Application Of Geopolymer Research Articles

Mechanical and microstructural properties of fiber-reinforced basalt rock cutting waste-based geopolymer composites exposed to high temperatures.

Managing basalt rock cutting waste in an environmentally responsible manner is crucial to mitigate its negative impacts and protect both the environment and human health. Recycling basalt rock cutting waste in geopolymer applications offers multiple environmental, economic, and performance benefits, making it a promising approach for sustainable construction practices. For this purpose, this study concerns about the performance of fiber-reinforced basalt rock-cutting waste-based geopolymer composites at high temperatures up to 1000°C. Geopolymer composites were manufactured by activating basalt rock cutting waste with sodium silicate. Alongside the fiber-free mixtures, fiber-reinforced geopolymer composites incorporating 0.5% and 1.0% basalt or polypropylene fibers by volume were synthesized. These composites underwent thermal curing at 100°C for two distinct durations: 8h and 24h. In addition, the geopolymer composites were subjected to thermal exposure at three different temperatures: 600°C, 800°C, and 1000°C. Changes in the strength and weights of the composites were determined after high-temperature exposure. In addition, XRD and SEM/EDX analyses were performed on the selected composites to investigate the changes in the microstructure of the composites. Thermal curing time and fiber content had significant influence on the high-temperature performance of the geopolymer composites. In this study, geopolymer mortars based on basalt rock cutting waste were successfully developed, demonstrating resistance to elevated temperatures up to 1000°C. No reduction in compressive strength was observed in any of the composites when exposed to 600°C, 800°C, and 1000°C. In fact, an increase in strength was recorded at varying rates, compared to the pre-exposure values.

Expansion in low calcium fly ash-based geopolymer concrete: chemical factors influenced by silica fume and NaOH concentration

Geopolymer technology offers a sustainable alternative to energy-intensive cement production, potentially reducing dependence on natural resources and mitigating environmental impact. Silica fumes (SF) are mostly used to enhance the fresh, hardened, and durable performance of geopolymers. However, their influence on geopolymerization may result in the expansion of the geopolymer mortar (GPM) due to reaction with alkaline liquid. In this study, the effect of NaOH concentration, particle size and dosage of SF, alkaline liquid-to-binder ratio, Na2SiO3-to-NaOH ratio, and sand-to-binder ratio on the expansion behavior of a low calcium fly ash (FA)-based GPM was investigated. FA-based GPMs were tested using two distinct SFs with varying particle sizes (SF1 = 9.5 µm and SF2 = 16.2 µm) and two varying dosages of SF (2.5% and 5%). Physical observations of GPMs revealed that NaOH concentration, particle size and dosage of SF are crucial factors that significantly impact the expansion which is concomitant with a reduction in compressive strength. Analytical techniques such as X-ray diffraction (XRD), Rietveld analysis, Fourier transform infrared spectroscopy (FTIR), and Thermo Gravimetric Analysis (TGA) were employed to comprehensively investigate reaction product(s) that led to the expansion of such GPMs. The chemical analysis confirmed the presence of excess analcime in the mortars fabricated by blending SF1 and FA at 12 M NaOH concentration. This study is the first to report the expansion of low calcium FA-based GPMs blended with a SF of particle size 9.5 µm. These findings emphasize the significance of selecting the appropriate SF particle size to prevent expansion and ensure optimal compressive strength in geopolymer applications.

Anti-dispersion, rheological, and mechanical properties of GBFS/FA geopolymer for underwater engineering applications

