Search Results (86)

The construction sector faces the dual challenge of reducing energy consumption and mitigating the environmental burden of construction and demolition waste (CDW). Geopolymers offer a low-carbon alternative to Portland cement, yet their performance depends strongly on precursor composition. This study presents an extensive investigation of precursor chemistry, mechanical performance and phase composition, focusing on the partial substitution of ground granulated blast furnace slag (GGBFS) with mechanically activated CDW powder (15% and 30% by weight) alongside fly ash (FA). The oxide composition, amorphous content and particle size distribution were analyzed, using XRF, XRD and laser diffraction to evaluate the reactivity. Mortar samples were subsequently synthesized and tested for compressive and flexural strength, ultrasonic pulse velocity, density and porosity. The results demonstrate that while mechanically activated CDW incorporation decreases early strength compared with GGBFS-rich systems, compressive strengths above 45 MPa were attained at 28 days, with continuous improvement to >69 MPa for aged composites. The relationship between precursor chemistry, precursor sizes and mechanical performance highlights the feasibility of CDW valorization in geopolymer binders, contributing to energy efficiency, circular economy strategies and sustainable construction materials. Full article

The current study investigated the effects of geopolymer composites formulated from pumice dust partially replaced by ground granulated blast furnace slag (GGBFS) and fly ash (FA) at levels of 10%, 20%, 30%, and 40% by weight. The mixtures were evaluated for flowability, compressive strength (7, 28, and 56 days), density, and water absorption (28 and 56 days) at ambient temperatures. Moreover, compressive strength, mass loss, density, and water absorption were evaluated after exposure of the mixtures to elevated temperatures (250 °C, 500 °C, and 750 °C) at 28 days. All specimens were initially cured at 60 °C for 24 h, followed by storage under ambient laboratory conditions until testing. The inclusion of GGBFS into the mixtures decreased flowability, and the inclusion of FA resulted in its improvement. At ambient temperature, GGBFS-based mixtures, which were high in calcium content, exhibited substantially superior compressive strength and reduced absorption relative to FA-based mixtures due to the development of dense C-A-S-H gel networks. However, the compressive strength of FA-based mixtures considerably increased when exposed to a temperature of 250 °C. Moreover, at 750 °C, the FA-based mixtures showed superior residual strength (up to 18.1 MPa), lower mass loss, and reduced absorption, indicating enhanced thermal stability due to the dominance of thermally resistant N-A-S-H gels. X-ray diffraction results further supported these trends by showing the rapid deterioration of calcium-rich phases under heat and the comparative stability of aluminosilicate structures in FA-based systems. Overall, the inclusion of up to 40% GGBFS is beneficial for early strength and densification, whereas the incorporation of up to 40% FA improves durability and mechanical retention under high-temperature conditions. Full article

The disposal of industrial waste poses a significant environmental challenge, often leading to pollution and degradation of surrounding and terrestrial ecosystems. This study investigates the sustainable valorization of such wastes through the development of one-part geopolymer mortars. Solid sodium silicate was employed as a dry alkali activator for binary blends comprising ground granulated blast-furnace slag (GGBS), clay brick powder (CBP), steel slag (SS), and fly ash (FA), with all mixtures cured under ambient conditions. The mortars were evaluated in terms of fresh properties (flow and setting time) and hardened characteristics, including compressive strength, density, water absorption, and porosity. Durability performance was assessed through mass loss, visual degradation, and compressive strength retention following exposure to acidic (H₂SO₄, HCl) and sulfate environments. Microstructural characterization using XRD, SEM, and FTIR provided insight into the mechanisms of gel formation and degradation in aggressive media. The results revealed that incorporating 5% FA into GGBS-based mortars enhanced 28-day compressive strength by 21.7% compared with the control mix. The inclusion of industrial by-products promoted the formation of C–S–H and C–(A)–S–H gels, contributing to a denser and more refined microstructure. Overall, the findings demonstrate that one-part geopolymer mortars offer a promising, eco-efficient, and durable alternative to traditional cementitious systems, while also addressing safety and handling concerns associated with liquid alkaline activators used in conventional two-part geopolymer formulations. Full article

