Calcium Silicate Hydrate Research Articles

Hydrated Calcium Silicate (C-S-H) Improves the Performance of Stone Powder as Cement Admixtures.

The low pozzolanic activity of recycled stone powder limits its application in cement-based materials. Calcium silicate hydrate (CSH) is one of the hydration products of cement and also has the function of promoting hydration and improving strength. Therefore, the behavior of CSH in enhancing the activity of stone powder has been studied, including the workability and mechanical properties, and the mechanism of activity enhancement has been explained at the microscopic level. The results showed that when the amount of stone powder was 30%, the setting time was shortened by 26.14% to 34.34%, the slump increased by 7.89%, and the compressive strength at 3 and 28 days decreased by 40.94% and 37.99%, respectively. On this basis, when CSH was added at a dosage of 1%, compared with the specimen with a dosage of 30% stone powder, the setting time was shortened by 18.29% ∼ 21.53%, the slump was increased by 2.44%, and the compressive strength at 3 and 28 d was increased by 15.95% and 16.25%, respectively. The pozzolanic activity of stone powder has increased from 62.00% to 71.82%, reaching the pozzolanic activity level of fly ash. The mechanism of CSH enhancing pozzolanic activity was explained at the micro level, which broadened the application channels for the high-dosage application of stone powder.

Synthesis, Characterization, and Cementitious Activity of the Magnesium Silicate Hydrate and Calcium Silicate Hydrate from Coal Gangue

Coal gangue, a prevalent solid waste in the coal industry, has long been a significant concern due to its substantial production volume and potential environmental hazards. However, it contains valuable components such as silica and alumina, making it a promising raw material for synthesizing cementitious materials. This study focused on the synthesis of coal gangue-based magnesium silicate hydrate (M-S-H) and calcium silicate hydrate (C-S-H) through mechanical–thermal–chemical composite activation treatment. The cementitious activity of coal gangue samples and the characterization of the resulting cementitious materials were analyzed using ICP-AES, FTIR, XRD, SEM, and DSC-TG. Results indicated that calcination temperature, calcination time, the Ca/Si molar ratio, and the Mg/Si molar ratio were key factors influencing the cementitious activity of coal gangue, exhibiting a positive correlation with the dissolution amounts of Si4+ and Al3+. When kaolin in coal gangue was fully decomposed into active Al2O3 and SiO2, the cementitious activity of coal gangue reached its peak. M-S-H and C-S-H were successfully synthesized after 7 days of curing at room temperature, significantly reducing the synthesis time. The synthesized M-S-H and C-S-H exhibited large specific surface areas, good mechanical properties, and well-developed pore structures, making them suitable as mesoporous materials that provide numerous active sites for adsorbing metal ions.

Mechanical Characteristics of Soft Clay Solidified by Incorporating Granulated Blast Furnace Slag, Magnesium Oxide, and Building Gypsum

Super sulfate cement (SSC) serves as a sustainable alternative to ordinary Portland cement, offering lower carbon emissions and superior performance. Magnesium oxide (MgO) and building gypsum (BG) were utilized as activators for granulated blast furnace slag (GBFS), and together they formed SSC, which was employed to stabilize the waste soft clay (SC). The mechanical strength development characteristics of solidified clay and the types of its hydration products were investigated through mechanical experiments, including unconfined compressive strength (UCS) tests as well as microscopic experiments, such as X-ray diffraction tests and scanning electron microscopy tests. The mass ratios of GBFS, MgO, and BG were 8:2:0 (A2) and 6:2:2 (B1), respectively; these ratios were employed to stabilize the clay, resulting in solidified clay samples designated as S-A2 and S-B1. The UCS of S-B1 increased by 36.5% to 49.3% compared to S-A2 at the curing time from 7 to 91 days. The strength residual coefficients were 34.5% and 39.1% for S-A2 and S-B1, respectively, after ten wet–dry cycles. After soaking in sodium sulfate solution, the UCS of S-A2 and S-B1 decreased by 49.1% and 29.8%, respectively, compared to the unsoaked condition. The results of microscopic tests showed that the hydration products of S-B1 mainly included needle-like calcium silicate hydrate (C-S-H) gel, flaky hydrothermal gel, and ettringite (AFt) crystals. BG promoted the formation of AFt, while MgO facilitated the generation of C-S-H gel. In this study, SSC was used to stabilize the waste clay, which provided a way for the application of waste SC and SSC.

