Hydrated Calcium Aluminosilicate Research Articles

Mechanical Behavior and Microstructure Evaluation of Quicklime-Activated Cement Kiln Dust-Slag Binder Pastes.

Cement kiln dust (CKD) is a by-product of cement production, which has the shortcomings of low utilization and high-temperature activation. This study combined CKD and slag as precursors for preparing pastes through quicklime activation under ambient conditions. The effects of quicklime and CKD content on the workability (flowability and setting time), macro-mechanical properties, and micro-structure of the CKD-slag binders were analyzed. The experimental results showed that the rapid precipitation of Ca2+, Si4+, and Al3+ ions from the CKD provided more nucleation sites for the formation of calcium aluminosilicate hydrate (C-(A)-S-H) gel and enhanced the reactivity of the binder system under the influence of the activator (CaO). The specimens had the highest unconfined compressive strength (UCS) (24.6 MPa) after 28 days with 10% quicklime content and 60% CKD content; scanning electron microscopy with energy-dispersive X-ray (SEM-EDX) analysis showed that the Ca/Si ratio of the C-(A)-S-H gel was minimized, leading to a denser microstructure and better binding ability under this mixing proportion. Therefore, this study may provide novel binder materials with a high proportion of CKD under ambient conditions.

Upcycling use of red mud-based solid waste in engineered cementitious composites: Properties, activation mechanism, and life-cycle assessment

In this study, a low-carbon engineered cementitious composite (ECC) was produced by combining alkali-activated red mud (RM)/ground granulated blast-furnace slag (GGBS) with polyvinyl alcohol (PVA) fibers as the reinforcement. Both calcium aluminosilicate hydrate (C-A-S-H) and sodium aluminosilicate hydrate (N-A-S-H) gels are detected in the reaction products. A higher modulus of sodium silicate in the activator results in a higher degree of reaction of silicates in the samples, but not promising a higher mechanical property. The potential mechanism of iron activation in the alkali-activation RM-based ECC system was revealed. The four-point bending test results indicate a large deflection ability and multiple cracking characteristics of the composite. Life cycle assessment of this system is also presented by calculating energy consumption and carbon emissions. This study not only sheds light on the feasibility of using RM in the preparation of high-toughness alkali-activated ECC but also provides a promising method to upcycle industrial solid wastes in a highly effective way.

Preparation of geopolymer based on municipal solid waste incineration fly ash-phosphorus slag and its function for solidification of heavy metals

Municipal solid waste incineration fly ash (MSWIFA) contains potential contaminants and needs to be efficiently solidified/stablized and so should be managed properly. To achieve this goal, alkali-activated MSWIFA and phosphorus slag (PS) based geopolymer solidified bodies were investigated. Therefore, the mechanical properties of the solidified body, heavy metal leaching characteristics, heavy metal chemical forms, and heavy metal solidification/stabilization mechanisms were also analyzed. The results show that: The addition of an appropriate amount of PS can promote the strength development of a solidified body. When the mass ratio of MSWIFA to PS is 7:3, the strength of the solidified body reaches 22.8 MPa at 90d curing age, which is 5.3 times higher than that of the unmodified material. The MSWIFA/PS immobilized Zn 99.9 %, Pb 99.4 % and Cd 99.8 % in 60 day leaching tests. Meanwhile, PS can significantly increase the proportion of chemically stabilized forms of heavy metals in the solidified body. PS affects on the hydration process of the solidified body. When the mass fraction of PS doping was 30 %, the main hydration products of the solidified body were calcium silicate hydrate (C-S-H) and calcium alumina (AFt). When the mass fraction of PS is 50 %, the main hydration products are calcium aluminosilicate hydrate (C-A-S-H), sodium aluminosilicate hydrate (N-A-S-H), and AFt. These hydration products have good solidification effects on heavy metals. Therefore, it can be concluded that the MSWIFA/PS solidified body is an environmentally friendly and efficient binder.

