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Alkali-activated concrete (AAC), a possible alternative to ordinary Portland cement (OPC), provides increased environmental advantages, notably lower carbon emissions. Likewise, similar to OPC, it faces durability problems under severe environments. This study evaluated the effectiveness and durability of alkali-activated concretes containing low-grade calcined clay and granulated blast furnace slag (GGBFS), using NaOH/KOH as activators and MgO and superabsorbent polymer (SAP) as additives. The study's focus was on their physical-mechanical characteristics and performance under accelerated carbonation and chloride diffusion. Findings showed that calcined clay-GGBFS alkali-activated concretes exhibited a compressive strength range of 41.2–53.3 MPa, positioning them as a viable concrete for many structural usages. Nevertheless, the modified-RCPT (10 V) and NT Build 492 tests showed all concretes falling into the "high chloride penetrability" category, with values exceeding 350 coulombs and 13.5 (×10−12 m2/s) for the non-steady-state migration coefficient (D nssm). NaOH and sodium silicate led to higher compressive strengths compared to KOH. Furthermore, the chloride migration coefficient of alkali-activated concrete blends ranged from 55.68 to 121.14 (× 10−12 m2/s). The incorporation of 0.6 % SAP decreased compressive strength but improved the non-steady-state migration coefficient (D nssm). Lastly, MgO-enriched samples showed the lowest water absorption and carbonation depth, attributed to the buffering action of magnesium phases, reducing carbonate formations, as revealed by XRD analysis. • Concretes cured at ambient conditions show suitable compressive strength for structural use, even in severe environments. • NaOH with sodium silicate as the activator produced superior compressive strength compared to KOH. • GGBFS content played a significant role in the properties of calcined clay/GGBFS alkali-activated concretes. • Higher GGBFS reduced carbonation depth; higher calcined clay kept pH higher after carbonation. • MgO reduced the carbonation depth due to a chemical buffering mechanism. [ABSTRACT FROM AUTHOR]

This study investigates the potential effect of curing temperature (80 °C and 100 °C), the effect of using waste tire rubber aggregates (WTRA), and silica fume (SF) on the properties of lightweight geopolymer (LG) composite. In LG, SF replaced 20 % of the ground granulated blast furnace slag (GGBS), and WTRA replaced pumice aggregate to varying degrees (15 %, 30 %, and 45 % by volume). The physical properties of the LG composite were assessed through apparent porosity, water absorption, and hardened density. The mechanical properties were examined by testing compressive strength (CS) and flexural strength (FS). The effect of high temperature (300 °C and 600 °C) was examined on CS and mass loss of LG composite. The durability of the LG composite was analyzed using mercury intrusion porosimetry (MIP), capillary water absorption, freeze-thaw, and thermal conductivity. The material characterization of the composite was done using scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential thermogravimetry (DTG) curves. After 28 days, LG composites showed increased porosity and water absorption with the increased WTRA and SF, with higher values at 100 °C. Compressive and flexural strengths decreased with the increased WTRA and SF, especially at higher temperatures. The TGA-DTG curves show that the LG-0–80 mix had the lowest mass loss (15.25 % at 400°C and 19.36 % at 600 °C), while the LG-SF-45–100 mix had the highest mass loss (22.22 % and 24.53 %, respectively). XRD and TGA-DTG analyses reveal that using SF increases Ca(OH)₂ peaks and alters the geopolymer composition, improving the mechanical performance of the LG-SF-0–80 mix and enhancing the thermal stability of the composites. • Increased WTRA and SF in LG composites elevate porosity and water absorption. • Compressive and flexural strengths decline notably with higher WTRA and SF. • TGA-DTG analysis shows varying mass loss, lowest in LG mix with no SF at 80 ºC curing. • SF enhances Ca(OH)₂ peaks, altering geopolymer composition for improved mechanical and thermal performance. [ABSTRACT FROM AUTHOR]

Exploring alternative precursors other than flyash, slag, metakaolin and palm oil fuel ash for geopolymer synthesis has become very essential owing to the need for reduction in cost and accumulation of solid waste that could contribute to environmental pollution. The use of coffee silverskin (CSS) in binary blending with flyash (FA) in geopolymer synthesis is not yet fully understood, although its performance in ternary blending with silica fume for ordinary Portland cement (OPC) mortar has been established. Thus, binary blended CSS (0–30 %) with FA - such that CSS/(FA+CSS) varied from 0 to 0.3 - was activated by sodium hydroxide (8MNaOH) and sodium silicate (Na 2 SiO 3), and then subsequently cured at 60 °C. Mechanical property, binder morphology, compound product phases and bond characteristics were studied through compressive strength test, scanning electron microscope (SEM/EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIRS), respectively. CSS (CSS/(FA+CSS) = 0.3) significantly contributed to strength loss due to microcracks, carbon content and fiber induced microstructural discontinuity, such that 7-,14-and 28-d strengths recorded were 5.2, 7.8 and 9.7 MPa, respectively. Maximum 28-day strength of 16.5 MPa was recorded in CSS/(FA+CSS) = 0.1. CSS caused the formation of monetite, and disappearance of muscovite and augite in flyash/coffee silverskin based (FACSS) geopolymer. • Coffee silverskin (CSS) and flyash binary geopolymer (AACSS-FA) binder was developed. • Incorporation of CSS in AACSS-FA caused presence of insoluble cellulose fibers in the matrix. • Presence of CSS in AACSS-FA caused microcrack, monetite formation and loss of strength • CSS in AACSS-FA caused formation of monetite and disappearance of muscovite in AACSS-FA. • CSS in AACSS-FA induced hydrogen bond vibration. [ABSTRACT FROM AUTHOR]

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 (Na 2 O≥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. • Hydroxypropyl methylcellulose (HPMC) has stability problems in geopolymer. • The workability of geopolymer is controlled by HPMC content and raw material ratio. • HPMC increases the porosity of paste and reduces the strength of geopolymer. • The strength of underground water samples is lower than that of land samples due to the large number of pores. [ABSTRACT FROM AUTHOR]

To recycle waste clay bricks and alleviate the physical and mechanical performance degradation of slag-based geopolymer foam concrete (SGFC) in thermal exposure, the brick powder (BP) was utilized to prepare slag-brick powder based geopolymer foam. The thermal stability of SGFC was evaluated comprehensively by introducing the strength and volume loss rate, and surface crack area after thermal exposure. Additionally, the composition and transformation of the phases before and after fire were quantitatively characterized by XRD, TG-DSC and FTIR. The results showed that the addition of BP significantly could greatly improve the thermal stability of SGFC, subsequently alleviate the volume shrinkage and reduce surface cracks after thermal exposure. The reason was that the BP changed the reaction products of SGFC and the phase transitions during thermal exposure. Specifically, the brick powder introduced a new phase, yoshiokaite, and decreased the melting sintering temperature (sintering point) of SGFC in fire. The SGFC with 20 wt% brick powder exhibited the optimal comprehensive thermal stability after 800℃ thermal exposure: the surface crack area decreased by 21.00 %, and the volume shrinkage reduced by approximately 10 %, with a residual strength of 1.06 MPa. This study demonstrates that ambient cured geopolymer foams prepared with slag and BP can achieve excellent thermal stability under temperature over 800℃. ● The thermal stability of slag-based geopolymer foam concrete was improved by the addition of brick powder. ● The unique hydrophilicity and loose surface structure of the brick powder play the role of internal curing and high temperature crack resistance. ● SGFC with 20% brick powder has excellent cracking resistance and volume stability after thermal exposure. ● The evolution of surface cracks and gel quantity after thermal exposure was quantitatively analyzed. [ABSTRACT FROM AUTHOR]

Unsorted Construction and Demolition Waste (CDW) from residential building was tested as solid precursor for obtaining eco-sustainable alkali activated materials with potential applications in the building industry. Suitable reactive systems for material consolidation were tested, including alkaline solutions of sodium hydroxides and/or silicates at different concentrations. Metakaolin (MK) was also tested as an additional precursor together with CDW in different ratios to optimize geopolymerization. An MK/CDW weight ratio of 40/60 and sodium silicate as alkaline activator allowed the production of a well-reacted and cohesive material, with a bulk density of 1.35 g/cm3, a monomodal mesoporosity with a modal pore size of 0.0214 µm (open porosity ∼42 vol%), and a compressive strength of 25 MPa, thus showing similar features to those of pure metakaolin based-geopolymers. Thermal characterization was performed up to 1000°C showing that the material can exhibit thermal stability up to 650°C. Above that temperature a shrinkage due to viscous flow occurred, followed by an expansion over 750°C with the formation of macropores and dense struts. Based on these results, the developed CDW-based geopolymer has the potential for use in green building applications, with adequate thermal stability up to medium-high temperatures. • Unsorted CDW was used as solid precursor for eco-sustainable AAMs. • Several alkaline solutions and CDW/metakaolin ratios were tested for consolidation. • Effects of relevant parameters and microstructural properties were investigated. • The thermal behavior of CDW/MK-based geopolymer was investigated up to 1000°C. • The optimized geopolymer exhibited a 28-days compressive strength of 25 MPa and thermal stability up to 650°C. [ABSTRACT FROM AUTHOR]

While high-performance fly ash geopolymers offer a demonstrably reduced carbon footprint in the construction industry, their inherent affinity for water (hydrophilicity) can facilitate the accumulation of moisture within the material matrix, potentially leading to the initiation and propagation of internal corrosion. The implementation of hydrophobic functionalization strategies on fly ash geopolymers demonstrably enhances their resistance to corrosive degradation. Nevertheless, a crucial challenge persists in the form of mitigating potential declines in mechanical strength. This investigation endeavors to attenuate the deleterious effects exerted by the hydrophobic aluminosilicate hydrate phase on the material's mechanical properties, while concurrently preserving its superhydrophobic character. Our approach involved the incorporation of a novel composite modifier, wherein polymethylhydrosiloxane (PMHS) served as the principal hydrophobic component. Graphene oxide (GO) was strategically introduced to achieve efficient pore filling, owing to its exceptional dispersibility. Furthermore, the presence of GO reinforces the mechanical performance of the composite due to its inherent superior mechanical properties. Additionally, the well-dispersed GO portion forms nano hydrophobic particles by covalently grafting hydrophobic groups, further enhancing the overall hydrophobicity of the composite. This synergistic interplay between PMHS and GO facilitated the successful development of a high-performance fly ash geopolymer composite characterized by exceptional mechanical strength, three-dimensional superhydrophobicity, and enhanced chemical stability. The graphene oxide reinforced high-performance three-dimensional superhydrophobic hybrid hydrogel geopolymer composites maintained high compressive strength while achieving a water contact angle of 153 ° and a water absorption rate of only 1.7 %. Remarkably, the geopolymer retains its high hydrophobicity even after 24 hours in an acid-base solution, with a contact angle exceeding 140° and water absorption rates lower than 4 %. [Display omitted] • Synthesis of 3D superhydrophobic geopolymer with good mechanical strength and chemical stability. • PMHS is grafted onto the surface of GO and geopolymer through co-condensation. • The 3D superhydrophobicity stems from GO-PMHS micro-nano hierarchy structure. • GO effectively counteracts hydrophobicity induced strength reduction via nano reinforcement and pore filling. [ABSTRACT FROM AUTHOR]