Surface-Engineered Cenospheres Encapsulating Phase Change Materials for Functional Cementitious Composites.

The escalating global energy demand underscores the critical need for advanced solutions for energy-efficient buildings. Passive thermal energy storage systems using microencapsulated phase change materials (PCMs) offer promise but face integration challenges in cementitious materials due to weakening mechanical strength, which arises from poor shell strength and weak interfacial bonding with cementitious phases. This study introduces a novel approach for synthesizing functionalized microencapsulated PCMs from fly ash-based cenospheres addressing interfacial compatibility. Cenospheres are perforated for PCM encapsulation and sealed using two different materials: 1) melamine-formaldehyde (MF), a standard polymeric shell; and 2) silica, selected for its chemical compatibility with cementitious phases. Experimental results show that the silica sealing improved mechanical strength by 50% over those of MF, corroborated by molecular dynamic simulations showing silica's binding energy with calcium silicate hydrate exceeded threefold, with more than twice the uniaxial tensile strength. Thermal analyses confirmed the preservation of PCM in both sealing approaches. This work establishes a transformative pathway for advancing PCM-based thermal energy storage in building materials.

Factors Affecting Synthesized C-S-H CO2 Uptake: Initial Alkalinity and Ca/Si

The dynamic evolution of alkalinity during hydration/carbonation of CO2-conditioned cements results in the formation of polymorphic hydrated calcium silicates (C-S-H), whose differences in carbon sequestration capacity have not been systematically investigated. However, the micro-nano structures and carbon sequestration capacities of C-S-H are controlled by the dynamic effects of pore solution alkalinity and Ca/Si. Accordingly, different alkalinity and Ca/Si were set to simulate the cement hydration environment for the synthesis of C-S-H, and tests such as thermogravimetric and 29Si nuclear magnetic resonance (NMR) were used to investigate the effects and mechanisms of initial alkalinity and Ca/Si on the morphology of the synthesized C-S-H, the CO2 uptake. The results showed that the C-S-H synthesized at pH 7.2–12.0 and Ca/Si ratio of 1.0–2.3 was in flocculated and acicular forms, which were well crystallized and dominated by Q2, while its CO2 uptake was positively correlated with Ca/Si. On the contrary, the synthesized C-S-H was poorly crystallized under the conditions of pH increasing to 13.5 and Ca/Si ratios of 1.0–2.3. With the increase in Ca/Si, the synthesized C-S-H evolved from Q2-dominated foil to Q1-dominated porous structure, and its CO2 uptake was non-positively correlated with Ca/Si. This was mainly related to the average pore diameter of C-S-H and its silica-oxygen tetrahedral structure. This was mainly related to the average pore diameter of C-S-H and its silica-oxygen tetrahedral structure.

Molecular Dynamics Simulation of CNT Reinforced Cement: A Step Toward Sustainable Construction

This study explores the potential of carbon nanotubes (CNTs) to enhance cement mechanical properties, aiming to develop more sustainable materials and reduce the industry’s carbon footprint. Using molecular dynamics (MDs) simulations, the effect of pristine and carboxyl-functionalized single-walled CNT incorporation on the mechanical properties of 11 Å tobermorite, a model for calcium–silicate–hydrate (CSH), was analyzed. The results demonstrated a significant increase in the elastic modulus (E) of the composite, with CNT content directly influencing this enhancement. Specifically, E increased from 77.05 GPa to 81.93 GPa upon the incorporation of pristine CNTs and further increased to 97.87 GPa with the introduction of carboxyl-functionalized CNTs. Composites containing functionalized CNTs exhibited a more pronounced increase in E, as the carboxyl groups formed hydrogen bonds with the tobermorite structure, thereby reinforcing interactions and improving mechanical properties. Thus, increasing functionalization allows for lower reinforcement content, reducing costs and CNT aggregation, as observed in experimental studies. These findings underscore the potential of functionalized CNTs to strengthen cementitious materials, offering an alternative to traditional additives. This approach could contribute to reducing the carbon emissions associated with cement production, thereby supporting the development of more sustainable and environmentally friendly cement alternatives.

