Hydrated Calcium Aluminosilicate Research Articles

Effects of K+ and CO32− on the performance of slag–ceramic blended geopolymers

Binders developed by using activation technology have received considerable attention as alternatives to Portland cement. The aim of this study was to investigate the effect of introducing K+ and CO32− into geopolymer samples on the properties of alkali-activated slag cement (AASC) composed of blast furnace slag (BFS) and ceramic waste powder (CWP). The CWP replaced 20% of the BFS in the AASC. The activator solutions used were Na2SiO3–NaOH (NSNH), Na2SiO3–KOH (NSKH), and K2CO3–NaOH (KCNH) hybrid solutions. Parameters for evaluating the samples included the heat of hydration, thermogravimetric and differential thermogravimeric curves, ultrasonic pulse velocity, compressive strength, attenuated total reflectance–Fourier transform infrared spectra, X-ray diffraction patterns, and resistivity. The results showed that after K+ was introduced into the geopolymer (NSNH to NSKH), the compressive strength of the NSKH sample was increased. Consequently, the formation of a hydrotalcite phase was promoted and that of a calcium aluminosilicate hydrate (CASH) gel was inhibited. After K+ and CO32− were introduced simultaneously (NSNH to KCNH), the compressive strength of the KCNH sample decreased, and the surface resistivity increased significantly. Moreover, the peak of the exothermic hydration rate moved forward. The accumulated hydration heat increased and carbonates were formed, thereby altering the composition of the three-dimensional network structure of the CASH gel, which significantly contributed to its strength.

Effect of nickel slag on the basic tensile creep of alkali-activated slag/nickel slag mortars

Alkali-activated slag (AAS) is used as a green cementitious material with high strength and good durability, while the cracking damage due to high shrinkage limits the application of AAS in engineering project. The tensile stresses due to shrinkage can easily lead to the cracking of structures, while basic tensile creep can relax part of the tensile stresses and reduce the cracking risk. This study aims to investigate the effect of nickel slag (NS) on the basic tensile creep of alkali-activated slag/nickel slag mortars (ASNms). NS content refers to the weight ratio of NS to the summation of slag and NS. The properties of ASNms, including microstructure, hydration heat, internal relative humidity, mechanical properties, autogenous shrinkage and basic tensile creep, are studied. Results show that the mechanical properties of ASNms decrease with the increase in NS content. By reducing the hydration degree, the incorporation of NS decreases the amount of calcium aluminosilicate hydrate (C-(A-)SH) of ASNms, and the internal relative humidity and nominal crystal-binder ratio of ASNms are increased. As a result, the autogenous shrinkage of ASNms was significantly mitigated by incorporating NS. Autogenous shrinkage is the driving force of tensile creep. With the increase in NS content, the Na+ content absorbed by C-(A-)SH decrease, and therefore reduces the basic tensile creep of ASNms.

Influence of Associated Cations on the Transport and Adsorption of Chloride Ions in the Nano-channel of Calcium Aluminosilicate Hydrate Gel: A Molecular Dynamics Study

Influence of Associated Cations on the Transport and Adsorption of Chloride Ions in the Nano-channel of Calcium Aluminosilicate Hydrate Gel: A Molecular Dynamics Study

Towards greener one-part geopolymers through solid sodium activators modification