Geopolymers, as sustainable alternatives to traditional cementitious materials, offer superior mechanical and durability properties; however, they face challenges with rapid setting, particularly in fly ash–slag systems. Retarders play a crucial role in tailoring the setting behavior and workability of geopolymers, especially in applications where extended setting time or placement under challenging conditions is required. Geopolymers, unlike traditional Portland cement, undergo a rapid alkali-activation process involving dissolution, polymerization, and hardening of aluminosilicate materials. This can lead to very short setting times, particularly at elevated temperatures. In this scenario, the present study investigates the effect of different retarders-including cellulose, starch, borax, and their different combinations the setting time. The effectiveness of a retarder depends on the geopolymer formulation, including the type of precursor, activator, and curing conditions. The initial and final setting times improved by the addition of retarders, whereas most of the retarders had a negative effect on compressive strength. The optimum retarder combination was starch and borax, with a remarkable improvement in setting time and a positive result on the compressive strength, while maintaining reasonable workability. The retarder was equally effective under both ambient and oven-cured conditions and for different mix proportions of fly ash (FA) and slag, indicating that its effectiveness depends only on the type of precursors used. The study reveals the use of borax along with cellulose- or sugar-based compounds, which balances the reaction kinetics, resulting in balanced mechanical characteristics. Full article

Composite geopolymer concrete (CGPC), is receiving growing attention in the construction sector for its sustainable nature, environmental benefits, and its valuable role in promoting efficient waste utilization. The strategic incorporation of reinforcing fibers into geopolymer concrete (GPC) matrices is critical for enhancing mechanical performance and meeting the durability requirements of high-performance construction applications. Although substantial research has focused on strength enhancement of fiber-reinforced geopolymer concrete (FGPC) individually, it has neglected practical considerations such as energy use for curing and life-cycle assessments. Thus, this study investigates the cost-effective aspects of FGPC cured under different regimes. Different cementitious binders were incorporated, i.e., fly ash (FA) and ground granulated blast-furnace slag (GGBS), in addition to alkaline activators (a combination of sodium hydroxide and sodium silicate), hooked-end steel fibers (HESFs), basalt fibers (BFs), and polypropylene fibers (PPFs), as well as aggregates (gravel and sand). The effect of different geopolymer-based materials, reinforcing fibers, and different curing regimes on the mechanical, durability, and economic performance were analyzed. Results showed that the applied thermal curing regimes (oven curing or steam curing) had a considerable impact on durability performance, compressive strength, and flexural strength development, especially for GPC mixes involving high FA content. Cost analysis outcomes suggested that the most affordable option is GPCM1 (100% FA without fibers), but it demonstrates low strength under ambient curing conditions; RGCM4 (100% GGBS and 0.75% HESF) provided the best strength and durability option but at higher material cost; RGCM7 (50% FA, 50% GGBS, and 0.75% HSF) exhibited a balanced choice since it offer satisfied strength and durability performance with moderate cost compared to other options. Full article

The ordinary Portland cement (OPC) manufacturing process is highly resource-intensive and contributes to over 5% of global CO₂ emissions, thereby contributing to global warming. In this context, researchers are increasingly adopting geopolymers concrete due to their environmentally friendly production process. For decades, industrial byproducts such as fly ash, ground-granulated blast-furnace slag, and silica fume have been used as the primary binders for geopolymer concrete (GPC). However, due to uneven distribution and the decline of coal-fired power stations to meet carbon-neutrality targets, these binders may not be able to meet future demand. The UK intends to shut down coal power stations by 2025, while the EU projects an 83% drop in coal-generated electricity by 2030, resulting in a significant decrease in fly ash supply. Like fly ash, slag, and silica fume, natural clays are also abundant sources of silica, alumina, and other essential chemicals for geopolymer binders. Hence, natural clays possess good potential to replace these industrial byproducts. Recent research indicates that locally available clay has strong potential as a pozzolanic material when treated appropriately. This review article represents a comprehensive overview of the various treatment methods for different types of clays, their impacts on the fresh and hardened properties of geopolymer concrete by analysing the experimental datasets, including 1:1 clays, such as Kaolin and Halloysite, and 2:1 clays, such as Illite, Bentonite, Palygorskite, and Sepiolite. Furthermore, this review article summarises the most recent geopolymer-based prediction models for strength properties and their accuracy in overcoming the expense and time required for laboratory-based tests. This review article shows that the inclusion of clay reduces concrete workability because it increases water demand. However, workability can be maintained by incorporating a superplasticiser. Calcination and mechanical grinding of clay significantly enhance its pozzolanic reactivity, thereby improving its mechanical performance. Current research indicates that replacing 20% of calcined Kaolin with fly ash increases compressive strength by up to 18%. Additionally, up to 20% replacement of calcined or mechanically activated clay improved the durability and microstructural performance. The prediction-based models, such as Artificial Neural Network (ANN), Multi Expression Programming (MEP), Extreme Gradient Boosting (XGB), and Bagging Regressor (BR), showed good accuracy in predicting the compressive strength, tensile strength and elastic modulus. The incorporation of clay in geopolymer concrete reduces reliance on industrial byproducts and fosters more sustainable production practices, thereby contributing to the development of a more sustainable built environment. Full article