Optimization of Ca/Si ratio in schists to enhance the pozzolanic supplementary cementitious material for OPC blending

AbstractSupplementary cementitious materials (SCMs) are partial substitutes for ordinary Portland cement (OPC) to reduce cost, the production of carbon dioxide (CO2), and fossil fuel consumption. Recent studies illustrated the effectiveness of calcined kaolinite clay as a proper partial replacement for OPC. Hence, schist‐type materials containing sufficient clay contents are regarded as promising candidates for OPC replacement. This study focuses on the possible use of activated calcium carbonates (CaCO3) to augment pozzolanic reactions of schists as a substitute for OPC. The use of activated calcium carbonates proved to be successful in expediting pozzolanic reactions and facilitating the formation of additional calcium aluminosilicate hydrate (C‐A‐S‐H). In this study, the optimal strength performance for blended cement was achieved by adjusting the total carbonate content to 30 wt.% of the schist. The decision to introduce carbonate to the schist was guided by calculations determining the need for an excess of calcium ions to fully harness the potential for C‐A‐S‐H formation. Virgin and augmented schists were activated by up to 80% of their respective potentials by heat treatment. Phase content and decomposition behavior of the active components were investigated by thermogravimetric analysis (TGA), x‐ray diffraction (XRD), and scanning electron microscopy (SEM). Cement paste samples incorporating 30 wt.% replacement of OPC with activated schist SCMs were prepared. The phase distribution and compressive strengths of these samples were assessed at hydration intervals of 2, 7, 28, 50, and 90 days. Cement formulations with activated calcium‐augmented SCMs exhibited compressive strength values at 109%, 101%, 96%, 95%, and 94% compared to pure cement paste at 2, 7, 28, 50, and 90 days, respectively. These values surpassed 90% of the compressive strength of pure OPC at equivalent hydration time points.

Reaction molecular dynamics study of calcium alumino-silicate hydrate gel in the hydration deposition process at the calcium silicate hydrate interface: The influence of Al/Si

Supplementary cementitious materials (SCMs) can partially replace cement in concrete production, forming calcium alumino-silicate hydrate (C-A-S-H). This enhances concrete durability while recycling waste. However, the early hydration reaction process of C-A-S-H and its deposition and aggregation behavior at the interface with the primary hydration product of cement, calcium silicate hydrate (C–S–H), remain unknown. Therefore, this study utilizes reactive molecular dynamics to model the deposition and growth behaviors of C-A-S-H precursors with different Al/Si ratios on C–S–H, and discusses the effects of the Al/Si ratio on C-A-S-H gel aggregation behavior and structural evolution at the C–S–H interface. The results show that increasing Al content significantly promotes the early hydration reaction rate of C-A-S-H gel, the degree of polymerization of silicate chains, and the amount of Qn(n ≥ 2) species. Moreover, higher Al content leads to the precursors aggregating among themselves rather than depositing on the C–S–H substrate surface. The incorporation of Al–O polyhedra can effectively bridge silicate chains on the C–S–H surface and alter the growth patterns of hydration products from linear chains to three-dimensional networks. This work provides molecular-level insights into the influences of the Al/Si ratio on the early hydration reaction process and interfacial deposition behaviors of C-A-S-H gel.

A Study on the Microstructure and Mechanical Properties of Portland Cement Incorporating Aluminosilicate Waste.

The influence of aluminosilicate pozzolanic waste, specifically spent fluid catalytic cracking waste (FCCW) and metakaolin waste (MK) from the expanded glass industry, on the properties of hardened Portland cement paste were analysed. The study involved replacing part of cement with FCCW and MK and observing their impact on the hydration, microstructure, density, and compressive strength of hardened cement paste. Various analysis methods were employed, including X-ray diffraction (XRD), thermogravimetric analysis (TG), and scanning electron microscopy (SEM), to understand the changes in the structure of the hardened cement paste during hydration. The findings revealed that FCCW tends to accelerate the cement hydration process due to its high surface area and pozzolanic activity. Notably, the formation of portlandite crystals was observed on FCCW particle surfaces in a specific direction. These crystals appeared smaller and developed in different directions in compositions containing a composite binder with mixture of FCCW and MK in a ratio 1:1. This could be influenced by pozzolanic reactions activated by fine particles of MK and the formation of calcium silicate hydrates (C-S-H) and calcium alumino silicate hydrates (C-A-S-H) in the presence of portlandite. The XRD and TG results indicated that the specimens containing a composite binder exhibited the least amount of portlandite. The compressive strength of these specimens increased compared to the control specimens, although the amount of cement was 9% lower.