This paper investigates the influence of various solid activators and their mixing parameters on the physical, mechanical and microstructural characteristics of greener one-part geopolymers (OPG) based on high calcium fly ash. The high calcium fly ash that has rarely been explored was utilised to develop OPG in this study. The anhydrous sodium metasilicate (Na2SiO3) with negative environmental impact propelled the partial replacement of Na2SiO3 with sodium hydroxide (NaOH) and sodium carbonate (Na2CO3). Two sets of high calcium fly ash OPGs were developed: (1) the MH-OPG comprised Na2SiO3 and NaOH; (2) the MC-OPG comprised Na2SiO3 and Na2CO3. The optimal MH-OPG (73 MPa) and MC-OPG (75 MPa) exhibited superior compressive strength, higher than the minimal requirement (>28 MPa) of ASTM C150/C150M-18 for construction binder material. Various solid alkali activators triggered different reaction mechanisms, yielding distinctive reaction products that contributed to strength growth. The sodium calcium aluminosilicate hydrate ((N,C)-A-S-H) gel was developed in MH-OPG, whereas the sodium carbonate hydrate, sodium aluminosilicate hydrate (N-A-S-H) and calcium aluminosilicate hydrate (C-A-S-H) binding phases were developed in the MC-OPG. Although Na2CO3 reduced the water demand, improved the fluidity and setting time, the MC-OPG was more sensitive to the alteration of mixing compositions, suggesting a tougher performance control during field application than the MH-OPG. The total embodied carbon (EC) of MC-OPG was lowered by 15.4% compared to that of MH-OPG. The embodied carbon index (ECI) of MH-OPG and MC-OPG were 81.3% and 84.7% less than that of OPC products. This work suggests that substituting Na2SiO3 with NaOH or Na2CO3 effectively produced a greener construction material without compromising mechanical strength.

Correlation between porous structure analysis, mechanical efficiency and gamma-ray attenuation power for hydrothermally treated slag-glass waste-based geopolymer

The main objective of this work is to compare conventional Portland cement pastes (OPC) and alkali-activated geopolymer pastes in terms of compressive strength, phase composition, micro-porosity, and attenuation ability against harmful gamma irradiation. OPC pastes were cured at 20 °C in tap water for up to 28 days, while geopolymer pastes were prepared by recycling two different industrial byproducts. Equal masses of slag (GGBFS) and recycled glass powder (RGP) were activated by two concentrations of NaOH (5% and 10% mass of total binders). The obtained geopolymer pastes were treated in different manners; some pastes were treated in high humidity at 20 °C and 80 °C for 28 days, while other pastes were cured in an autoclave for different time intervals (2, 4, 8 and 12 hrs) and different steam pressures (4, 6 and 8 bar). A Gamma attenuation capacity test was performed to determine the linear attenuation coefficient (µ) for some selected hardened pastes. Two sources of gamma-ray were used (137Cs/661.6Kev &60Co/1332.5Kev). To correlate mechanical performance and attenuation behavior, the N2-adsorption/desorption technique was conducted to analyze the micro-porosity. The results indicated GGBFS-RGP geopolymer pastes activated by 5 wt% NaOH and thermally hydrated at 4bars for 8hrs possessed the highest compressive strength (86 MPa), highest attenuation ability (µ = 0.156 and 0.126 cm−1), highest BET "Brunauer-Emmett-Teller model" surface area (10048 cm2/g) and minimum BJH "Barrett-Joyner-Halenda model"-average pore diameter (23.6 nm) as compared with OPC pastes and other all geopolymer pastes. After the autoclaving process, calcium-silicate-hydrate (C-S-Hs), calcium-alumino-silicate-hydrate (C-A-S-Hs), calcium-alumino-hydrate (C-A-Hs), sodium-alumino-silicate-hydrate (N-A-S-Hs) and hexagonal zeolite phase has been achieved via X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscope (SEM/EDX).

Na2SO4 modified low-carbon cementitious binder containing commercial low-reactivity metakaolin for heavy metal immobilization: Mechanism of physical encapsulation and chemical binding

In this study, a Na2SO4 modified low-carbon cementitious binder based on commercial low-reactivity metakaolin (MK) and cement was utilized for the immobilization heavy metals (Cu2+, Ni2+, Cd2+ and Zn2+). The compressive strengths and leaching concentrations of the immobilization systems were investigated to evaluate the immobilization effect for heavy metals. Meanwhile, the pore structure and chemical compositions of the immobilization systems were characterized to study the immobilization mechanisms. Results demonstrate that the MK-blended systems exhibit excellent heavy metal immobilization effect and low releasing risk under the effect of Na2SO4. The incorporation of Na2SO4 significantly improve the compressive strength of the MK-blended systems due to the promotion effect on the early hydration kinetics of cement, the formation of ettringite and the pozzolanic reaction of MK. Moreover, the incorporation of Na2SO4 decreases the capillary porosity and/or increases the tortuosity of the MK-blended systems, which enhances the physical encapsulation to heavy metals. The MK-blended systems have higher chemical binding capacities to heavy metals than pure cement immobilization systems. This is due to the increase in the Si/Ca and Al/Ca atom ratios of calcium aluminosilicate hydrate that introduces more negative charged silicon and aluminium sites to bind heavy metal cations.

