Search Results (99)

The growing demand for sustainable construction materials has led to significant advancements in ultra-high-performance concrete (UHPC), with a particular focus on geopolymer-based systems as an alternative to conventional cementitious binders. This review explores the latest developments in sustainable Ultra-High-Performance Geopolymer Concrete (UHPGPC) by analysing key material composition, mechanical, durability and microstructural properties. The incorporation of ground granulated blast furnace slag (GGBFS), silica fume (SF), and fly ash (FA) has demonstrated notable improvements in compressive strength, durability, and workability. Additionally, the use of activators such as sodium silicate and sodium hydroxide optimizes geopolymerization, resulting in a denser microstructure and enhanced mechanical performance. This review highlights the critical role of fibre reinforcement in UHPGPC, where steel fibres (SFs) and hybrid fibres significantly enhance compressive and tensile strength, as well as crack resistance. The inclusion of waste materials such as rice husk ash and recycled glass promotes sustainability by reducing CO₂ emissions while maintaining structural integrity. However, higher waste-glass content may adversely affect bonding due to its smooth surface texture. The findings highlight the potential of UHPGC as a high-performance, eco-friendly alternative to traditional cement-based UHPC. By integrating industrial by-products and alternative activation techniques, UHPGPC can contribute significantly to the global shift towards sustainable and low-carbon construction materials. Full article

The increasing generation of ceramic waste from manufacturing defects, construction activities, and demolition operations poses significant environmental and waste management challenges worldwide. This study presents a preliminary investigation into the incorporation of ceramic waste aggregates (CW) as partial and full replacement for natural coarse aggregates in fly ash-based geopolymer concrete (GPC) under water-curing conditions. Five mix compositions were prepared with ceramic waste aggregate replacement levels of 0%, 20%, 40%, 60%, and 100%. Fresh and hardened properties were evaluated using flow table and early-age compressive strength tests at 7 and 14 days. The 20% replacement mix achieved the best compressive strength value of 5.52 MPa at 14 days, slightly exceeding the control GPC mix (5.09 MPa) among the limited mixtures investigated in this preliminary study. However, higher replacement levels resulted in reduced compressive strength, which may be associated with increased porosity, weaker aggregate–matrix bonding, and limitations related to the adopted water-curing regime. Workability remained within acceptable flow ranges for most mixes, although reduced flowability was observed for the 40% replacement. The comparatively low strength values obtained across all mixtures may largely be associated with the absence of heat curing and the inclusion of additional water to improve workability, both of which likely limited the geopolymerization efficiency. Based on the comparatively low compressive strength values obtained, the investigated mixtures, in their current form, are only suitable for low-strength or non-structural applications rather than structural concrete applications. Overall, this study provides preliminary insights into the influence of ceramic waste coarse aggregates on the workability and early-age compressive strength behavior of fly ash-based geopolymer concrete under the adopted experimental conditions. Further optimization of the curing regimes, mix design parameters, and long-term mechanical and durability performance is necessary before broader engineering applicability can be established. Full article

Geopolymer gel concrete (GPC) is a kind of environmentally friendly concrete, which has become a potential alternative material to replace ordinary concrete. Traditional mix design of GPC is carried out under experimental conditions, which is time-consuming and labor-intensive. Geopolymer concrete (GPC) is intended for use in hydraulic structures, which are often exposed to water environments. Water flow exerts significant abrasion and erosion on these structures. If the abrasion resistance (AR) of the material is poor, the service life and service quality of hydraulic structures will be substantially reduced under the action of water flow. Therefore, AR is a key performance indicator for GPC in hydraulic engineering applications. This abrasion resistance can be enhanced by using fibers (for example, steel fibers, polyvinyl alcohol (PVA) fibers, and basalt fibers) and nanomaterials. Furthermore, there is a complex nonlinear relationship between the proportions of fibers and nanoparticles added and the properties of GPC. In this study, the circular ring test method and the underwater steel ball test method were conducted to investigate the AR of nano-SiO₂ (NS) and hybrid fiber (NHF) reinforced geopolymer gel concrete (NHF-GPC). A backpropagation (BP) neural network (BPNN) model optimized by the Grey Wolf Optimizer (GWO) (GWO-BPNN) is established to predict the abrasion resistance strength (ARS) and the abrasion rate of NHF-GPC based on the circular ring test method. In addition, the ARS, abrasion rate, and average abrasion depth (AAD) based on the underwater steel ball test method were also predicted. The results indicate that the GWO-BPNN model demonstrates superior performance over the standard BPNN, exhibiting higher prediction accuracy, better fitting performance, and faster convergence speed. Specifically, for the circular ring test method abrasion rate prediction, GWO-BPNN reduced the root mean square error (RMSE) by 30.3% and lowered the mean absolute percentage error (MAPE) to 8.4%. The GWO-BPNN model established in this study can provide efficient and reliable theoretical support for the optimization of the NHF-GPC mix design. Full article

