Revealing the nanoscale mechanism of water states in the interparticle cohesion of calcium silicate hydrate

The hydration of calcium silicate hydrate (CSH) is crucial in determining the mechanical properties and durability of cement-based materials. In this study, we investigate the impact of graphene oxide (GO) on the hydration process of CSH using molecular dynamics simulations. The primary focus is on how GO influences the nucleation, ion distribution, and structural evolution of CSH gels during cement hydration. The results reveal that GO significantly accelerates the nucleation process, especially in the formation of short-chain and long-chain CSH structures, through its oxidized functional groups, which interact with calcium ions (Ca2+) and promote their aggregation. GO’s presence alters the distribution of Ca2+ and silicon atoms, with a more pronounced effect on Ca2+ ions, leading to localized high-concentration regions and enhancing the nucleation process. In contrast, Si atoms exhibit a more uniform distribution in the system, indicating a weaker adsorption effect. Additionally, GO improves the structural ordering of Si-O bonds in CSH, which accelerates the formation of CSH gels, although it has minimal impact on the bond angle distribution. Overall, GO acts as a heterogeneous nucleation agent, increasing the number and density of nucleation sites, thus improving the early-stage hydration process, microstructure, and potentially the mechanical properties and durability of cement-based materials. The findings provide valuable insights into the role of GO in enhancing cement hydration, offering a promising approach to improving the performance of cement-based materials in construction.

Synergistic effect of silica fume and nano silica on multiscale pore structure regulation and permeability enhancement of full coral aggregate concrete

In-situ generation of calcium silicate hydrate and porous magnesium silicate for the removal of manganese from acid mine drainage

To meet the growing demand for high-performance self-healing microcapsules in cementitious systems, it is essential to refine microcapsule wall architectures. This study elucidates the microscopic adsorption enhancement mechanism of modified double-layer microcapsule wall materials using molecular dynamics (MD) simulations, combined with adsorption experiments detected by ultraviolet-visible (UV-vis) spectroscopy. Ethyl cellulose (EC) serves as the primary wall component, and tobermorite (11 Å) is employed as a crystalline analog of calcium silicate hydrate (C-S-H). Comprehensive analyses of adsorption energy, structural deformation, atomic diffusion, and tensile response were performed. The computational framework was validated by comparing simulated adsorption energies and glass transition temperature (Tg) with experimental benchmarks. Critically, interfacial hydrogen-bond dynamics were identified as the predominant factor governing variations in adsorption energy, with molecular structural reorganization directly modulating adhesion efficacy. Spatially resolved diffusion trajectories further revealed that the spatial distribution of molecular components within the wall architecture significantly influences both the diffusion range and kinetics of tobermorite species. Nanoindentation tests and tensile simulations demonstrated consistent mechanical integrity across different wall configurations. These findings establish a mechanistic understanding of adsorption enhancement in double-layer microcapsules, providing design principles for engineering microcapsules with optimized durability and self-healing functionality for sustainable concrete infrastructure.

The early hydration of calcium silicate hydrate (C-S-H) plays a crucial role in the development of key mechanical properties in cement, yet an atomic-level description of this reaction remains elusive. Here, to understand the early stages of the hydration reaction, we introduce a method to quantify dilute silicate species as a function of reaction time using ex-situ solid-state 29Si magic-angle spinning dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) spectroscopy. Samples are flash-frozen and separated by centrifugation, allowing for kinetic analysis of the supernatant and structural studies of the precipitate over time. With DNP-enhanced 29Si NMR, we can determine the concentrations of various silicate species throughout the reaction and track the growth of the silicate chains, which form the dreierketten backbone of C-S-H. In our low Ca/Si ratio system, we observe a vast majority of the supernatant silicate species to be monomers, with small amounts of dimers. The initially precipitated C-S-H, which has a mean chain length of 2.6 and is composed primarily of dimers, is shown to significantly differ from the C-S-H present after 3 h of hydration, which has an average length of 4.2.