Novel application of low carbon limestone calcined clay cement (LC3) in expansive soil stabilization: An eco-efficient approach

This article presents the novel application of new ternary low carbon limestone calcined clay cement (LC3) to deal with construction problems associated with problematic expansive soils. Such soils exhibit high volumetric change behavior and cause extreme distress or failure to the overlying engineering structures. Various calcium-based admixtures such as lime and ordinary Portland cement (OPC) have been extensively used to mitigate its adverse effects, but have a huge environmental impact in terms of high carbon footprints. In this regard, recently developed low carbon LC3 has been applied in concrete technology for various purposes, however, its efficacy for expansive soil stabilization is still unknown. Therefore, this study for the first time investigates a wide spectrum of macro-micro properties of LC3-treated soil and reveals its underlying stabilization mechanism. LC3 addition exhibits complete mitigation of swelling behavior, reduced saturated hydraulic conductivity along with significant improvement in compressive strength considering the long-term curing period. The stabilization mechanism reveals that corresponding amelioration in engineering properties falls under three phases; 1) cation exchange; 2) flocculation or agglomeration, and 3) hydration products such as calcium aluminosilicate hydrate (CASH), coupled with AFt (ettringite) phases which act as a filler material by creating a high pH environment. Estimation shows that LC3 usage in place of OPC for expansive subgrade of the 1-km two-lane road can save consumption of approximately 350 GJ and 12594 kWh of thermal and electrical energies, respectively, and CO2 emission of around 27420 kg of C. Overall, the LC3 application in problematic expansive soil stabilization not only adds a new dimension but also provides a sustainable and environmentally friendly alternative to reduce the carbon footprints of traditional techniques.

The effect of alkaline activators and sand ratio on the physico-mechanical properties of blast furnace slag based mortars

Alkali activation of blast furnace slag with sodium silicate (SS) and sodium hydroxide (NaOH) or potassium hydroxide (KOH) has been extensively studied, however a comprehensive and comparative study between NaOH and KOH activated blast furnace slag without SS is limited, especially in terms of drying shrinkage. Therefore, the present study focused on the effect of using NaOH or KOH as sole alkaline activators to produce alkali-activated slag mortars (AASMs) and to comparatively evaluate their effects on the rheological properties, setting time, drying shrinkage, compressive strength and microstructural properties. Furthermore, statistical analysis was performed to establish relationship between selected parameters. The results showed that using KOH as the sole activator provided advantages such as enhanced fluidity and compressive strength and NaOH provided benefits such as reduced setting time, water absorption and drying shrinkage. In addition, the increase in the molarity of either alkaline solution decreased the yield stress and plastic viscosity of the paste. The X-ray diffraction analysis revealed major peaks of calcium silicate hydrate, calcium aluminosilicate hydrate, and hydrotalcite as reaction products in both NaOH and KOH activated mixes. The higher molarity of NaOH or KOH solution led to a decrease in the total porosity of the paste mixes but increased macro-pores as identified by mercury intrusion porosimetry analysis. The use of higher amount of sand reduced the permeable pore volume and the drying shrinkage of the mortar samples. The development of capillary pore volume and the drying shrinkage were well correlated irrespective of the alkaline activator types and sand ratio. Statistically significant relationships were found to predict compressive strength and drying shrinkage of AASM depending on mix design parameters and curing time.