Development of highly reactive partially calcined dolomite precursor: Synergistic effect CaO and MgO

AbstractThis study introduces a novel rapid calcination method for partially calcined dolomite (PCD) precursors, offering a transformative approach to sustainable cementitious materials. Unlike traditional partial calcination, which involves prolonged thermal treatment, this rapid process (0–5 min) minimizes energy consumption and CO₂ emissions by leveraging the distinct decomposition kinetics of MgCO3 and CaCO3. This method's tailored Mg/Ca ratio significantly enhances hydration kinetics, producing a core‐shell microstructure that synergistically balances early strength and long‐term durability. Thermodynamic modeling and experimental analyses reveal that the early hydration is dominated by CaO, forming calcium silicate hydrate (C‐S‐H). In contrast, the gradual hydration of MgO supports long‐term stability through magnesium silicate hydrate (M‐S‐H) and hydrotalcite phases. This method provides a scalable pathway for upcycling low‐grade dolomite into high‐performance cementitious materials, offering a sustainable solution for the construction industry.

Exploring the interfacial stability mechanism between minerals and calcium silicate hydrate from a microscopic perspective

Exploring the interfacial stability mechanism between minerals and calcium silicate hydrate from a microscopic perspective

Heating-induced transformations in calcium silicate hydrate (C-S-H): In-situ investigations of composition, structure, and morphology

Heating-induced transformations in calcium silicate hydrate (C-S-H): In-situ investigations of composition, structure, and morphology

Investigation into the micro-brittleness of calcium silicate hydrate generated through chemical synthesis and cement hydration

Investigation into the micro-brittleness of calcium silicate hydrate generated through chemical synthesis and cement hydration

Application of Carbon Nanotube (CNT) to Improve Mechanical Properties of Concrete: A Comparative Analysis with Superplasticizer

Many researchers' interest in carbon nanotube (CNT) materials has grown as a result of their potential use in the construction industry. This is mostly related to the mechanical, electrical, thermal, kinetic, and chemical properties of CNT, which have a big impact on the way concrete functions. Hydrated calcium silicate is a complex network of binding particles that compose the cement composite material known as concrete. Since it has nanoscale features, CNT will interact most strongly with hydrated calcium silicate, improving the concrete's mechanical qualities. The purpose of this study is to ascertain the impact of adding CNT to concrete mixtures. Three distinct mixes were created by varying the types and amounts of admixtures that were added to the concrete mix. Two mixed variations employed CNT at various doses, while one mixed variation used admixture type F (superplasticizer), and the performance of one was compared to the other. Concrete that was both new and hard underwent specimen testing. On fresh concrete, a slump test was conducted using ASTM C163, while for hard concrete, cylindrical specimens measuring 100 mm x 200 mm were tested for unit weight and compressive strength at 7, 14, and 28 days following ASTM C39. According to the test results, utilizing CNT at a lower dose than the typical superplasticizer dose leads to greater workability and compressive strength. The results of the workability and compressive strength tests will be improved by the inclusion of CNT.