This study investigates the prediction of carbon emissions from fly ash and ground granulated blast furnace slag-based geopolymer concrete (GPC) using advanced ensemble machine learning (ML) techniques. Although ML has been extensively utilized to model GPC’s mechanical performance, its application in estimating environmental impacts, specifically carbon emissions, is limited. The research employs six ensemble ML models, such as random forest, gradient boosting, extreme gradient boosting (XGB), CatBoost, and light gradient boosting machine (LGBM), including versions optimized using ant colony optimization (ACO). Among them, the ACO-enhanced XGB model demonstrated the highest predictive accuracy with a coefficient of determination (R²) of 0.97, with low prediction errors (MAE = 3.92, RMSE = 6.17). However, cross-validation and uncertainty analyses indicate that the performance differences among top models are relatively small. Conversely, LGBM exhibited the least predictive reliability. Feature importance analysis revealed that curing parameters, specifically initial curing time, curing temperature, and the dosage of dry sodium hydroxide, had the most influence on carbon emissions. To evaluate model robustness and interpretability, Monte Carlo simulation and Gaussian white noise analyses were conducted. Results confirmed that CatBoost and ACO–gradient boosting (ACO-GB) demonstrated greater stability under varying and noisy conditions, whereas XGB-based models, although highly accurate, were comparatively more sensitive to input variability. Overall, the research establishes a data-driven, efficient framework for quantifying carbon emissions in GPC, highlighting the importance of evaluating both predictive accuracy and model robustness, advancing sustainable material design through intelligent modelling. Full article

In this study, an eco-friendly geopolymer concrete (GPC) was synthesized using fly ash, slag, and rice husk ash as precursors, and glass fibers were incorporated to enhance its mechanical properties. And then this study investigates the residual mechanical properties and microstructure evolution of glass fiber-reinforced geopolymer concrete (GFGPC) following elevated temperature exposure and subsequent cooling. Specimens incorporating varying glass fiber volume fractions (0–2.5%) were subjected to temperatures ranging from 25 °C to 800 °C, followed by either natural cooling or water-spraying cooling. The uniaxial compressive strength, Brazilian splitting tensile strength, and three-point flexural strength of the glass fiber-reinforced GPC were experimentally determined. Furthermore, fracture performance indicators—including the energy absorption capacity at failure, characteristic length, and double-K fracture parameters—were systematically analyzed. Results indicate that a glass fiber content of 1.5% optimally enhances the composite’s mechanical performance. Under natural cooling, splitting tensile and flexural strengths exhibit a non-monotonic trend, peaking at 200 °C. Conversely, water-spraying cooling induced thermal shock generally degrades tensile and flexural properties. However, at extreme temperatures (600 °C and 800 °C), water-spray cooling facilitates matrix densification and secondary geopolymerization, resulting in a residual compressive strength increase of 12.16% and 20.77% compared to natural cooling. Furthermore, based on composite damage theory, a binary nonlinear prediction model was developed to accurately capture the coupled effects of temperature and fiber characteristics on the residual compressive strength (R² > 0.90). Coupled with scanning electron microscopy (SEM) observations, the profound effects of elevated temperatures and thermal shock on the GPC gel matrix were elucidated, and the microscopic mechanisms underlying the failure of the fiber-bridging effect at high temperatures were thoroughly investigated. The findings of this study provide a solid theoretical foundation and scientific reference for the performance assessment and repair decision-making of GPC structures post-fire exposure. Full article