Cyclic freezing and thawing can irreversibly damage the microstructure of geopolymer materials in the monsoon freezing zone, thereby deteriorating their load-bearing capacity. In this study, polypropylene fibres were added in geopolymer cemented aeolian sand to carry out research on the mechanical behaviour and fine-structure damage evolution characteristics of geopolymer during its life cycle under different conditions. The results show that: with the increase of fibre doping, the bias stress value and cohesion value of the specimen are first increased and then decreased, the elastic modulus and the weakening modulus show the trend of first decreased and then increased. When the fibre content is 5 ‰, the fibre is evenly dispersed in the sample, and the local best strengthening effect is achieved. When the fibre content is 7 ‰, the fibre bunching phenomenon appears in the sample. With the increase in the number of freeze-thaw cycles, the bias stress value, cohesion value, and modulus of elasticity of the specimens decreased as a whole, and the phenomenon of increasing the weakening modulus and the angle of internal friction occurred. After the same number of freeze-thaw cycles, the performance degradation of the specimens doped with appropriate amount of fibre was lower than that of the specimens without fibre. The deterioration of macroscopic mechanical properties is essentially caused by the superposition and evolution of microscopic mechanical effects. During the freeze-thaw cycle, the microcracks and pores increase significantly in both number and size, and the incorporation of fibres strengthens the connection of the matrix inside the specimen, optimizes the internal spatial structure, and reduces the fatigue damage produced by freeze-thaw on the specimen. The related research results are of great significance for assessing the safety of in-service geopolymer structures in cold regions, and provide a reference basis for optimizing the frost resistance of pipe trench backfill geopolymer in seasonally frozen areas. • Expand the application range of geopolymer. • Fibers improve the freeze-thaw damage resistance of geopolymers. • SEM was used to reveal the strength deterioration mechanism of geopolymers. • Numerical simulations were used to demonstrate the evolution of the failure form of geopolymers. [ABSTRACT FROM AUTHOR]

Silica fume (SF) is widely used to improve the workability of geopolymers, while its effects on the hydration evolution and microstructural characteristics of geopolymer systems are not well understood. In this study, the involvement mechanism of SF in the fly ash-slag-based geopolymers (FSG) was investigated. An appropriate amount of SF (15 wt%) increases the 7-day compressive strength of FSG to 56.7 MPa by 24.9 % and promotes the hydration of FSG, resulting in the C(N)-A-S-H products with the highest Si/Al and Q3(1Al) contents. The dark rim (outer layer of hydration products) of the slag particles is reduced due to the addition of SF. The introduction of a small amount of soluble Si can accelerate the formation of highly polymerized C-A-S-H gel around the slag, resulting in a delay in the hydration of the internal slag (Q0 structure increases and Ca2+ in the dark rim decreases). When the SF content continues to increase (20 wt%), although it will further promote the hydration of slag and FA, there will also be polymerization and precipitation of N-A-S-H and silicone gel, resulting in a decrease in mechanical properties. This study would provide a thorough and unique comprehension of varying SF contents in the early hydration process and microstructure evolution of FSG. [Display omitted] • Soluble Si accelerates the formation of highly polymerized C-A-S-H gels. • 5 % SF delays the slag hydration (Q0 increases and Ca2+ in the dark rim decreases). • 15 % SF promotes the formation of C(N)-A-S-H with high Si/Al and Q3(1Al) contents. • 20 % SF causes polymerization and precipitation of N-A-S-H and silicone gel. [ABSTRACT FROM AUTHOR]

The construction of a lunar base is deemed a significant move for mankind's exploration into deep space. Geopolymer solidification is considered as an effective technique for regolith to achieve promising mechanical properties, while extreme temperature on the lunar surface could negatively affect the mechanical properties of geopolymer samples. In this study, a new lunar regolith simulant and basalt fiber were used to develop geopolymer samples with various fiber dosages of 0 %, 0.3 %, 0.7 %. These samples were cured at temperature approaching actual lunar surface temperatures at recommended locations (−196 ℃–118 ℃) for 3d, 7d, 14d, and 28d. A range of tests were conducted on geopolymer samples to study the effects of fiber dosage and curing condition, including P-wave, compressive strength, flexural strength, AE, SEM-EDS, FTIR, and XRD. The addition of 0.3 % fiber into the samples results in an increase of tensile cracking, while the addition of 0.7 % fiber induces an increase in shear cracking within the samples. These findings, corroborated by SEM observations, substantiate the mechanism of fiber clustering and bridging. High-temperature curing is beneficial for the geopolymerization, it also results in zeolite products and higher growth rate of N-A-S-H gel while low-temperature causes some degradation. High rates of temperature change can cause thermal stress cracks, which also degrade the geopolymer. With an increase in curing time, the geopolymer samples exhibit a higher quantity of N-A-S-H gel and higher cross-linked C-N-A-S-H gel. ● Geopolymer matrix retains a flexural strength of 6.08 MPa and compressive strength of 48.56 MPa after being cured at lunar temperature. ● Adding 0.3 % of fiber can increase the strength of geopolymer samples by 13.52 % (flexural) and 30.95 % (compressive). ● Fiber can affect the crack pattern inside the geopolymer, the tensile cracks caused by matrix cracking account for 77.88 %, respectively. ● Samples cured at high temperature produce gel faster than samples cured at low temperature. [ABSTRACT FROM AUTHOR]

The present study explores the repurposing of large amounts of phosphoric acid by-products, specifically phosphogypsum (PG), by evaluating its effectiveness as a precursor in acid-activated geopolymer technology. Geopolymers were elaborated using PG and calcined clays, activated with phosphoric acid. The research focused on evaluating the mechanical properties and microstructure of these geopolymers after a 28-day curing period. X-ray diffraction (XRD) analysis revealed the formation of new crystalline phases, including brushite, newberite, and berlinite. Fourier-transform infrared (FTIR) spectroscopy confirmed the presence of P-O and Si-O-Al bonds, indicative of successful geopolymerization. Scanning electron microscopy (SEM) imaging demonstrated a dense, cohesive microstructure in optimized samples. Based on the response surface methodology, the study identified optimal conditions for maximum compressive strength: 28.83 % PG content, 14.39 mol/L phosphoric acid concentration, and a curing temperature of 72.45°C. This optimized formulation produced a dense, cohesive microstructure with a notable compressive strength of 21.46 MPa. The leaching test confirmed that no harmful substances were released from the geopolymer samples. These results suggest that PG can be effectively recycled through geopolymer technology for use in the construction industry. [Display omitted] • Phosphogypsum and red clays serve as precursors in acid-activated geopolymer synthesis. • Optimal mix achieves 21.46 MPa strength with 28.83 % phosphogypsum at 72.45°C curing. • Phosphoric acid activation at 14.39 mol/L concentration yields best mechanical properties. • Toxicity tests confirm geopolymer safety for construction industry applications. [ABSTRACT FROM AUTHOR]

Geopolymer materials exhibit excellent resistance to CO 2 corrosion and low carbon emission characteristics, which are very suitable for cementing in CCUS/CCS wells. However, it is difficult to control its thickening time, which limits its popularization and application. The substitution of NaOH with Na 2 C 2 O 4 and Ca(OH) 2 to activate geopolymers was tried to investigate their influence on thickening time and strength of the geopolymer. The precursors used were fly ash sinker beads and slag (the mass ratio is 8:2). Results indicate that at 75°C, the thickening time of geopolymers activated by NaOH is difficult to extend with retarders, whereas those activated by Na 2 C 2 O 4 +Ca(OH) 2 can be effectively extended using D-Gluconic acid sodium (D-GA) or ethylene diamine tetra methylene phosphonic acid sodium (EDTMPS). Additionally, geopolymers activated by Na 2 C 2 O 4 +Ca(OH) 2 exhibit good strength properties, with compressive strengths of 25.3 MPa for 24 h and 25.6 MPa for 48 h at 75°C. Furthermore, geopolymer curing next to water-bearing rocks showed that geopolymer can also achieve excellent solidification when surrounded by water-bearing rocks, which is favorable for its application under the well cementing construction. • Na 2 C 2 O 4 +Ca(OH) 2 is firstly introduced as activator for geopolymer. • Na 2 C 2 O 4 +Ca(OH) 2 activated geopolymer's thickening time is more easy adjusted. • Na 2 C 2 O 4 +Ca(OH) 2 activated geopolymer's strength is similar with NaOH activated one. • Na 2 C 2 O 4 +Ca(OH) 2 activated geopolymer could solidify well surrounded by water. [ABSTRACT FROM AUTHOR]

Industrial solid waste pollution is one of the current environmental problems that needs to be solved urgently. The construction of geopolymer gel materials using industrial solid wastes as precursors has become a research hotspot for solid waste recycling due to its preparation of excellent properties. Exploration preparation of ternary-based mass polymers (COSGM) from coal gangue powder (CGP), oil shale ash (OSA), and ground granulated blast furnace slag (GGBS) to address this challenge. In an extensive experiment involving forty-eight samples, three ratios of CGP to OSA (2:1, 1:1, 1:2), a liquid-to-binder ratio of 0.45, and GGBS content (15 %, 20 %, 25 %, and 30 %) were explored. Additionally, the impact of Na 2 SiO 3 modulus (0.4, 0.6, 0.8, 1.0 M) and alkali activator content (16 %, 18 %, 20 %, 22 %) on the COSGM's fluidity, setting time, compressive strength, and flexural strength was thoroughly investigated. In addition, microanalytical methods including XRD, FTIR, SEM, and EDS were utilized to reveal the mechanism of their work performance. The results indicated that the COSGM presented a higher strength with the optimal ratio range of COSGM at 30 % of GGBS content, Na 2 SiO 3 modulus at 0.4–0.6 M, and alkali activator content at 20 % and 22 %. Its compressive and flexural strength can reach up to 46.3 MPa and 6.1 MPa respectively, which means it can be employed to replace cement. The factors affecting the working performance of COSGM are in the order of GGBS content> Na 2 SiO 3 modulus>alkali activator content>CGP:OSA. The higher density and quantity of N-A-S-H, C-A-S-H and C-N-A-S-H gels in the COSGM contribute to the increase in the strength of the geopolymer. Therefore, the developed ternary geopolymer has the potential to promote a large-scale utilization of industrial solid wastes. • Proposed a novel ternary CGP-OSA-GGBS geopolymer. • The feasibility of replacing cement with ternary CGP-OSA-GGBS geopolymers is demonstrated. • Both OSA and GGBS play key roles in the properties of COSGM. • The type and density of the gel can reflect the geopolymer strength. [ABSTRACT FROM AUTHOR]

