Geopolymerization Process Research Articles

Molecular simulations of the initial stage's induction and formation process of N-A-S-H Gel based on NaOH-activated Metakaolin

In this work, the geopolymerization process was simulated by molecular dynamics based on the NaOH-activated metakaolin system. The structural changes and reaction kinetics during geopolymerization were systematically studied. The results show that the layered structure of MK was gradually destroyed, and the SiO4 and AlO4 monomers were formed. These monomers then reacted with each other to form the network-structured geopolymer. The Alumunum was dissolved prior to silicon and preferentially participated in geopolymerization reaction. The Al3+ acted as a charge-balanced ion to attract the surrounding oxygen linked to Si, making the O-Si-O bond smaller. This study provides a theoretical basis for understanding the reaction kinetics and mechanism of geopolymerization.

Durability of geopolymer cutoff wall backfill incorporating reactive MgO particles under dry-wet cycles

Vertical cutoff wall has been employed for decades to control groundwater flow and subsurface contaminant transport. The barrier performance of cutoff wall material may significantly deteriorate under dry-wet cycles due to precipitation, drought, and groundwater fluctuation. This study adopted active magnesium oxide (MgO) particles to enhance the durability of geopolymer cutoff wall backfill (GCWB) under dry-wet cycles. The influence of particle size and proportion of MgO on the unconfined compressive strength (UCS), hydraulic conductivity, self-healing capacity and durability of GCWB were comprehensively examined. The results indicate that the incorporation of active MgO particles hindered the geopolymerization process of GCWB to a certain extent, leading to an increase in hydraulic conductivity and a decrease in UCS. But the overall performance of GCWB was still favorable. The hydraulic conductivity of samples with MgO gradually increased to more than 1 × 10−8 m/s after at least two dry-wet cycles. In the subsequent cycles, the samples with MgO exhibited a pattern of first gradually declining then ascending in hydraulic conductivity. This is due to hydration and carbonization of the remained MgO in matrix during the dry-wet cycles, which converts into oxygen-rich carbonates, forming well-ramified networks and reducing the proportion of macropores. Thus, the durability of GCWB with MgO is significantly more favorable than that devoid of MgO. In particular, large particle size MgO can exert more persistent self-healing effect, endowing the samples with superior durability under the prolonged dry-wet cycles.

Fe/Mn oxide-based foams via geopolymerization process as novel catalysts for tar removal in biomass gasification

Novel ceramic foams loaded with Fe and Fe/Mn oxides were developed via geopolymerization process as catalysts for tar removal in syngas cleaning operations. The foams were realized through polymer scaffold template replica, by impregnating polyurethane or cellulose foams with a metakaolin based geopolymer slurry loaded with 19 wt% powdered Fe2O3 and Mn2O3 metal oxides. A thermal treatment up to 900 °C was applied to vitrify and partially crystallize into leucite the geopolymer binder. Foams from cellulose showed better structural properties compared to those from polyurethane. Preliminary test in real gasification conditions were carried out on a lab scale double fixed bed reactor. In working conditions, vitrified phases derived from geopolymer binder promoted the formation of mixed phases of (Fe, Mn) oxides and silicates, beneficial for improving the catalytic activity. Furthermore, foams loaded with mixed Fe-Mn oxides were more effective than granules in reducing the produced tar.

The impact of slag on the process of geopolymerization and the mechanical performance of mine-tailings-based alkali-activated lightweight aggregates