Increasingly extreme environmental conditions demand structural materials that combine mechanical robustness with sustainability. Natural wood is renewable and mechanically adaptable but suffers from high porosity and hydrophilicity, leading to moisture absorption, fire vulnerability, and environmental degradation. Ceramics provide high stiffness, thermal stability, and chemical resistance but are inherently brittle. Here we report ceramic wood, a composite formed by integrating a natural wood scaffold with uniformly distributed ceramic nanoparticles. A calcium silicate precursor infiltrates the aligned nanofluidic channels of wood and undergoes in-situ self-assembly into calcium silicate hydrate nanoparticles under room-temperature conditions. The resulting ceramic network fills micropores and forms strong interfacial bonding within the wood scaffold. Ceramic wood exhibits high compressive strength, enhanced toughness, excellent fire resistance, and improved durability against moisture, fungiattack, and alkaline environments. CO₂ uptake further reduces the carbon footprint, highlighting ceramic wood as a sustainable structural material for extreme environments.

Oil-well cement stone is inherently brittle and prone to cracking, posing serious threats to construction safety and long-term zonal isolation. To improve wellbore sealing integrity and service life, mullite whiskers were synthesized via a molten-salt method. A novel synergistic toughening system combining mullite whiskers and halloysite nanotubes (HNTs) is proposed to reduce cement brittleness and cracking. Mechanical tests reveal an optimal blend of 0.7% mullite whiskers plus 1% HNTs (labeled M7-H1). Compared with the neat reference, this formulation increases 3-day and 7-day compressive strength by 49.39% ± 3.5% and 58.37% ± 3.5%, respectively, and raises tensile strength by 32.23% ± 3.1% and 29.30% ± 2.9%. XRD, TGA, and MIP analyses demonstrate that both mullite whiskers and HNTs act as nucleation sites for hydration products, accelerating secondary hydration and promoting calcium–silicate–hydrate (C-S-H) gel formation. A “bridging–nucleation–filling” tri-modal reinforcement mechanism is thereby established. The concurrent refinement of the pore structure reduces total porosity from 33.38% ± 0.42% to 24.34% ± 0.25% and cuts the fraction of detrimental pores (>50nm) from 59.9% to 36.2%. Owing to the facile, low-cost synthesis of the mullite whiskers, the proposed approach offers a readily deployable, high-performance solution for achieving durable cement-sheath sealing and life extension in deep and shale oil/gas wells.

This study addresses the challenges of highly expansive clay soils by stabilizing them with two industrial by-products: electric arc furnace (EAF) slag and water treatment sludge (WTS), thereby addressing the limited research on their combined (synergistic) use in soil stabilization. The potential of these additives to enhance soil strength and stiffness while mitigating swelling was evaluated using clay samples treated with 0, 10, 20, and 30% EAF slag and 0, 5, 10, 20, and 30% WTS replacement, after curing for 7, 28, and 56 days. Unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) tests were employed as primary indicators of mechanical performance, while free swelling tests were carried out to assess volume stability. In addition, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analyses were performed to provide micromechanical insights into the mechanisms underlying the observed improvements. Results indicate that the combined use of 30% EAF slag and 20% WTS replacement produced the most favorable outcomes in terms of strength, stiffness, and swelling reduction. UCS increased by more than fourfold compared with untreated soil, reaching approximately 2800kPa, while UPV rose to nearly 1700m/s. The swelling potential of the optimized mix decreased dramatically from 270% in the natural clay to only 8% after 56 days of curing. Microstructural analyses confirmed the development of cementitious gels, primarily calcium-silicate-hydrate (C-S-H) and calcium-aluminate-hydrate (C-A-H), which filled voids, bonded particles, and created a denser, more stable matrix resistant to moisture-induced expansion. These findings demonstrate that the combined use of EAF slag and WTS provides an effective approach to improving the mechanical and volumetric performance of expansive soils.