Red mud, fly ash, ground granulated blast furnace slag, and carbide slag are industrial byproducts posing significant environmental challenges. The synthesis of geopolymers represents a promising approach for their sustainable valorization. This study investigated the strength development mechanisms and microstructural evolution of Red Mud–Class F Fly Ash-Based Geopolymer under co-incorporation of ground granulated blast furnace slag and carbide slag through compressive strength tests, X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy–Energy Dispersive Spectrometer (SEM-EDS). Key findings include the following: (1) single incorporation of ground granulated blast furnace slag achieved a 60-day compressive strength of 11.6 MPa—6.4× higher than carbide slag-only systems (1.8 MPa); (2) hybrid systems (50% ground granulated blast furnace slag/50% carbide slag) reached 8.8 MPa, demonstrating a strength peak at balanced ground granulated blast furnace slag/carbide slag ratios; (3) the multi-source geopolymer systems were dominated by monomeric gels (C-A-H, C-S-H, C-A-S-H), crystalline phases (ettringite and hydrocalumite), and poly-aluminosilicate chains ((-Si-O-Al-Si-O-)n); (4) elevated Ca levels (>40 weight percent in ground granulated blast furnace slag/carbide slag) favored C-S-H formation, while optimal Si/Al ratios (1.5–2.5) promoted gel polycondensation into long-chain polymers (e.g., Si-O-Al-O), consolidating the matrix. These results resolve the critical limitation of low strength (≤3.1 MPa) in ambient-cured red mud–fly ash geopolymers reported previously, enabling scalable utilization of red mud (46.44% Fe₂O₃) and carbide slag (92.43% CaO) while advancing circular economy paradigms in construction materials. Full article

This experiment investigated the mechanical performance and acid resistance (when subjected to 28 days of exposure to sulfuric and nitric acid of five percent) of ambient-cured geopolymer concrete. Geopolymer concrete (GPC)—which is produced by using industrial by-products, including fly ash and ground granulated blast furnace slag (GGBS)—is a low-carbon and strong substitute of Ordinary Portland Cement (OPC). This experiment examines the mechanical and acid-resisting properties of ambient GPC with different GGBS (10, 30, and 50 percent) contents. The compressive, tensile, and flexural strengths were measured at 7, 14, and 28 days, and durability was measured under an exposure of 5% sulfuric and nitric acids. X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that gypsum and ettringite were formed by sulfuric acid that weakened the structure, whereas surface decalcification was mostly caused by nitric acid. Mixes with a high fly ash content had more amorphous structures and better acid resistance, whereas those having high GGBS contents had high early strength because of high densities of the C–A–S–H gel. The findings indicate a strength–durability trade-off, which can be used to control the optimized mix design to produce sustainable and long-term infrastructure. Full article

This study investigates the adhesion of polypropylene (PP), steel and basalt fibres to geopolymer matrices of varying composition. Geopolymers formed via alkali activation of fly ash (FA) and ground granulated blast-furnace slag (GGBFS) offer significant environmental advantages over Portland cement by reducing CO₂ emissions and energy consumption. The addition of water treatment sludge (WTS) was also investigated as a partial or complete replacement for FA. Pull-out tests showed that replacing FA with WTS significantly reduces the mechanical properties of the matrix and at the same time the adhesion to the fibres tested. The addition of 20% WTS reduced the compressive strength by more than 50% and full replacement to less than 5% of the reference value. Steel fibres showed the highest adhesion (9.3 MPa), while PP fibres had the lowest, with adhesion values three times lower than steel. Increased GGBFS content improved fibre adhesion, while the addition of WTS weakened it. Calculated critical fibre lengths ranged from 50 to 70 mm in WTS-free matrices but increased significantly in WTS-containing matrices due to reduced matrix strength. The compatibility of the fibres with the geopolymer matrix was also confirmed via SEM microstructural observations, where a homogeneous transition zone was observed in the case of steel fibres, while numerous discontinuities at the interface were observed in the case of other fibres, the surface of which is made of organic polymers. These results highlight the potential of fibre-reinforced geopolymer composites for sustainable construction. Full article

