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Kaolinite is a single 2D layer of kaolin or metakaolin (MK), common clays that can be characterized as layered 3D materials. We show that because of its chemical composition, kaolinite can be converted into an amorphous 3D material by chemical means. This dimensional transformation is possible due to the large surface to volume ratio and chemical reactivity of kaolinite. We investigate the formation and influence of quasi- or nanocrystalline phases in MK-based alkali-activated materials (AAM) that are related to the Si/Al ratio. We analyze the formation of an AAM from a MK precursor, which is a 3D bonded network that preserves the layered structure at the nanometer scale. We also exfoliate the remaining layered phase to examine the effects of the alkali-activation in the final sheet structures embedded within the amorphous network. The final material can be used as a cement with no carbon dioxide produced by the transformation reaction. [ABSTRACT FROM AUTHOR]

This study presents the development of a novel Hybrid Laminate Material (HLM), particularly a dual-layered system combining an Ultra High Performance Fiber Reinforced Concrete (UHPFRC) and a Fire Resistant Geopolymer (FRG). The novel material is engineered to provide blast and impact as well as fire resistance, seeking to address the critical challenge of explosive spalling of concrete under high and rapidly rising temperatures while preserving structural integrity to withstand blast and impact loads. The FRG layer composition is optimized for environmental friendliness and cost, while assuring the formation of refractory phases at high temperatures to ensure adequate resistance to extreme temperatures. In parallel, a blast and impact-resistant UHPFRC layer is further optimized, aiming to provide exceptional compressive and flexural strength while minimizing fiber content and cost. The results highlight the development of a promising HLM that offers an environmentally friendly, cost-effective solution for enhancing the safety and resilience of critical infrastructure, incorporating robust, multifunctional building materials that can resist blast, impact, and endure extreme thermal conditions. The two layers demonstrate excellent results in their respective functions. The developed FRG successfully maintained its compressive strength while withstanding temperatures up to 1050 °C. Furthermore, an environmentally friendlier UHPFRC was designed, including 2% steel and 1% Polyvinyl Alcohol (PVA) fibers, without sacrificing the capacity to withstand blast and impact. [ABSTRACT FROM AUTHOR]

Despite the steady progress of research on the alkali activation of wastes or subproducts from established industrial processes, the brittleness of the hardened alkali-activated materials frequently results in questionable mechanical reliability, particularly in industrial applications beyond construction materials. This work used a 33 factorial Design of Experiments to examine the effect of three different particle size distributions on the compressive strength and mechanical reliability (Weibull modulus) of a sodium silicate-activated blast-furnace slag under the same processing conditions. As expected, curing temperature and time were strongly correlated, and the corresponding response surfaces showed that, for all studied particle sizes, compressive strengths above 60 MPa with mechanical reliability above 5.0 could be obtained by curing at ~60 °C for ~40 h. The particle size differences caused no significant changes in the extent of alkali activation, as seen in the infrared-spectroscopy results. However, the intersection of the response surfaces showed that a coarser and narrower particle size distribution extended the working area (time × temperature) and favored mechanical reliability. Thus, the precursor's particle size distribution, which governs particle packing and viscosity during processing, also determines the permeability of the set binder, which affects water removal during drying and the dried binder's mechanical performance. [ABSTRACT FROM AUTHOR]

The durability problems in Portland cement are related to decalcification of C–S–H; alkali-activated composites are proposed as alternative, focusing on acid exposure and resistance. They were prepared from recycled materials, basic oxygen furnace carbonated and desulfurization slags. The standard material is 100% metakaolin geopolymer compared to slag-based alkali-activated materials (AAMs) with and without reinforcement of fibers (basalt, and cellulose), added in 4 wt%. The acidic environments are H2SO4, HCl, and HNO3N = 2.14 (10, 7.5, and 12.5 wt%, respectively). The chemical resistance is improved by the addition of basalt fibers. The decrease in weight loss is 48% in HNO3 and 47% in HCl for AAM-Bas sample, while for AAM-Cell it is 9% in HCl and 34% in HNO3. The compressive strength of the AAM and AAM-Bas samples remains constant after HCl attack, while this acid attacks cellulose samples, which are stable in HNO3 and have a compressive strength of 10 MPa. [ABSTRACT FROM AUTHOR]