Gypsum and rice husk ash for sustainable stabilization of forest road subgrade

Forest roads are crucial for economic development and resource accessibility, especially in regions with extensive wood demand driven by construction growth. These roads require consistent maintenance to prevent structural issues, even though they experience lower traffic. Traditionally, gypsum has been used for soil stabilization due to its cation exchange capability with clay minerals and flocculation properties. However, its water solubility in wet conditions necessitates innovative solutions. This study explores a novel approach by combining gypsum with rice husk ash (RHA), an abundant agricultural waste, to address the challenges posed by expansive and low-bearing clay soils in forest road construction. In this study, an expansive soil with high plasticity and swelling potential is treated with varying combinations of RHA (5–20%) and gypsum (2–6%), followed by curing for 7, 15 and 30 days. Mechanical property tests revealed reduced plasticity and swelling pressure, alongside increased unconfined compressive strength. Microscopic analysis illustrated the formation of calcium silicate hydrate (CSH) and calcium aluminosilicate hydrate (CAH) gels, which possibly contributes to improved stability. This research underscores the potential of sustainable soil stabilization using gypsum and RHA synergy to fortify forest roads against expansive clay soil challenges, promoting eco-friendly and resilient infrastructure solutions.

Uniaxial tensile study of calcium aluminosilicate hydrate (C-A-S-H): Structure, dynamics and mechanical properties

Calcium aluminosilicate hydrate (C-A-S-H) is the main hydration product of environmentally friendly concrete, which uses aluminum-rich industrial waste residue to partially replace cement raw materials. In order to understand the structure and properties of C-A-S-H gel at the molecular level. The structure, dynamics and mechanical properties of C-A-S-H gel at different Al/Si ratios were studied by reactive molecular dynamics simulation. The results showed that the doping of aluminates substances caused changes in the silicate-aluminate skeleton and inter-layer water molecules in C-A-S-H gels. As the Al/Si ratio increased, more water molecules dissociated and associated with Al atoms to produce Al-O(H)-Si and Al-OH. In addition, the presence of Al-O-Si chains not only imposed geometrical constraints on the inter-layer water molecules, but also increased the attraction of the substrate for water molecules. Furthermore, the mechanical behavior and deformation mechanism of C-A-S-H gels were investigated based on uniaxial tensile tests. The inter-layer bond strength and stiffness of C-A-S-H gels increased significantly with increasing tensile load and aluminate branching structure.

Calcium wastes as an additive for a low calcium fly ash geopolymer

A geopolymer is a low-carbon cement based on the utilization of waste ash in alkali-activated conditions. Coal fly ash is widely used as a source material for geopolymer synthesis since it contains a sufficient amount of reactive alumina and silica for geopolymerization. Geopolymer products are known to have beneficial fire resistance and mechanical properties. Class F or low-calcium fly ash (LCFA) is generally used as a primary aluminosilicate source; however, heat curing is required to complete the reaction and hardening process and achieve a strong composite. Furthermore, calcium additives are often required to improve the strength of LCFA geopolymers. This paper presents the potential of reusing calcium waste for this purpose. Three calcium wastes, namely calcium carbide residue (CCR), limestone waste, and waste cement (WC) slurry in powder form were used as additives and compared with the use of ordinary Portland cement (OPC). LCFA was replaced with the calcium additives at 20%. However, 20% CCR resulted in flash setting, hence 5% CCR was used instead. A durability test using 3% HCl solution was also performed. The results showed that the reactivity of calcium additives played an important role in strength development. In the calcium–aluminosilicate–alkali system, calcium silicate hydrate (CSH) and calcium aluminosilicate hydrate (CASH) were formed. The maximum strength of 21.9 MPa was obtained from the OPC/LCFA geopolymer, and 3% HCl solution had a deleterious effect on the strength. OPC and CCR were favorable reactive sources of calcium compounds to blend with LCFA. From the thermogravimetric results, lower thermal weight changes with higher strength gains were achieved. Low CaCO3 decomposition at 750 °C according to the TGA curves indicated the more formation of thermally stable CSH and high compressive strength of Ca/LCFA geopolymers.