Retraction notice to "Cost-effective fabrication of fluorite tailings-based calcium silicate hydrate for excellent adsorption performance of Cr (III) from aqueous solution" [Environ. Res. 285 (2025) 122318

To promote the high-value utilization of industrial solid wastes and address the disposal of excavated soils, a novel low-carbon composite cementitious material, solid waste-based geopolymer cement (SGPC), was developed, consisting of soda residue (SR), granulated blast furnace slag (GGBS), phosphogypsum (PG), and ordinary Portland cement (PC) in a mass ratio of 10:81:9:25, with industrial solid wastes accounting for 80% of the binder. The effects of water-to-solid ratio (W/S = 0.41–0.49) on the workability, mechanical performance, and microstructural evolution of SGPC-stabilized soil were systematically investigated to provide a sustainable alternative to conventional cement-based stabilizers. The results indicate that the optimum water-to-solid ratio is 0.43 (SGPC43), with a 28-day unconfined compressive strength of 1450 kPa, exceeding the engineering requirement of 0.8 MPa and reaching over 85% of that of a pure cement system (C43). The flowability remained 163 mm after 60 min, with initial and final setting times of 43 h and 58 h, respectively. Microstructural analysis revealed that the alkalinity provided by soda residue promotes the hydration of slag and phosphogypsum, forming interwoven calcium (alumino) silicate hydrate (C–(A)–S–H) and ettringite (AFt), which fill pores and form a dense structure, thereby enhancing mechanical performance. Environmental and economic assessments show that the CO2 emission of SGPC43 per ton of binder decreases from 930 kg CO2-e/t to 235 kg CO2-e/t (approximately 74.7% reduction), while the material cost decreases from 110 USD/t to 53 USD/t (approximately 51.8% reduction). A simplified uncertainty analysis indicates that the carbon reduction remains at 70% ± 5% and the cost reduction at 50% ± 5%, confirming the robustness of the results. Overall, SGPC43 demonstrates excellent engineering performance, environmental benefits, and economic feasibility, highlighting its potential as a low-carbon and sustainable stabilizing material.

Calcium silicate-based root canal sealers are widely used because of their bioactivity and favorable properties. However, their resistance to chemical challenge and the role of chelating and acidic solutions in retreatment remain unclear. This study evaluated the effects of short-term EDTA and organic acids exposure on the microhardness and structure of two sealers (CeraSeal and TotalFill BC Sealer) and explored the underlying mechanisms. A total of 160 disc-shaped samples (80 per sealer) were prepared and incubated at 37°C and 100% relative humidity. Vickers microhardness was measured weekly. X-ray diffraction (XRD) analyses were performed at weekly intervals using different samples, starting from the first measurable microhardness and continuing during material maturation. The final microhardness was defined as the plateau in value. After the final microhardness was reached, the samples were immersed for 5 min in 17% ethylenediaminetetraacetic acid, 10% citric acid, 10% formic acid, or distilled water to simulate retreatment conditions. Postexposure microhardness, phase changes, and surface morphology were evaluated via Vickers hardness testing, X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. Statistical analyses included the Shapiro-Wilk test, t tests or nonparametric equivalents, one-way and Welch's ANOVA, and linear mixed model analysis (p < 0.05). CeraSeal appeared to reach its final microhardness earlier than TotalFill BC Sealer did, whereas TotalFill BC Sealer tended to exhibit higher ultimate microhardness values. Exposure to the test solutions significantly reduced the microhardness of both sealers (p < 0.001), with the greatest reductions observed in the formic acid (58%) and citric acid (52%) groups. XRD and SEM analyses suggested dissolution of the calcium silicate hydrate and calcium carbonate phases, increased surface porosity, and a possible tetragonal-to-monoclinic zirconia transformation in TotalFill BC Sealer, whereas no clear evidence of zirconia phase transformation was observed in CeraSeal. Within the limitations of this in vitro study, TotalFill BC Sealer presented higher final microhardness values; however, it was more susceptible to structural degradation following exposure to the test solutions, which was associated with a marked reduction in microhardness values. In contrast, CeraSeal, despite demonstrating a lower final microhardness, exhibited comparatively smaller percentage reductions after solution exposure, suggesting relatively greater resistance to solution-induced degradation.