Rice Husk Ash and Waste Marble Powder as Alternative Materials for Cement

Concrete, a cornerstone of modern construction, owes its widespread adoption to global industrialization and urbanization, with mortar being an essential component. However, the cement production process is energy-intensive and generates significant CO2 emissions. This study explores the use of agricultural (rice husk ash, RHA) and industrial (waste marble powder, WMP) waste materials as partial cement replacements in mortar. Despite extensive research on RHA and WMP individually, studies examining their combined effects remain scarce. This research assessed cement replacement levels from 0% to 30% in 5% increments, evaluating the fresh, mechanical, durability, and microstructural properties of the mortar. The findings showed that replacing 20% of cement with RHA and WMP increased compressive strength by 20.65% after 28 days, attributed to improved homogeneity and pozzolanic reactions that produced more calcium silicate hydrate. Water absorption decreased from 8.3% to 6.34%, indicating lower porosity and enhanced uniformity. Microstructural analyzes showed a denser mortar with 13% less mass loss at 20% replacement level. However, higher replacement levels reduced workability due to the increased surface area of RHA and WMP. Generally, using RHA and WMP as partial replacements of up to 20% significantly enhances mortar properties and supports sustainability.

Laboratory based accelerated carbonation approach to simulate long term field carbonation in cementitious mixtures

Abstract Calcium silicate hydrate (C-S-H) phases precipitated during cementitious reactions are responsible for strength gain in lime and cement-stabilized subgrade layers. Exposure of these treated layers to environmental factors can lead to carbonation of C-S-H phases which can be detrimental to the long-term performance of these materials. The study focuses on understanding the physio-chemical changes incurred in C-S-H phases during carbonation and developing an approach to shorten the timescale required for carbonation studies where field carbonation needs to be simulated. For micro scale studies, pure C-S-H phases were synthesized in laboratory and were subjected to varying levels of carbon dioxide (CO₂) exposure under controlled conditions. Lime treated soil prepared using bentonite-sand mixture was used to evaluate the effect of carbonation at macroscopic scale. Impact of diffusion of CO₂ was identified based on changes in Ca/Si ratio, pH values and morphology variations and changes in concentrations of calcium carbonate and residual lime in the samples. Observations suggest that carbonation of C-S-H phases in presence of moisture is a multistep process where metastable calcium bicarbonate phases form initially. 30-day exposure to one percent CO₂ was observed to mimic 720 days of infield carbonation due to atmospheric exposure.

Molecular Dynamics Simulation of Polymer Concrete Enhanced by Carbon Nanoparticles: Effect of Surface Functional Groups.

Polymer concrete (PC) has attracted considerable interest for its excellent deformation resistance and durability. However, the mechanical drawbacks of polymers, particularly their limited compressive strength, constrain the wider application and design flexibility of PC. While experimental techniques such as X-ray diffraction and scanning electron microscopy provide insights into nanoparticle interactions within the polymer matrix, they lack the resolution to fully elucidate nanoscale mechanisms. To bridge this gap, this study utilizes molecular dynamics (MD) simulations to analyze the shearing behavior of carbon nanoparticle (CNP)-reinforced PC composites. MD simulations allow for atomic-level insights into the interactions between CNPs and the polymer matrix, providing a more detailed understanding of how surface-modified CNPs enhance mechanical properties. Our results show that surface-modified CNPs influence the distribution and conformation of epoxy within the PC system. Amino-functionalized CNPs strengthen the epoxy and calcium silicate hydrate (C-S-H) interface by facilitating calcium-oxygen bond formation. These interactions play a crucial role in improving the mechanical properties of PC. This study provides a fundamental understanding of how surface-modified CNPs reinforce PC and offers valuable insights for optimizing the performance of CNP-reinforced cementitious composites.