A pivotal limitation in the widespread adoption of geopolymer stems from their notable and substantial drying shrinkage properties, which significantly constrain their potential applications. The complex reaction processes and amorphous gel structures make it difficult to quantitatively calculate the drying shrinkage rate. In this study, alkali-activated slag-metakaolin-based geopolymer was used to develop a method for predicting drying shrinkage. By analyzing the internal relative humidity changes, contact angles on the structure surface at different ratios, and the surface tension of pore solutions, the capillary tensile stress within the structure was calculated. This analysis was combined with measurements of drying shrinkage, elastic modulus, and porosity to establish a predictive method for the drying shrinkage of alkali-activated slag-metakaolin-based geopolymer. The results indicated that as the system's relative humidity decreased, the surface tension of the pore solution increased, the interface contact angle reduced, and the capillary tensile stress, as calculated using the Young-Laplace equation, increased. These changes intensified the microstructural shrinkage and, consequently, increased the geopolymer's overall shrinkage rate. At the same time, the larger the porosity of the geopolymer system, the smaller the elastic modulus, the larger the dry shrinkage rate of the geopolymer. At a porosity of 29.0 %, an elastic modulus of 1.83 GPa, and a capillary tensile stress of 3.6 MPa, the dry shrinkage of the geopolymer is only 0.899 %. By adjusting the porosity and elastic modulus to 38.3 % and 1.60 GPa, respectively, and increasing the capillary tensile stress to 10.84 MPa, the dry shrinkage of the geopolymer reaches a maximum of 1.942 %. The prediction method for geopolymer drying shrinkage, established based on these factors, has a correlation coefficient of 0.97, effectively predicting the trend of geopolymer drying shrinkage rate characteristics. The current study provides a theoretical basis for methods to reduce shrinkage in geopolymers and their application in engineering. • The drying shrinkage performance of Alkali-activated Slag Metakaolin (ASM) based geopolymer was studied. • Drying shrinkage is quantified by capillary pulling force. • Propose a method to predict the drying shrinkage of ASM-based geopolymer under multi-factor conditions. [ABSTRACT FROM AUTHOR]

The abundance of date palm trees in Saudi Arabia generates a sizable quantity of agricultural waste annually, including midribs, fronds, leaves, stems and coir. Date palm waste is either discarded as landfill or burned on local farms; very little of the waste is utilized. This study was conducted in an effort to promote an alternative waste-management option that aims to reduce or eliminate its negative impact and exploit the economic opportunity of recycling the waste into valuable engineering construction products. In this context, date palm ash (DPA) generated from palm tree waste was employed to produce an alternative, more sustainable and green binder material utilizing geopolymer or alkali-activated composites. To achieve these objectives, six metakaolin (MK) based geopolymer mixes were synthesized with DPA replacing 0 %, 10 %, 20 %, 30 %, 40 % and 50 % by weight of MK. The impact of the DPA on the fresh and hardened characteristics of the mortar was comprehensively studied, including setting time, flowability, mechanical properties at various curing ages and conditions, microstructure and thermal performance at elevated temperatures. It was observed that DPA significantly improved the flowability of MK-based geopolymer mixes, and also accelerated the setting time. Also, DPA positively improved the mechanical properties at room temperature and after exposure to 600°C compared to mixes containing 100 % MK. Due to the presence of highly reactive silica and alumina in the source materials, SEM analysis revealed that the addition of DPA to the mortar caused structural alterations in the geopolymer mortar that could be linked to the formation of packed and dense matrix. • Utilizing DPA promotes the production of sustainable geopolymer composites. • DPA enhanced the mechanical properties of the mortar. • DPA significantly improved the flowability and accelerated the setting time. • Incorporation of DPA achieved an improvement in the pore structure of the mortar. [ABSTRACT FROM AUTHOR]

Geopolymer have been considered as a promising alternative for the development of high-ductility and eco-friendly engineered materials. In this study, modified PVA fibers grafted with MWCNTs(PM) are used as additives to investigate their impact on the drying shrinkage, autogenous shrinkage and chemical shrinkage of Engineered Geopolymer Composites(EGC). Additionally, various micro-structure techniques, including X-ray Diffraction(XRD) and Scanning Electron Microscopy(SEM), are employed to examine the morphology and chemical composition of EGC. The experimental findings indicates that PVA fibers and MWCNTs both help to mitigate the drying shrinkage and autogenous shrinkage of the EGC. When the PVA fiber content is 2.0 % and the MWCNT content is 1.0 ‰, the 90-day drying shrinkage and autogenous shrinkage values of the EGC are minimized, reducing by 31.67 % and 34.16 %, respectively, in comparison to the control group. However, the incorporation of MWCNTs increases the chemical shrinkage of the geopolymer matrix, with the chemical shrinkage value reaching its maximum when the MWCNT content is 1.0 ‰. Micro-structural analysis reveals that the inclusion of PM leads to an improvement in the quantity of reaction products without affecting their type. Furthermore, the incorporation of PM refines the overall pore structure, restricts the crack development and enhances the interfacial bonding effect of EGC. Notably, a correction prediction model for drying shrinkage strain and autogenous shrinkage strain, incorporating the influence coefficients of PVA fibers and MWCNTs, is constructed under constant humidity and temperature conditions. This significantly improves the prediction accuracy of drying shrinkage and autogenous shrinkage of EGC. • The utilization of PVA fibers grafted with MWCNTs is an effective way to decrease the shrinkage behaviors of EGC • The MWCNTs also help refine the overall pore structure in the geopolymer matrix. • The prediction models of geopolymer improves the prediction accuracy of the shrinkage models for geopolymers. [ABSTRACT FROM AUTHOR]

Shotcrete mortar is used in various construction works, including repair, tunneling, mining, and slope stabilization, among others. Traditionally, cement is used to produce shotcrete mortars with high viscosity, flowability, and early strength. Geopolymers (GP) have the potential to replace cement in shotcrete mortars, owing to their ability to reduce the material's environmental footprint without compromising performance. This investigation assesses the feasibility of utilizing fly ash and blast furnace slag-based GP mortars produced with dune sand in shotcrete applications while comparing them to cement-based mixtures. The GP and cement-based shotcrete mortars were designed to have similar yield stress values. The evaluated properties included the initial flow, thickness layer, rebound material, rheological properties, setting time, compressive strength, ultrasonic pulse velocity, and pull-off bonding strength. Test results showed direct relationships between the yield stress and initial flow values, as well as between the buildup thickness and plastic viscosity, revealing that GP mortars were suitable for shotcrete applications, specifically those produced with flow values of 18.5 cm or less. GP mixtures produced with higher slag content than fly ash, higher sand content compared to binder, higher SH molarity, and lower solution content achieved higher buildup thickness owing to their higher viscosity. In the second phase, the performance of four mixes with different initial flows was assessed at various pumping flow rates and distances between the wall and machine pipe nozzle. The findings confirmed that these spraying parameters are crucial to improve the shotcrete performance of GP mortar with varying fresh behaviors. • The feasibility of using fly ash-slag blended geopolymer mortars for shotcrete applications was investigated. • Fly ash-slag blended geopolymer shotcrete displayed superior shotcreting properties to cementitious counterparts. • Higher plastic viscosity and lower yield stress in geopolymer shotcrete led to higher buildup thickness and less rebound. • Optimizing flow rate and nozzle-slab distance were critical to improve buildup thickness and rebound. [ABSTRACT FROM AUTHOR]

Rice husk ash (RHA) and Span-40 modified waste rubber particles (WRP) were mixed into geopolymer recycled concrete (GRC) to improve its frost resistance in normal and chlorine environment. The freeze-thaw and static loading test results show that GRC has the best freeze-resistance when 5 %RHA and 10 %WRP are added. The strength loss rate of GRC after 200 freeze-thaw cycles in normal environment and chlorine salt environment is 8.3 % and 8.8 % lower than that of GRC without RHA and modified WRP, respectively. Based on the test results, the material damage model and strength loss model of GRC doped with RHA and modified WRP were established. The failure probability and service life of GRC were predicted. The results showed that the failure probability of GRC mixed with 5 %RHA and 10 %WRP was reduced by more than 10 % compared with that of GRC mixed with no RHA and modified WRP at 200 freeze-thaw cycles under normal environment and chlorine salt environment, and the failure probability decreased with the increase of cycle times. The life prediction results showed that the service life of GRC mixed with 5 %RHA and 10 %WRP increased by 17.9 % and 21.6 %, respectively, compared with that of GRC mixed with no RHA and modified WRP under the freeze-thaw cycle of normal environment and chlorine salt environment. • Use Span-40 to modify waste rubber. • Improved the salt-freeze resistance of geopolymer recycled concrete. • The interaction mechanism of rice husk ash and modified rubber was revealed. • The material damage model and the compressive strength loss model were established. • Predict the service life of geopolymer recycled concrete. [ABSTRACT FROM AUTHOR]