Alkali-activated lightweight aggregates (LWAs) made of alkali-activated aluminosilicate-rich mine tailings (MTs) offer a promising alternative to natural lightweight aggregates. The comprehensive investigation of lightweight aggregate production using aluminosilicate-rich MTs in combination with commercial slag as a reactive aluminosilicate remains largely unexplored. In this study, mixtures of MTs and slag were pelletized through the application of a pan pelletizer machine. The study focused on examining the impact of different slag concentrations on the chemical, physical, mechanical, mineralogical, and morphological properties of the produced LWAs. Furthermore, a comparison was made between the physical and mechanical characteristics of the resulting LWAs and those of flay-ash (FA)-based LWAs. The results revealed that the inclusion of slag in LWAs, as compared to FA, led to the production of LWAs with superior physical and mechanical properties. Specifically, as the slag content increases, the water absorption, dissolution, and porosity of LWAs significantly decreased, while the bulk density and compressive strength increased. It is important to note that these changes occur without affecting the specific gravity of the LWAs. The scanning electron microscope (SEM) images clearly showed that the addition of slag, similar to FA, especially at concentrations of more than 20% and higher, promoted uniform geopolymerization within the specimens. Furthermore, the energy-dispersive X-ray spectroscopy (EDS) analysis revealed that all LWAs with concentrations of 20% slag and higher exhibited a Si:Al ratio exceeding three, indicating a higher likelihood of geopolymer backbone formation. The X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) analyses revealed that the alkali activation process led to the depletion of gypsum, originally present in the MTs, and the emergence of sodalite and zeolite in the LWAs. Thermogravimetric analysis (TGA) tests provided additional confirmation of the ongoing geopolymerization process in slag-based LWAs, particularly those containing 20% slag or higher.

Composite Geopolymers Based on Mechanically Activated Fly Ash Blended with SrCO3 (Strontianite) and BaCO3 (Witherite)

In this study, geopolymers based on mechanically activated mixtures of fly ash (FA) with SrCO3 (strontianite) and BaCO3 (witherite) were synthesized. NaOH solution was used as an alkaline agent and curing was carried out under ambient conditions. XRD, FTIR spectroscopy, thermogravimetry, and SEM were used to study the geopolymerization process and microstructure. The product of geopolymerization of the milled (FA + SrCO3) and (FA + BaCO3) blends was X-ray amorphous N-A-S-H gel. The beneficial impact of mechanical activation on the compressive strength of geopolymers was most evident during the initial stages of the curing process. The strength of geopolymers based on the (FA + carbonate) blends after 7 d was either less than the corresponding strength of geopolymers based on the 100% FA or, within the measurement accuracy, equal to it. With increasing curing time, the strength development of geopolymers synthesized from (70% FA + 30% carbonate) blends exceeded the strength growth of geopolymers containing less carbonates; after curing for 180 d, these geopolymers showed the highest compressive strength (20–27 MPa). This trend was more pronounced for the geopolymers based on the (FA + SrCO3) blends. The influence of SrCO3 and BaCO3 addition to the FA on the strength of composite geopolymers was explained by dilution and microfiller effects. The geopolymers based on the FA blended with SrCO3 and BaCO3 exhibit potential applications in immobilizing radioactive strontium and producing radiation shielding materials.

Optimization of constituent proportions for compressive strength of sustainable geopolymer concrete: A statistical approach

Geopolymer concrete (GPC) is an environmentally friendly and sustainable concrete produced through the geopolymerization process, involving the combination of alumino silicate materials with alkaline solutions. It has unique advantage of being carbon-negative which helps reduce carbon dioxide levels in the atmosphere. One challenge with making GPC is the significant variation in compressive strength that arises from differences in constituent proportions, specimen ages, andcuring conditions. There is a need to optimize the GPC constituents to achieve the desired compressive strength. To address this issue, a comprehensive dataset comprising 1242 data points from existing literature on fly ash-based GPC (FA-based GPC) was compiled for the purpose of optimizing the constituent proportions of GPC using statistical analysis. Nine independent variables were selected to develop the predictive models for compressive strength using linear (LRA), multilinear (MRA), and non-linear (NRA) regression analyses. The models were assessed using scatter plots between experimental and predicted responses and adopting the performance criteria such as the statistical significance of the model unknowns, R2 values, root mean square error (RMSE), mean absolute error (MAE), and scatter index (SI). LRA revealed that the compressive strength of GPC is not dependent on any single independent variable. Therefore regression analysis with multiple independent variables was conducted. From MRA, ±15 % error for training dataset and (15–20) % error for validating dataset was estimated. The R2, RMSE, MAE, and SI values were found to be 0.8086, 6.11, 5.35, and 0.21. NRA predicted the compressive strength more efficiently because it provides the error ±10 % for both training and validating datasets with R2, RMSE, MAE, SI values of 0.8321, 5.46, 4.77, and 0.19. Further, curing temperature, specimen age, Na2SiO3/NaOH ratio, I/b ratio, and aggregate content were found as the most significant independent variables. The time and cost-effective design mix for FA based GPC can be prepared using the regression models presented in the current work.