This study aims to explore the effect of using three distinct silicate- and aluminate-rich rock powders—granodiorite (GDP), alkali-feldspar granite (AFGP), and mafic metavolcanic (MMVP)—sourced from Egypt’s largely unexploited Eastern Desert geological resources, as supplementary cementitious materials (SCMs) in concrete production. Rock samples were processed into ultrafine powders (1.4–1.5 μm average particle size) and utilized as partial cement replacements at 3%, 6%, 9%, and 12% by weight. These rock powders were confirmed to meet ASTM C618 requirements for natural pozzolans, qualifying them as viable SCMs. Pozzolanic activity was confirmed through Strength Activity Index (SAI) testing, with values of 79%, 82%, and 76% for GDP, AFGP, and MMVP, respectively, all exceeding the 75% minimum threshold required by ASTM C618. Fresh concrete workability decreased progressively with increasing rock powder content. Mechanical testing demonstrated optimal replacement levels of 9% for GDP and AFGP, and 6% for MMVP, achieving 28-day compressive strength improvements of 14.1%, 16.0%, and 14.9%, respectively, compared to plain Portland cement concrete without any rock powder replacement (control mix). Splitting tensile strength increased by 14.7%, 12.7%, and 16.3% at optimal dosages. Microstructural analysis via SEM revealed enhanced matrix densification and reduced porosity through physical filler effects and pozzolanic reactions. Energy-dispersive X-ray spectroscopy (EDX) confirmed reduced Ca/Si ratios, indicating enhanced calcium silicate hydrate (C-S-H) gel formation with superior binding characteristics. Results demonstrate that these previously unexploited rock powders effectively function as sustainable SCMs, reducing cement consumption by up to 12%, offering significant environmental benefits through reduced CO2 emissions and efficient utilization of natural geological resources in sustainable construction practices.

This study presents a hierarchical conductive-network strategy to overcome the performance trade-off in cement structural supercapacitors (CSSCs). By incorporating one-dimensional carbon nanotubes (CNTs) and two-dimensional graphene oxide (GO) into Portland cement, we simultaneously enhance its electrochemical and mechanical properties. The approach exploits the complementary roles of the two nanomaterials: CNTs establish a three-dimensional percolation network that facilitates electron transport, while GO promotes formation of a denser calcium silicate hydrate (C-S-H) gel and refines the pore structure by complexing with calcium ions, thereby improving ionic pathways. The k12gc sample attains a specific capacitance of 66.8 F g−1 at 0.1 mA cm−2, a 58.4% rise in conductivity and a 63% reduction in charge-transfer resistance. At the same time, the composite reduces harmful macropores by 27.9% and strengthens the material, with compressive and flexural strengths increasing by 4.8% and 8.3%, respectively. This work establishes a rational design principle based on functional division between CNTs and GO for developing high-performance, multifunctional CSSCs.

Hybrid MTMS–silica aerogels incorporating calcium silicate hydrate (C–S–H), the primary hydration product in cementitious systems, were synthesized via sol–gel processing followed by freeze-drying. The influence of C–S–H loading on pore structure, density, wettability, and thermal transport was investigated. The lowest thermal conductivity (0.068 W/m·K) and tap density (0.30 g/cm3) were obtained at 10% C–S–H loading (wM-CSH10), while the thermal conductivity increases to approximately 0.075–0.082 W/m·K at higher C–S–H content. All samples exhibit mesoporous structures with pore diameters in the range of 10–21 nm. Increasing C–S–H content progressively densified the network, reduced mesopore volume, and enhanced high-temperature mass retention up to 540 °C. FTIR analysis confirmed Si–O–Ca interfacial interactions, while nitrogen adsorption demonstrated persistent mesoporosity across all compositions. Thermal conductivity showed a positive correlation with density, indicating that bulk densification governs heat transport in the hybrid system. Beyond structural modification, the incorporation of C–S–H introduces chemical and microstructural features relevant to cement-based materials, suggesting potential compatibility with cementitious matrices. The results highlight the compositional trade-off between insulation efficiency and structural stability and demonstrate the potential of C–S–H-modified MTMS–silica aerogels for future integration into cement-based composites. These findings provide fundamental insight into their possible use in thermal insulation applications, such as building envelope systems (walls, façades, and roofs used for thermal insulation).