Stacked graphene oxide reinforced calcium silicate hydrate atomic-level interfacial structures and mechanical properties

Stacked graphene oxide reinforced calcium silicate hydrate atomic-level interfacial structures and mechanical properties

Enhancing tunnel muck properties with ternary industrial solid wastes: optimal mixing ratios and microscopic mechanisms

Calcium carbide slag (CCS), phosphogypsum (PG), and red mud (RM), three types of industrial solid wastes, were employed to improve tunnel muck for assessing the feasibility of their reuse. A series of indoor tests were conducted to investigate the effects of their contents on the physical and mechanical properties of the improved tunnel muck. Microscopic tests were also conducted to reveal the improvement and interaction mechanisms involved. Results indicate that the incorporation of CCS, PG, and RM can significantly improve and enhance the physical and mechanical properties of tunnel muck. The improved tunnel muck containing 2% PG and 6% RM shows higher early strengths as CCS content exceeds 4%. However, after curing for more than 14 days, the unconfined compressive strength (UCS) of the tunnel muck with 4% PG and 4% RM is the maximum regardless of the CCS content. Microscopic analysis shows that reactive substances in industrial solid waste react chemically with soil components, exchanging ions and forming cementitious products such as calcium hydroxide, calcium silicate hydrate (C-S-H), calcium aluminosilicate hydrate (C-A-S-H), and ettringite (AFt). They bind, fill, and encapsulate soil particles, compacting the soil and significantly enhancing the physical and mechanical properties of tunnel muck. Moreover, there is a notable mutual synergy between PG and RM, primarily attributed to their acid-base neutralization and the complementary action of reactive ions. The improved tunnel muck containing 4% CCS, 4% PG, and 4% RM demonstrates the highest enhancement efficiency.

Enhancing mixed recycled aggregate properties using water glass coating: optimization and performance in concrete applications

The rapid advancement of global infrastructure has resulted in a significant increase in construction and demolition (C&D) waste, raising urgent environmental issues stemming from inadequate disposal and management strategies. Recent research has focused on recycling C&D waste as mixed recycled aggregate (MRA) in concrete, majorly in developing countries, to promote sustainability. This study investigates a novel method for improving MRA characteristics by treating it with a water glass (WG) coating solution. A central composite design (CCD) model was used to identify the best treatment conditions considering WG concentration, water-to-aggregate ratio, and soaking duration as independent variables to facilitate treatment in MRA. The model’s performance was evaluated using water absorption, Los Angeles (LA) abrasion resistance, and apparent density. The microstructural analysis demonstrated that WG treatment enhanced MRA by forming calcium silicate hydrate (C-S-H) gel, which improved the pore structure and interfacial transition zone (ITZ). The optimised treated MRA was incorporated into the concrete at replacement levels of 0, 25, 50, 75, and 100% to assess workability, mechanical properties, and microhardness. The results indicated that substituting 25% of natural coarse aggregate with treated MRA led to significant enhancements in workability by 11.76%, compressive strength by 4.83%, split tensile strength by 2.94% and flexural strength by 3.43% while maintaining comparable hardness values to conventional concrete. The improvement was linked to the densification effect of the WG coating, resulting in enhanced bonding and mechanical performance. The results demonstrate a viable way to recycle C&D waste while maintaining structural integrity in concrete applications.

Resource recovery from MSW incineration residues through the ‘Ash-by-Ash Treatment Method’ (AATM): optimization of water and bottom ash contents

ABSTRACT Fine-fraction of Municipal Solid Waste (MSW) incineration bottom ash (IBA) contains amorphous silica, known as pozzolan is one of the potential heavy metal stabilizers in MSW incineration fly ash (IFA) by forming the cementitious compounds of calcium silicate hydrates (C – S – H) and calcium aluminate hydrates (C-A-H). The technique can be called the ‘Ash-by-Ash Treatment Method’ (AATM). To optimize the AATM, effects of water (L/S ratios) and IBA amounts (IFA/IBA ratios) were examined in this study. IFA and IBA were provided by two distinct incineration plants; IBA was utilized at fractions d < 250μm because of its high reactive amorphous pozzolan. The testing involved mixing ashes at different L/S (ml/g) and IFA/IBA ratios, leaving the air dry at ambient temperature, afterward settling for periods of 4, 8, 16, 30, and 60 days. The results confirmed that various L/S (ml/g) ratios have no discernible influence on the immobilization of heavy metals. At 60 days, even a lowered moisture content could maintain more than 99% of Pb immobilization efficiency and 100% of Cr and Cu immobilization efficiency. In another experiment, using up to 30% of IBA with L/S (ml/g) ratios of 0.6 also demonstrated >99% of Pb immobilization. No discernible change has been observed between the different L/S (ml/g) and IFA/IBA. Consequently, increasing IBA and decreasing water could assist in optimizing AATM. The immobilization process involves carbonation and pozzolanic reactions, which are substantiated by the leaching solution's pH decrease, the formation of calcite, the appearance of multiple new minerals, and the cementitious products C–S-H gels.