Correlation Study on the Effect of Sintering Mechanism with the Properties of Geopolymer-Based Ceramic

Nepheline geopolymer-based ceramics are emerging as a promising alternative to traditional ceramics due to their eco-friendly production and sustainable nature. Therefore, this study aims to comprehensively investigate the relationship between mechanical behaviour and sintering mechanisms in the production of kaolin geopolymer-based nepheline ceramics. Sodium hydroxide and sodium silicate were mixed to act as the alkaline activator to facilitate the geopolymerization process. The experimental analysis involved varying the sintering temperature within the range of 200°C to 1200°C. The findings from the correlation study highlight that the flexural strength and densification process is in linear relation with R2 of 0.9369, whilst the water absorption and volumetric shrinkage exhibited an inversely linear relationship with the R2 value of 0.8733. The maximum flexural strength of 78.92 MPa and density of 2.56 g/cm3 were achieved when sintered at 1200°C. Meanwhile, the water absorption decreases with the increase of volumetric shrinkage, which might relate to the densification process of the geopolymer-based nepheline ceramic. The outcome of this research contributes a deeper understanding of the interplay between mechanical behaviour and sintering mechanism, enabling the design of superior sintered materials.

Valorization of mineral wool waste in Class F fly ash geopolymer: Geopolymerization, macro properties, and high temperature behavior

The tension between the non-recyclable nature of mineral wool wastes (MWW) and the scarcity of landfill space emphasizes the imperative to explore sustainable ways to valorize these wastes. In this work, the potential of utilizing MWW as both co-precursor and fiber reinforcement in Class F fly ash geopolymer is investigated. The phase composition and microstructure are systematically learned by multiscale physicochemical analysis, followed by the determination of macro properties and high temperature behavior. Results indicate that the ion dissolution and dimension of MWW have a synergetic effect on the microstructural formation and macro performance of the hybrid geopolymer. The inclusion of MWW, particularly in fine particle form, accelerates the geopolymerization process, leading to enhanced gel formation and increased Al uptake in the N-A-S-H gel. With increasing MWW content (0–12 wt%), a denser gel forms, but greater macropore formation increases porosity, subsequently reducing compressive strength. The desired pore structure with optimal MWW substitution significantly reduces drying shrinkage and enhances flexural properties. At elevated temperatures, MWW poses a healing effect on the matrix, achieving a 98.5% increase in compressive strength with MWW-m incorporation. While a drastic thermal shrinkage arises from the substantial mass loss and partial melting of MWW.

Impact of magnesia and titania nanoparticles on characteristics of alkali-activated slag mortars exposed to sulfuric acid solution and elevated temperatures

Nanotechnology is being employed as potential solution to alleviate limitations of alkali-activated slag mortars (AASMs). The current study investigated the impact of prepared magnesia (NMg) and titania nanoparticles (NT) at various dosages (0, 1, 3 and 5 wt%) on mechanical and durability characteristics of AASMs. Specimens were either fully immersed in an aqueous solution of sulfuric acid (1 wt% concentration) or subjected to elevated temperatures (250, 500 and 750℃). Microstructural development and densification were analyzed by XRD, FTIR, and SEM with EDX technique to determine the primary improvement mechanism imparted as a result of employing nanoparticles to AASMs systems. Optimum performance prior to and after exposures was achieved for specimens containing 3% NMg and 1% NT in terms of compressive strength, water absorption for unexposed specimens, and weight loss and compressive strength retention for specimens exposed to sulfuric acid solution and elevated temperature. Nanoparticles produced more densified mixtures imparted by their ability to accelerate geopolymerization processes, filling effect and formation of voluminous compounds that further block available spaces in the microstructure.