Basic oxygen furnace slag (BOFS) is a high-volume waste resulting from the production of steel from pig iron. Due to its high free lime content, BOFS is difficult to recycle and/or include into conventional cement systems. Alkali-activation technology offers a pathway to transform industrial wastes such as BOFS into low-carbon cements. Alternative precursors for cement systems are needed as the reliance on commonly used materials like ground granulated blast furnace slag (GGBFS) is becoming unsustainable due to decreasing availability. This study investigates alkali-activated cements incorporating 20 and 30 wt.% of naturally weathered BOFS as a replacement for GGBFS, in both sodium silicate- and sodium carbonate-activated systems. A fraction of BOFS subject to mechanical activation is compared against the untreated BOFS in the 20 wt.% systems. It is observed that in naturally weathered BOFS, a significant portion of the free-lime is found to convert to portlandite, which accelerates alkali-activation kinetics. In sodium silicate-activated systems, the high pH of the activator results in incomplete reaction of the portlandite present in BOFS. The sodium carbonate-activated system shows near complete conversion of portlandite, causing an acceleration in the kinetics of reaction, setting, and hardening. These findings confirm the viability of sodium carbonate activated GGBFS-based systems with only a minor loss in strength properties. BOFS can be utilised as a valuable cement additive for the production of sustainable alkali-activated cements utilising sodium carbonate as a less carbon-intensive activator solution than the more commonly used sodium silicate. Mechanical activation of BOFS offers further optimisation potential for alkali-activation. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cement kiln dust (CKD), which consisted of mullite, quartz, fused silica, and calcite (49, 23, 11, and 10 mass%, respectively) was alkali-activated ([NaOH]: 4–12 M) and cured under different conditions (25 ≤ T ≤ 85 °C, time (t): up to 30 days). The microstructure of the cured samples was investigated using X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy. The mechanical/physical properties of the cured samples were related to the above factors using response surface methodology. The results showed that increasing the levels of these factors enhanced the reactivity of mullite and quartz, leading thus to the formation of hydrosodalite along with geopolymer. Conversely, a pseudo-amorphous phase along with a limited amount of geopolymer occurred with lower levels of the factors. Moreover, samples prepared with concentrated solutions of NaOH or cured at high temperatures were the object of the formation of zeolite ZK, and semi-crystallized hydroxysodalite, respectively. Tobermorite and hydroxysodalite were formed at long and short curing times, respectively. The mechanical/physical properties of the cured samples were well related to the operating factors through quadratic models, and their changes were discussed in relation to the microstructure characterization. The results of the desirability approach demonstrated that the optimal values for bending strength, compressive strength, porosity, and water absorption (10.4 MPa, 9.1 MPa, 16.4%, and 28%, respectively) are obtained at: [NaOH] = 10 M, T = 73 °C, and t = 23 days. In light of these results, the CKD is suitable as a binder for mortar and bricks. Highlights: With a high silica and alumina content (77% by mass), the studied CKD is suitable for geopolymer synthesis. Upon activation and curing of CKD, geopolymer, zeolite ZK, hydroxysodalite and tobermorite were formed. The influence of operating factors on cured samples properties was assessed using quadratic models. The optimal operating factors were NaOH concentration = 10 M, curing temperature = 73 °C, and curing time = 23 days. The CKD demonstrates the potential for manufacturing brick-and-mortar binders. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Using waste as a raw material for the synthesis of construction materials is gaining increasing attention due to the declining availability of natural resources. This research seeks to assess the impact of using cellulose acetate microfibers (CAMs) derived from discarded cigarettes as a reinforcement for alkali-activated materials (AAMs). In this context, seven blends were elaborated with the addition of various percentages of CAMs (0%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, and 1.5%) per dry mass of fly ash, and using an alkaline solution composed of Na2SiO3 and 10 M NaOH solution. Then the physico-mechanical, thermal, and environmental properties of these composites were evaluated. The experimental results indicated that the addition of CAMs led to lighter composites, which decreased compressive strength, P-wave velocity, and density, while slightly increasing flexural strength, porosity, and water absorption. Moreover, a slight enhancement in thermal insulation capacity was observed (up to ∼9.28%). The microstructural analyses, encompassing XRD, FT-IR, and SEM/EDX examinations, revealed the formation of geopolymeric gels N-A-S-H and C-A-S-H in all specimens. The Toxicity Characteristic Leaching Procedure indicated that the released contaminants were within the regulatory limits, as well as the binder exhibited a remarkable decrease in carbon dioxide emissions and energy demand by 77.23% and 57.92% in comparison to cement. Thus, the prepared materials are viewed as a more environmentally responsible choice for reducing greenhouse gas emissions while avoiding potential toxicity issues.

Understanding the strength behavior and leaching characteristics of mining tailings stabilized with alkali-activated cements in the short, medium, and long term is crucial for the feasibility of material applications. In this context, this study assessed the stabilization/solidification of iron ore tailings (IOT) using alkali-activated binder (AAB) composed of sugarcane bagasse ash and eggshell lime at curing times of 7, 28, 60, 90, 180, and 365 days. Additionally, leaching tests were conducted, along with the examination of possible changes in the chemical and mineralogical composition resulting from exposure to acidic environments. Tests included unconfined compression strength (UCS), leaching, X-ray diffraction, and Fourier-transform infrared spectroscopy for the IOT-AAB mixtures. The highest increase in UCS was observed between 7 and 60 days, reaching 6.47 MPa, with minimal variation thereafter. The AAB-bonded IOT exhibited no metal toxicity over time. Elements Ba, Mn, Pb, and Zn present in IOT and ash were encapsulated in the cemented matrix, with complete encapsulation of all metals observed from 90 days of curing time. The mineralogy of the stabilized/solidified tailings showed no changes resulting from leaching tests. Characteristic bands associated with the presence of N-A-S–H gel were identified in both pre-leaching and post-leaching samples for all curing times analyzed. Exposure to acidic environments altered bands related to carbonate bonds formed in the IOT-AAB mixture. [ABSTRACT FROM AUTHOR]