The geotechnical behaviour and microstructural characteristics of the alkaline residue/cement-stabilized expansive soil under wetting–drying cycles

In order to explore the geotechnical behaviour of expansive soil stabilized by alkaline residue/cement (ARC) under wetting–drying (W–D) cycles, the shrink–swell characteristics, unconfined compressive strength (UCS), compressibility and microstructural characteristics are experimentally investigated in this study. The findings indicate that the incorporation of ARC, particularly with an alkaline residue (AR) content of less than 5%, significantly mitigates the shrink–swell behaviour, reduces soil compressibility and enhances the UCS of the soil. Beyond this threshold, the soil's strength decreases and compressibility increases with increasing W–D cycles. Microstructural analysis reveals the formation of beneficial cementitious products such as calcium aluminate hydrate (C-A-H), calcium silicate hydrate (C-S-H) and ettringite (AFt) that contribute to improving the engineering performance in the early stages of the W–D cycles. Nevertheless, as the W–D cycles continue, these beneficial products diminish, leading to an increase in soil cracks and pores, which indicates a degradation in soil performance. The research posits that ARC can effectively serve as a partial substitute for cement in the stabilization of expansive soils, with the amount of AR within 5%. Despite ARC's environmental advantages as an alternative binder, it may encompass harmful elements. Therefore, a comprehensive environmental risk assessment is essential. Further studies are needed to discern the enduring effects of environmental variables on soils stabilized with ARC.

Basic Research on the Preparation of Electrolytic Manganese Residue-Red Mud-Ground Granulated Blast Furnace Slag-Calcium Hydroxide Composite Cementitious Material and Its Mechanical Properties.

A novel composite cementitious material was constructed by synergistically utilizing multiple industrial solid wastes, including electrolytic manganese residue (EMR), red mud (RM), and ground granulated blast furnace slag (GGBS), with calcium hydroxide [Ca(OH)2] as an alkaline activator. In addition, the mechanical properties of the composite cementitious materials were systematically analyzed under different raw material ratios, alkali activator dosages, and water-binder ratios. To further investigate the hydration products and mechanisms of the composite cementitious material, characterization methods, for instance, XRD, FT-IR, SEM-EDS, and TG-DTG, were employed to characterize the materials. To ensure that the composite cementitious material does not cause additional environmental pressure, it was analyzed for toxic leaching. The relevant experimental results indicate that the optimal ratio of the EMR-RM-GGBS-Ca(OH)2 components of the composite cementitious material is EMR content of 20%, RM content of 15%, GGBS content of 52%, calcium hydroxide as alkali activator content of 13%, and water-binder ratio of 0.5. Under the optimal ratio, the composite cementitious material at 28 days exhibited a compressive strength of 27.9 MPa, as well as a flexural strength of 7.5 MPa. The hydration products in the as-synthesized composite cementitious material system primarily encompassed ettringite (AFt) and hydrated calcium silicate (C-S-H), and their tight bonding in the middle and later curing stages was the main source of engineering mechanical strength. The heavy metal concentrations in the 28-day leaching solution of the EMR-RM-GGBS-Ca(OH)2 composite cementitious material fall within the limits prescribed by the drinking water hygiene standard (GB5749-2022), indicating that this composite material exhibits satisfactory safety performance. To sum up, it is elucidated that the novel process involved in this research provide useful references for the pollution-free treatment and resource utilization of solid wastes such as red mud and electrolytic manganese residue in the future.