Mechanical, Microstructural, and Durability Properties of Soil Stabilized with Alkali-Activated Jarofix for Road Applications

In this study, we investigated the feasibility of jarofix [a zinc (Zn) smelter by-product] as a potential geopolymer binder in soil stabilization for road applications. Different combinations of soil–jarofix (SJ) mixtures were prepared using sodium hydroxide (NaOH), sodium silicate (Na2SiO3), and a combination of NaOH + Na2SiO3 as alkali activators. Unconfined compressive strength (UCS) tests were performed to examine the mechanical performance of SJ mixtures, and the effects of the jarofix content, curing conditions, and curing time were investigated. Changes that occurred during the geopolymerization process were further corroborated using field-emission scanning electron microscope (FESEM) images and energy-dispersive X-ray spectroscopy (EDS) analysis. Durability tests were also performed to examine the weathering resistance of selected SJ mixtures against 12 cycles of alternating wetting and drying. Based on the experimental results, the compressive strength of bare soil was increased 8.8 times, from 0.31 to 2.75 MPa, under ambient curing (AC, at 27 ± 2°C) conditions and 6 times, from 1.1 to 6.55 MPa, under dry curing (DC, at 60°C) conditions. This increase in compressive strength was attributed to the formation of sodium alumino-silicate hydrate (N–A–S–H) gel structures during the geopolymerization process, which led to a compact soil matrix, as confirmed by the FESEM images. The specimens cured under DC conditions showed greater strength improvement than those cured under AC conditions owing to the faster rate of the geopolymerization reaction at elevated temperatures. In addition, the Na2SiO3 and NaOH + Na2SiO3 solutions were found to be the most efficient alkali activators for the SJ mixtures cured under AC and DC conditions, respectively. This durability study revealed that the alkali-activated SJ mixtures exhibit a significantly smaller loss in mass than bare soil when exposed to 12 cycles of alternating wetting and drying. Moreover, the specimens cured under DC conditions were found to be more resistant to weathering than those cured under AC conditions. Overall, soil amended with 15% jarofix (through alkali activation) satisfies the minimum strength and durability criteria recommended by Indian standards for its use as a subbase and subgrade material. The current study shows that jarofix has the potential to be used as a geopolymer binder for soil stabilization, which can help the mining sector in minimizing the volume to be stored in tailings storage facilities.

Effect of Micro Lime on The Ambient Cured Sugarcane Bagasse Ash-Based Geopolymer Concrete

Geopolymer concrete has been the ideal replacement for Ordinary Portland cement concrete in producing green concrete. The binder in geopolymer concrete is a cementitious paste made from amorphous Aluminosilicate and activated by an Alkaline solution. The geopolymerization process is initiated at elevated temperatures. Thus, the curing requires elevated temperatures. This curing method limits the application of geopolymer concrete in the construction industry. In a geopolymer mix, the presence of Calcium ions allows the formation of Calcium Aluminate Silicate and Calcium Silicate Hydrate gels, allowing ambient temperature curing. Therefore, this study investigates the effect of micro lime on the Sugarcane Bagasse Ash-based geopolymer concrete. The micro lime was added to the geopolymer concrete in 1, 3, 5 and 7% by the Sugarcane Bagasse Ash weight. A mix design was based on a Densified Mix Design Algorithm. The tests carried out included compressive strength and water absorption. Ambient curing of the SCBA-based geopolymer concrete was achieved with 1% of the micro lime. The compressive strength increased with the increase of the micro lime, 10N/mm2 at 1%, to 18.25N/mm2 at 7% micro lime. The ambient temperature-cured geopolymer concrete at 3% micro lime had the lowest water absorption rate.

Dynamic behavior of geopolymer stabilized kaolin clay under long-term cyclic loading

Geopolymer has emerged as an alternate cementitious material with a low carbon footprint, as they improve the engineering properties of soft soil without causing a detrimental effect on the environment. This study focuses on developing a combination of geopolymer materials that can fully replace the utilization of traditional binders to stabilize soft soil foundations in geotechnical engineering. Soft kaolin clay was stabilized using ground-granulated blast furnace slag (S) and dolomite (D) as a precursor (P) with combined content of 20% and NaOH: Na2SiO3 ratio of 25:75 as a liquid alkali activator (L) in the geopolymerization process. A series of Unconfined Compressive Strength (UCS) tests were conducted to analyze the influence of various parameters, such as the ratio of S and D, water content of kaolin clay, curing period, and L/P ratio, to select the optimum mix proportions based on strength improvement. This paper also discusses the behavior of geopolymer-stabilized kaolin clay under long-term cyclic loading in stress-controlled conditions. The effect of the S:D ratio, cyclic stress ratio (CSR), curing time, frequency, and confining pressure (CP) on the dynamic shear modulus (G), damping ratio (λ), and degradation index (G/Gmax) were analyzed. The results indicate that the S:D ratio of 16:4 with an L/P ratio of 1, NaOH: Na2SiO3 ratio of 25:75, and water content of liquid limit (LL) cured for 28 days gives the highest UCS value of 1.47 MPa. The initial dynamic shear modulus (Gmax) increases by 60% as the S:D ratio changes from 20:0 to 16:4. The cyclic performance of geopolymer-stabilized kaolin clay in terms of accumulative strain as a function of the number of loading cycles was also enhanced. The findings of the study provide guidance to a better understanding of the long-term dynamic behavior and application of geopolymer-stabilized kaolin clay as a greener approach to ground improvement.