This paper presents the numerical modeling and experimental testing of steel-reinforced columns composed of three types of concrete: reinforced cement concrete (RCC), geopolymer concrete (GPC), and geopolymer concrete incorporating quarry rock dust (GPCD). GPC columns were produced using fly ash (FA) and furnace slag (SG) in equal proportions (50% each), with the addition of 0.75% steel fibers by volume. In GPCD columns, 20% of SG was replaced with quarry rock dust (QRD). A total of twenty columns (200 mm × 200 mm × 1000 mm), designed for a compressive strength of 40 MPa (fc’), were tested under static loading. The experimental data were validated using finite element (FE) modeling in ABAQUS, where the Concrete Damaged Plasticity (CDP) model was adopted to describe concrete behavior. Calibration of the FE model for the control specimen was carried out by adjusting viscosity parameters, dilation angles, shape factors, plastic potential eccentricity, stress ratios, and mesh sizes. The calibrated control model was then employed for comparative analysis and validation against experimental results. For concentrically loaded columns, the predicted axial load and axial and lateral deflection responses closely matched the experimental observations. However, for eccentrically loaded columns, the FE model over-predicted the load-carrying capacity as well as axial and lateral deflections. The experimental findings indicate that both GPC and GPCD columns exhibited lower load-carrying capacities compared to RCC columns; however, the inclusion of steel fibers enhanced their performance. Overall, the proposed FE model demonstrated a good agreement with experimental observations, providing a reliable framework for predicting the structural behavior of geopolymer-based columns. Full article

The environmental urgency of reducing Portland cement consumption has driven research into geopolymer concrete (GPC) as a sustainable alternative. However, its inherent brittleness limits structural applications. This study addresses this critical challenge by investigating the efficacy of steel fibers (SF) and polypropylene fibers (PP) in enhancing the mechanical properties of slag-based GPC. Thirteen mixtures, including a control, were designed with varying fiber types, lengths (35/60 mm for SF, 40/60 mm for PP) and dosages (25–75 kg/m³ for SF, 3–9 kg/m³ for PP). Comprehensive tests evaluated workability, flexural/compressive strength, and toughness. Results demonstrated that while both fibers reduced workability (PP > SF), they significantly improved ductility, with SFs increasing toughness by 6–15 times. A key finding was the time-dependent performance: SF enhanced early-age flexural strength by up to 38%, though this benefit declined at 28 days for most mixes under ambient curing. PP fibers reduced flexural strength by 25–40% at 28 days. Compressively, SF increased strength by up to 60%, while PP led to reductions up to 27%. The study conclusively establishes SF’s superiority due to its superior bonding and crack-bridging capabilities, providing essential insights for designing durable fiber-reinforced GPC. This research directly contributes to advancing sustainable construction materials by overcoming a fundamental limitation of geopolymers. Full article

The use of cementless concrete (geopolymer concrete (GPC)) incorporating fly ash and bundled steel fibers to produce full-scale precast concrete pipes is an economical, viable and sustainable solution for sewer infrastructure for decreasing the overall carbon impacts. This research explores the mechanical behavior of precast full-scale pipes (450 mm inner diameter) incorporating cementless concrete and bundled steel fibers. The GPC mixture was produced by completely substituting cement with fly ash generated by the local coal power plant. The bundled steel fibers were locally manufactured from long wires. The proportions investigated of the bundled steel fibers in the GPC pipes were 20 and 40 kg/m³. A total of six full-scale GPC pipes and two conventional cement concrete pipes were cast in a commercial precast pipe unit. The crushing strength under external load was evaluated using the three-edge bearing test (TEBT) on the pipes without fibers, showing comparable cracking and ultimate loads of GPC pipes and conventional cement concrete pipes. Both types of pipes satisfied the strength requirement of ASTM C76 class III. The use of bundled steel fibers in GPC pipes improved the cracking and ultimate loads by 18% and 22%, respectively, when 40 kg/m³ of bundled steel fibers were added. This upgraded the ASTM C76 strength class from class III to IV due to the improved crack resistance and ultimate load. Conventional cement concrete pipes and GPC pipes exhibited similar cracks at the critical regions (springlines, invert and crown). However, GPC pipes with bundled steel fibers showed a well distributed pattern of multiple secondary cracks along the longitudinal axis of the pipes. The final failure was governed by the flexure action and radial tension in the tested pipes. The economic analysis of cement concrete and GPC pipes showed comparable costs. However, the incorporation of fibers increased the cost of GPC pipes due to the limited local availability of proprietary fibers. This study highlights a new horizon of GPC for the manufacturing of sustainable and economical precast pipes as an environmentally friendly substitute to conventional cement concrete pipes for sustainable sewer infrastructure and adds novelty to the current state-of-the-art knowledge. Full article

