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.

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 paper investigates the application of recycled steel powder as an additive in concrete to increase the thermal properties of radiant floor heating systems. The project aimed to increase the efficiencies of thermal conductivities, allowing radiant heat to produce higher energy-efficient outputs for heating. Thermocouple readings measured lower temperatures with similar heating conditions as a standard mix slab due to heat transfer occurring evenly through a large surface area, thus transferring heat to the air at faster rates. The tests were completed by casting two 400 × 400 × 200 mm (width × length × depth) slabs enclosing radiant heating pipes. Water was pumped at 40 and 60°C through the pipes. The temperature was recorded at various positions throughout the slab that would allow the multi-layered cylinder approach to analyse the rate of heat transfer, and calculate the efficiency of the heat transfer. The crushing strength of the proposed mix using steel powder replacement is shown to be reduced by 26% when a mix with 12.4% of steel powder is used. Contrary to the original hypothesis of this research, the investigation found rates of heat transfer during the heating stage were 3% lower for the mix containing steel powder compared to the standard mix.

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.

Using waste plastics as a partial natural aggregate replacement and monitoring strength and workability reduction in pavement structures is vital to net-carbon zero. This study explores the utilisation of waste plastic as a fine aggregate replacement in medium-strength reinforced concrete pavements, for improving plastic aggregate performance and the intrinsic reasoning for observed strength performance. Various weight fractions of fines were substituted by the same weight of plastic aggregates ranging from 5–15% according to the appropriate standards (Eurocodes and British Standards). The physical and mechanical properties of the composites were analysed. The results indicated that the use of polymeric materials as a partial replacement for fines contributed to a decrease in workability, compressive strength and push-out bond between steel reinforcement and concrete. Despite these trends, 5% replacement of fine aggregates with plastic waste surpassed all the feasibility criteria. Furthermore, using 10% of plastic replacement by weight was deemed feasible in non-structural applications such as roads, pavements, and facades. The outputs have demonstrated environmental engineering concepts in tackling plastic waste, providing an alternative to conventional aggregate. Environmental benefits can arise due to the removal of potentially hazardous plastics from entering ecosystems as well as minimising dredging of global sand reserves.

Industrial and urban wastes have been generated over time due to urban development with severe environmental and health implications. This paper reports the valorisation of waste and industrial by-product (magnesium oxide waste - MG1 and Ground Granulated Blast furnace Slag - GGBS) to develop an alternative cementitious binder for suppressing swelling in high sulphate bearing soils due to the formation of a highly expansive crystalline hydrate (ettringite) upon treatment with Portland Cement - PC or lime. Cylinder test specimens were developed using three MG1:GGBS proportions by weight (10:90, 20:80 and 30:70) to stabilise a natural Gypsum marl soil (GM) containing high levels of sulphate at varying stabiliser dosages (6, 8 and 10 wt%), with PC as the control binder. UCS, Linear Expansion and SEM investigations were employed to assess the engineering suitability of the MG1:GGBS stabilised GM cylinder test specimen. Results suggest the viability of producing an alternative cementitious binder using up to 30 wt% MgO-waste to successfully activate GGBS at stabiliser dosages of 6-10 wt %. From a mechanical perspective, the MG1:GGBS stabilised GM soil was 1.5-3 times more than the control at 28 days moist curing age, while the resistance to linear expansion produced near-zero swellings (0.13%-0.2%) after 56 days, in comparison with the control of 3.2%. SEM micrographs showed a more compact structure with lesser voids and no morphology of ettringite. This new technology is expected to mitigate the environmental concerns of using PC and promote sustainable techniques of reusing industrial by-product materials for stabilising sulphate soils.

The current study investigated the development of a sustainable thermo-chemical approach to effectively optimize MgO-waste activated GGBS formulations, using four types of magnesium oxide (MgO) waste materials with ground granulated blast-furnace slag (GGBS) to develop binary cementitious systems (MgO-GGBS). This stems from the expected complexity of cementitious binder optimization outcomes into a simpler analytic form, enhancing the rapid delivery of optimization results and contributing to the global awareness of sustainable approaches and use of industrial wastes. Three levels of Portland cement by weight (90, 80, and 70 wt.%) was replaced with MgO wastes including an industrial by-product (GGBS) to develop an experimental regime. Investigation was carried out by employing an experiment-based optimisation technique (thermo-chemical approach), which involved the design of an experimental regime and application of experimental tests (pH measurements, thermogravimetric and derivative thermogravimetric analysis-TG/DTG and isothermal calorimetry), establishment of design variable/parameters, measurement of the design performance of the identified design parameters, and review of the relationship between the independent (control) and dependent variables (MgO wastes and their compositions). The experimental test results successfully optimised the binder compositions, established the best performing binder system (MG1), and provided an in-depth insight into the thermal stability and hydration kinetics of the investigated binder systems.