Waste glass powder and metakaolin were used to prepare geopolymer mortar. The effects of alkali activator with different sodium silicate modulus and liquid-solid ratios on the fluidity and mechanical properties of the waste glass powder-metakaolin geopolymer mortar were investigated, and the crystal structure, thermochemistry, pore structure, and micromorphology of the geopolymer mortar were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric-differential scanning thermal (TG-DSC), mercury in piezoelectricity (MIP), and scanning electron microscopy (SEM). The results show that the sodium silicate modulus and liquid-solid ratio have more obvious effects on the fluidity and mechanical properties of the geopolymer mortar. With the increase of sodium silicate modulus, the fluidity and strength of geopolymer mortar increase first and then decrease. When the sodium silicate modulus is 1.25, the alkali activator has the best excitation effect on the material, which increases the degree of reaction of the geopolymer, generates more hydration products, optimizes the pore structure of the matrix, and the compressive strength of 28 d reaches 43.0 MPa. The increase of liquid-solid ratio improves the fluidity of the geopolymer mortar, but decreases the compressive strength and has a negative effect on the pore structure. Moreover, the XRD, FTIR and TG-DSC results show that the waste glass in the geopolymer participates in the hydration reaction, provides Ca2+, and promotes the generation of C-S-H and C-A-S-H gels. [ABSTRACT FROM AUTHOR]

This contribution presents the results of structural investigations on the cured and high temperatures of three series of geopolymers. The specimens were synthesized at 80 °C from coal fly ash and three activators of variable composition based on sodium hydroxide and sodium silicate solutions. Structural and microstructural analysis was performed, especially using in-situ measurements of XRD patterns and IR spectra as a function of temperature. The cured compounds' phase content and compressive strength changed slightly depending on the starting chemical composition. All analyzed materials experience a mass loss due to water removal at 300 °C, followed by increased porosity from disintegrating compounds above 300 °C. Higher alkali content improves strength (400–600 °C) possibly due to nepheline formation. The amorphous phase gradually softens during heating, influenced by alkali content. Structural analyses were supported by model calculations of a number of aluminosilicate structures. The cluster analysis using the k-means algorithm was used to divide the PCA space into regions that represent structural similarities, and analyzing specific point positions in the space allowed for several conclusions to be drawn about the studied materials, including that changes in chemical composition and thermal treatment can promote the transformation from sodalite to nepheline and that the glass network has elements that are nepheline-like and may promote its crystallization. [ABSTRACT FROM AUTHOR]

Electric arc furnace slag (EAF) and sandstone waste (SW) are two of the most abundantly generated industrial wastes whose utilization as precursors and supplementary cementitious materials has not been exhaustively studied. The current research study comprehensively investigates the effects of incorporating varying proportions (0–90%) of re-melted EAF as a co-additive on the engineering properties of elevated (80 °C) and ambient (30 °C) cured alkali-activated SW-based binders. Extensive laboratory tests were conducted to assess the physio-mechanical and durability performance of the resulting alkali-activated materials (AAM). Detailed mineralogical and microstructural characterization of SW, EAF, and alkali-activated samples was carried out using sophisticated analytical techniques. Results advocated that irrespective of the curing temperatures, SW-based AAM showed improved setting behavior, compressive strength, water absorption, and porosity characteristics with the increment of EAF at all substitution levels due to the concomitant development of CASH-CSH-NASH gel phases. Overall, it can be inferred that EAFs as a pozzolanic material successfully augmented the properties of SW-based alkali-activated binders, providing an efficient solution for disposal and negative environmental impacts associated with industrial wastes. [ABSTRACT FROM AUTHOR]

Service life predictions of reinforced concrete structures are underpinned by the passivation film chemistry, structure, and thickness. In this work, we present how the formation of passive films at the steel–concrete interface of reinforced alkali‐ and salt‐activated slag materials can be affected by the pore solution chemistry, namely, pH, Eh, and chemical composition. Thermodynamic simulations are used to illustrate the time‐dependent changes to the pore solution chemistry, where estimated electrical conductivities of the pore solution are used as a single‐value parameter to understand the solution complexity and capacity for charge transfer. A set of passivation reactions are proposed to understand the effects of OH− and HS− (reduced sulfur species) competition on the passivation pathways. These passivation reactions become more complex considering that a reducing pore solution might not establish until 3 days into the curing process—a crucial factor explaining the significant differences in the phase composition of passive films of activated slag materials (FeOOH, FeS). This study sheds light on recent progress in understanding these initial passivation reactions, emphasizing the essential role of material design and, therefore, the pore solution chemistry of these cements, along with significant insights for vital research and development concerning the corrosion durability of activated slag materials. [ABSTRACT FROM AUTHOR]

The repair of concrete structures is increasing in prevalence. Conventional repair mortars are expensive materials rich in Portland cement (PC) and other organic and inorganic components that question their economic efficiency and carbon footprint. Alkali-activated materials (AAMs) are an eco-friendly alternative to PC that possess properties desirable for repair mortars. The article presents the mix design, mechanical, bond, and shrinkage properties of alkali-activated binary mortars intended for structural concrete repair. Mix optimisation based on mechanical properties of repair mortar and utilisation of glass waste (GW) is presented together with total and restrained shrinkage, pull-off bond tests, and life cycle assessment (LCA) for selected configurations. Results demonstrate good compressive and flexural strength, exceeding 45 N/mm2 and 7 N/mm2, an excellent pull-off bond strength (1.8–2.3 N/mm2) of the alkali-activated mortar to the concrete substrate, in spite of extensive shrinkage, with an order of magnitude of a couple of thousands of microstrains, which is also reported. Shrinkage appears to increase with the increase of the applied GW in the mixture. LCA revealed that alkali-activated mortars have up to 54% lower CO2 eq. emissions compared to PC-based repair mortar. [ABSTRACT FROM AUTHOR]