Cementitious materials used in underwater engineering primarily face challenges such as water infiltration, chloride ion penetration, and sulfate attack. Therefore, the use of fast curing, strong corrosion resistance, and high-performance geopolymers is critical in underwater engineering. In this study, NaOH was selected as the activator, with granulated blast furnace slag (GBFS) and fly ash (FA) serving as precursors. The effects of hydroxypropyl methylcellulose (HPMC) content, alkali content, and the GBFS/FA ratio on the anti-dispersion, rheological, and mechanical properties of the geopolymers were systematically investigated. The results indicated that when the Na₂O content was below 5 wt%, increasing the HPMC enhanced the anti-dispersion properties of the geopolymer paste. However, in a highly alkaline environment (Na2O≥7 wt%), HPMC did not enhance the anti-dispersion properties of the paste. Infrared spectrum analysis suggested that the degradation of HPMC chemical bonds was responsible for the loss of underwater anti-dispersion properties in the geopolymer paste. The workability of the paste was negatively impacted by the thickening effect of HPMC. As the HPMC content increased, both the yield stress and plastic viscosity of the paste rose. FA enhanced the paste's workability, increasing its flowability by 13.36 %. At a constant alkali content, the rheological behavior of the paste was significantly affected by the HPMC content and the GBFS/FA ratio. The Bingham and modified Bingham (MB) models were employed to fit the rheological curve of the geopolymer paste, yielding satisfactory results. While GBFS contributed to the improvement of early strength, FA had a contrary effect. HPMC could delay the hydration process, increase the porosity of geopolymers, and reduce the strength of the samples. Underwater pouring further exacerbated the porosity, negatively affecting the geopolymer's strength. This study offers valuable insights for the application of geopolymers in underwater engineering.

Early properties and reaction mechanism of hybrid alkali-activated cements (HAACs)

Geopolymers have received extensive attention due to their greenhouse effect. However, the application of geopolymers has been restricted by their workability and manufacturing technique. Hybrid alkali-activated cements (HAACs), which are transition materials between cement and geopolymers, have gradually been developed. The chemical reactions of HAACs are complicated, and adjusting their performance is difficult. In this study, the competitive reactivities and phase contents of commonly used HAACs with different raw material compositions and curing conditions are examined. The reaction degrees of the clinker (RoC), C-(A)-S-H+N(C)-A-S-H gel and unreacted amorphous particle (UAP) contents were calculated. The experimental results indicated that the quantity and structure of the gel were optimized when the Si2O/Na2O and Na2O contents of HAAC-G3 were 1.5 and 4 %, respectively, and the cement: mineral admixture ratio was 1:4. Moreover, a large amount of N-A-S-H with a dense structure was produced by alkali reactions rather than cement hydration reactions in HAAC-G3; these reactions improved the macroscopic mechanical properties. Additionally, the effects of steam curing on the properties of the HAACs were slight because of the internal water competition reaction mechanism. This research clarified the influence of different coordination methods on the internal reaction mechanism of HAACs and could be used to promote the engineering application of HAACs. Moreover, HAACs play an important role in mitigating greenhouse effects worldwide.

Synchronous vacuum hot pressing ultra-high performance geopolymer: Ultrafast polymerization and early strength development

To overcome the application bottleneck of geopolymer in high-end industries, this study aims to develop ultra-high performance geopolymer products. By employing Synchronous Vacuum Hot Pressing, we have significantly enhanced the rate of polymerization and mechanical properties of Geopolymer based on Metakaolin-Fly Ash. The influence of Si/Al ratio, alkali equivalent, and molding time on the geopolymerization process, mechanical properties, and microstructure of geopolymers was investigated, while elucidating the underlying mechanisms. The compressive strength of SVHP-MFG reaches 90.92 MPa when the Si/Al ratio is 2, alkali equivalent is 8 %, and molding time is 30 min, owing to increased production of aluminosilicate gels and matrix structure densification. The ongoing reaction of unreacted particles and the subsequent transformation from "alumina-rich gel" to "silica-rich gel" in later stages further enhance the mechanical properties of the material. Additionally, the mean pore diameter of Synchronous vacuum hot pressing of metakaolin-fly ash geopolymer measures below 13.24 nm, thereby significantly enhancing the pore structure of the geopolymer. The synchronous vacuum hot pressing metakaolin fly ash-based geopolymers synthesized in this study represents a novel category of ultra-high performance ceramic-like geopolymers, exhibiting exceptional early strength and early stability. The research aims to promote the application of geopolymer in high-end industry and provide technical and theoretical support for the development of ultra-high performance geopolymer based products.