Acid rain corrosion is a critical factor contributing to the increased susceptibility of concrete pavements to cracking and reduced service life, raising significant safety concerns. This research aims to investigate the acid rain corrosion resistance and purification performance of geopolymer recycled pervious concrete (GRPC) with top-bottom interconnected channels under acid rain soaking and spraying simulation tests. The impacts of acid rain exposure on the compressive strength, permeability coefficient, mass loss, neutralization depth of GRPC, and the pH value of percolating acid rainwater were analyzed. The results proved that GRPC exhibited excellent resistance to simulated acid rain with a pH of 4.0. Furthermore, employing a combination of sodium hydroxide and sodium silicate as alkali-activators provided the optimal acid rain corrosion resistance. Additionally, in the early stage of acid rain exposure, acid rain was neutralized by the sodium carbonate formed through efflorescence. While in the middle-later stage, the migrating alkaline substances in GRPC matrix directly neutralized the pH of acid rain. Notably, after 28 days of simulated acid rain spraying, GRPC maintained its ability to purify the acid rain flowing through its channels, successfully raising the pH from 4 to a range between 7 and 8, demonstrating an effective acid rain purification capability. In conclusion, GRPC can transform the efflorescence issue in concrete into an effective means to counteract acid rain corrosion, thereby equipping concrete pavements with the dual advantages of alleviating urban waterlogging and resisting acid rain corrosion. This renders GRPC a promising avenue for both academic research and practical engineering applications. • A comparative analysis was performed between acid rain soaking and spraying simulation tests. • A dedicated acid rain spraying simulation system was designed to replicate realistic on-site acid rain exposure. • After soaking and spraying exposure, changes in compressive strength, permeability and mass of GRPC were negligible. • The acid rain flowing through GRPC was effectively purified, resulting in a percolating rainwater pH between 7 and 8. [ABSTRACT FROM AUTHOR]

A geopolymer paste (GP) synthesised using fly ash, slag, and metakaolin was developed to enhance the heat resistance of industrial by-product-based geopolymers. The GP exhibited a 28-day strength of 60 MPa and maintained at least 80 % of its initial strength and elastic modulus even at temperatures up to 900°C. Subsequently, the GP was blended with aggregates (sands and stones) to produce geopolymer concrete (GPC) with a 28-day strength of 45 MPa. Compressive tests on the GPC after exposure to 100–1000°C revealed that the GPC retained 90 % of its compressive strength up to 500°C, but experienced a 60 % loss in elastic modulus and a fourfold increase in peak strain after 300°C exposure. Stress-strain relation, physical properties, and microstructure were analysed to explore the property evolution mechanisms after heat exposure. The combined effect of geopolymer shrinkage (100–780°C), stone expansion (> 200°C), and stone decomposition (> 500°C) was the primary factor for the GPC property decline. At 800°C, a complete loss of mechanical properties in both the stone and interface transition zones led to significant deterioration of the GPC. These findings offer valuable insights for developing durable construction materials suitable for high-temperature applications, ensuring structural integrity and performance under extreme thermal conditions. • Developed geopolymers (60 MPa) retained strength and elastic modulus up to 900°C. • Strengths of concrete had increased below 500°C, but modulus decreased after 300°C. • Elevated temperatures significantly changed stress-strain curve characteristics. • Severe concrete deterioration resulted from expansion and decomposition of stone. [ABSTRACT FROM AUTHOR]

The vanadium-bearing shale tailing (VST) with large reserves pollutes the environment and urgently needs to be utilized as a resource. Due to its main component being silica, VST has great potential as a raw material for geopolymer. Therefore, this study uses VST to prepare the solid alkali activator (SAA) by thermochemical methods. Analysis show that the temperature and NaOH dosage of thermochemical reaction significantly affect the alkaline activation effect of SAA. Temperature affects the silicate content and the amount of NaOH affects the soluble silicate content in SAA. When the reaction temperature is high (such as above 900 ℃) and the amount of sodium hydroxide is low (such as the mass ratio of sodium hydroxide to VST is 0.6), quartz almost transforms into silicates, but the silicates have a stable cyclic chemical structure and are difficult to dissolve during the geopolymerization reaction. When the reaction temperature is low (such as less than 700 ℃) and the amount of sodium hydroxide is high (such as the mass ratio of sodium hydroxide to VST is 0.9), quartz in VST is difficult to fully convert into silicates, there are unreacted quartz and sodium hydroxide in SAA, and SAA has poor alkaline activation performance. The optimal synthesis process conditions for SAA are as follows: synthesis temperature is 900 °C and the mass ratio of sodium hydroxide to VST is 0.95. The main silicate components of SAA are Na 2 SiO 3 and Na 15.6 Ca 3.8 Si 12 O 36. During the synthesis of one-part geopolymer (OPG), Na 2 SiO 3 dissolution generates a strong alkaline reaction environment and provides active silicon-oxygen tetrahedron monomers or oligomers, Na 15.6 Ca 3.8 Si 12 O 36 is bonded with geopolymer gel structure by stable cyclic silicate structure, which makes OPG have a compact integrated structure. When the mass ratio of SAA to MK is 1:1.3, the 7-day compressive strength of the prepared OPG is about 49 MPa, SAA has the potential as a substitute for commercial sodium silicate to prepare geopolymers. [Display omitted] • Clarifying that reaction temperature and alkali dosage significantly affect the performance of solid alkali activator. • Using vanadium-bearing shale tailing to synthesize solid alkali activator with excellent performance. • Revealing that the stable cyclic silicate structure is directly involved in the formation of geopolymer gel structure. [ABSTRACT FROM AUTHOR]

The influence of pure calcium carbonate (CaCO 3) on the alkali-activation kinetics, microstructure, and compressive strength of sodium metasilicate-activated metakaolin (MK) geopolymer cements was investigated herein. Experimental results showed that replacing 10–50 % of MK with ground CaCO 3 particles delayed the acceleration stage of alkali-activation regardless of replacement amount. However, 10 % CaCO 3 replacement increased the overall degree of reaction and yielded pastes with similar 14- and 28-day compressive strengths compared to the experimental control with no CaCO 3 addition. In comparison, 50 % CaCO 3 replacement led to a lower overall degree of reaction and lower compressive strengths through 28 days of curing. Experimental evidence substantiates that N-A-S-H gel forms in samples containing 0 % and 10 % CaCO 3 , while N-(C)-A-S-H gel and/or C-(N)-A-S-H are also present in the binding matrix near CaCO 3 particles in samples with higher CaCO 3 contents (i.e. , 30 % and 50 %). While the CaCO 3 particles were primarily composed of calcite, vaterite, a less stable form of CaCO 3 , was also evident in the samples containing 30 % and 50 %, suggesting that the CaCO 3 particles were moderately reactive during the alkali-activation. This study isolates the effects of pure CaCO 3 in sodium metasilicate-activated geopolymer systems, providing novel insights into its impact on geopolymerization kinetics and microstructural development for optimizing sustainable geopolymer cement formulations. • Calcium carbonate was incorporated in the metakaolin-based geopolymer cements. • 10 % replacement of metakaolin by CaCO 3 improved the overall degree of geopolymerization. • Vaterite was found to precipitate in the samples with 30 % and 50 % replacement level. • CaCO 3 was reactive during alkali-activation, evidenced by N-(C)-A-S-H and (C)-N-A-S-H gel formation. [ABSTRACT FROM AUTHOR]

With certain formulations, Geopolymer (GP) exhibits intumescence (expansion upon heating), forming a porous structure, providing a thermal barrier effect. However, there have been no studies demonstrating the mechanism of the intumescence and the corresponding structural changes before and after heating. In this study, GPs are made based on metakaolin and silica fume. Then, GP with two aluminum-to-silicon molar ratio (Al/Si = 0/0.55) are investigated under heating conditions. The GP (Al/Si = 0) exhibits initial softening followed by hardening of the structure (from 50°C to 175°C), with intumescence observed within this temperature range. In contrast, the GP (Al/Si = 0.55) does not exhibit softening or expansion. Solid-state Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) analysis of 29Si and 1H were then conducted on both GPs at ambient temperature and after heating at 105/200/300°C for 24 h. Results show that GP softening is due to the transition from Si(Q2) to Si(Q3) silicate units, while hardening is caused by the transition from Si(Q3) to Si(Q4) silicate units. Additionally, the proton mobility of GP is higher for lower Al/Si ratios after curing. During heating, the mobility decreases for both GPs due to the removal of free water and the breaking of hydrogen bonds. Our results extend the knowledge of GP intumescence mechanism and call attention to low Al/Si GP for fire/high temperature application. • As the temperature rises, intumescence is observed in GP (Al/Si=0). • The conversion from Q2 to Q3,4 induces material softening. • The mobility of protons is high in GP (Al/Si=0), but low in GP (Al/Si=1.5). [ABSTRACT FROM AUTHOR]

Frost heave in cold regions requires urgent measures to improve the mechanical properties of soils. However, harsh climatic and environmental conditions escalate the costs of engineering construction and operation. Therefore, it is imperative to enhance the sustainability of engineering designs. In this study, different sisal fibre contents, specific proportions of metakaolin, and alkaline activators were added to silty clay to alleviate frost heave, as well improve the mechanical properties of soils. Firstly, the unconfined compressive strength (UCS) and shear strength of soil samples containing varying sisal fibre geopolymer were tested before and after freeze-thaw cycles (FTCs). To analyse the effect of FTCs on thermal conductivity, the thermal conductivity of fibre-geopolymer solidified soil (FGSS) with different sisal fibre contents was evaluated. Subsequently, X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry were conducted on the samples before and after the FTCs. Then, the variations in soil temperature, volumetric unfrozen water content, heat flux, vertical deformation, and soil pressure during the FTCs were analyzed. The results indicated the following: 1) Sisal fibre and geopolymer improved the mechanical performance and adhesion among soil particles of FGSS after the FTCs. 2) The thermal conductivities of FGSS showed a tendency of initially increasing, then decreasing, and finally increasing as the sisal fibre content increased. 3) The addition of sisal fibres did not cause new chemical reactions but inhibited the reaction between metakaolin and the alkaline activator. 4) The combination of sisal fibre and geopolymer effectively mitigated frost heave. 5) Sisal fibre incorporation reduces CO 2 emission index and economic efficiency index. Therefore, FGSS is proposed to provide a green and effective approach for addressing geotechnical engineering issues in cold regions. • Hydro-thermal-mechanical properties of FGSS are investigated. • Sisal fibre and geopolymer improve the mechanical properties of FGSS exposed to FTCs. • 0.3 wt% sisal fibre can mitigate the frost heave of GSS by 68.51 %. • Sisal fibre effectively reduces the CIco 2 of GSS during the FTCs. [ABSTRACT FROM AUTHOR]