To reduce carbon dioxide emissions from cement and concreteproduction, in accordance with Sustainable Development Goals 3, 9,and 11, colloidal nanosilica has been investigated as a tool to advancealternative and sustainable cementitious material production by evaluatingits effect on the early performance of mechanical and microstructuralproperties of wood ash cement paste, mortar, and concrete. In thisstudy, the control group with Portland Cement without nanosilica andwood ash (WA) in mortar will be denoted as CM and CC in concrete,respectively. The experimental groups are labeled Zawa 5–25,indicating the use of South African WA as a partial replacement ofcement at various proportions (5, 10, 15, 20, and 25). The nanosilicasolution (NSS) of 0.265 mol/L was used throughout; NSS was made bydissolving 3.5 g of nanosilica (SiO2) in 13.201 L of distilledwater. Eighteen combinations having different mixtures of mortar sampleswere made with a standard sand and water/binder ratio of 0.5. Similarly,144 concrete mixtures having a constant 0.5 water/binder ratio wereprepared, and they were evaluated for both compressive and splittingtensile strength. Compressive and flexural tests were performed onthe mortar samples at a 28-day curing period and the concrete samplesat 3, 7, 14, and 28-day curing periods for splitting tests. The investigationinvolves examination of chemical composition, specific gravity, andsize distribution of the wood ash and fine and coarse aggregates usedin the mix. The paper assesses the uniformity of the fresh cementpaste characteristics using flowability and setting time. The hardenedproperties, like compressive strength and flexural strength of themortar, were examined. The CC concrete samples were also examinedin terms of the mechanical properties (compressive and splitting tensilestrength) and microstructure. A mixing formula of 5% WA showed animproved workability with an initial setting time of 250.09 s anda final setting time of 348.13 s, showing a favorable ratio betweensetting time and workability, as the mixture of 5% WA gives the bestspread. The time of initial setting of the WA cement paste with 5%is greater than that of the control sample by 10.4%. In addition,the optimal strength development was realized on 28 days with themixture of 5% WA with mortar and corresponding strengths of 59.2 MPaof mortar, which is an improvement of 8% over the control mix. At28 days, the compressive strength of the concrete samples with 5 and10% levels of WA is increased by 8 and 14%, respectively, comparedto the reference concrete samples. On the other hand, irrespectiveof the percentage of replacement of WA at 28 days of curing, the resultsshowed that the splitting tensile strength decreased with time. Thisreduction in the tensile strength of splitting could be explainedby the higher porosity and microstructure alteration related to thehigher wood ash content of the concrete mix. The filling effect ofNSS is very important in making the concrete denser and stronger byphysically filling the openings left by cementitious materials, capillaryholes, and calcium silicate hydrate crystals, resulting in denserand more uniform hydration products. The novelty of the present researchis that wood ash and nanosilica addition may result in the formationof a high-performance, cost-effective green concrete. The commercialimplications of the energy sector are enormous as the world evolvesto greener technologies. The research findings may lead to the developmentof innovative solutions not only to reduce carbon discharge but alsoto improve the qualities of construction materials.