Fresh and Hardened Properties of Alkali-Activated POFA-GGBFS Pastes Cured in Ambient Temperature – An Initial Mix Design

Weak soils are characterised by their high compressibility and low shear strength, which requires stabilisation to improve their compaction and strength characteristics before being used for construction projects. Recent trends in soil stabilisation show an increased interest in the application of waste-derived geopolymers as low-carbon materials to address the carbon emission problem related to cement production. This paper presents the preliminary findings of using Palm Oil Fuel Ash (POFA) and Ground Granulated Blast Furnace Slag (GGBFS) binary blends as geopolymer precursor materials. These binary waste material blends were activated using alkaline solutions, namely Sodium Hydroxide (NH) and Sodium Silicate (NS), to synthesise geopolymers at ambient temperatures. Three main factors were considered for the optimisation of the geopolymer mix design, as recommended by past research: alkali equivalent (8-11.5%), activator modulus (0-0.7), and slag replacement (fixed at 30%). Alkali equivalent and activator modulus parameters were varied and tested to establish its initial and final setting times, workability and strength properties, while the slag replacement percentage was set at 30%. This study aimed to determine the most influential parameters to produce the geopolymer material with the highest compressive strength and satisfactory setting times and workability. Single-source alkali activators (NH only) used on POFA-GGBFS produced specimens with smaller flow diameters, longer initial and final setting times, and lower compressive strength than specimens activated with NH and NS. Geopolymer specimens synthesised with NH and NS produce stiffer compounds possessing higher compressive strength values and explosive-type failure modes due to their higher silica content. At ambient temperatures, TM-Mix 2 (7% alkali equivalent and 0.7 activator modulus) produced the highest compressive strength value of 67.3 MPa at 28 days curing, flow diameter of 227 mm, with the initial and final setting time of 25 minutes and 45 minutes, respectively. Consequently, the results show that the preliminary POFA-GGBFS geopolymer mix design could produce sustainably sourced geopolymer compounds with adequate strength and acceptable setting time and workability. This study is part of a current investigation to further optimise the POFA-GGBFS mix design for the purpose of weak soil stabilisation.

Geopolymers: Enhancing Environmental Safety and Sustainability in Construction

This study underscores the significant environmental advantages of geopolymer, notably its capacity for substantial CO2emission reduction and sustainable waste management by repurposing industrial by-products, enhancing the environmental safety in oil and gas projects. Central to our investigation is the identification and strategic overcoming of critical obstacles to the broader application of geopolymer, aiming to bridge the gap between its recognized potential and practical implementation in construction practices. Through a comprehensive analysis involving pilot, main, and validation surveys among construction industry professionals, we employed exploratory factor analysis (EFA) and structural equation modeling (SEM) to elucidate the relationships between various barriers and the success of geopolymer concrete applications. Our findings reveal that standards and knowledge significantly influence the adoption of geopolymer concrete, with an R² value of 0.873 indicating a high predictive utility of these constructs. The research underscores the critical need for enhanced support in research and development to improve geopolymer concrete's durability and performance over time. Significantly, this study contributes novel insights into overcoming the industry's hesitancy towards geopolymer concrete, highlighting its importance for sustainable construction practices and reducing the environmental footprint of building materials. Doi: 10.28991/CEJ-2024-010-10-015 Full Text: PDF

Geopolymer-based insulated wall incorporating construction and demolition waste: Experimental assessment of thermo-physical behavior

The benefit of the application of geopolymers in the building sector is nowadays undisputed. In addition to good structural characteristics, these are characterized by interesting thermophysical properties, obtained through a production process, that reduces CO2 emissions and could incorporate recycled material, thus responding to environmental sustainability. However, it is noted the lack of studies regarding the in-field thermal performance. Thus, the aim of the present study is to investigate the thermal performance, under real conditions, of an innovative geopolymer-based insulated wall. It incorporates over 70% of net weight of Construction and Demolition Waste materials. The wall is conceived within the European project called “Green INSTRUCT” aimed to realize modular prefabricated building elements, for retrofitting and new construction of buildings. Two wall prototypes are analysed, which differ for the type of lightweight aggregate of geopolymer matrix, 3% by weight: expanded polystyrene or extruded polystyrene. The study refers to almost one year of continuous monitoring within a full-scale test room located in southern Italy. The method developed consists of 5 different phases and it involves also a normative-insulated reference wall. The results show higher insulation level of the proposed wall package, with a reduction of the heat flux of about 66% and more stable indoor thermal conditions, compared to the reference wall. Also the inertial properties are satisfactory, showing an experimental decrement factor equal to 0.05 and a time-shift of decrement factor higher than 6 h. All told, the experimental results can provide valuable insights into the real impact of innovative technology on energy efficiency and indoor thermal comfort.