This study investigates the acid corrosion resistance of an alkaline-activated material (AAM) composed of ground granulated blast-furnace slag (GGBFS) and water treatment residue (WTR) as precursors. WTR, a byproduct of the drinking water treatment process rich in aluminium and silicon, proves to be a suitable precursor for AAM after cost-effective pre-treatment involving calcination and grinding. As its low-Ca content and aluminosilicate nature of the treated WTR, the AAM incorporating WTR exhibits significant potential for improving acid resistance. This is attributed to the formation of less acid-reactive N-A-S-H gels than C-A-S-H gels in high-Ca AAMs, indicating its applicability in concrete sewage pipes where microbiologically generated acid corrosion is prevalent. In the paper, a comprehensive analysis, including mechanical performance, ion leaching behaviour, and microstructural characteristics, was conducted on mortar samples containing varying WTR/GGBFS ratios before and after exposure to sulfuric acid. Incorporating WTR up to 40 % effectively reduced acid-induced strength loss compared to neat-GGBFS AAM. The obtained results reveal that high-Ca AAMs facilitate gypsum formation during acid attack, leading to mechanical degradation. The inclusion of WTR induces a Si-rich transition layer between the corroded and intact matrix, mitigating sulfate diffusion. The release of aluminium from WTR promotes secondary precipitation of aluminosilicate, beneficially increasing the thickness of the transition layer. This thicker transition layer in the higher WTR samples is advantageous in reducing the likelihood of cracks and reducing the sulfate transportation into the intact matrix. [Display omitted] • Alkaline-activated material from water treatment waste showed great acid resistance • Less amount of harmful gypsum was formed in the samples with higher WTR content • A Si-rich transition layer was found to prevent sulfate transportation • Involving WTR could increase the thickness of the transition layer [ABSTRACT FROM AUTHOR]

Durability is crucial for materials development in construction and transportation industries. This paper investigates the mechanical strength and durability of alkali-activated granulated blast-furnace slag (GBFS) and modified geopolymer with varying contents of metakaolin (MK) and functionalized beta-silicon carbide whiskers (β-SiC w). Functionalized β-SiC w were prepared utilizing successful chemical methods. Macroscopic experiments tested mechanical strength, bulk density loss rate after exposure to severe conditions, and durability through sulfate wet-dry and freeze-thaw cycles. Microscopic experiments, including SEM-EDS, XRD, TG-DSC, and BET, revealed the microstructure mechanisms. Results showed that MK and functionalized β-SiC w improved mechanical strength by creating a more reactive phase and denser pore structures. Reduced bulk density loss rates and enhanced durability were observed, with a 71.9 % mass loss and 63.4 % compressive strength loss reduction after 50 freeze-thaw cycles, and a 12.2 % decrease in compressive strength loss after 56 days of sulfate wet-dry cycles, compared to control groups. The modified geopolymer had higher tortuosity and finer porosity due to more gel formation and nucleation sites, and functionalized β-SiC w effectively bridged micro-cracks and micro-pores. • Mechanical strength and durability of functionalized β-SiC w and MK modified geopolymer were investigated. • The mechanism between functionalized β-SiC w and GBFS-MK geopolymer were revealed. • Hydroxylated β-SiC w effectively compensated the damages influence of freeze-thaw and sulfate corrosion. • Functionalized β-SiC w and MK improved gels products. [ABSTRACT FROM AUTHOR]

The study investigates the impact of the fibres' hornification, subjected to 5 wetting/drying cycles, on the physical and mechanical properties of short hemp fibre-reinforced fly ash-based geopolymer mortars at distinct ages (1, 2.5 and 18 months) cured under laboratory conditions and additionally of the mortars underwent the accelerated ageing of 10 wet/dry cycles. The study reveals that fibres' hornification induced fibrillation and fibres' cleaner surfaces, most likely enhancing fibres' dispersion within the matrix. This phenomenon leads to suppressing the degradation of all tested mortar's properties. Considering the curing under laboratory condition, in the case of the density, the suppression is more pronounced in the long term. After 18 months, the hornificated fibre-reinforced mortar nearly matches the water absorption capacity of the plain mortar. Furthermore, the fibres' hornification contributes to the enhancement in compressive- and flexural strengths of the reinforced mortar at the age of 18 months. In the long term, by increasing the pre-peak segment of the force-displacement curves, the fibres' hornification slightly increases the energy absorption capacity of the raw fibre-reinforced geopolymer mortar. In the case of the mortars' curing under wet/dry cycles, the hornification proves to slightly (10 %) improve the physical (increase in density, decrease in water absorption) and mechanical properties (increase in compressive- and flexural strength, as well as energy absorption capacity) of the fibre-reinforced mortar. Due to the mortars' exposure to the dry cycles (happen at 60 °C), the further geopolymerisation speeds up, which results in the denser matrix, increase in its compressive- and flexural strengths, but a general fibre/matrix bond deteriorates and therefore the fibre-reinforced mortars' energy absorption capacity decreases, when compared to their counterpart tested at the same age but cured under laboratory condition. • Hornification improves initial and long-term properties of raw fibre geopolymer. • Hornification mitigates density decline and decreases water absorption of mortars. • Compressive- and flexural strength improves after fibres hornification. • Fibres hornification led to long-term toughness increase. • Wet/dry cycles do not boost the toughness of the fiber-reinforced geopolymer. [ABSTRACT FROM AUTHOR]

Thermal pretreatment has proven to be an effective method to improve the reactivity of red mud to be valorized as an aluminosilicate precursor for geopolymer production. This approach offers the dual advantage of recovering caustic residue in red mud and encapsulating heavy metal, thus, achieving the transformation of red mud into a cleaner and value-added construction material. However, the inconsistent properties of red mud, including variations in chemical composition, particle size, and amorphous content pose challenges and can lead to instability in geopolymer as well as the effectiveness of thermal pretreatment, limiting the scalability of red mud valorization. Here in this study, thermal pretreatment was employed on five types of red mud from three refineries by calcining each red mud at 800 ○C for 2 h and its effect on the reactivity of each red mud was evaluated by comparing the performance of the resultant geopolymer. The results demonstrated a significant enhancing effect from thermal pretreatment, particularly noticeable at NaOH concentrations of 4 M and 8 M. This again highlighted the potential of thermal pretreatment in the conversion of red mud into construction material. However, amplified disparities between each thermal pretreated-red mud were also observed. To further address the challenges associated with thermal pretreatment variability, the dissolubility of reactive content from each thermal pretreated-red mud under alkali environments was quantified through alkali leaching tests and correlated to the mechanical properties of its resultant geopolymer. A strong negative correlation was observed between the concentration of Si, Al, and Fe from thermal pretreated-red mud and the mechanical properties of its resultant geopolymer. This correlation has the potential to facilitate quality control measures for thermal pretreated-red mud and its derived geopolymer, enabling better process optimization and consistency in geopolymer production. • Alkali leaching tests were conducted on five types of RM before and after TP. • Caustic residue in RM reduces extra alkali needed in activator. • TP enhances the reactivity of RM and contributes to higher geopolymer strength. • TP improves the dissolubility of Si from RM, but significantly reduces that of Al. • The dissolubility of RM is positive to the strength of its resultant geopolymer. [ABSTRACT FROM AUTHOR]

Bricks are one of the most used construction materials worldwide. Conventional bricks are produced by utilizing fertile soil or ordinary Portland cement; both emit greenhouse gases to the environment during production. In an attempt to lessen the brick industry's significant carbon footprint, numerous academicians are working towards the development of innovative and sustainable bricks by utilizing numerous waste materials. This present paper provides an up-to-date review of the development of sustainable and environment-friendly geopolymer brick by utilizing solid industrial waste materials such as fly ash, ground granulated blast furnace slag, red mud, rice husk ash, mine tailings, sugarcane bagasse ash, and municipal solid waste incineration fly ash, respectively. Geopolymer bricks can be produced by the reaction between an aluminosilicate source material and an alkaline solution. The source material can be naturally occurring minerals like kaolinite, clays, etc. or by-product materials such as fly ash, slag, silica fume, metakaolin, rice husk ash, red mud, etc. The sodium and potassium-based alkali material solution can be used as an alkali liquid. Sometimes, the combinations of sodium hydroxide or potassium hydroxide and sodium silicate or potassium silicate solutions or various combinations are used. The selection of raw materials for geopolymer bricks depends on the availability, cost, and type of application. The geopolymer bricks specimen prepared with various waste materials shows excellent mechanical strength (compressive strength, flexural strength) and durability under harsh environments. To manufacture and use bricks from various waste materials on a large scale in a sustainable manner, more research and development are needed. This includes work on standardization, public education about waste reuse and recycling, government policies, etc. [Display omitted] • Utilization of various industrial solid waste for the synthesis of geopolymer brick is discussed. • Geopolymerisation is one of the preferable technologies for producing sustainable environment-friendly bricks. • Factors affecting mechanical and microstructural properties are discussed. • Challenges and future research opportunities are discussed. [ABSTRACT FROM AUTHOR]

This study investigated the development of fly ash geopolymer composites with rice husk, aiming to create sustainable building materials with improved sound absorption, thermal insulation, and hygric properties, while maintaining adequate mechanical strength. Rice husk was incorporated as bio-lightweight aggregate at various volume fractions (40 %-70 %). The results showed that compressive strength decreased with increasing rice husk, and the R40 and R50 mixes remained suitable for non-load-bearing applications (0.83–0.33 MPa). On the contrary, sound absorption increased, with the R50 mix showing the highest performance (noise reduction coefficient of 0.60). Moisture buffer value significantly improved, particularly in the 40 %-60 % mixes classified as "good" by the NORDTEST method. The R50 mix demonstrated the most balanced moisture regulation (MBV of 1.23 g/m².%RH), potentially benefiting indoor air quality and energy efficiency in building applications. Furthermore, thermal conductivity decreased with increasing rice husk content; the R40 and R50 mixes exhibited promising thermal insulation properties (0.230–0.195 W/m∙K). These findings suggest that fly ash geopolymer-rice husk composites are attractive and sustainable building materials for non-load-bearing applications, offering significant advantages in acoustics, moisture control, and thermal performance. • Geopolymer-rice husk composites with enhanced sound absorption, thermal insulation, and hygric properties were made. • The composites are suitable for non-load-bearing applications. • The optimum noise reduction coefficient was 0.60, MBV of 1.23 g/m².%RH, thermal conductivity of 0.195 W/m∙K. [ABSTRACT FROM AUTHOR]