Geopolymer concrete (GPC) has emerged as a promising low-carbon alternative to ordinary Portland cement (OPC), yet wider adoption is limited by the lack of standardised mix-design procedures. Precursor, activator, curing, and aggregates strongly interact to affect properties, but findings are scattered and hard to generalise. This review consolidates and normalises published findings to clarify how key parameters-precursor type, activator dosage and concentration, activator-to-binder ratio, curing temperature, and aggregate gradation-control fresh and hardened performance. Overall trends indicate that calcium-rich systems enhance early strength by 80–100% at typical replacement levels; while optimum activator conditions of 12 M NaOH and sodium silicate/sodium hydroxide ratio = 2.5 commonly improve strength by 40–60% relative to sub-optimal ratios; alkaline activator-to-binder ratios of 0.4–0.7 provide the most practical strength-workability balance. Heat curing at 80–100 °C significantly accelerates early-age property development by 50–200% compared to ambient curing, depending on duration and activator chemistry. A target-strength mix design is demonstrated through a 40 MPa case study. Using a compiled dataset for fly ash (FA)-based GPC, a modulus–strength framework is proposed; common OPC code equations over-predict elastic modulus for 15–50 MPa, and calibration yields a conservative, code-compatible relation: E = $2.75\sqrt{f{c}_{MPa}}$. Key limitations are highlighted, including variability in raw materials and durability uncertainties, and future directions are proposed toward performance-based design and standardisation to support structural use of GPC in sustainable infrastructure. Full article

This research investigates the shear performance of sustainable self-compacting reinforced geopolymer concrete (GPC) beams incorporating granite waste powder (GWP) and ground granulated blast-furnace slag (GGBFS) as eco-friendly binding agents through experimental and numerical analyses. Five geopolymer reinforced concrete beam specimens (100 mm × 150 mm × 1500 mm) were tested under two-point loading conditions to evaluate the influence of longitudinal reinforcement ratio (0.85% to 2.0%) and shear span-to-effective depth ratio on the structural shear performance. The experimental investigation revealed that geopolymer reinforced concrete beams exhibit shear behavior characteristics similar to conventional Portland cement concrete beams, with the 2.0% reinforcement ratio achieving 18.3% higher shear strength compared to the 0.85% reinforcement ratio, while shear capacity increased proportionally with increasing shear span-to-depth ratio. Experimental data, including load–displacement response, shear strength measurements, strain distributions, failure modes, and crack patterns, were studied. Finite element nonlinear analysis was conducted by modifying the concrete modulus and stress–strain relationships to reflect the properties of geopolymer concrete using ABAQUS software integrated with the concrete damaged plasticity model. The results demonstrated that for the tested geopolymer reinforced concrete beams, first cracking load, steel yielding load, and ultimate load capacity increased systematically with increasing tension steel reinforcement ratio and proportionally with higher shear span-to-depth ratios. Full article