Thermal Behaviour and Microstructure of Self-Cured High-Strength Plain and Fibrous Geopolymer Concrete Exposed to Various Fire Scenarios

The fire resistance of construction materials is an essential part of safety requirements in the construction industry. In this work, experimental investigations were conducted to understand the thermal behaviour, spalling, transfer characteristics, strength, and microstructures of self-cured high-strength plain (HSGC) and steel-fibre-reinforced geopolymer concrete (S–HSGC) under severe fire scenarios with peak temperatures of 275, 560, and 825 °C; the peak was maintained for a period of 120 min after reaching it. Forty-eight standard cylindrical specimens for each mixture were prepared to test and analyse their time–heat response, gradients, visual appearance, spalling, density change, water absorption, and compressive strength before and after fire exposure. Additionally, Scanning Electron Microscopy (SEM) along with Energy Dispersive X-ray Analysis (EDX) were utilised to analyse the internal structures and phase transformations. The thermal analysis showed that no cases of explosive spalling were recorded during sample exposure to various fires, while the used hook-end steel fibres had an influence on the considered test variables. The sample cores almost reached the target heat, and the thermal saturation degree at the peak ranged from 55 to 97%. The experimental findings also revealed slight surface cracking after exposure to 560 °C fires, while the surface cracking was more obvious for specimens exposed to 825 °C. Moreover, the residual compressive strength of the S–HSGC at various fires was noticeably 10.20% higher than that of the HSGC. Also, state-of-the-art research data were used to discuss the prediction model’s performance. The SEM and EDX results showed that the self-cured geopolymerization process was effective and successful in producing gels, in addition to the significant phase transformations in microstructures at different fires. This study presented sophisticated data on the behaviour of HSGC and S–HSGC exposed to fires up to 825 °C.

Early performance and bonding mechanism of metakaolin (MK)- ground granulated blast furnace slag (GGBS) based geopolymer road repair mortar

ABSTRACT Metakaolin (MK) and ground granulated blast furnace slag (GGBS) based geopolymers have been utilised as materials for concrete road repair. However, their early-stage performance and bonding mechanism as rapid repairs are not well understood. This research investigated the workability, early strength development and bonding mechanism of geopolymer repair mortars with different GGBS contents. The reaction kinetics and reaction products of the geopolymer repairs were analyzed through reaction heat evolution and FTIR, and the microstructure of the bonding interface was examined using BSE-EDS. Results showed that geopolymer repair mortars with higher GGBS content exhibited shorter setting times, higher flowability, and higher compressive strength. Geopolymers demonstrated a one-dimensional rod-shaped nucleation pattern during hardening, and the crystallization rate decreased with GGBS addition. GGBS increased the formation of C-A-S-H gels and accelerated the geopolymerization process. However, excessive GGBS reduced bond strength due to the introduction of microcracks. A GGBS content of 60 wt.% is recommended in this investigation. The study also revealed that the cement substrate could absorb alkali activator, leading to the formation of high-Ca gels and strengthening the interface.

Impact of Low-Reactivity Calcined Clay on the Performance of Fly Ash-Based Geopolymer Mortar