The present investigation studied the use of agro-industrial waste, sugar cane straw ash (SCSA), to partially replace commercial metakaolin (MK) in geopolymers (0 %, 15 %, 30 %, and 45 % percentages of substitution by mass). The study presented solid precursors characterization, microstructural studies of pastes, and compressive strength of mortars assessed between 1 and 90 days of curing at 25 ºC. The chemical composition of MK was mainly based on SiO 2 (54.1 wt%) and Al 2 O 3 (35.9 wt%), and SCSA was mainly composed of SiO 2 (58.6 wt%). Microstructural studies of pastes showed that occurred a formation of N-A-S-H amorphous reaction products and no crystalline phases were formed; SCSA contributed to the formation of geopolymer reaction products as a secondary role to the main reaction of MK; the presence of SCSA slightly increased the porosity and did not excessively modify the pore distribution; and the pastes with SCSA presented a heterogeneous microstructure. The compressive strength of mortars reached values over 50 MPa after 90 days of curing. Therefore, SCSA was a sustainable replacement for MK in producing geopolymers. • Sugar cane straw ash (SCSA) replaced partially metakaolin (MK) in geopolymers. • SCSA content assessed in geopolymers was until 45 wt%. • SCSA presented a secondary role in the geopolymer reaction according to microstructural studies. • The presence of SCSA contributed positively to the compressive strength of geopolymer samples. • SCSA could be a more sustainable option to replace partially MK in geopolymers based on this study. [ABSTRACT FROM AUTHOR]

Coal gasification slag (CGS) is an industrial solid waste produced during coal gasification, and it is mostly deposited on the land at present, resulting in serious environmental pollution. In order to promote its resource utilization, geopolymer was synthesized from CGS in this study. The influence of important factors containing the water-solid ratio, alkali activator dosage, activator modulus and curing temperature on the mechanical properties and microstructure of geopolymers were investigated. Micromorphology, chemical composition, mineralogy and chemical bonding of the geopolymer were assessed by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), respectively. Results indicate that the compressive strength of geopolymer can be improved by reducing the amount of initial water. The optimal mechanical properties of geopolymer are obtained when the alkali activator dosage is 25 % and the activator modulus is 1. The moderate temperature (e.g. 60 °C) is the most favorable to the compressive strength development of geopolymer. Under these optimal conditions, the 90 days compressive strength of the CGS-based geopolymer (CGSG) can reach 58.3 MPa. The Si/Al molar ratio of the geopolymer gels is between 2.0 and 3.1, and the Al/Na molar ratio is around 1.0. These results can provide a reference for recycling of the CGS and production of eco-friendly building materials. • CGSG with high compressive strength was successfully synthesized. • The mechanical properties of CGSG are better when the Si/Al molar ratio of geopolymer gel is high. • A moderate temperature of 60 ℃ is the most favorable for the development of compressive strength of CGSG. [ABSTRACT FROM AUTHOR]

To address the slow hardening and poor performance of low-calcium fly ash (FA) geopolymers at ambient temperatures, this study investigated the effects of silica fume (SF), ordinary Portland cement (OPC) content, and curing regimes on the compressive strength, capillary water absorption, and drying shrinkage of fly ash-based geopolymer mortar (FA-GPM). Microstructural analysis was used to examine the evolution of the microstructure and hydration products. Additionally, Nuclear Magnetic Resonance (NMR) testing analyzed the effects on pore size distribution and porosity of the geopolymer mortar (GPM). The results showed that GPM with a 30 % replacement of SF and OPC achieved the highest 28-day compressive strength of 50.52 MPa, a 78.39 % increase compared to the specimen with 0 % replacement. Among the curing regimes, steam curing at 60°C resulted in the highest compressive strength. It was also confirmed that 12-hour carbonation curing benefits compressive strength development. However, excessively high-temperature steam curing and prolonged carbonation curing may damage the GPM matrix, adversely affecting performance. NMR results showed that adding OPC and SF reduced the number of pores in the mortar, gradually transforming harmful pores into harmless ones, resulting in a denser structure. Microstructural analysis revealed that adding OPC and SF promoted the formation of sodium-alumino-silicate-hydrate (N-A-S-H) and calcium-alumino-silicate-hydrate (C-(A)-S-H) gels, with C-(A)-S-H significantly impacting the strength and pore structure of FA-GPM. Notably, carbonation curing formed more strength-contributing gels, with the carbonates combining with the gels to form a binding phase that retains the original structure. The curing regime influences GPM performance by altering the quantity of gel products. This study highlights the benefits of adding SF and OPC to FA-GPM and identifies low-carbon, environmentally friendly curing regimes, providing new perspectives for research and large-scale applications in FA-based geopolymers. • The addition of OPC and SF significantly increased the compressive strength of the GPM. • In binder ratios, the mixture with the best strength also has the best shrinkage and capillary water absorption. • Reasonable carbonation curing can well improve the capillary water absorption, shrinkage and pore structure of GPM. • Microanalysis showed that the gels were mainly C-(A)-S-H and N-A-S-H. The C-(A)-S-H gel had a large effect on the properties. • LF NMR analyses showed that both binder ratios and curing conditions had a large effect on the pore structure. [ABSTRACT FROM AUTHOR]

This study investigates the fresh-state properties and the hardened-state physical and mechanical properties of a total of 64 alkali-activated mortars incorporating different wastes as binders, such as fly ash (FA), recycled concrete (RC), recycled brick (RB), and recycled tile (RT). These waste materials were activated using sodium hydroxide (NaOH) and sodium silicate (Na 2 SiO 3). Linear regression analysis was employed to evaluate the impact and significance of Na 2 O concentration (9 % or 15 %), modulus of silica (0.5 or 1), curing time in the oven (24 or 48 h), and temperature (50 °C or 70 °C) on the properties of the mortars. The results, analysed using ANOVA, indicate that all properties were affected by these parameters, except for the initial curing time in the oven for mortars made with construction and demolition waste (CDW), which showed no significant differences between periods of 24 and 48 h. Compared to mortars produced with RC, the contribution of these parameters to mechanical properties was more prominent in the mixes with RT and RB. The highest compressive strength at 28 days, for the mortars with CDW binders, was obtained by incorporating RT with 12 % of Na 2 O, modulus of silica of 1 and 70 °C for 48 h of initial curing, reaching 12.5 MPa. This value is 2.1 times higher than the strength obtained in mixes with RB or RC. The results also show that the performance of the mortars is highly related to the reactivity of the waste material (mortars with RT performed better) and prove that each raw material has its own optimum criterion. • Several alkali-activated mortars (64 mixes) incorporating different wastes as binders were analysed. • The impact and significance of four parameters on the properties of the alkali-activated mortars were evaluated. • All properties were affected significantly by these parameters, except for the initial curing time in the oven. • The contribution of these parameters to the mechanical properties was particularly significant in the mortars with RT and RB. • The statistical analysis allow to verify that each raw material has its own optimum criterion. [ABSTRACT FROM AUTHOR]

A critical part of civil engineering infrastructure works is to develop innovative construction materials for a low-carbon future development. This study delved into the feasibility of using metakaolin (MK) as a low-carbon precursor for one-part and two-part geopolymer stabilization of recycled demolition wastes. In this research, the effects of MK precursor were evaluated in combination with construction and demolition (C&D) waste aggregates such as crushed brick (CB), reclaimed asphalt (RAP) and recycled concrete (RCA) using one-part and two-part geopolymer activation. Various geotechnical tests were performed including compaction tests, repeated triaxial loading tests (RLT), unconfined compressive strength tests (UCS) and microstructural analysis. Results from this study indicated significant strength development of MK mixtures for both one-part and two-part geopolymer options. Furthermore, one-part geopolymer also showed better activation than two-part geopolymer under 7 days and 20℃ curing condition. Additionally, 30 % MK mixtures were optimal for road construction applications based on the obtained results. At 28 days or 40 ℃, MK mixtures performed best with RCA and CB as main aggregates, showing strength improvement of up to 250 % compared to 7 days and 20 ℃ curing condition. Resilient modulus (M r) results indicated that the optimal mixtures experienced good resilient behavior with average M r values ranging from 150 MPa to 200 MPa. Overall, MK precursor was found to be a suitable material for stabilizing demolition aggregates using geopolymer under various curing conditions. • A low-carbon metakaolin precursor for the stabilization of demolition wastes. • One-part and two-part geopolymer activation of demolition wastes. • Evaluation of unconfined compressive strength at different precursor dosages and curing conditions. • Excellent strength development for pavement applications. [ABSTRACT FROM AUTHOR]

A significant challenge in developing suitable advanced materials in the construction sector is urgent face to the natural disasters affecting our infrastructure and endanger the world population. At this stage, geopolymers renowned as a green and low-carbon material has received considerable attention. Here, novel properties are revealed for Na-based and K-based metakaolin geopolymer paste reinforced by carbon nanotubes with various dosage, exposed to high temperatures. Results show that adding 1.08 wt% of CNT makes the geopolymer matrix thermally stable and resistant up to 1327 °C. It comes out that geopolymer nanostructure with low CNT concentration became tough to shear deformation along (001) plane up to 1127 °C and is easier to shear along (100) plane for highest CNT content. Calculations predict that low CNT dosage double the ductility of Na-based and K-based geopolymer matrix at room temperature. Heating up to 1327 °C enhances the stiffness of both nanostructures. The micro-hardness doubles at 800 °C for Na-based rather than K-based geopolymer matrix when adding low CNT dosage. • 1.08 wt% of CNT makes the geopolymer matrix thermally stable and resistant up to 1327°C. • At low CNT concentration, geopolymer become tough to shear deformation along (001) plane up to 1127°C. •. Heating up to 1327°C enhances the stiffness of Na-based and K-based geopolymer matrix. • 1.08 wt% of CNT dosage double the ductility of geopolymer nanostructure. • The micro-hardness doubles at 800°C for Na-based rather than k-based geopolymer matrix at low CNT dosage. [ABSTRACT FROM AUTHOR]

The solid waste treatment problem generated in the process of coal mining has always been an important factor restricting safe and environmentally friendly production, and the coal slurry from the coal mine road surface is a new type of mine solid waste, so it is of great significance to treat and efficiently utilize the coal slurry. Currently, a common method of solid waste utilization is to add modifying reagents to prepare functional materials. Select coal slurry, slag powder and fly ash as raw materials, and sodium sulfate and sodium hydroxide were used as alkali exciters to prepare coal slurry based geopolymer pavement material (CSGPM). Response surface methodology was used to establish regression equations between the design optimization objectives (coagulation time, compressive strength) and the variables (mass fraction, mass ratio of slag powder to fly ash, mass ratio of sodium sulfate to sodium hydroxide). The effects of two-by-two interactions of the factors on the optimization objective were explored, and the use of different raw materials was obtained. Under the optimal proportioning parameters, the coagulation time of CSGPM was 33 min and the compressive strength of 24 h of curing was 11.20 MPa. In addition, the generation mechanism of AFt and C-S-H gel substances inside the specimen was explained with the help of microscopic scanning. CSGPM showed good mechanical properties in both load-bearing numerical simulations and acoustic emission tests. Numerical simulation was used to establish the relationship between the design objective of the roadbed (maximum subsidence of the roadbed after bearing) and the design variable (thickness of CSGPM paving). Comparative analyses yielded an optimal subgrade surface layer design thickness of 5 cm, with a maximum subsidence of 0.0033 m after bearing vehicles. Synchronization of roadbed material and concrete damage in combined specimen acoustic emission tests with uniform load transfer. The final coal mine pavement was successfully paved and the total cost of CSGPMD is 63.2 per cent of C30 concrete. Those results are important for the preparation of new pavement functional materials. [Display omitted] • This research realizes the efficient synergistic use of coal slurry, slag powder and fly ash, and reduces environmental pollution. • Determined the mixing ratios of coal slurry, slag powder, fly ash and alkali exciters. • Determined the maintenance time and laying thickness of the CSGPM. • The engineering application of CSGPM was realized and the total cost of CSGPM was 63.2% of that of C30 concrete. [ABSTRACT FROM AUTHOR]