Recycling aluminosilicate-based solid wastes is imperative to realize the sustainable development of constructions. By using alkali activation technology, aluminosilicate-based solid wastes, such as furnace slag, fly ash, red mud, and most of the bio-ashes, can be turned into alternative binder materials to Portland cement to reduce the carbon footprint of the construction and maintenance activities of concrete structures. In this paper, the chemistry involved in the formation of alkali-activated materials (AAMs) and the influential factors of their properties are briefly reviewed. The commonly used methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG), nuclear magnetic resonance spectroscopy (NMR), and X-ray pair distribution function technology, to characterize the microstructure of AAMs are introduced. Typical characterization results of AAMs are shown and the limitations of each method are discussed. The main challenges, such as shrinkage, creep, efflorescence, carbonation, alkali–silica reaction, and chloride ingress, to conquer for a wider application of AAMs are reviewed. It is shown that several performances of AAMs under certain circumstances seem to be less satisfactory than traditional portland cement systems. Existing strategies to improve these performances are reviewed, and recommendations for future studies are given. [ABSTRACT FROM AUTHOR]

Admixtures used in concrete have been produced for conventional concrete and the behavior of these additives in geopolymer/alkali‐activated systems is still complicated. In this study, the effects of different types of water‐reducing admixtures on the fresh and mechanical properties of Class F fly ash‐based geopolymer mortars and alkali‐activated slag mortars were investigated. For this purpose, flow diameter, rheological examination, compressive and flexural strength tests were carried out. The data obtained showed that the admixtures used in the study did not have a positive effect on the fresh properties of geopolymer/alkali‐activated mortars, and the improvements in the flow properties were due to the extra water contributed by the admixture. The flow diameters of the mixtures containing the same amount of water with the mixture containing plasticizer were generally higher than those of the mixtures prepared with the admixture up to 10.3% in the fly ash‐based mortars and 15.4% in the slag‐based mortars. Addition of plasticizers reduced the compressive strength of fly ash‐based geopolymer and slag‐based alkali‐activated mortars up to 31.7% and 29.7%, respectively. [ABSTRACT FROM AUTHOR]

In order to achieve the resource utilization of beach silty soil and industrial wastes, and quantitatively optimize the critical factors of geopolymer cured silty soil, the mix ratio of alkali-activated slag-fly ash based geopolymer cured silty soil was optimized based on the Box-Behnken response surface method. The slag content, alkali activator modulus and alkali activator content were selected as the main factors to be investigated, and the curing mechanism was analyzed by combining the macroscopic properties and microscopic morphology. The results show that: the optimum mix ratio of cured soil is slag content 86.5% (mass fraction), alkali activator modulus 0.84, alkali activator content 7.3% (mass fraction), the unconfined compressive strength of cured soil at 7 and 28 d under the optimum mix ratio is 5 823 and 7 027 kPa, respectively. The prediction value has a small error with the actual value, and the established model is accurate and reliable in fitting the actual data. The hydration products of cured soil are mainly amorphous gel hydrated calcium silica-aluminate (C-(A)-S-H) and silica-aluminate polymer (N-A-S-H), which enhance the densification and skeletal structure of soil body, thus improving the strength of cured soil. This study provides a theoretical basis and experimental foundation for alkali-activated geopolymer cured silty soil. [ABSTRACT FROM AUTHOR]

This study investigated the carbonaluminate cementitious materials (i.e., sodium aluminate (NaAlO2)-activated limestone pastes) with gradient calcite (CaCO3)/NaAlO2 molar ratios ranging from 1:1 to 6:1 (samples M1 to M6). NaAlO2 dosage affected the reaction process, hydration product, and cementitious property of the formed pastes. The thermonatrite (Na2CO3·H2O) and AH3 phase as hydration products exist in all the samples. Microcrystalline AH3 phase (crystallite size is near 22 nm) held a superior cementitious property, which was evidenced by diffraction spots scattered on concentric rings in transmission electron microscopy (TEM) results. Other hydrates varied with the CaCO3/NaAlO2 ratio. In case of lower CaCO3/NaAlO2 ratio (i.e., M1), NaAlO2 was incompletely consumed. The residual NaAlO2 promoted the formation of cubic-shaped katoite (3CaO·Al2O3·6H2O). Such hydrate barely contributed to the cementitious property of the formed matrix. When the CaCO3/NaAlO2 ratio reached 1.5:1 (e.g., M1.5-M6), NaAlO2 was entirely consumed, and monocarboaluminate (Mc, 3CaO·Al2O3·CaCO3·11H2O) instead of katoite was preferentially generated. The amounts of total hydrates decreased with the increasing CaCO3/NaAlO2 ratio, leading to the degraded properties of formed matrix. Thus, the 28-day compressive strength of M1.5 was the highest among these samples, reaching 35.55 MPa.

Abstract Alkali-activated concrete (AAC) has attained great popularity since finding it as an alternative to Portland cement concrete due to its superior characteristics in terms of mechanical properties and durability, and its low negative environmental impact. This research investigated both experimentally and analytically the bond behavior between alkali-activated slag concrete (AASC) and steel rebars considering some important parameters (rebar diameter and development length-to-diameter ratio) before and after exposure to elevated temperature using beam-end bond testing technique. The obtained experimental results were compared with those obtained from applying the CEB-FIP model and the well-known available equations in the literature. A modified model was proposed for predicting the bond behavior of AASC. Results have showed that the CEB-FIP model provides more conservative values for bond strength compared to the experimentally obtained results which increases the safety level when estimating the bond strength for design purposes. The proposed modified model achieved a higher correlation with the experimental results than the CEB-FIP model at ambient temperature.