Availability of aluminosiliceous materials is essential for the production and promotion of geopolymer concrete. Unlike fly ash, which can only be found in industrial regions, clays are available almost everywhere but have not received sufficient attention to their potential use as a precursor for geopolymer synthesis. This study investigates the effectiveness of calcined clay as a sole and binary precursor (with fly ash) for the preparation of geopolymer mortar. Fly ash-based geopolymer containing between 0 and 100% low-grade calcined clay was prepared to investigate the effect of calcined clay replacement on the geopolymerization process and resultant mortar, using a constant liquid/solid ratio. Reagent-grade sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) were mixed and used for the alkali solution preparation. Six different mortar mixes were formulated using sand and the geopolymer binder, comprising varying fly ash-to-calcined clay ratios. The combined effect of the two source materials on compressive strength, setting time, autogenous shrinkage, and porosity was studied. The source materials were characterized using XRD, SEM, FTIR, and XRF techniques. Isothermal calorimetry was used to characterize the effect of low-grade calcined clay on the geopolymerization process. The addition of calcined clay reduced the surface interaction between the dissolved particles in the alkali solution, leading to slow initial reactivity. Geopolymer mortar containing 20% calcined clay outperformed the reference geopolymer mortar by 5.6%, 17%, and 18.5% at 7, 28, and 91 days, respectively. The MIP analysis revealed that refinement of the pore structure of geopolymer specimens containing calcined clay resulted in the release of tensional forces within the pore fluid. Optimum replacement was found to be 20%. From this study, the mutual reliance on the physical and inherent properties of the two precursors to produce geopolymer mortar with desirable properties has been shown. The findings strongly suggest that clay containing low content of kaolinite can be calcined and added to fly ash, together with appropriate alkali activators, to produce a suitable geopolymer binder for construction applications.

Performance of nano titania-reinforced slag/basalt geopolymer composites

In Egypt, basalt manufacturing generates waste materials at a rate of about 33%. The disposal of basalt waste through the manufacturing of cementitious materials is an economically feasible approach. This work involved the fabrication of a one-part slag/basalt waste geopolymer cement (GP) enhanced by nano-TiO2. The physico-mechanical properties of the different GP mixes were investigated. The durability against fire at up to 750 °C, sulfate (SO4−2) attack, and irradiation with significant dosages of γ-rays at up to 1500 kGy were assessed. Phase composition and microstructure were explored through various techniques as XRD, TG, and SEM. The findings demonstrated that basalt incorporation up to 20% within the GP mix boosted its mechanical characteristics after 28 and 90 days of curing by 8.5 and 2.5%, respectively, while 60% replacement diminished the strength by 30%. Slag/basalt GP showed a comprehensible resistance to SO4−2 ions attack, and its strength was intensified by 14% after 4 months of immersion. Additionally, the blended GP mixes could preserve 40% of their strength after being exposed to 1500 kGy of γ-rays and about 50% of their strength after firing at 750 °C. Admixing GP by NT showed a synergic impact for diminishing setting times, boosting compressive strength by 5 ~ 15% compared to reference mix along with an improvement in the microstructure. Furthermore, distributing NT through GP greatly improved durability after firing at 500 and 700 °C and irradiating with high dosages of γ-rays. This feature is mostly connected to the catalytic capabilities and filling activities of NT in boosting geopolymerization processes.

Impact of Sulfate in the Sand on the Compressive Strength of Metakaolin-Based Geopolymer Mortar

The advancement of cement alternatives in the construction materials industry is fundamental to sustainable development. Geopolymer is the optimal substitute for ordinary Portland cement, which produces 80% less CO2 emissions than ordinary Portland cement. Metakaolin was used as one of the raw materials in the geopolymerization process. This research examines the influence of three different percentages of sulfate (0.00038, 1.532, and 16.24) % in sand per molarity of NaOH on the compressive strength of metakaolin-based geopolymer mortar (MK-GPM). Samples were prepared with two different molarities (8M and 12M) and cured at room temperature. The best compressive strength value (56.98MPa) was recorded with 12M with lower sulfate content (0.00038%) at 28 days. Also, an inverse relationship is recorded between the increasing sulfate percentages in the sand and the compressive strength values of (MK-GPM). A higher reduction in the compressive strength results at 28 days (60.88% per 8M/NaOH) and (62.23% per 12M/NaOH) was associated with a higher percentage of SO3 in the sand (16.24%).

Early age strength of ambient-cured geopolymer mortars from waste concrete and bricks with different alkaline activators.