Investigation of the Impact of Geotextile Incorporation on the Mechanical Properties of Geopolymer

Geopolymers assume an irreplaceable position in the engineering field on account of their numerous merits, such as durability and high temperature resistance. Nevertheless, geopolymers also demonstrate brittleness. In this study, geotextiles with different layers were added to geopolymer to study its compressive strength and stability. Laboratory materials such as alkali activators, geotextiles and granite residual soil (GRS) were utilized. The samples were characterized via XRD, TG-DTG, SEM-EDS and FT-IR. The results indicate that the toughness of geopolymer is significantly enhanced by adding geotextiles, and the strength increase is most obvious when adding one layer of geotextile: the strength increased from 2.57 Mpa to 3.26 Mpa on the 14th day, an increase of 27%. Additionally, the D-W cycle has a great influence on geotextile polymers. On the 14th day, the average strength of the D-W cyclic sample (1.935 Mpa) was 1.305 Mpa smaller than that of the naturally cured sample (3.24 Mpa), and the strength decreased by 40%. These discoveries offer a novel approach for further promoting the application of geopolymers, especially in the field of foundation reinforcement.

Exploring the Potential of Using Waste Clay Brick Powder in Geopolymer Applications: A Comprehensive Review

The application of geopolymers has recently been given significant attention to address climate change and the growing scarcity of construction materials in the 21st century. Researchers have utilized industrial waste or supplementary cementitious materials containing high levels of silica and alumina as precursors along with different alkaline activators. Furthermore, the technical challenges associated with waste brick management or recycling include both land use changes and financial implications. The existence of amorphous aluminosilicates in waste clay bricks, which can be used as geopolymer binders, has drawn attention recently. This paper reviews the recent advancements of the integration of clay brick wastes in geopolymer applications, individually as well as its use with other alternative materials. Prior studies suggest that waste clay bricks can effectively serve as the primary source material in geopolymer applications. This review covers various aspects, including the assessment of fresh, mechanical, microstructure, and durability-related properties. It specifically focused on enhancing these properties of waste clay bricks through mechanical and thermal treatments, through varying curing conditions, utilizing different types of alkaline activators, and considering their properties and corresponding ratios in the development of geopolymer products using waste brick powder. Furthermore, this paper portrays a critical review of the sustainability implications of the utilization of clay brick waste in geopolymer applications. Conclusively, this review provided the lessons learnt, research gaps, and the future direction for investigation into the feasibility of geopolymers derived from waste clay brick powder.

Fatigue analysis of ambient-cured geopolymer concrete for high-traffic pavements.

The building sector is growing at a rapid rate, leading to an increased demand for construction materials. Concrete made with Ordinary Portland Cement (OPC) has long been the preferred choice due to its excellent bonding properties and versatility as demanded by construction process. However, the manufacturing of Ordinary Portland Cement (OPC) leads to negative impacts on the environment, with the cement sector responsible for around 5-8% of global CO2 emissions. In addition, the manufacture of OPC necessitates significant amounts of natural raw materials and energy. Contrastingly, using geopolymers promises to save substantial amounts of energy and reduce CO2 emissions. This potential has sparked growing interest in the application of geopolymers within transportation infrastructure. For pavements, the workability requirement is less, and hence, geopolymer concrete (GPC) is a viable option, but fatigue-resistance of GPC is not seen reported in literatures. This article evaluates the properties of geopolymer concrete with low-calcium fly ash partially replaced with ground granular blast furnace slag (GGBS) with 8M NaOH alkaline solution and cured under ambient atmospheric conditions to evaluate its usage in pavements and develop an environmentally sustainable and durable GPC capable of withstanding heavy traffic. The study involves adjusting the pavement quality concrete (PQC) mix design; evaluating the mechanical characteristics, abrasion resistance, and shrinkage strain of the GPC; and analyzing its microstructure. Additionally, the study compares the fatigue life of GPC to that of PQC using various Weibull distribution approaches. The results showed that GPC4 (70% Fly ash and 30% GGBS) mix achieved best results at 28days, with a compressive strength of 45.68MPa, split tensile strength of 3.76MPa, and flexural strength of 4.62MPa. Also, shrinkage strains were nearly 31% lesser than PQC at 90days. In addition, developing GPC needs 27% lesser embodied energy than PQC. Fatigue analysis prove that ambient cured fly ash-GGBS based geopolymer concrete with 8M NaOH exhibits less stress development than PQC at medium loads, even though it is brittle. Thus, the study proves that it is suitable as a material for pavements to resist medium-loaded traffic-resisting pavements.