The production process of dolomite aggregate yields a huge content of the rejected size, namely dolomite waste. This waste causes many environmental problems including increasing the wastage area, disposal of landfill, and increasing the air pollution. This work pay attention to the sustainable disposal of this waste in the production of an innovative binder using chemical exchange reaction. This work aims to examine the role of metakaolin (MK) and diatomite (DT) in enhancing the physicochemical properties of alkali-activated binder-based dolomite waste (AADW). The DW powder was combined with varying weight percentages of MK and DT. The resultant admixtures were activated via Na2SiO3, followed by curing at room temperature. The fabricated mixtures possess a wide range of compressive strength values, dependent on the contents of the additives (MK and DT). AADW without any additives represents a compressive strength of 34.6 MPa. DT was found to have a minimal effect on early compressive strength but significantly enhanced later strength. In contrast, incorporating MK into the alkali-activated system materially improved the early compressive strength, while it recorded 28-day strengths similar in hardness to the hardened sample with DT. Specifically, AADW-DT10 and AADW-MK10, which contain 10 wt% DT and MK, respectively, exhibited 7- & 28-day compressive strengths of 14.4 MPa & 32.1 MPa and 57 MPa & 56.2 MPa, respectively. Replacing DW with DT reduced drying shrinkage of the resultant hardened alkali-activated materials. However, incorporating MK up to 10 wt% reduced the drying shrinkage of AADW, while the sample with 15 wt% recorded the highest drying shrinkage. Nonetheless, AADW-DT exhibited lower drying shrinkage than that of AADW-MK at all curing ages up to 90 days. Overall, the result indicated that the higher reactivity and high alumina content of MK provide suitable conditions for synthesizing hardened materials with better physical and mechanical properties when compared to AADW-DT.

Steel slag composite grout (SSCG) was prepared by a large amount of steel slag (SS) to reinforce expressway photovoltaic (PV) slopes and reduce carbon emission. Laboratory tests were conducted to investigate SSCG properties, including flowability, effective water-solid ratio (W/S), stone rate, initial and final setting time, as well as flexural strength (FS), unconfined compressive strength (UCS), FS/UCS ratio and microstructure of SSCG stone body. Ordinary Portland cement (OPC, 42.5) and sulphoaluminate cement (SAC, 42.5) grouts were selected to make contrasts. Based on the performance results, the recommended SSCG composition for engineering application is 40 % SS + 25 % blast furnace slag (BFS) + 20 % silicate cement clinker (CC) + 10 % fly ash (FA) + 5 % flue gas desulfurisation gypsum (FGDG). and the recommended admixture is: 6 % AA + 2 % bentonite + 0.4 % FND-C. With the above SSCG and related grouting techniques for slope soils, the soil cohesion was increased by 7.3–12.2 % and the angle of internal friction was increased by 10.2–19.7 %. To further validate the beneficial effects of SSCG on slope stability and the safe application of PV systems, numerical modelling calculations were conducted based on the soil sample test results. The simulations demonstrated the positive effect of SSCG in enhancing slope stability and facilitating the secure installation of PV systems on expressway slopes. The successful operation of grid-connected PV systems provided compelling evidence for the technical applicability of SSCG and it contributed to the application feasibility of PV systems to expressway slopes. The innovative use of SSCG in this study not only ensures the safety of construction projects but also contributes to environmental sustainability through the application of industrial slags.

In this study, central composite design (CCD) was used to optimize the porosity structure of NaOH-activated volcanic scoria (VSc) and rice husk ash (RHA) composite materials. The synthesis conditions, namely VSc and RHA fractions by mass and NaOH concentration were used as the input (independent) variables and the porosity parameters, iodine index and methylene blue index, as the output variables. The optimum conditions that gave the material, CM, with the highest iodine index and methylene blue index, and hence porosity structure, were attained at 0.67 VSc (2g)/RHA (3g) ratio by mass and 5 M NaOH. The CM and precursors were characterized using FTIR, SEM, pHpzc, Methyl Blue index, and Iodine index. The CM and the precursor VSc were used to sorb crystal violet (CV) dye from synthetic wastewater. The pseudo-second-order kinetic and Langmuir models best-described CV adsorption by both materials. The adsorption mechanism was controlled by Coulombic interactions. At an initial CV concentration of 20–60 mg/L, 0.1g/30 mL adsorbent dosage, and pH of 6 at 25 °C, the CM had a slightly higher (∼1.13 times) adsorption capacity (11.06 mg/g) for the uptake of crystal violet dye than the precursor VSc (9.75 mg/g) consistent with their methylene blue indices. Electrostatic interactions and ion exchange are proposed dominant adsorption mechanisms. The porosity and adsorption performance of the VSc-RHA alkali-activated materials are shown to be strongly and significantly dependent on the RHA fraction and NaOH concentration relative to VSc.