In this study, the effects of fly ash and granulated blast furnace slag based geopolymer on the mechanical properties of high plasticity clayey soils were investigated. For this purpose, experimental studies were carried out using the Taguchi Method. The Taguchi L 16 orthogonal array was used with various amounts of class F fly ash (12 %, 16 %, 20 %, and 24 %), granulated blast furnace slag (8 %, 10 %, 12 %, and 14 %), and alkaline hydroxide solution NaOH molarity (6, 8, 10, and 12). After 7 and 28 days of curing, unconfined compressive strength (UCS) and California bearing ratio (CBR) were carried out. Permeability test was carried out as well after 28 days of curing. The effects of the variables on the experimental results were determined using S/N and variance analyses (ANOVA). The microstructure and phase composition of geopolymer samples were identified via scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The findings indicate that the strength of geopolymer-stabilized soil is significantly affected by the stabilizer content, fly ash–slag ratio, and molarity of alkaline activator (M). The optimal mix proportions for geopolymer-stabilized high plasticity clayey soil were found to be as follow: 38 % geopolymer content (24 % fly ash, 14 % slag) and an alkaline activator content of 25.75 % with a molarity of 12 M. This study concluded that fly ash and granulated blast furnace slag based geopolymer can serve as a feasible alternative material to cement, being sustainable and applicable. It could be utilized to enhance the strength characteristics of high-plasticity clay soil, while simultaneously, reducing permeability. • The Taguchi methodology was applied for optimization of geopolymer. • Utilizing FA-GBFS contributes to environmental conservation. • An increase in NaOH concentration leads to an improvement in geopolymerization. • Significant results in UCS, permeability and CBR have been achieved. [ABSTRACT FROM AUTHOR]

The expansion of biomass power stations, while advancing carbon neutrality, generates abundant biomass ash waste whose disposal is a challenge. This study uses crop biomass ash (CBA) waste from a power plant to produce geopolymers. Geopolymers are an alternative for reducing CO 2 emissions and resource extraction in construction. This paper studies geopolymers made with raw and alkali-fused CBA. A sodium silicate activator with varying [Na+] and SiO 2 /Na 2 O ratios is tested to optimise geopolymerisation. A low fusion temperature (600°C) is used to preserve the environmental credentials of the geopolymers. The geopolymers made with (only) raw CBA have extremely low carbon emissions and environmental impact; they attained the lowest strengths (7.46 and 2.99 MPa-compressive and flexural respectively), a strength range suitable for most construction applications unless higher strength is required for load bearing purposes. Partly replacing the raw ash with slag raised their strength to over 25 MPa and 7 MPa-compressive and flexural respectively. The slag released active Si4+, Al3+and Ca2+ that participate in the polymerization reaction, forming cements that enhanced strength. Alkali-fusing the ash, even at low temperatures (600°C), enhances reactivity; it breaks down the silicates comprising the ash, providing active radicals that polymerise and form cementing gels that increase strength: the geopolymer made with (only) alkali-fused ash achieved high strengths of 39.35 and 10.74 MPa-compressive and flexural respectively. The geopolymers made with alkali-fused ash and slag consistently show outstanding performance (42–44 MPa compressive strength), and the slag stabilized the system against fluctuations in activator composition. The geopolymers have vitreous structures of cementing gels with high Si4+ and Na+ contents, consistent with an alkaline, silico-aluminate hydrate gel (N-(A)-S-H) which is a typical product of polymerisation. The FTIR results show ample Si-O-Si(Al) bonds in the geopolymer made with alkali-fused CBA. The presence of slag significantly increased the absorption intensity of these bonds, indicating the presence of more abundant C(N)-A-S-H which improved mechanical properties. Incorporating slag vitrifies the geopolymer structure significantly more than alkali-fusing the ash. However, there is no direct proportionality between increasing vitreousness and escalating strength as the crystalline geopolymer (made with alkali-fused CBA only) is nearly as strong as the vitreous, CBA-GGBS geopolymer (39 vs 44 MPa). • A Crop Biomass Ash (CBA) from a power plant, with high Si and Al contents is used as precursor. • Alkali fusion in enhances the reactivity of inert silicate waste for geopolymer production. • A geopolymer with a compressive strength of 29.83 MPa was produced using raw CBA and slag (GGBS). • Alkali-fusing CBA increased strength by 55.78 %, reaching 46.47 MPa. [ABSTRACT FROM AUTHOR]

Geopolymeric matrices allow for the incorporation of a wide variety of waste materials. Therefore, this study aimed to evaluate ternary mixtures composed of metakaolin, water treatment plant sludge (WTPS), and porcelain tile polishing residue (PPR). Firstly, the chemical and physical properties of the materials were investigated using scanning electron microscopy (SEM) and thermogravimetric analysis (TG). Afterwards, the geopolymeric pastes were assessed by rotational rheometry, compressive strength, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analysis. Estimations of the geopolymer energy embodied (EE) and carbon equivalent emissions (ECO 2-eq) were also calculated. The results showed that yield stress increased progressively with fresh WTPS and, to a lesser extent, calcined WTPS due to the kaolinite content. The reduction in viscosity in the formulations suggested lower reactivity, impacting the geopolymerization reactions. FTIR and XRD results align with calorimetric results, revealing minimal changes and reduction in geopolymerization with high metakaolin substitution. The compressive strength was maintained, even with only 35 % MK, possibly attributed to physical effects compensating for the lower reactivity of the residues. The reductions in ECO 2-eq and EE were not significant due to the high environmental burden of the activators. A cost reduction of ∼16 % was achieved by replacing 65 % metakaolin. Finally, more eco-efficient geopolymer cements were produced, with only 35 % MK and resistance similar to the control mixture. [Display omitted] • 65 % of metakaolin was replaced by waste. • Compressive strength greater than 80 MPa, with only 35 % MK. • 30 % calcined WTPS + 15 % PPR resulted in 90 MPa compressive strength. • Replacing 65 % of MK with waste reduced costs by ∼16 %. [ABSTRACT FROM AUTHOR]

Geopolymer materials offer environmental benefits and strong mechanical properties but face limitations such as efflorescence, shrinkage, thermal stability and poor mechanical performance at high temperatures. This study introduces a novel solution using silane-functionalized graphene oxide nanocomposites (GO-APTS) to address these challenges. Experiments on metakaolin-based geopolymers demonstrate that incorporating GO-APTS improves dispersion, enhances mechanical strength, refines pore structures, and boosts resilience to high temperatures while reducing shrinkage and efflorescence, without compromising the workability of the mixes. Although the structural integrity of the material at nanoscale degrades beyond certain temperatures, the overall thermal resistance is significantly increased, with treated geopolymers displaying a ∼6 % improvement in porosity, ∼20 % higher residual compressive strength and ∼15 % reduction in shrinkage compared to control samples after exposure to heat. Our work reveals the promising potential of silanized graphene oxide nanocomposites in crafting cementitious materials suitable for high-temperature applications, paving the way for their broader use in innovative construction and industry solutions. • GO-APTS significantly enhance mechanical strength and thermal properties of geopolymer. • GO-APTS reduces shrinkage and efflorescence in geopolymer. • APTS delays deterioration of GO up to approximately 620 °C – compared to 580 °C for pure GO. • Formation of new geopolymer reaction products at elevated temperatures are observed. • Simultaneously, structural deterioration and nanoscale degradation are evident. [ABSTRACT FROM AUTHOR]

The combined need to propose new solutions for the structural reinforcement of existing buildings and for the reduction of CO 2 emissions is leading to the development of more sustainable composite materials, such as those based on alkali-activated mortars (AAM). In this study, different formulations of AAM, based on metakaolin or fly ash, have been evaluated as possible matrices for Textile Reinforced Mortar (TRM) systems. Two different bidirectional textiles, made of AR glass or basalt fibers, were used as internal reinforcement. The physical-mechanical properties of TRM systems based on AAM were evaluated and compared with those of commercial systems with cementitious or lime-based matrices. Direct tensile tests on TRM coupons and shear bond tests on clay brick substrates were carried out. Then, their energy and environmental-related performance have been compared. Results showed that alkali-activated matrices can be very promising and eco-friendly alternative solutions to traditional mortars in TRM systems. • Development of alkali-activated mortars (AAMs), to be used as inorganic matrices for Textile Reinforced Mortar (TRM) systems. • Physical-mechanical characterization of TRM composites based on AAMs and comparison of performances with commercial TRM systems. • Evaluation of the Environmental and Energy performances, in relation to the obtained mechanical performances, of different TRM systems. [ABSTRACT FROM AUTHOR]

Even though the demand for utilizing geopolymers is growing, the need for current standard guidelines to regulate compliance to address the complexity of the mix design could be one of the major hurdles of utilizing geopolymers vastly in construction. There is no straightforward standard that addresses the complexity of the mix design of geopolymers. Thus, this work addresses main factors affecting the compressive strength of slag based geopolymers and provide a tool for predicting it. This article includes experimental work to evaluate the properties of slag-based geopolymer binders and the development of a model using Artificial Neural Network (ANN) algorithms for predicting the performance of these slag-based geopolymer binders. In this paper, we have utilized and developed ANN models for optimizing slag-based geopolymer mixes based on precursor materials' physiochemical properties and activation solutions constituents that can enhance performance compressive strength prediction in construction applications. • A high-accuracy DOE model was developed and used to characterize the Geopolymeric paste. • A developed ANN model was superior in forecasting the compressive strength of AAS systems. • The choice of the alkali activator has minimal impact on the compressive strength. • The optimal water-to-slag ratio is approximately 0.28. • The optimal alkali oxide concentration is 6 %. [ABSTRACT FROM AUTHOR]