Alkali-activated system of carbide lime and rice husk for granular soil stabilisation

This study investigated the utilisation of an alkali-activated system to stabilise a granular soil. Rice husk ash (RHA) was used as the precursor and carbide lime (CL) as the activator. An experimental programme was carried out to analyse the strength and stiffness of sand–RHA–CL mixtures. Different binder contents (10 and 20%), densities (15.5, 16.5, 17.5 kN/m3), curing periods (7 and 28 days) and calcium/silicon dioxide (Ca/SiO2) ratios (1, 1.5, 2) were evaluated. Microstructural analyses were conducted on the mixed materials. The increase in binder content, dry density and curing period led to the improvement of strength and stiffness, while the increase in calcium/silicon dioxide ratio hindered the mechanical behaviour. The statistical analysis revealed that all factors studied influenced the mechanical behaviour of soil–binder mixtures. The condition to obtain the highest strength and stiffness was evidenced in the combination of higher dry unit weight, binder content, curing period and lower molar ratio. The alkali-activated system was shown to be a promising binder agent for soil stabilisation for both strength and stiffness. Finally, two calcium aluminosilicate hydrate structures were identified in the soil–binder mixtures, soulunite and jaffeite, indicating ideal structures for the composition of cement hydrates.

The nanomechanical properties of non-crosslinked calcium aluminosilicate hydrate: The influences of tetrahedral Al and curing age

Calcium aluminosilicate hydrate (C-A-S-H) is the binding phase of both blended cement-based and alkali-activated materials. The intrinsic mechanical properties of non-cross-linked C-A-S-H are important while experimentally unvalidated. Here, the properties are for the first time measured using high-pressure X-ray diffraction. The incompressibility and bulk modulus K0 of C-A-S-Hs are correlated to their nanostructure and stability using nuclear magnetic resonance and X-ray absorption spectroscopies. Al coordination in stable C-A-S-H (Al/Si = 0.1) cured for 546 days is purely tetrahedral (AlIV), while in metastable C-A-S-H (Al/Si = 0.05) cured for only 182 days is both AlIV and pentahedral (AlV). The stable C-A-S-H is stiffer along the a,b,c-axis with higher K0 relative to C-S-H. Short-curing-induced metastable C-A-S-H (Al/Si = 0.05) shows expanded interlayer and softer c-axis, thus lower K0 than C-S-H and the stable C-A-S-H. Our results highlight the stiffening effect of AlIV incorporation and the negative influences of insufficient curing on the nanomechanical properties of non-cross-linked C-A-S-H at Ca/Si = 1.

Development of potentials for molecular dynamics simulations of dry and hydrated calcium aluminosilicate glasses by force matching and refinement

Potential development and refinement to improve the applicability and transferability of the forcefield is important to atomistic simulations of glass materials and their interactions with the environment. In this paper, we demonstrate potential development of calcium aluminosilicate glasses with and without water using a reactive potential framework by adopting the force matching technique and subsequent refinement. Accordingly, we have reproduced the forces on atoms of the system from a DFT based ab-initio molecular dynamics (AIMD) simulations by adjusting the potential parameters. We chose the diffuse charge reactive potential (DCRP) as the classical potential as it has been previously demonstrated to accurately and efficiently simulate interactions between water and silicate-glasses. The obtained force matched parameters were further refined to accurately reproduce the structures and dynamics of dry and hydrated calcium alumino silicate glass and gel structures. The Ca2+ behavior in solution was correctly reproduced with an average local coordination equal to 6.12 and a diffusion coefficient close to the experimental values. This force field also correctly reproduces the local environment of Al3+ in glass, but it falls short in describing Al3+ ion coordination in solutions as compared to AIMD results, suggesting a direction of future improvement. This set of potential can thus be used for simulations of calcium aluminosilicate glasses with various technological applications and hydrated gel structures resulted from corrosions of boroaluminosilicate glasses.

Effect of Hydration Process on Properties and Microstructure of Coal Gangue Admixture Concrete