AbstractA lot of energy is released during the cement manufacturing process, and a large amount of carbon dioxide (CO2) is discharged into the environment. Presently, researchers are focusing on reducing CO2 emissions by researching sustainable alternatives to traditional Portland cement-based materials. A comparative study on the material characterization of both calcined agro-based waste ash (calcined ash) and uncalcined agro-based waste ash (uncalcined ash) and its utilization as a binder along with granulated blast furnace slag (GGBS) in the alkali activation process is carried out in this paper. The study regarding calcined and uncalcined ash would help in better understanding the variation in the properties of the material and its behavior during the alkali activation process. The tests conducted on both calcined and uncalcined ash along with GGBS include specific gravity, X-ray fluorescence, X-ray diffraction, scanning electron microscopy, reaction degree, Brunauer-Emmett-Teller (BET) analysis, particle size distribution, and the Puntke test for understanding its microstructural characteristics. Later, alkali-activated mortars are prepared using 30% weight of agro-based waste ash (both calcined and uncalcined) and 70% weight of GGBS. A comparison of the compressive strength of alkali-activated mortars prepared using calcined and uncalcined ash was studied, which showed a promising increase in the strength by 11.02% of mortar prepared using calcined ash (23.46 MPa) for 28 days when compared to mortar prepared using uncalcined ash (21.13 MPa). The major finding from this study indicates that calcined agro-based ash with GGBS shows better results compared to uncalcined agro-based ash with GGBS.

This study reports the full recycling of dolomite waste (DW) in the fabrication of a novel cementitious material through a facile and eco-efficient method. The proposed technique includes mixing different alkali-activators (i.e., NaOH and Na2SiO3) with DW powder, followed by curing at room temperature. Based on the alkali-activator type, sodium oxide concentration, and curing time, the formulated mixtures yield a wide range of compressive strengths. When DW powder is mixed with different contents of NaOH (2.5, 5, and 7.5 wt.% Na2O), the resulting hardened materials exhibited modest compressive strengths (less than 11 MPa) due to the formation of the gaylussite Na2CO3·CaCO3·5H2O phase. Concerning the other chemical activator (Na2SiO3), a significant improvement in the compressive strengths of the resulted hardened materials was detected. This was ascribed to the formation of calcium silicate hydrate, with a high binding capacity, through the exchange reaction between Na2SiO3 and CaCO3 inside DW. The sample activated with Na2SiO3 (silica modulus of 1.5) equivalent to Na2O of 7.5 wt.% offered the highest 90-day compressive strength (34 MPa). At silica modulus lower or higher than 1.5, a noticeable decrease in the performance of the hardened materials was observed, which could be attributed to the alter in binding phase composition. Overall, the present work presented a new approach in utilizing the available and low cost carbonate-based wastes as main precursors in the family of promising alkali-activated materials. [ABSTRACT FROM AUTHOR]

As research regarding the production and optimization of geopolymer materials is constantly increasing and is fundamentally motivated by the need, identified both in the global ecological context and at national level, new materials can be developed using this type of binder. Sustainable consumption of resources, focuses on the capitalization of existing waste and prevention of generating new ones, therefore adopting the Sustainable Development principles. The increase in the utilization of sand from rivers for various construction purposes, which also disturbs the environment can be considered another damaging factor for the environment. Recycling of garnets and their use as replacement for sand aggregates could provide an ecological solution for the production of the alkali-activated fly ash-based geopolymer binders. The aim of this paper is to present preliminary results regarding the use of spent garnet as replacement for sand aggregates in the production of alkali-activated fly ash-based geopolymer binders using Romanian local raw materials and to study its influence on the mechanical performances of the binder.

Green liquor dreg (GLD) is a side stream generated by pulp industry. Due to its complex physicochemical nature, it has been reported to be difficult material to utilize. Here, a novel approach towards utilization of moist and dry green liquor dreg as binder and filler in alkali-activated lightweight artificial aggregates was developed. Dried GLD and moist GLD were granulated with blast furnace slag (BFS) and Bioash in different mixtures using alkali activation. The effect of the GLD nature (dried and moist) on strength, microstructure and durability of the lightweight granules were determined and compared. Results show that the method used in homogenizing the moist GLD and other powders was efficient and improved the frost resistance. The reaction product identified in the granule’s includes calcium silicate hydrate, Mg–Al layered double hydroxides, and ettringite. These results demonstrate the potential of GLD as a binder and fillers in cementitious applications.

Alkali-activated concrete (AAC) has attained great popularity since finding it as an alternative to Portland cement concrete due to its superior characteristics in terms of mechanical properties and durability, and its low negative environmental impact. This research investigated both experimentally and analytically the bond behavior between alkali-activated slag concrete (AASC) and steel rebars considering some important parameters (rebar diameter and development length-to-diameter ratio) before and after exposure to elevated temperature using beam-end bond testing technique. The obtained experimental results were compared with those obtained from applying the CEB-FIP model and the well-known available equations in the literature. A modified model was proposed for predicting the bond behavior of AASC. Results have showed that the CEB-FIP model provides more conservative values for bond strength compared to the experimentally obtained results which increases the safety level when estimating the bond strength for design purposes. The proposed modified model achieved a higher correlation with the experimental results than the CEB-FIP model at ambient temperature. [ABSTRACT FROM AUTHOR]

Portland cement production is an energy-intensive process, and more sustainable substitutes are needed, e.g., alkali-activated binders originated from industrial wastes. Thus, this paper analyzes the combination of sugarcane bagasse ash (SCBA) and hydrated eggshell lime (HEL) as precursors for an alkali-activated binary system, a combination, to our best knowledge, not studied in past research. The mechanical and microstructural behavior of the SCBA-HEL alkali-activated pastes has been discussed through unconfined strength tests, and x-ray fluorescence, x-ray diffraction (XRD), Fourier transform infrared spectroscopy, and scanning electron microscopy (SEM) and energy-dispersive detector (EDS) microstructural analysis. In addition, an analysis of variance was applied to investigate the impact of a three-factor combination, i.e., SCBA/HEL ratio, NaOH concentration, and water/binder ratio (W/B), on the paste's compressive strength. The highest compressive strength is associated with 80% of SCBA and 20% of HEL (ratio equals 4), 1 M molarity, and W/B relation of 0.8 (2.61% of Na2O). A C─ (N)─ A─ S─ H gel is observed in the form of an amorphous hump through the XRD pattern. SEM images show that the material synthesized from alkali-activation has a cementing effect, with a structure less dense and more porous than that of conventional cementing materials. The EDS display areas are rich in Ca, Si, Na, and Al. The bands found for the alkali-activated paste are consistent with vibrations characteristic of C─ A─ S─ H and N─ A─ S─ H gels. [ABSTRACT FROM AUTHOR]