The cracking problem of cement-based materials seriously threatens their mechanical properties and durability. This study innovatively develops a fast-response self-healing capsule based on superabsorbent polymers (SAPs) and crystalline admixture to enhance the crack self-healing ability of cement mortar. The study systematically investigates the release and migration behavior of healing agents within cracks, with a particular focus on the influence of environmental humidity, as well as the effects of different capsule dosages on the pore structure and hydration heat of the mortar. In addition, the enhancing effects of the capsules on crack self-healing performance, including healing width and volume filling rate, and on impermeability performance, including permeability coefficient and plugging air leakage rate, are evaluated. The results indicate that environmental humidity significantly raises the release behavior, migration area, and migration distance of healing agents. Increasing the capsule dosage moderately increases the porosity of the mortar and reduces the total hydration heat release. A key finding is that the incorporation of the capsules significantly improves the self-healing efficiency of the mortar, as the maximum crack healing width reaches 453 μm, the internal volume filling rate reaches 90.25%, and the permeability coefficient is significantly reduced by 92.62%. In contrast, the air permeability is reduced by 93.34%. Microscopic analysis confirms that the healing products within the cracks are mainly composed of calcium carbonate (CaCO3), calcium hydroxide (Ca(OH)2), SAP residues, and hydrated calcium silicate (C-S-H) gel. This study provides an important theoretical and practical basis for the development of efficient self-healing cement-based materials.

Calcium silicate hydrate from simulated alkali-activated industrial waste residue: Adsorption and immobilization mechanism of Pb2+ and Mn2+

The depletion of natural resources and the substantial carbon emissions associated with ordinary Portland cement (OPC) production pose critical environmental challenges to the construction sector. This study investigates the development of a sustainable quaternary blended cement system incorporating steel and iron industry by-products, i.e. Linz-Donawitz slag (LDS), ladle furnace slag (LFS), and ground granulated blast furnace slag (GGBFS), in combination with OPC. Binder pastes were formulated with varying proportions of LDS and LFS, while maintaining OPC at 50% and GGBFS at 10% by mass. The blended systems were comprehensively evaluated with respect to mechanical performance, durability in aggressive environments, phase assemblage, microstructural characteristics, and thermogravimetric behaviour. The optimised composition, consisting of OPC (50%), GGBFS (10%), LDS (20%), LFS (20%), and 10% chemical activator, achieved a 28-day compressive strength of 62.9MPa, significantly surpassing the OPC control (53.4MPa). Microstructural and mineralogical analysis confirmed the formation of a dense and homogeneous calcium silicate hydrate (C-S-H) gel network, consistent with thermogravimetric findings indicating enhanced hydration and reduced portlandite content. Durability assessment of the optimised mix demonstrated superior resistance to exposure to MgSO₄ and HCl. The control mix showed weight changes of 0.70% and 0.64% in the presence of MgSO4 and HCl, respectively, while the optimised mix exhibited the lowest gains at 0.45% and 0.49%, respectively. Furthermore, exposure to sulphate and acid solutions reduces strength. The control mix exhibited strength losses of 6.37% and 9.55% under sulphate and acid exposure, whereas the optimised mix demonstrated comparatively lower reductions of 1.74% and 5.08%, respectively. The ingress of sulphate and chloride ions from the MgSO4 and HCl solution into the pore structure of the binder matrix initiates chemical reactions with the calcium hydroxide and monosulphate phases, leading to the formation of expansive products, such as gypsum and ettringite. Although a marginal increase in drying shrinkage of the optimised mix (0.038%) compared with the control (0.034%) was observed, the overall durability performance remained superior to that of conventional OPC systems. The optimised blends met the requirements of Indian and ASTM standards for OPC 43-grade cement, confirming their technical viability for practical implementation. Beyond performance improvements, the study highlights significant sustainability and economic implications. Partial substitution of clinker with steel and iron slags reduces embodied CO₂ emissions, diverts industrial by-products from landfills, and advances circular economy principles within the construction industry. While initial production costs are comparable to conventional OPC due to supplementary cementitious material processing, lifecycle benefits, including reduced clinker demand, improved durability, extended service life, and potential environmental incentives, enhance overall cost-effectiveness. In conclusion, this research establishes steel and iron slags as viable constituents in high-performance quaternary blended cements. By demonstrating enhanced strength, improved durability, regulatory compliance, and environmental benefits, the study provides a practical pathway for lowering the carbon footprint of cementitious materials.

Structure of calcium silicate hydrate