Australia consumes approximately 29 million m³ of concrete each year with an estimated embodied carbon (EC) of 12 Mt CO_2e. High consumption of concrete makes it critical for successful decarbonization to support the achievement of ‘Net Zero 2050’ objectives of the Australian construction industry. Portland cement (PC) constitutes only 12–15% of the concrete mix but is responsible for approximately 90% of concrete’s EC. This necessitates reducing the PC in concrete with supplementary cementitious materials (SCMs) or using alternative binders such as geopolymer concrete. Concrete mixes including a combination of PC and SCMs as a binder have lower embodied carbon (EC) than those with only PC and are termed as low-carbon concrete (LCC). SCM addition to a concrete mix not only reduces EC but also enhances its mechanical and durability properties. Fly ash (FA) and granulated ground blast furnace slag (GGBFS) are the most used SCMs in Australia. It is noted that other SCMs such as limestone, metakaolin or calcinated clay, Delithiated Beta Spodumene (DBS) or lithium slag, etc., are being trialed. This technical paper presents a methodology that enables selecting LCCs with various degrees of SCMs for various elements of bridge structure without compromising their functional performance. The proposed methodology includes controls that need to be applied during the design/selection process of LCC, from material quality control to concrete mix design to EC evaluation for every element of a bridge, to minimize the overall carbon footprint of a bridge. Typical properties of LCC with FA and GGBFS as binary and ternary blends are also included for preliminary design of a fit-for-purpose LCC. An example for a bridge located in the B2 exposure classification zone (exposed to both carbonation on chloride ingress deterioration mechanisms) has also been included to test the methodology, which demonstrates that EC of the bridge may be reduced by up to 53% by use of the proposed methodology. Full article

Today, several conventional wastes (fly ash, ground granulated blast furnace slags, etc.) are used as valid precursors for geopolymer synthesis. However, there are several new wastes that can be studied to replace geopolymer precursors. This study investigates the behavior of four industrial wastes—suction dust (SW1), red mud (SW2), electro-filter dust (SW3), and extraction sludge (SW4)—as 20 wt.% substitutes for metakaolin in geopolymer synthesis. The objective is to assess how their incorporation before alkali activation affects the structural, thermal, mechanical, chemical, and antimicrobial properties of the resulting geopolymers, namely GPSW1–4. FT-IR analysis confirmed successful geopolymerization in all samples (the main Si-O-T band underwent redshift, confirming Al incorporation in geopolymer structures after alkaline activation), and stability tests revealed that none of the GPSW1–4 samples disintegrated under thermal or water stress. However, GPSW3 showed an increase in efflorescence phenomena after these tests. Moreover, compressive strength was reduced across all waste-containing geopolymers (from 22.0 MPa for GP to 12.6 MPa for GPSW4 and values lower than 8.1 MPa for GPSW1–3), while leaching tests showed that GPSW1 and GPSW4 released antimony (127.5 and 0.128 ppm, respectively) above the legal limits for landfill disposal (0.07 ppm). Thermal analysis indicated that waste composition influenced dehydration and decomposition behavior. The antimicrobial activity of waste-based geopolymers was observed against E. coli, while E. faecalis showed stronger resistance. Overall, considering leaching properties, SW2 and SW3 were properly entrapped in the GP structure, but showed lower mechanical properties. However, their antimicrobial activity could be useful for surface coating applications. Regarding GPSW1 and GPSW4, the former needs some treatment before incorporation, since Sb is not stable, while the latter, showing a good compressive strength, higher thermal stability, and leaching Sb value not far from the legal limit, could be used for the inner reinforcement of building materials. Full article