Coal gasification crude slag can be used as a precursor to prepare geopolymer, and its high temperature resistance needs to be further explored. In this paper, geopolymers prepared by mixing 10% of TiO2, 30% of fly ash and 30% of slag in coal gasification crude slag were treated at high temperature, and the thermal stability of four 28d geopolymers at different temperatures was explored. The results show that at 100 ℃, the compressive strength of the sample is not much different from that at room temperature. At 200 ℃, 400 ℃ and 800 ℃, the compressive strengths of the four samples all decreased to different degrees. The strength attenuation is most obvious in the samples doped with mineral powder, and the strength attenuation of the samples doped with TiO2 is smaller at high temperature. With the increase of temperature, the geopolymers cracked: at 100 ℃ and 200 ℃, only the coal gasification coarse slag geopolymers cracked; at 400 ℃, the geopolymers only mixed with TiO2 did not crack; at 800 ℃, all geopolymers cracked. Geopolymers doped with TiO2 have better high temperature resistance due to the anatase content.

This paper discusses the design of hybrid alkali-activated binders at ambient temperature, specifically the development of mixes based on ground granulated blast-furnace slag (GGBFS) with calcium aluminate cement (CAC) as an additive, aiming to obtain high early strength binders with optimised Al incorporation, increased crosslinking and degree of polymerisation. The effects of 10 wt% CAC replacement of GGBFS, activated with sodium silicate with varying modulus (SiO2/Na2O molar ratio) or with sodium hydroxide, on fresh and hardened properties are investigated. The inclusion of CAC in GGBFS mixtures activated using sodium silicate results in an unexpected retardation of the polycondensation reactions required to form the main calcium aluminosilicate hydrate gel phase. This is due to incomplete dissolution of the GGBFS precursor, inhibited by the rapid formation of additional reaction products (especially cubic aluminate hydrates, C3AH6) resulting in lowered reaction kinetics, and thus delayed setting and hardening times. For sodium silicate activators, this retarding effect appears to be only slightly dependent on the activator solution modulus. When activating with 4 M NaOH, the retarding effect is reduced, along with the incorporation of CAC in the C-A-S-H gel, increasing the amount of reactive aluminium present in the binder to form a more compact gel product. Increasing the molarity of NaOH solutions results in a similar delay in reaction kinetics. The results suggest the existence of only a limited pH range in which the addition of CAC can promote the formation of a binding gel with enhanced mechanical properties, whilst other factors including the effect of sodium silicate inclusion in CAC systems are still unclear. The typical hydration products of CAC were not detected in this study.

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was used to demonstrate the reaction mechanisms of alkali-activated materials (AAMs) and the early stage of structure formation in the materials. The effects of different types of alkali activator solutions on the structure formation and reaction mechanisms of AAMs were studied. The results revealed that the main peaks of the ATR-FTIR spectra of the AAMs in the 1300–650 cm−1 range shifted to a low wavenumber with changing patterns, depending on the activator solution used, indicating that the dissolution and reorientation of metakaolin had occurred. Silica and alumina monomers were dissolved by the NaOH solution to produce crystalline zeolites. Although the reaction between metakaolin and Na2SiO3 solution is slow, the condensation between the Al-OH from metakaolin and the Si-OH from Na2SiO3 solution bonded the chain to be longer. Therefore, the Na2SiO3 solution acted as a template-bonded monomer, formed long chains of Si–O–Si and Si–O–Al, and produced an amorphous AAM structure. In the mixed solution, when the NaOH in it dissolved the Si and Al monomers, the Na2SiO3 in the solution also bonded with monomers and produced a complex structure. The different reaction that metakaolin had with different alkali activator solutions reflected the different phases, microstructures, and mechanical properties of the AAMs produced. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Worldwide, it is now known that industrial by-products rich in silicon (Si) and aluminum (Al) can be transformed by alkaline activation into so-called "green concrete", an efficient and sustainable material in the field of construction; the geopolymer material. In this work, geopolymer materials produced using fly ash and marble dust or blast furnace slag were studied to assess the influence of these substitutions on the performances of the final product. Geopolymer materials have been characterized by physico-mechanical methods, FTIR spectroscopy and microscopically. The analysis of the results indicates the reduction of the mechanical strength performance by substituting the fly ash as the raw material. [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]

Recycling aluminosilicate-based solid wastes is imperative to realize the sustainable development of constructions. By using alkali activation technology, aluminosilicate-based solid wastes, such as furnace slag, fly ash, red mud, and most of the bio-ashes, can be turned into alternative binder materials to Portland cement to reduce the carbon footprint of the construction and maintenance activities of concrete structures. In this paper, the chemistry involved in the formation of alkali-activated materials (AAMs) and the influential factors of their properties are briefly reviewed. The commonly used methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG), nuclear magnetic resonance spectroscopy (NMR), and X-ray pair distribution function technology, to characterize the microstructure of AAMs are introduced. Typical characterization results of AAMs are shown and the limitations of each method are discussed. The main challenges, such as shrinkage, creep, efflorescence, carbonation, alkali–silica reaction, and chloride ingress, to conquer for a wider application of AAMs are reviewed. It is shown that several performances of AAMs under certain circumstances seem to be less satisfactory than traditional portland cement systems. Existing strategies to improve these performances are reviewed, and recommendations for future studies are given.