Maximizing the pozzolanic potential of superfine iron tailings for low-carbon stabilization: Application of high-calcium geopolymer

Superfine iron tailings (5–75 μm) are difficult to be reused with traditional binders. The reaction behavior of newly developed high-calcium geopolymer (ASF), the activation effect of the ASF on the pozzolanic potential of tailings, and the application effectiveness of the ASF-stabilized mixtures have been discussed. The results show that highly cross-linked calcium aluminosilicate hydrates were the main hydration products, and there were some crystal products, e.g., stratlingite, ettringite, and crystalline calcium silicate hydrate. The ASF can activate and release magnesium ions in superfine tailings to form magnesium-based products. Second, the cumulative pore volume of stabilized tailings was reduced by 24.4% with the dosage increase of ASF binder from 3% to 8%. Finally, the strength of 8% ASF-stabilized tailings increased from 1.83 MPa to 3.44 MPa (7 d to 28 d). The alkalinity of ASF-stabilized tailings was weaker than that of the cement-based counterpart (∼0.6), reducing environmental pressure during application.

Development of sustainable ternary cementitious binder with OPC integrating calcined clay and LF slag

Pursuit to sustainable cementitious binders, application of supplementary cementitious materials (SCMs)/waste materials is increasing day by day. In the current article, OPC was partially substituted with alternative resource materials e.g., processed ladle furnace (LF) slag and calcined clay in fabricating a ternary binder. Performance of developed ternary binder was examined with respect to hydration, mechanical characteristics, phase analysis, microstructural behaviour and durability. Optimised ternary binder paste (50% OPC, 30% calcined clay and 20% Processed LF slag) demonstrated excellent mechanical properties. The optimised paste showed highest peak intensity of calcium silicate hydrate and calcium alumino-silicate hydrate in the mineralogical study, which was further validated by micro-structural studies. Hydration studies showed more cumulative heat flow (95 J/g) in optimised binder than other binders. Performance of optimised binder paste with respect to durability, which includes water absorption, porosity and drying shrinkage, was comparable with OPC. Whereas the performance of optimised ternary mix under chloride and sulphate exposure was found better than OPC. This route of developing ternary binder as sustainable alternative to OPC will definitely fulfil the commitment towards net zero emissions by 2050.

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).

Assessment of lithium slag as a supplementary cementitious material: Pozzolanic activity and microstructure development

In this study, lithium slag was utilised as a supplementary cementitious material (SCM) to develop pozzolanic activity and reduce CO2 emissions related to cement production, with a focus on comprehensive chemical tests and microstructural assessments. Lithium slag was primarily characterised through laser particle size analyser, X-ray fluorescence, X-ray diffraction, scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, and thermogravimetry. These tests indicate that lithium slag holds 31.6% amorphous phase with rich aluminosilicate minerals, making it an excellent candidate as pozzolan. The unsaturated lime and electrical conductivity pozzolanic activity precursor tests evaluated the potentiality of using lithium slag as a low carbon pozzolan. The optimum percentage of lithium slag as a supplementary cementitious material was determined from Frattini, strength activity index, and R3 tests by replacing 0–60% cement. Results show that 40% lithium slag mortar could achieve 93% strength activity index in 28 days. The microstructure development of lithium slag was assessed and ettringite, monocarboaluminate, and intermixed calcium aluminosilicate hydrates were formed at 56 days.

Structural deterioration of calcium aluminosilicate hydrate by sulfate attack: Atomic processes of Al-Si chain breaking

Calcium-aluminosilicate-hydrates (C-A-S-H) is the major hydration product of sustainable concrete that incorporates industrial waste as a partial substitute for cement. Although C-A-S-H is considered a durable material, it’s susceptible to sulfate attack. To better understand this phenomenon, the atomic process of sulfate attack on C-A-S-H was studied using semi-empirical quantum chemical methods. The results showed that sulfate attacks can be broken down into several subprocesses: adsorption, vibration, and breaking. The underlying causes of these processes were revealed through electronic structures, in which the weak AlO bond and strong electronegativity are the main factors leading to Al-Si breaking. The Atom in Molecular theory revealed that the weak electron localization of the [AlO4] tetrahedron leads to a lower water-assisted bond dissociated energy for breaking the AlO bond (18.3KJ/mol) than the SiO bond (109.4KJ/mol). This study provides valuable insights into the sulfate attack on C-A-S-H and its implications for improving the durability of sustainable concrete.