This study investigates the composition–property relationships in ternary engineered geopolymer composites (EGCs) using a simplex centroid design method to optimize the synergy between ground granulated blast furnace slag (GGBS), fly ash (FA), and metakaolin (MK). Mechanical testing revealed that compressive strength (>85 MPa) peaked at 75% GGBS/25% MK, demonstrating MK’s dominant role in enhancing densification, while flexural strength showed a negative correlation with GGBS content but consistent improvement with MK addition. Strain-hardening behavior was most pronounced in 75% GGBS/25% MK and 83% GGBS/8% FA/8% MK mixtures, with the latter achieving optimal precursor synergy. Fiber dispersion uniformity showed a strong linear correlation (R² = 0.98) with tensile strain capacity, confirming its critical role in strain-hardening performance. Mercury intrusion porosimetry analysis demonstrated that the G83F8M8 mixture exhibited the lowest porosity (<10%) and finest pore size distribution (50–100 nm dominant), directly linking pore refinement to superior mechanical properties. Full article

Numerous researchers have successfully made alkali-activated material or geopolymer using fly ash, ground granulated blast furnace slag, or metakaolin, either individually or in combination. However, few researchers first determined the reactive Si:Al of their solid precursor and then used this information to develop a formulation with a specific targeted Si:Al for their alkali-activated material. Even if a targeted Si:Al is chosen, few researchers check if the actual Si:Al of the geopolymer matches the targeted values. Characterisation of the precursor, setting target Si:Al values for the geopolymer and verifying target Si:Al values are present in the geopolymer are all part of quality control and essential if high quality products are to be manufactured. Quality control is critical but does not provide the target Si:Al value. This work presents results from a range of geopolymers made with different Si:Al values using sodium aluminate, sodium hydroxide and sodium silicate, either by themselves or in combination. Results reveal, surprisingly, for samples tested, that compressive strength exhibits a maximum for samples with Si:Al less than and greater than the starting Si:Al of the precursor. A strength minimum was found to be present close to the starting Si:Al of the precursor and between the strength maxima. This new information extends the usability range of aluminosilicate precursors and at the same time, makes available a broader range of applications based on Si:Al. Selection of an optimum Si:Al for a geopolymer based on strength can only be made when first a complete spectrum of Si:Al ratios have been evaluated. Full article

This study aims to estimate the carbon footprint and relative uncertainties for design components of conventional and geopolymer concrete. All the design components of alkaline-activated geopolymer concrete, such as fly ash, ground granulated blast furnace slag, sodium hydroxide (NaOH), sodium silicate (Na₂SiO₃), superplasticizer, and others, are assessed to reflect the actual scenarios of the carbon footprint. The conjugate application of the life cycle assessment (LCA) tool SimPro 9.4 and @RISK Monte Carlo simulation justifies the variations in carbon emissions rather than a specific determined value for concrete binders, precursors, and filler materials. A reduction of 43% in carbon emissions has been observed by replacing cement with alkali-activated binders. However, the associative uncertainties of chemical admixtures reveal that even a slight increase may cause significant environmental damage rather than its benefit. Pearson correlations of carbon footprint with three admixtures, namely sodium silicate (r = 0.80), sodium hydroxide (r = 0.52), and superplasticizer (r = 0.19), indicate that the shift from cement to alkaline activation needs additional precaution for excessive use. Therefore, a suitable method of manufacturing chemical activators utilizing renewable energy sources may ensure long-term sustainability. Full article

The construction of concrete pavements has increased due to their better durability, lifespan, and lower maintenance costs. However, this has resulted in the increased consumption of Portland cement, which is one of the major contributors to carbon emissions. Consequently, the research on alternative binders such as geopolymer concrete has increased in recent times. There are several research studies that investigate the feasibility of geopolymer concrete as a construction material, with limited studies exploring its application in concrete pavements. Therefore, this review study explores the material properties of geopolymer concrete pertinent to the performance of concrete pavements. It also discusses the potential of various industrial and agricultural waste as precursor material in geopolymer concrete. The findings of this paper show that most of the studies used fly ash and ground granulated blast furnace slag (GGBFS) as precursor material in geopolymer pavement-quality concrete, and there is a vast scope in the exploration of other industrial and agricultural waste as precursor material. The mechanical and durability properties of geopolymer pavement-quality concrete are superior to conventional pavement concrete. It is also observed that the drying shrinkage and coefficient of thermal expansion of geopolymer pavement-quality concrete are lower than those of conventional pavement concrete, and this will positively benefit the long-term performance of concrete pavements. The results of fatigue analysis and mechanical load test on the geopolymer pavement-quality concrete indicate its improved performance when compared to the conventional pavement concrete. Full article