Introduction. Recent years have seen a pressing need to dispose of municipal solid waste due to rapid urbanization. The municipal solid waste incineration fly ash (MSWIFA) produced from solid waste incineration power plant exhibits pozzolanic properties and poses concern of toxicity leaching when used directly as building materials. This paper presents an alkali-activation method to produce sustainable alkali-activated MSWIFA materials (AAFMs) with various MSWIFA dosages and investigate the corresponding fabrication and performance. Materials and Methods. Composited alkali activators activate the MSWIFA with constant alkalinity of 5% and the molar ratio of Si/Na = 0.86. The resulting geopolymers' bulk densities, mineral composites, morphology, and compression strength are thoroughly examined. Results and discussions. Results show that the use of MSWIFA may lead to more loose structures because the bubbles are generated from metallic aluminum and alkali activators. Additionally, the production of multiple crystals also accounts for increasing porosity. The generated multi-crystals such as Sylvite, Halite, Hydrocalumite, Calcium Hydroxide, and Ettringite are further detected from the morphology and mineral analysis. Furthermore, compression tests and toxicity characteristic leaching procedures (TCLP) are conducted to investigate the mechanical performance and heavy metals solidification performance of AAFMs, with an optimal compression strength of 19.99MPa at 28 days for AAFM-10 while toxicity leaching is subject to regularity limits. Conclusions. This study shows that great potential of using the alkali-activation method to recycle hazardous municipal solid fly ash into construction materials with both ecological safety and high performance.

A lot of energy is released during the cement manufacturing process, and a large amount of carbon dioxide (CO2) is discharged into the environment. Presently, researchers are focusing on reducing CO2 emissions by researching sustainable alternatives to traditional Portland cement-based materials. A comparative study on the material characterization of both calcined agro-based waste ash (calcined ash) and uncalcined agro-based waste ash (uncalcined ash) and its utilization as a binder along with granulated blast furnace slag (GGBS) in the alkali activation process is carried out in this paper. The study regarding calcined and uncalcined ash would help in better understanding the variation in the properties of the material and its behavior during the alkali activation process. The tests conducted on both calcined and uncalcined ash along with GGBS include specific gravity, X-ray fluorescence, X-ray diffraction, scanning electron microscopy, reaction degree, Brunauer-Emmett-Teller (BET) analysis, particle size distribution, and the Puntke test for understanding its microstructural characteristics. Later, alkaliactivated mortars are prepared using 30% weight of agro-based waste ash (both calcined and uncalcined) and 70% weight of GGBS. A comparison of the compressive strength of alkali-activated mortars prepared using calcined and uncalcined ash was studied, which showed a promising increase in the strength by 11.02% of mortar prepared using calcined ash (23.46 MPa) for 28 days when compared to mortar prepared using uncalcined ash (21.13 MPa). The major finding from this study indicates that calcined agro-based ash with GGBS shows better results compared to uncalcined agro-based ash with GGBS. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The disposal of municipal solid waste incineration fly ash (MSWIFA) has become a prominent issue due to high environmental risks. In this study, as a potential aluminosilicate precursor, MSWIFA was further alkali-activated as a sustainable construction material in the form of an alkali-activated MSWIFA-based material (AAFM), with a low leaching level of heavy metals. Various 3D-printed polymeric lattices were designed and inserted into the AAFM to promote its inherent brittleness. A special coating was also considered to enhance the alkali resistance of the PEGT lattices. Through a flexural tension test with a 3D digital image correlation (3D-DIC) technique, the failure patterns and strain distributions of the 3D-printed polymeric lattice-enhanced MSWIFA-based composites were tracked. These polymeric lattice-containing composites indicated the promotion of mechanical performance, i.e., higher flexural strengths and good ductility. The 3D polymeric lattice-enhanced MSWIFA-based composites showed application prospects as sustainable construction materials, gaining both environmental benefits and good mechanical performance.

The high-temperature transformations and crystallization of K-based inorganic polymers made from FeO-SiO 2 and FeO-SiO 2 -Al 2 O 3 iron-rich model slags were investigated, with particular focus on the effect of the Al/K and Si/K molar ratios. Upon firing to 1100 °C, the main crystalline phases were hematite and (iron) leucite. Addition of corundum decreases the crystallization rate of leucite. Increasing the Al/K molar ratio increased the thermal stability due to the substitution of Al3+ for Fe3+ in leucite. The Si/K molar ratio impacted the crystallization of leucite. Upon firing to 1100 °C and 1350 °C there was a linear correlation between the amount of leucite and the Si/K molar ratio. Higher Si/K molar ratio resulted in ceramics with higher glass content and lower thermal stability. Thus, the phase assemblage can be adjusted by changing the amount of activator. • Hematite and (iron) leucite were the main crystalline phases upon heating. • Increasing Al/K molar ratio was beneficial for thermal stability. • The leucite content was linearly correlated with the Si/K molar ratio. • Samples with lower Si/K < 2.25 showed good thermal stability up to 1350 °C. [ABSTRACT FROM AUTHOR]