The implementation of Australia’s 2024 waste export ban has increased pressure on domestic recycling systems, resulting in an additional 650,000 tonnes of waste annually. This emphasises the urgent need for high volume landfill waste material recovery, especially in sustainable construction materials such as geopolymer concrete (GPC). Geopolymer concrete is recognised as a sustainable construction material; however, the scientific understanding of the compatibility between landfill waste and the geopolymer matrix, particularly under harsh environments, remains unknown. This paper presents an experimental investigation on five types of geopolymer concrete (GPC) mixes. The study included a control mix with natural stone chips and four additional mixes in which stone chips were 100% replaced with waste materials including shredded plastic, cardboard, crushed glass, and granular crumb rubber as fine aggregates. The mechanical performance, durability behaviour and stress-strain characteristics of these mixes were evaluated. Concrete samples were exposed to normal air, a saline environment with 10% salinity, and a hygrothermal environment at 60 °C and 98% humidity for four months to assess durability performance. The results demonstrate that GPC is compatible with landfill waste aggregates and enables the production of a workable mixture. As a result of saline environments, waste aggregate-based geopolymer concrete reduces compressive strength by 15%, while natural stone chips-based geopolymer concrete decreases strength by 45% during the same period, indicating that waste aggregates are more appropriate than natural aggregates in marine environments. Although the inclusion of waste aggregates reduces the strength and stiffness of the GPC, the materials continue to meet the mechanical property requirements for non-structural applications. A theoretical model considering the elastic modulus, ultimate strength and corresponding strain has been developed to predict compressive stress–strain behaviour of waste-based GPC. High modulus aggregates, typically ranging from approximately 10.0 GPa to 85.0 GPa such as stone chips and glass sand demonstrate parabolic stress–strain behaviour. In contrast low modulus aggregates, generally ranging from 1.0 GPa to 5.0 GPa including plastic, cardboard, and crumb rubber, exhibit a bilinear stress–strain response. Full article

The oceanic wet–thermal and chloride salt environment creates extremely harsh service conditions for marine infrastructures. As a green construction material, geopolymer concrete has a promising application prospect in marine engineering due to its excellent durability. The impact resistance of geopolymer concrete subjected to wet–thermal and chloride salt environment is of great significance for the durability and quality of marine engineering structures. This study uses nano-SiO₂ (NS) and hybrid fibers (HF) to enhance the impact resistance of geopolymer gel concrete (GPC). Radial basis function (RBF) and back-propagation (BP) composite neural networks are used to predict the impact resistance of NS and HF-reinforced geopolymer gel concrete (NSHFGPC). The impact resistance of NSHFGPC specimens is characterized by two indicators: the cumulative number of repeated impact blows required to initiate the first visible crack (N₁) and the cumulative number of impact blows corresponding to ultimate failure (N₂). To evaluate the durability of NSHFGPC under oceanic conditions, specimens were exposed to a simulated marine environment within a simulation test chamber for 60 days prior to impact testing. The 60-day duration was selected to achieve a sufficient level of chloride penetration and matrix aging. Based on the resulting experimental database, an RBF-BP neural network was constructed to predict the material’s impact resistance. In this study, grid search and K-fold cross-validation were employed to select the optimal hyperparameters. Compared to standalone RBF and BP models, the RBF-BP network demonstrated superior performance, achieving R² values of 0.900 and 0.922. These results represent improvements of 20.18% and 11.18% over the standalone RBF model, respectively. Consequently, the RBF-BP algorithm serves as an experimental tool for predicting NSHFGPC impact resistance and guiding future mix design optimization. Full article

Fly ash-based geopolymer concrete (GPC) is a sustainable alternative to conventional cementitious materials; however, its compressive strength is governed by complex and highly correlated mixture parameters, making experimental optimization expensive and data-driven modeling challenging. While machine learning (ML) techniques have been widely applied to predict GPC strength, most studies prioritize predictive accuracy without explicitly addressing multicollinearity among input variables, which can distort feature importance, reduce model stability, and limit engineering interpretability. This study proposes a multicollinearity-integrated and interpretable ML framework that systematically embeds correlation diagnostics and structured feature screening within the modeling pipeline rather than treating interpretability as a post-processing step. Multiple conventional and ensemble learning algorithms were comparatively evaluated using cross-validation to ensure generalization robustness. The proposed framework achieved a maximum coefficient of determination (R²) of 0.96 with low prediction error, outperforming baseline regression models while demonstrating improved stability under correlated input conditions. Unlike existing studies that rely solely on black-box optimization, the integrated interpretability analysis revealed physically consistent dominance of curing temperature, alkali content, and water-related parameters in governing strength development. By explicitly coupling predictive performance with multicollinearity mitigation and engineering-oriented interpretability, this work advances beyond accuracy-driven ML applications and provides a robust and transparent decision-support tool for sustainable geopolymer mix design. Full article