Background: The dataset in this work emanates from preliminary studies comparing early-age compressive strengths of geopolymer mortars produced from construction and demolition wastes (CDW) commonly found in Qatar using different alkaline activators. Methods: Waste concrete, waste bricks and steel slag - an industrial waste produced in large quantities in the country - were used as aluminosilicate sources. Waste concrete was used as fine aggregate (75 μm to 4 mm), while solid or hollow red clay bricks were used together with steel slag as aluminosilicate powders. Solid red clay brick (75 μm to 1.4 mm) was also used as fine aggregate in some mixes. Different alkaline activators including solid powder or ground pellet forms of Ca(OH)2, CaO, and Ca(OH)2-NaOH, NaOH-CaCO3 and Na2SiO3-Na2CO3-Ca(OH)2 mixtures were employed by just adding water. A few mixes included both solid powder Ca(OH)2 and viscous solutions of NaOH and NaOH-Na2SiO3 as alkaline activators. The geopolymer mortars also included small amounts of some other additives such as gypsum, microsilica and aluminium sulfate to enhance the geopolymerization and hydration process. Random proportions of the materials were considered in the range-finding experiments, and the mortars produced were tested for compressive strength. Results: The data show the 7-day compressive strengths and densities of the 40 mixtures considered with mostly ambient temperature (20°C) curing. It also shows such data for mixtures in which variables such as curing at 40°C, mixing with hot water at 50 - 60°C temperature, grading of waste concrete aggregates, and collective grinding of the powdered materials were considered. Conclusions: The dataset shows possible early-age compressive strengths of different geopolymer mortar mixture designs and the materials and mixture design methods that can be used to achieve desired early-age strengths from waste concrete and bricks.

Utilization of municipal solid waste incineration fly ash with coal fly ash/metakaolin for geopolymer composites preparation

The geopolymer technique is a promising method for the solidification/stabilization (S/S) treatment of municipal solid waste incineration fly ash (MSWIFA). To investigate the feasibility of resource utilization in MSWIFA by geopolymerization process, the macroscopic and microscopic properties of the coal fly ash/metakaolin-based geopolymer composites containing MSWIFA were studied. The leaching test was conducted to evaluate the S/S effect of geopolymer. Results showed that CFA/MK-based geopolymer demonstrated effective stabilization of heavy metals in MSWIFA. The flowability of geopolymer composites increased with the MSWIFA content, where 40% replacement ratio of MSWIFA significantly improved the slump and consistency of geopolymer mortar by 86.3% and 80.4%. However, 40% content of MSWIFA reduced the compressive strength and splitting tensile strength of geopolymer composites by 80% and 62%. The strength development rate in early ages of geopolymer composites was accelerated by mixing less than 15% MSWIFA. Whereas, the strength development at 7–28 days was almost unaffected by MSWIFA. The addition of MSWIFA decreased the amount of sodium-(calcium) aluminosilicate hydrate and sodium aluminosilicate hydrate gels. Although the addition of MSWIFA refined the gel pores in geopolymer, the pore volume and porosity increased and the compactness of microstructure decreased with the increment of the MSWIFA content in geopolymer composites. Based on these results, it is feasible to realize resource utilization of MSWIFA using geopolymer composites with low content of MSWIFA (less than 15% was recommended in this study).

Factor Analysis of the Physical–Mechanical Properties for Geopolymers Based on Brick Dust and Biomass Bottom Ash as Eco-Friendly Building Materials

The production of building materials is unavoidable if the well-being and development of society are to be maintained. However, in manufacturing these materials, significant greenhouse gas emissions and environmental effects are produced. For this reason, and with the aim of reducing the impact of the manufacture of these materials, this work developed a geopolymeric material made up solely of wastes, brick dust and biomass bottom ashes which replaced the traditional ceramic materials. To evaluate the quality of this sustainable geopolymeric material, different groups of specimens were formed with different percentages of both residues, subsequently determining the physical properties of the new-formed geopolymers and guaranteeing they accomplish the prescriptions of the ceramic regulations for construction. In addition, the results of the geopolymer characterisation tests were statistically analysed using factor analysis, with the sole purpose of establishing connections and interdependence between the variables that influence the geopolymerisation process. Thus, it was possible to demonstrate that the combination of brick dust and biomass bottom ashes produced geopolymers with adequate qualities to replace traditional ceramics, as well as that the different combinations of both residues produced feasible materials to be used as ceramics with various characteristics, with two main factors determined by factorial analysis that governed the physical properties of the geopolymer obtained: the percentage of brick dust and the theoretical porosity.