer design to improve the workability of the geopolymer mix. Therefore, the SSA alkaline solution using PP showed some potential for developing geopolymer concrete for low-strength construction applications.

This chapter reports on stabilized ecology-based green clay–hemp brick material. Ground granulated blast-furnace slag (GGBS) was used as a partial substitute for conventional stabilizers (lime or Portland cement) to stabilize Lower Oxford Clay (LOC) incorporating industrial hemp. The development of stabilized ecology-based green clay–hemp brick material is expected to underpin the potential of commercial production of nonfired stabilized hemp walls, hemp blocks, and hemp bricks, with the potential to offer an environmentally friendly alternative to traditional concrete, fired clay bricks, and cement bricks. The parameters considered in this study are as follows: (1) material characterization, (2) unconfined compressive strength, (3) linear expansion, and (4) cost. The 50-day linear expansion results for the test specimens showed that the maximum overall expansion rate for all the stabilized mixtures was 2%. The expansion behavior of all stabilized clay–hemp material was significantly reduced with the presence of GGBS. The cost analysis results showed that the stabilized clay–hemp material manufactured with lime–GGBS system had the lowest net present value.

The main thrust of this research was to establish any benefits of mellowing, and the optimal moisture content (OMC) for compacting mellowed sulphate-bearing clay soil undergoing the stabilization process. Two three-day mellowing regimes were carried out, prior to final compaction, at different initial moisture contents of 30% or 40% OMC. The unmellowed specimens were compacted immediately after mixing with the blended stabilizers. A blend of quicklime (L) with a sustainable by-product, silica fume (SF), at a 1:1 ratio (2%L–2%SF) was used. Linear expansion and unconfined compressive strength (UCS) tests were carried out to evaluate the benefits of mellowing. The test results suggested that the mellowed test specimens achieved better UCS and swelling properties compared to the unmellowed specimens. Mellowing at 1.2 OMC produced better strength performance than at 1.4 OMC, whereas mellowed specimens at 1.4 OMC showed better resistance to linear expansion compared to 1.2 OMC. The research findings suggested that optimal performance was achieved by mellowing at the higher initial moisture condition of 40% OMC and compacting the materials at the lower moisture condition of 1.2 OMC.

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.

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.

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.

The world’s growing population and industrialization have led to increased construction activities. This has increased the amount of waste aggregates which can be recycled in construction and cut the cost of infrastructure development. This study, therefore, reports the experimental findings for the effect of immobilizing Bacillus megaterium on the compressive strength and water absorption of laboratory prepared test mortar. Bacterial solution used in this work had a concentration of 1.0 × 107 cells/mL. The impact of recycled mortar impregnated with bacteria was studied after curing the specimens in water, saturated lime water, and 1.5% sulfuric acid. Compressive strength for test specimens cured in the three media was determined at the 2nd, 7th, 28th, and 56th day of curing. SEM analysis was done for mortars cured in acidic media and saturated lime water after curing for 28 days. The test results indicated that curing in water and saturated water improved the compressive strength, while the acidic medium lowered it. Recycled mortar is, therefore, an ideal material for immobilizing Bacillus megaterium before introduction into fresh concrete/mortar. The use of recycled mortar is a good strategy to reduce wastes from construction activities, save on the cost of construction materials, and enhance environmental conservation.

The use of silica fume and ground granulated blast-furnace slag (GGBS) as a precursor to lime has been proven to be an effective sulfate soil stabilisation technique. However, which precursor is superior, in terms of both strength and swelling, is still questionable. Accordingly, the binary blends of lime–silica fume and lime–GGBS were separately added to pure kaolin soil and sulfate-dosed kaolin soil at a fixed combination dosage of 3L7S and 3L7GGBS. Then, a multi-scale investigation including unconfined compression strength (UCS), linear expansion, derivative thermogravimetric (DTG), X-ray diffraction and scanning electron microscopy (SEM), was performed to assess their performance. The engineering tests indicated that the binary blends of lime–silica fume and lime–GGBS are effective in the stabilisation of non-sulfate and sulfate-dosed soil, with the former being superior in terms of the expansion and the latter being superior in terms of UCS. This disparity in performance is partly attributed to the higher calcium oxide content of 3L7GGBS which induces a relatively higher amount of ettringite, and partly due to the higher pozzolanic activity of silica fume which accelerates the consumption of lime and restricts the formation of ettringite on the expense of fabric modification.

Recycled aggregate (RA) from construction and demolition waste can readily be used to replace natural aggregate in concrete. Nonetheless, the poor quality of RA adversely affects the properties of recycled aggregate concrete, limiting its use to only non-structural applications. This study examined the effects of various treatment methods by testing the aggregate impact value (AIV) and water absorption (WA) of recycled coarse aggregate before and after treatments as an indicator to examine the efficiency of these treatments. The results showed that the untreated RA achieved 17% and 6.1% for AIV and WA, respectively. Accelerated carbonation treatment at 50% CO2 concentration level for six days of CO2 exposure time achieved the best results among other carbonation conditions, showing 11% and 46% enhancements in the AIV and WA, respectively. The RA treated with cyclic limewater combined with accelerated carbonation exhibited better improvement in the AIV and WA compared to the sole use of accelerated carbonation treatment. Coating RA with cement-silica fume slurry at 0.1 mm coating thickness was found to be optimal, achieving 12% and 54% enhancements in the AIV and WA, respectively. Soaking RA in a 10% Portland cement - pulverized fuel ash - silica fume solution for 4 h was found to be optimal, recording enhancements of 13% and 54% in the AIV and the WA, respectively among other soaking solutions. Soaking RA in 5% sodium silicate – silica fume solution for 4 h was found to be optimal, obtaining 8% and 33% enhancements in the AIV and the WA, respectively. The treatment techniques proposed can be a powerful tool for promoting the use of RA in the construction industry.