The mineral of coal gangue is mainly kaolinite, which can be used as mineral admixture after activation. In order to study the effect of coal gangue on the hydration process of concrete, 20% coal gangue powder was used to replace cement to prepare concrete. The phase composition, microstructure morphology and pore structure of concrete hydration products at different ages were observed by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). At the same time, the experimental study on the compressive strength, splitting tensile strength and flexural strength of coal gangue admixture concrete with time and relationship was carried out. The results indicate that the addition of coal gangue powder significantly affected the hydration process of cement. In the cement-coal gangue powder-water system, coal gangue particles adsorbed a large amount of CH generated by cement hydration after curing for 14 d. The (AlO4)4− group in the coal gangue power replaced the (SiO4)4− on the calcium silicate hydrate (C-S-H) structure of the hydration product, thereby generating a new flocculated polymer calcium aluminosilicate hydrate (C-A-S-H). Until the curing age exceeded 56 d, the CH content in the slurry was less, and the hydration reaction rate of coal gangue became slowe. The unhydrated coal gangue particles played the “micro-aggregate effect”, filled in the pores and reduced the number of macropores and pores. The density of concrete microstructure increased, which promoted the continuous increase of concrete strength.

Antimicrobial performance and biodeterioration mechanisms of alkali-activated slag

Eco-friendly antimicrobial alkali-activated slag (AAS) binders show great promise in newly designed and existing wastewater infrastructure threatened by microbial induced concrete corrosion (MICC). This work investigates the antimicrobial performance and biodegradation mechanisms of a new benzoate (BZ)-modified AAS binder. The bacterial activity, corrosion morphology, and material degradation mechanisms, of the novel BZ-modified antimicrobial AAS post-simulated MICC tests are analysed. The bacterial activity assessments (pH value, sulphate concentration, and live/dead staining) results demonstrate the remarkable antimicrobial efficacy of BZ-modified AAS in killing sulphur-oxidising bacteria A. thiooxidans and inhibiting biogenic acidification. The BZ-modified AAS demonstrates excellent microbial corrosion resistance with greatly suppressed production of deleterious gypsum and corrosion depth. The mechanisms of biodeterioration of antimicrobial AAS matrix are revealed, suggesting the nanoscale rupture of calcium-aluminosilicate-hydrate (C-A-S-H) in short chains and networking of aluminosilicate unites upon the removal of interlayer CaO polyhedral. The removal of Al-tetrahedra from bridging sites of C-A-S-H is more susceptible than that of Si-tetrahedra in AAS pastes under microbial corrosion. This study has demonstrated the potentials of novel antimicrobial AAS-based concrete as the next-generation construction materials for wastewater infrastructure.

Strength properties and microstructural characteristics of clay treated with alkali activated mortar and fiber

Chemical stabilization, along with strengthening and reinforcing the soil with the use of fibers are among the methods employed for soil improvement. In recent years, the application of alkali-activated mortars has received considerable attention due to less CO2 emissions along with no need to precure the pozzolans used to make the mortar. Application of fibers in addition to chemical stabilizers can be effective to increase the ductility and tensile strength of improved soils and delay the rupture process. Basalt fibers, which are of natural origin and have very high resistance in acidic, alkaline, and saline environments, are considered as suitable options for reinforcement of alkali-activated mortars. In the present study, the improvement of a type of clay has been examined using basalt fibers and the alkali-activated mortar. To investigate the strength parameters of the improved clay soil, a combination of basalt fibers and alkali-activated mortar (Clay improved with 3% wollastonite and 16% potassium hydroxide alkaline solution) was prepared and was then subjected to uniaxial compressive strength and indirect tensile strength tests after curing times of 7, 14, 28 and 90 days. Also, electron microscope images (SEM) and EDX analyses were performed on the samples to interpret the results. The results showed that in samples improved with alkali-activated mortars, the formation of calcium silicate hydrate(C-S-H) and calcium aluminosilicate hydrate (C-A-S-H) gels and their polymerization after the curing time increased the compressive and tensile strengths. In the samples improved with alkali-activated mortars reinforced with basalt fibers, the ductility of the samples also increased in addition to the increase in the compressive and tensile strengths as the gels formed were interlocked among the fibers.