Direct evidence for the mechanism of early-stage geopolymerization process

Geopolymer, an alternative construction material to cement, acquires strength and endurance through the geopolymerization process. However, the study on the early-stage geopolymerization is rare since it occurs rapidly and involves liquid phase, viscous slurry, and gel-like material, making the observation of this process complicated. This research addresses the challenge of observing this process by providing real-time evidence through in situ techniques: Fourier-transformed infrared (FTIR) spectroscopy, X-ray absorption spectroscopy (XAS), and environmental scanning electron microscopy (E-SEM). These methods consistently confirm the formation of aluminosilicate oligomers, short chains of silicate and aluminate species, in the polycondensation Stage I within the initial 5 minutes. This stage involves the reaction of Si-O and Al-O monomers, released during a dissolution process, with available Na2SiO3 from alkaline solutions in the system. In the subsequent polycondensation Stage II, aluminosilicate oligomers polymerize, creating a three-dimensional network of aluminosilicate chains through the crosslinking of Si-O-Si and Si-O-Al bonds. This process continues beyond the initial 5 minutes, gradually nearing completion around 30 minutes, as consistently confirmed by various experimental techniques. Rheological studies on the geopolymer paste flow rate support these interpretations. The study provides compelling direct evidence into the mechanisms of early-stage geopolymerization, significantly contributing to the research field and paving the way for widespread utilization in geopolymer applications.

Optimisation of mechanical properties and pore structure of lightweight geopolymer concrete

Lightweight geopolymer has good physical and mechanical properties, thermal and chemical stability and low carbon dioxide emissions. The development of high-strength lightweight geopolymer concrete (LGC) for load-bearing structures can expand geopolymer applications. The use of ground granulated blast-furnace slag (GGBFS) to improve the mechanical properties and pore structure of LGC was investigated. The ultimate compressive stress of LGC containing GGBFS were analysed, as well as the variation in microscopic pore structure. Specimens of LGCs with different strengths (LC20, LC30 and LC40) were investigated. As the GGBFS content increases, the ultimate compressive stress and specific strength of LGC increases, while the strain corresponding to the peak stress decreases, indicating that the mechanical properties and deformation resistance of LGC are improved. The carbon dioxide emissions of LGC are less than those of cement-based lightweight concrete, indicating that LGC has good sustainability. Moreover, the addition of GGBFS can produce more gel and reduce the volume proportion of capillary pores and air pores, resulting in LGC densification. Recommended GGBFS contents for strength grades LC20, LC30 and LC40 are 0–12.7%, 12.7–24.6% and 24.6–30%, respectively. The LGC is lightweight and has high strength, and has potential for application in civil engineering.

Microstructure and transport properties of metakaolin-based geopolymers subjected to accelerated leaching

Towards the development of net-zero carbon concrete and the wider application of geopolymers, understanding the durability of geopolymers has become essential. However, knowledge on the evolution of microstructure and transport properties of the materials under aggressive conditions due to their interaction with external chemicals is limited. Therefore, this study investigated the leaching behaviors of metakaolin-based geopolymers with high water-to-binder (w/b) ratios under a 6 M NH4NO3 attack, focusing on their microstructure and transport properties. Microstructural insights were assessed through N2-adsorption, Mercury intrusion porosimetry, and water porosity analyses. After 28 days of leaching, total porosity slightly decreased, but pore size distribution (PSD) shifted towards larger pore sizes. The materials close to the exposed surface exhibited a relatively higher porosity and larger PSD than the deeper parts. The potential formation of Al(OH)3 and silica layers as a result of dealumination, confirmed by mass gain and SEM/EDS, contributed to the pore structural evolution. These alterations led to slight reductions in water permeability and CH4 diffusion coefficients but mostly increased the He diffusion coefficients of the geopolymers after 28-day leaching. These findings underscored the inherent microstructural characteristics of geopolymers (e.g., porosity, pore size distribution, and tortuosity) and the size of diffusing species as key factors shaping the transport properties. Notably, the permeability and diffusivity of both leached and intact geopolymers exhibited exponential correlations with the accessible porosity.