The sharp increase in the utilisation and demand of construction materials across the world, especially in road, pavements and transportation sectors has resulted in an unsustainable surge in the amount of carbon emissions. This study investigated the use of low-carbon materials in permeable pavements systems (PPS) and the effects of various low-carbon engineered materials on the mechanical, absorption and infiltration performance of PPS according to relevant standards. This was achieved by the critical analysis of four (4) different materials (recycled grit, recycled glass, recycled rubber) and comparing their performance with normal materials used in conventional pavements. The four materials were implemented into concrete mixes of the permeable pavers and embedded in various layers and sub-sections making up the permeable pavement structure. As a result, the outcome required of this research is to find which mix of concrete blocks (permeable pavers) perform the best when tested for absorption and compression and which permeable pavement works best when tested for infiltration. Compression test was utilised to establish the maximum allowable compressive force, while the absorption test identified the concrete mix that could hold the least amount of water when soaked in water for 24 hours. This was expected to reduce the possibility of breakage of the concrete blocks. Finally, the infiltration test was employed to establish the best performing pavement material based on the rate and amount of infiltration of a fixed volume of effluent. The results obtained from the laboratory tests shows improved performances of the pavements embedded with recycled materials. Therefore, it can be recommended that the use of recycled materials in the development of low-carbon permeable pavements, possesses the ability to perform efficiently in comparison with conventional PPS in the construction and built environment sectors.

This study covers an in-depth investigation into the properties and practicality of the utilization of up to 40% Alumina Waste Filler (AWF) as a partial Portland Cement (PC) replacement material. AWF is a by-product from the recycling of aluminium, produced when salt slag is smelted and cleaned. Its use in concrete will lessen the landfill requirements for AWF disposal, and reduce the strain of the growing requirements and cost of PC. The results obtained from this study showed that the addition of AWF to the concrete mix caused a reduction in the compressive and tensile splitting strength values, and a less-workable concrete was achieved for every increase in the quantity of AWF added to each mix. The addition of AWF influenced the hydration reaction process and reduced the cumulative production of the heat of hydration over time, whilst the permeability of the concrete decreased.

Ground Granulated Blast-furnace Slag (GGBS) and Pulverised Fuel Ash (PFA) were used to replace up to 60% of Portland cement (PC) in concrete. The testing program of the concrete included the determination of the consistency of fresh concrete, the measurement of the density and compressive strength of the hardened products cured for up to 56 days and the evaluation of their durability via visual inspections and strength loss calculations after the freeze and thaw cycles. The results showed that the blend proportion and type had affected the consistency of the fresh concrete. Replacing the PC with 20% for PFA or 40% for GGBS had similar performances as the control mix. The durability of concrete subject to freeze and thaw had little effect on the concrete specimens. It was observed that the concrete without blends suffered the worst, resulting in chips along the edges of the cube and scaling of the faces compared to mixes with 20% GGBS and 20% PFA which resulted in increased durability. However, blended concrete exhibited more loss in strength compared to the concrete without cement blends.

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.

This report presents a computational research on Eurocode 2 (EC2) tension lap lengths (lo) design in a normally reinforced concrete beam, using ANSYS Workbench simulation software program by simulating a laboratory 4-point beam loading test system under static loading(discrete model approach). A typical 4-point laboratory setup loading system was modelled using an innovative and sustainable Finite Element Analysis (FEA) approach. In order to investigate the EC2 tension lap lengths (lo) design recommendation, a total of 100 analysis cases of lap lengths were considered for different reinforcement bar diameters of 10mm, 12mm, 16mm, 20mm and 25mm. The study has considered beam failure types, effects of failure load on the various lap length reduction cases and effects of steel reinforcement bar size changes on the design lap lengths. The analysis of results revealed that the yield strength of steel (f(yk)), diameter of tension reinforcement bar, (d(b)), tensile strength of concrete (f(ctd)) and concrete cover (c(d)) are the main parameters for a tension lap length design according to EC2. While a linear relationship exists between tension steel reinforcement bar sizes (d(b)) and the obtained lap lengths (l(o)). The study reveals a potential use of 15% and 20% reduction in lap length (l(o)) for tension steel reinforcement bar sizes of 10mm, 16mm and 12mm and 20mm in comparison with the recommended design lap length of EC2. It was concluded that EC2 tension lap length design recommendation is conservative.