Researchers recently have focused on geopolymer concrete as it has several advantages compared to traditional Portland cement, such as lower carbon footprint, high early strength, chemical resistance and long-lasting structural performance. This paper designed 192 pull-out specimens to investigate the influence of factors on the bond-slip behavior between geopolymer and steel bar such as curing condition (ambient and 80 °C for 7 hours), longitudinal rib angle, the position of longitudinal bar, bar diameter (12 mm and 24 mm), stirrup usage (with and without stirrup) and bond length (2d and 4d). The maximum bond strength, bond failure modes, and bond stress-slip relations were discussed. The test results showed that the longitudinal rib angle, and the position of rebar play a vital role in determining the bond strength as well as the bar diameter. In comparison with the specimens without the stirrup, the bond performance of specimens with stirrup increased more significantly, and this phenomenon became even more pronounced as the bar diameter increased. The stirrup usage in samples under ambient and heat cure increased the bond strength by an average of 45 % and %40, respectively. Moreover, it has been determined that the curing conditions have a significant effect on the bond performance, as especially the compressive and tensile strengths of the samples under heat cure improve. In samples exposed to both ambient and heat cure, doubling the bond length increased the bond strength by 70 %. Furthermore, increasing the bar diameter increased the bond strength of the samples exposed to ambient and heat curing by a maximum of 84 % and 79 %, respectively. The findings lay the groundwork for understanding the bond behavior of geopolymer, which is critical for the successful application of geopolymer-bonded rebar. • Bond between geopolymer concrete and rebar at different cure conditions are quantified • Failure modes of the pull-out specimens with different parameters were studied. • Effects of bar diameter, longitudinal rib angle, the position of longitudinal bar, bond length on bond strength were studied. • Heat curing resulted in a significant bond strength increase. • Bond strength change by varying the steel bar diameter from 12 mm to 24 mm. [ABSTRACT FROM AUTHOR]

Surface hydrophobic modification is a critical technology for enhancing the application properties of materials, crucial for the development of geopolymer materials in oil-water separation. in this study, a lightweight porous slag-based geopolymer highly hydrophobic materials (PSGHHMs) were successfully prepared in-situ using slag and liquid water glass by varying different influencing factors, such as the amount of water/foaming agent/polymethylhydrosiloxane (PMHS) and the curing temperature. The PSGHHMs exhibited high strength, large flux and excellent highly hydrophobic properties, with contact angle reaching 156.14° and a sliding angle of less than 2°. SEM-EDS, TG-DSC and FT-IR analysis reveal that the in-situ modification mechanism of PSGHHMs involves the hydrolysis of Si-H in PMHS under alkaline conditions to form Si-OH. This subsequently reacts with Ca-OH in C-S-H gel to produce Ca-O-Si. Consequently, the PSGHHMs retained their excellent highly hydrophobicity even after calcination at 450℃ for 2.5 h. The PSGHHMs demonstrated robust resistance to acid/alkali/salt corrosion, as well as to friction, with the ability to quickly restore damaged highly hydrophobic properties. Additionally, the PSGHHMs could quickly absorb light/heavy oils, and achieving a desorption efficiency of over 99 %. They were also capable of continuously separation of oil-in-water emulsions and oil-water mixtures. Given these properties, the PSGHHMs have broad potential applications in antifreezing, antifogging, drag reduction and oil-water separation. [Display omitted] • Preparation of PSGHHMs with high strength and flux by simple coating method. • PSGHHMs have outstanding resistance to high temperature, friction and acid/alkali/salts. • PSGHHMs have excellent anti-fouling, highly hydrophobic and superoleophilic. • PSGHHMs achieve continuous separation of oil-water emulsions and oil-water mixtures. • Providing a new idea for industrial oil-water separation. [ABSTRACT FROM AUTHOR]

Ceramics are highly valued for their exceptional thermal resistance and ability to withstand high temperatures. This study investigated the production of ceramic-like pressed geopolymer, focusing on the effects of aging period and sintering temperature. The results showed that the 7-day pressed geopolymer achieved the highest compressive (134.7 MPa) and flexural (34.9 MPa) strengths after sintering at 1000°C, with a density retention of 93.7 %, a mass loss of 7.9 %, and a thermal shrinkage of 1.4 %. Microstructural analysis at 1000°C showed a dense ceramic-like structure with nepheline formation. Phase analysis of the 7-day pressed geopolymer revealed a decrease in the amorphous phase as temperature increased, with nepheline formed at 800°C (26.0 %) and maximized at 1000°C (61.0 %). This work offers an optimal aging period and sintering temperature to maximize the mechanical strength and nepheline crystal formation, making them perfect for fire-resistant panels and precast construction products. • Pressed geopolymer was formed at various aging times and sintering temperatures. • The highest mechanical strength was achieved by the 7d pressed geopolymer at 1000°C. • The residual compressive strength at 1000°C ascends in 28d < 7d < 1d. • Gel matrix transformed into a ceramic-like structure with rising temperature. • The 7d pressed geopolymer has the most nepheline phase formation at 1000°C. [ABSTRACT FROM AUTHOR]

This study explores enhancing geopolymer mechanical robustness and reducing efflorescence by adjusting precursor compositions and ratios, complemented by incorporating select admixtures. The integration of slag facilitates the geopolymerization process while concurrently diminishing the sodium ion leaching concentration, contributing to a reduction in efflorescence manifestations. The employment of metakaolin is further identified as a significant factor in the substantial decrease of free sodium ions, thereby curtailing efflorescence. While polycarboxylate and carboxymethyl cellulose exhibit differential impacts on the structural strength, their excessive application may exacerbate efflorescence. Notably, sodium polyacrylate is highlighted for its proficiency in markedly diminishing water permeability and virtually eradicating efflorescence through establishing a compact network that impedes the mobility of water and sodium ions, thereby forestalling their surficial migration. • Efflorescence and mechanical properties of geopolymer with varying precursor composition and proportions were studied. • Efflorescence and mechanical properties of geopolymer with different admixture types and concentrations were studied. • Impact of admixtures and optimal admixture dosage on geopolymer properties were clarified. [ABSTRACT FROM AUTHOR]

In this paper, ground granulated blast-furnace slag was used to enhance the properties of recycled concrete powder based geopolymer cured at ambient conditions. The rheology, workability, strength, hydration reaction kinetics, microstructure, and air-void characteristics of the geopolymer were investigated. The results showed that adding the slag accelerated the setting process and reduced the water absorption and porosity of the geopolymer mixtures. Excellent mechanical properties were achieved when the slag content exceeds 30 %. The 28-d compressive and flexural strength of the geopolymer with 50 % slag addition reached 61.2 and 5.17 MPa, respectively. The yield stress and plastic viscosity of the geopolymer increased as the slag content increased. A quantitative model between the slag content, resting time, and rheological parameters was established, with high accuracy, realistically reflecting the rheological properties of the geopolymer. The addition of the slag provided nucleation sites for the C-S-H gel, which promoted the hydration reaction, increased the hydration products and the total heat release, and formed a denser and more uniform microstructure, thereby increasing the strength of the geopolymer. The slag addition was also found to reduce the air content, spacing factor, and average chord length of the geopolymer matrix. As the slag content increased, the air bubbles became smaller and more stable, and exhibited a more uniform distribution. • Recycled powder (RP) partly replaced by ground-granulated blast-furnace slag (GGBS). • GGBS used to prepare alkali-activated recycled powder (AAR) at room temperature. • GGBS significantly accelerated the hydration rate and increased the total heat release of AAR system. • The quantitative model between GGBS content, resting time, and rheological parameters was established to reflect the rheological characteristics of geopolymer. • The air-void characteristics, including the air content, spacing factor, and average chord length of AAR with different GGBS content are investigated. [ABSTRACT FROM AUTHOR]

This study investigates the effects of water loss and temperature on the electrical properties of metakaolin-based geopolymer (MKG) using electrochemical impedance spectroscopy (EIS). The results show that the electrical behaviour of MKG involves two processes during water loss: the charged ions exhibited Warburg diffusion behaviour in the pore solution (slow process) and the non-ideal diffusion behaviour of charged ions at the geopolymer/electrode interface (fast process). As the water loss increases, the electrical conductivity mechanism changes from the slow process dominant to the fast process dominant. The slow process of dried MKG is mainly influenced by temperature. Dried MKG with low water/binder (w/b) ratio shows increased conductivity with temperature, while MKG with high w/b ratio maintains stable conductivity. A conductive mechanism indicates that the small pore of MKG with low w/b ratio has difficulty in removing water. At high temperature, the enhanced mobility of ions allows them to move through the remaining pore solution network, resulting in reduced impedance. • Water loss in geopolymers involves two processes: slow process and fast process. • The conductivity of the dried geopolymer is influenced by temperature and w/b ratios. • A conductive mechanism of geopolymer during water loss is proposed. [ABSTRACT FROM AUTHOR]

This study proposed to use barite-enhanced ultra-high performance geopolymer concrete (UHPGC) as the composite matrix to develop high-strength, cement-free, and sustainable radiation shielding materials. The physical properties, γ ray attenuation capacity, microstructure, and environmental and economic impacts of prepared barite-enhanced radiation shielding UHPGC were determined and compared with normal concrete and ultra-high performance concrete (UHPC). The combination of steel fibers and barite aggregate increased the density of UHPGC, thereby enhancing its γ ray attenuation capacity. Multi-scale γ ray shielding simulation results demonstrated that although thickness was the more decisive factor of γ ray attenuation capacity of composites, the enhancement of the shielding capacity of the material helps reduce the floor area and the cost of radiation shielding structure. The micro-analysis results revealed that barite-enhanced UHPGC exhibited compact microstructure and excellent interfacial performance. Furthermore, life cycle assessment results demonstrated that UHPGC was more suitable as a composite matrix than UHPC to develop sustainable and low-cost radiation shielding materials. [Display omitted] • Barite-based UHPGC was developed for the proposal of high-strength, cement-free and sustainable radiation shielding materials. • Compressive strength and flexural strength of developed barite-enhanced UHPGC exceeded 140 MPa and 15 MPa. • Compared with normal concrete, gamma ray shielding capacity of barite-enhanced UHPGC was enhanced 8.8 %. • Barite-enhanced UHPGC exhibited enormous ecological and environmental benefits compare with UHPC. • Barite-enhanced UHPGC is a promising radiation shielding material applied in nuclear power plants. [ABSTRACT FROM AUTHOR]