Mechanical properties and hydration of fly ash-based geopolymers modified by copper slag

Copper slag (CS) is mostly used as concrete aggregate due to its low activity, which limits its application. Although CS can exhibit high activity in geopolymer systems, the mechanical properties of high-volume CS geopolymers are still poor, which limits the utilization of CS and the application of geopolymers. In this paper, CS and fly ash (dry grinding fly ash (DFA) and wet grinding fly ash (WFA)) were used to prepare geopolymers with high-volume CS, and the effects of CS on the mechanical properties, microstructure and hydration of fly ash-based geopolymers were investigated. The results showed that the addition of CS could effectively improve the compressive strength of fly ash-based geopolymers. Compared with geopolymer samples without CS, 40 % CS can increase the 7d and 28d compressive strength of dry grinding fly ash-based geopolymers by 37.8 % and 33.6 %, respectively; 50 % CS can increase the 7d and 28d compressive strength of wet grinding fly ash-based geopolymers by 59.2 % and 49.2 %, respectively. The addition of CS can promote the formation of N(C)-A-S-H and Fe-rich gels, and then improve the mechanical properties and microstructure of fly ash-based geopolymers.

Evaluation of Locally Available Calcined Clay-Based Geopolymer for the Stabilization of Expansive Soils

Geopolymers (GPs) have been effectively used as an alternative to traditional calcium-based stabilizers for treating problematic expansive soils over the last decade. However, the high cost of precursors and limited availability of traditionally manufactured GPs pose significant challenges for commercial implementation. Utilizing locally available sources to manufacture GPs could address such limitations and promote sustainable development. A research study was designed and implemented to evaluate the efficacy of locally available calcined clay-based GP stabilizers to improve the performance of expansive soils and the results were compared with lime-treated and untreated soils. An array of laboratory studies was conducted using two natural clayey soils and two types of GPs to assess improvements in several engineering properties, including unconfined compressive strength before and after capillary soaking, resilient moduli, and moisture-induced strains. Supplemental microstructural studies using X-ray diffraction, optical microscopy, and scanning electron microscope imaging were conducted to identify the mineralogical changes and detect the precipitation of new reaction products. The engineering studies demonstrated that the application of GP significantly enhanced the strength, durability, and stiffness while reducing the swelling and shrinkage strains in the GP-treated soils. Microstructural analysis revealed that the precipitated GP gels effectively coated the soil particles and provided a uniformly bonded GP–soil matrix that enhanced the engineering performance. Overall, this study provides a comprehensive understanding with respect to the potential of using locally available calcined clay-based GPs as a sustainable and durable alternative in enhancing the engineering properties of expansive soils for the long-term performance of transportation infrastructures.

Synthesis of multifunctional mesoporous geopolymer under hydrothermal curing: High mechanical resistance and efficient removal of methylene blue from aqueous medium

This study created green multifunctional geopolymeric sorbent material with strong cationic dye adsorption capacity and superior mechanical strength to broaden lead sludge (LS)-based geopolymer applications. In this study, two geopolymeric sorbents (Go and G) were fabricated using slag blended with 0 and 50 wt% LS, respectively and activated with 6 wt% NaOH. The Go and G specimens were normally cured for up to 28 days, while G specimens were hydrothermally cured at different steam-pressures to modify/improve histological characteristics as well as mechanical resistance. The selected sorbents were characterized via XRD, FTIR, TGA/DTG, XPS, N2-adsorption/desorption and SEM/EDX techniques. G/5 bar′s high strength and adsorption capacity may be due to the production of CSH, CAH, CASH, and NASH, which formed a fine mesoporous zeolitic structure with the highest BET-surface area (64.55 m2/g) and lowest BJH-maximum pore diameter (9.68 nm). The maximum MB adsorption capacity of the synthesized adsorbent was 230.4 mg/g.