Mineralogy of tricalcium aluminate hydration with silica nanoparticles

Formation of siliceous-hydrogarnet (Si-hydrogarnet) and stability of katoite (C3AH6) in tricalcium aluminate (C3A) system in presence of silica nanoparticles (n-SiO2) have been examined in the present study. C3A hydration in presence of n-SiO2 upto 24 h show retardation in hydration due to the surface coverage of C3A grain through calcium-silicate-hydrate (C-S-H)/calcium-alumino-silicate-hydrate (C-A-S-H) (previous study). However, in the present investigation, hydration was studied upto 10 days using QXRD, TGA, FTIR, FESEM, EDS and Mapping and 29Si NMR techniques. QXRD results show that in case of control samples, the katoite content increases from 61 to 73%, while in n-SiO2 incorporated C3A samples, it decreases from 28 to 15% as the hydration proceeds showing katoite phase destabilization in presence of n-SiO2. Further, FTIR results show symmetric stretching vibration of Si-O-Si at ∼784 cm−1 and ∼818 cm−1, while asymmetric stretching vibration of Si–O–Si/Si-O-Al at ∼1028 cm−1 indicating the formation of C-S-H/C-A-S-H and Si-hydrogarnet in presence of n-SiO2. In 29Si NMR results, Q2u peak at −89 ppm confirm the formation of Si-hydrogarnet at 10 days of hydration. The present study is important from performance and durability point of view as formation of C-A-S-H and Si-hydrogarnet can act as an aluminum reservoir, which may prevent severe chloride and sulphate attack.

Synthesis of nanoparticles from slag and their enhancement effect on hydration properties of CaO/CaSO4-activated slag binder

Developing a low-cost and eco-friendly alternative to cement is of great significance for reducing the CO2 emissions. CaO/CaSO4-activated slag binder may only be served as a promising cementitious material when the severe defect in the early strength is overcame. In this study, gel-like nanoparticles with an average size of ∼ 328 nm were prepared from the slag through dissolution at room temperature and reprecipitation at 50 °C. Subsequently, synthetic nanoparticles (SNPs) were added as a supplementary additive to enhance the strength of CaO/CaSO4-activated slag binder. The effects of SNPs on the strength development, hydration kinetics, hydration products, and microstructure of the slag binders were investigated. The results indicated that the addition of moderate SNPs shortened the duration of induction period and improved the reaction rate in the acceleration period of the slag binders. As a result, large amounts of calcium aluminosilicate hydrate (C-A-S-H) gel was generated at early hydration ages. Meanwhile, SNPs increased the polymerization degree of this gel through the nucleation effect. Gel products’ well-filled the pore spaces between slag particles and yielded a compact microstructure, consequently enhancing the binder strength. The sample with adding 1.5 wt% SNPs exhibited the optimum strengths of 7.78 and 39.86 MPa after 1 and 28 days.

Antimicrobial alkali-activated slag through self-intercalation of benzoate in layered double hydroxides

Antimicrobial alkali-activated slag (AAS) with biocidal effectiveness is a promising cementitious binder for concrete infrastructure threatened by microbially induced concrete corrosion (MICC). In this work, the influence of sodium benzoate on the chemical reaction, phase assemblage, microstructure, and nanostructure of AAS was studied, with a particular focus on the potential in-situ formation of benzoate-intercalated layered double hydroxides (BZ-LDHs). In addition, the lattice structure, molecular bonds, and intercalation chemistry of pure BZ-LDHs synthesised using rehydration method were investigated. The results evidence the in-situ formation of BZ-LDHs in AAS incorporating sodium benzoate during alkaline activation. The benzoate anions are spontaneously intercalated in a bilayer manner in the interlayers of LDHs, with an average basal spacing of 1.568 nm. The incorporation of BZ slightly lowers the reaction degree of slag in AAS, but barely affects the composition and structure of calcium-aluminosilicate-hydrate (C-A-S-H) formed. The developed antimicrobial AAS with BZ-LDHs demonstrates remarkable bactericidal efficacy with a 95.0% effectiveness (when admixed with 3% BZ) in suppressing the growth of sulphur-oxidising bacteria Acidithiobacillus thiooxidans in this study.