The cement industry is a major source of anthropogenic CO₂ emissions due to its energy-intensive production process and calcination of limestone. Producing one ton of cement emits approximately one ton of CO₂, and cement accounts for about 5% to 8% of global CO₂ emissions. In this context, cement-less one-part (“just-add-water”) ambient-cured geopolymer concrete (GPC) has gained attention due to its environmental friendliness and practicality for large-scale cast-in-situ construction. However, field adoption remains limited, mainly due to the scarcity of data on mechanical properties and durability, as well as the lack of widely accepted standards and specifications. This paper is part of the larger research on tensile performance of anchors embedded in GPC. It is well understood that the tensile performance of anchors installed in concrete substrate is largely influenced by their effective embedment depth and the substrate’s mechanical properties, particularly the fracture energy and modulus of elasticity. Therefore, prior to the investigation of the tensile performance of anchors in GPC, it is crucial to understand the mechanical behaviour of the GPC substrate itself. This study examined key parameters that influence the compressive strength of one-part ambient-cured slag/fly ash-based GPC. The alkali content, slag content, water-to-solid (W/S) ratio, and aggregate content were investigated. Additionally, various mechanical properties such as uniaxial tensile strength, splitting tensile strength, elastic modulus, and fracture energy of the hardened GPC are presented. The test results revealed that higher slag and activator content enhanced compressive strength, whereas a higher aggregate content reduced the strength. The strength gain was also attributed to higher alkali content, lower W/S ratio, and increased binder content; however, excessive alkali and an overly low W/S ratio caused rapid setting due to accelerated reaction kinetics. The 7-day compressive strength ranged from 62% to 78% of the 28-day strength, while there was no notable strength gain after 28 days of curing. The developed GPC attained compressive strengths of over 40 MPa at 28 days and 50 MPa at 56 days. The uniaxial tensile strength test demonstrated a ratio of 0.87 relative to splitting tensile strength. The findings also indicated that the aggregate conditions and curing regimes (whether using as-is aggregates with moisture curing or oven-dried aggregates with sealed curing) had no meaningful effect on the mean compressive strength of GPC and its reproducibility. Full article

This review study promotes the sustainability of civil infrastructure by advancing the materials science of alternative cementitious materials. Supported by extensive global research and industrial trials, geopolymer cement has emerged as a promising approach to reducing the ecological impact of ordinary Portland cement (OPC) due to its superior engineering properties and eco-friendly benefits from industrial waste utilization. Geopolymers are inorganic polymers formed by the polymerization of aluminosilicate precursors, such as fly ash (FA), slag, and metakaolin, in the presence of alkaline activating solutions. This work integrates findings across multiple domains, including precursor chemistry, microstructural evolution, mechanical and durability performance, and sustainability metrics like carbon footprint and energy consumption. A key contribution of this review is the comparative evaluation of FA-based and slag-based GPC systems against OPC concrete, emphasizing the factors influencing their mechanical and durability properties, while also distinguishing differences in environmental impact, microstructural development, and overall performance. The findings highlight that slag-based systems generally exhibit lower environmental impacts, especially in energy demand and emissions, while regional differences in precursor availability constrain how widely the LCA and economic results can be applied. Building on previous reviews that have considered these topics, this study jointly examines technical performance and sustainability indicators and identifies regional variations that influence feasibility. The synthesis provides a balanced, evidence-based assessment of the potential and limitations of GPC as a lower-carbon alternative to OPC, supporting efforts to reduce the climate impact of future concrete construction. Full article