HISTORY OF DEVELOPMENTS IN GEOPOLYMER SCIENCE IN NEW ZEALAND: A BRIEF REVIEW

This brief review covers some of the highlights of the research into the chemistry and various applications of aluminosilicate geopolymers carried out in the Chemistry Department of Victoria University of Wellington over the last 20 years. Because these materials are generally amorphous to X-rays, the technique of Nuclear Magnetic Resonance with Magic Angle Spinning (MAS NMR) played a unique and important role in these studies. Many potential applications of geopolymers, were investigated over this period, including their use as structural materials, catalysts for commercially important organic reactions, bioactive materials and photoactive materials. Most of the initial work was carried out on clay-based starting materials because of their purity, but more practical materials were also developed, based on the by-products of industrial processing (fly ash, blast furnace slag, red mud, etc) This work led to more than 62 published papers in international journals, some of which are discussed here.

Investigating the impact of alkaline activator on the sustainability potential of geopolymer and alternative hybrid materials

Geopolymer binders are considered highly sustainable due to their utilization of industrial wastes. However, previous studies highlight the limited industrial-scale applications of geopolymers. Therefore, this study critically investigates the strength, cost, and environmental impact of geopolymers and alternative hybrid cement mixes to provide a complete picture for the sustainability analysis. Geopolymers and hybrid cement mixes are designed with varying proportions of alkaline activator (sodium hydroxide 5–25 wt%) and ordinary Portland cement (OPC) (15–35 wt%) respectively for the comparative analysis. The strength characteristics of designed mixes have been assessed by analyzing their compressive strength and microstructure. A comparative economic assessment has been made by contemplating the manufacturing and production costs of different materials used in geopolymer and hybrid cement mixes. ReCiPe Midpoint Life cycle assessment (LCA) has been performed to examine the environmental performance by considering the manufacturing and production processes of various binder and aggregate materials used in geopolymer and hybrid cement mixes. Mechanical and microstructural analysis shows that hybrid cement mix with 35 wt% of OPC yields the highest strength due to the formation of excess calcium aluminum silicate hydrate (C-A-S-H) and calcium silicate hydrate (C–S–H) gels than geopolymer mix containing 25 wt% of NaOH. Economic and life cycle assessment reveals that the geopolymer mix with 5 wt% NaOH offers the lowest cost and environmental impact as compared to others containing higher proportions of alkaline activator and OPC. Owing to the conflicting nature of the results, multi-criteria decision making approach has been used which presents the hybrid cement mix (with 35 wt% OPC) as the optimal and sustainable solution for the construction applications. The study's findings offer a sustainable direction for the construction industry by suggesting the application of hybrid concretes.

Development of a Low-Density Waste-Based Geopolymer Construction Material

The construction industry, integral to national infrastructure development, faces environmental challenges attributed to Portland cement’s high energy consumption and carbon dioxide emissions during production. To address this challenge, this study integrated waste fly ash and polystyrene into geopolymers to enhance environmental sustainability and economic feasibility. The objectives included developing low-density geopolymers using polystyrene inclusion, optimizing component mixing ratios, assessing activator concentration effects, determining the optimal curing conditions, and characterizing the resulting geopolymers. Through experimental investigation, low-density geopolymers were developed with optimized component ratios and curing conditions. The experimental procedure began with the classification of fly ash to determine its suitability for various applications, revealing it to be type F. Geopolymers were fabricated using a mixture of fly ash, water, sodium hydroxide activator, and polystyrene. Varied concentrations of sodium hydroxide and polystyrene were employed. Two curing temperatures, 60 °C and 100 °C, were explored. The results showed that greater sodium hydroxide concentrations improved the structure and compressive strength of the geopolymers. The results also demonstrated a significant correlation between the curing conditions and the mechanical properties of the produced geopolymers. The goal of reducing the density of the geopolymers for lightweight thermal-resistant applications was achieved through polystyrene incorporation. However, polystyrene incorporation negatively impacted the compressive strength. The optimum production conditions for the sodium hydroxide-varied samples were 8 g sodium hydroxide/g sample cured at 100 °C, while the optimum production conditions for polystyrene-varied samples were 1 g polystyrene/g sample cured at 60 °C. The findings confirmed the viability of utilizing fly ash and polystyrene wastes to produce sustainable, low-density, thermal-resistant construction materials. Overall, increasing activator concentration enhances the strength and durability of geopolymers, while polystyrene contributes to the development of lightweight geopolymers, provided the appropriate amount is utilized. To ensure replicability, the formulation procedure and input quantities must be tailored according to the intended geopolymer application. These insights offer practical guidance for optimizing geopolymer manufacturing processes towards enhanced sustainability and performance.