Phase Analysis of Alkali-Activated Slag Hybridized with Low-Calcium and High-Calcium Fly Ash

This paper investigates the hydrated phase assemblage, microstructure, and gel composition of sodium hydroxide (NaOH)-activated fly ash–slag blends with either low-calcium or high-calcium fly ash. The results show that the nature of precipitated calcium–aluminosilicate–hydrate (C-A-S-H) and alkali aluminosilicate-hydrate (N-A-S-H) depends on the fly ash composition and slag-to-fly ash ratio. However, regardless of fly ash composition and slag-to-fly ash ratio, a universal linear compositional relationship exists between Al/Ca ratio and Si/Ca ratio in precipitated gels. This indicates that there exists a structural limitation on the incorporation of Al3+ for Si4+ in the tetrahedral silicate of C-A-S-H, N-A-S-H, or metastable N-C-A-S-H gels. In a hybrid slag–fly ash system, the framework structure of precipitated gels is an assemblage of aluminosilicate units with heterogeneous Ca2+ and Na+ distribution. The amount and reactivity of calcium and alkalis seem to play a critical role in determining the structure and properties of precipitated gels in hybrid systems. The low cementitious capability in alkali-activated high-calcium fly ash may be attributed to the unstable N-C-A-S-H gel structure with concurrent high Na and Ca contents.

The influence of calcium hydroxide on the performance of MK-based geopolymer

Zeolite Socony Mobile-5 (ZSM-5) micropores are blocked after repeated use; therefore, their performance is compromised, forming ZSM-5 waste. This work synthesized a new type of multiscale pore structured geopolymer that could be exploited as a zeolite material precursor. The raw materials were metakaolin, calcium hydroxide, and ZSM-5 waste. The action of ZSM-5 waste is synergistic foaming with hydrogen peroxide and as an extra source of silicon in geopolymer generation. The final geopolymer samples were analysed via mechanical performance tests, thermogravimetry, X-ray diffraction, FT-IR spectral analysis, scanning electron microscopy and mercury intrusion methods. The influence of adding calcium hydroxide on the properties of the products was investigated. Metakaolin was replaced by 0, 10, 20 and 30 g of calcium hydroxide. The geopolymer specimens with added calcium hydroxide showed a more compact structure, a higher bulk density and an enhanced compressive strength performance. Moreover, the incorporation of calcium hydroxide increases the geopolymer paste viscosity and limits the foaming action of ZSM-5 waste and hydrogen peroxide, which makes the geopolymer product structure denser. The gel product was significantly associated with the added calcium hydroxide, and the amount of gel product, mainly hydrated calcium aluminosilicate gels (C-(A)-S-H), increased with the incorporation of calcium hydroxide. In general, calcium hydroxide accelerates the geopolymerization process and has a positive impact on the performance of geopolymer products. This study described the influence of calcium hydroxide on multiscale pore structure metakaolin-based geopolymers, and the results can be considered as a reference for the application of multiscale pore structure geopolymers with calcium hydroxide.

Optimization of alkali-activated ladle slag composites mix design using taguchi-based TOPSIS method

This study examines the effect of various parameters on the properties of alkali-activated composites made with unprocessed ladle furnace slag. Taguchi method was used to design the experiments. A total of five factors, each with four levels, were considered, including ladle slag content (LS), alkaline-activator solution-to-binder ratio (AAS/B), sodium silicate-to-sodium hydroxide ratio (SS/SH), sodium hydroxide molarity (M), and crushed sand replacement by dune sand (CSR). A total of 16 alkali-activated ladle slag mixtures were designed, cast, and tested. The performance responses were the workability, setting time, and compressive strength. To assess the influence of the factors on the responses, Taguchi analysis and ANOVA were employed while determining the signal-to-noise (S/N) ratios. Further, TOPSIS analysis was carried out to optimize the mixture proportions of alkali-activated ladle slag composites. The optimum mix entailed 650 kg/m3 of ladle slag, AAS/B ratio of 0.45, SS/SH of 2, and CSR of 25% to maximize strength and workability. Meanwhile, the optimum mix to maximize workability and setting time included 650 kg/m3 of ladle slag content, AAS/B ratio of 0.6, SS/SH of 2.5, and CSR of 50%. Anticipated results of the optimum mixes were experimentally verified. Microstructure analysis of the optimum mixes (isothermal calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy) highlighted the accelerated rate of the activation reaction, the amorphous morphology, and the formation of calcium aluminosilicate hydrate gel.