NaOH molarity influence on mechanical and durability properties of geopolymer concrete made with fly ash and phosphogypsum

Fly ash (FA), rich in aluminosilicates, and phosphogypsum (PG), rich in free calcium, could be excellent precursor materials to synthesize geopolymer concrete (GPC). In this paper, by using PG as feedstock to FA as per circular economy model, geopolymer concrete is developed. PG from 10 to 50% and molar concentration of NaOH from 8 to 14 M are varied to create the GPC. Further mechanical and durability properties are evaluated to ascertain the impact of NaOH molarity and PG content. The maximum strength of 47.97 MPa and durability results demonstrate that 30% PG and 12 M NaOH concentration are optimum dosages for successfully synthesis of GPC with the combination of FA and PG. The study pertinent to leaching illustrates that the optimal dosage of binder materials is efficacious in preventing release of potentially toxic elements (PTEs) from GPC, endorsing that its usage in all practical applications do not endanger people or the environment. Micro-characterization discloses that free available calcium ions exquisitely participated in hydraulic reaction to form affluent cementitious gels such as calcium alumino-silicate hydrate (C-A-S-H) and sodium alumino-silicate hydrate (N-A-S-H). The interpretation of various results portrays that both NaOH molarity and amount of free calcium has significant influence on GPC and played a crucial role in high strength attainment. A linear relationship for compressive strength versus durability properties imply that the developed GPC is more durable and sustainable exhibiting overall performance in all practical applications.

A Review: Progress in Molecular Dynamics Simulation of Portland Cement (Geopolymer)—Based Composites and the Interface between These Matrices and Reinforced Material

Molecular dynamics (MD) is an important method for studying the molecular and atomic scale of cement (geopolymer)-based composites which provides an effective method for the optimal design of cementitious materials. In this paper, the research progress of MD simulation in Portland cement and geopolymer-based materials is discussed in detail, including molecular structure models of calcium silicate hydrate, calcium aluminosilicate hydrate, sodium aluminum silicate hydrate gel, and auxiliary experimental techniques. The basic mechanical properties of calcium silicate hydrate, calcium aluminosilicate hydrate and sodium aluminum silicate hydrate in Portland cement-based materials (CBM) and geopolymer-based materials are reviewed. In addition, the dynamic simulation of the interface between CBM and reinforcement materials such as rebar, synthetic fibers, plant fibers and nanoparticles is also discussed. Through the macroscopic experimental results of cement (geopolymer)-based materials and the performance analysis of an MD microscopic model, MD helps to better explain the macroscopic properties of materials, and can quickly and conveniently analyze the mechanical properties, transport properties and interface properties of composite materials, so as to improve the fine design of cement (geopolymer)-based materials. Existing structural models and force fields are affected by environment and time, and MD simulation shows great differences in application range and characterization ability. It is necessary to further study and reveal the internal mechanism for improving concrete performance through a large number of experiments and MD simulation, and lay a theoretical foundation for preparing the next generation of (super) high-performance concrete.

Wind erosion control using alkali-activated slag cement: Experimental investigation and microstructural analysis

This paper aims to mitigate wind erosion of soil by employing alkali-activated slag. Wind tunnel tests were conducted on soil samples treated with varying percentages of slag at different wind speeds (7, 14, 21, and 28 m/s) and under a sand bombardment condition. In the absence of saltating particles, the erodibility ratios of the alkali-activated slag-treated samples with weight percentages of 1%, 2%, 4%, and 6% to the untreated sample at the highest wind speed (i.e., 28 m/s) correspond to 0.19%, 0.10%, 0.08%, and 0.06%, respectively. Moreover, in the presence of saltating particle bombardment, these samples exhibited erodibility reductions of 98.5%, 98.8%, 99.4%, and 99.6% compared to the untreated sample. The strength of the formed crusts, determined by penetrometer tests, increased significantly for the treated samples, ranging from 1300 to 6500 times greater than the untreated sample. The complementary analysis using x-ray diffraction and field emission scanning electron microscopy revealed the formation of albite and anorthite crystals along with the formation of calcium aluminosilicate hydrate, sodium aluminosilicate hydrate, and calcium silicate hydrate gels in the cementation process. Overall, the study highlights the effectiveness of alkali-activated slag in forming strong crusts that provide substantial protection against wind erosion, resulting in a significant decrease in wind erodibility.

Strength and Microstructure Assessment of Partially Replaced Ordinary Portland Cement and Calcium Sulfoaluminate Cement with Pozzolans and Spent Coffee Grounds.

Supplementary cementitious materials are considered a viable and affordable way to reduce CO2 emissions from the cement industry's perspective since they can partially or nearly entirely replace ordinary Portland cement (OPC). This study compared the impact of adding spent coffee grounds (SCGs), fly ash (FA), and volcanic ash (VA) to two types of cement: OPC and calcium sulfoaluminate cement (CSA). Cement samples were characterized using compressive strength measurements (up to 210 days of curing), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), attenuated total reflection infrared spectroscopy, and hydration temperature measurements. In all the studied systems, the presence of SCGs reduced compressive strength and delayed the hydration process. CSA composite cement containing 3.5% SCGs, 30% FA, and 30% VA showed compressive strength values of 20.4 MPa and 20.3 MPa, respectively, meeting the minimum requirement for non-structural applications. Additionally, the results indicate a formation of cementitious gel, calcium silicate hydrate (C-S-H) in the OPC-based composite cements, and calcium alumino-silicate hydrate (C-A-S-H) as well as ettringite in the CSA-based composite cements.

Mechanical properties and interface microscopic characterisation of fibre-reinforced slag-fly ash geopolymer agglutinated iron tailings filling materials

In order to study the deformation resistance of fibre-reinforced alkali activated slag-fly ash geopolymer agglutinated iron tailings filling materials, the mechanical properties test, scanning electron microscope (SEM) and X-ray diffraction (XRD) microscopic test are performed using the macro-micro cross-scale method. Then, the evolution law of mechanical behaviour and microstructure of samples are studied, revealing the internal relationship between macro-mechanical properties and fibre parameters. The results show that based on experimental results, as the fibre content increases, the compressive strength of the sample first increases and then decreases. When 6‰ 9-mm fibre is added to the sample, the compressive strength and flexural strength of the sample reach the maximum. Through SEM and XRD, it was found that fly ash and slag in an alkaline environment to generate polymerization products hydrated calcium silicate and hydrated calcium aluminosilicate filled in the basic skeleton formed by iron tailings sand particles, making the filling material more dense. When the fibre content is 4–5‰, the fibre exists as a single embedded fibre. When the fibre content is 6‰, the occurrence form shows a three-dimensional (3D) network structure, and when the fibre content exceeds 6‰, the fibre appears to be entangled in the sample. The mechanical properties of the filling material are improved by the single embedded fibre and the 3D reticular knot distribution fibre through the wrapping effect and the reticular inhibition effect, respectively. The results obtained can provide a reference for theoretical research and practical applications of polypropylene fibre-reinforced geopolymer materials.

The correlation between Al incorporation and alkali fixation by calcium aluminosilicate hydrate: Observations from hydrated C3S blended with and without metakaolin

This study aims to investigate the correlation between Al incorporation and Na fixation by C-(A)-S-H, which was derived from hydrated C3S blended with and without 10 wt% metakaolin at 1, 2, and 3 wt% Na2O content. C-(A)-S-H compositions were calculated based on mass balance method. NMR was used to calculate the fraction of different coordinations of Si and Al in C-(A)-S-H. Results show that the incorporation of Al into C-S-H enhances the polymerization of silicate chains, it also increases the Ca/Si of the formed C-A-S-H because more Ca ions are required to stabilize the incorporated Al(VI). The increased Ca/Si subsequently decreases the alkali fixation capacity of C-A-S-H compared to that of C-S-H. Increasing alkali concentration favors the polymerization of C-A-S-H by incorporating more Al(IV) in bridging sites and shows less effect on Al(VI)/Si and Ca/Si due to the different negative charges and calcium coordination environment regarding Al(VI) and Al(IV).