Calcium leaching is a critical durability concern for cement-based materials under long-term aqueous exposure. The incorporation of aluminum (Al) into calcium silicate hydrate (CSH) and calcium alumino-silicate hydrate (CASH) gels has been proposed as a strategy to mitigate this issue by influencing the dissolution behavior of calcium ions (Ca2+). This study investigates the dissolution behavior of Ca2+ from CSH and CASH gels with varying Al/Si ratios (0, 0.1, and 0.2) under aqueous conditions through molecular dynamics simulations. The research explores the microscopic mechanisms by which aluminum incorporation influences Ca2+ stability. The results reveal that with increasing Al/Si ratio, both the number and rate of Ca2+ release decrease. In CASH systems, Ca2+ dissolution reaches equilibrium after approximately 30 ns of simulation, while in CSH systems, dissolution continues at a relatively high rate. Aluminum incorporation enhances the coordination between Ca2+ and the gel matrix, reducing Ca2+ dissolution by enabling coordination with Al-OH groups and forming Si-Al chains, which strengthens the substrate-Ca2+ binding and improves structural densification. Additionally, interfacial water molecules exhibit more localized distribution and a more ordered hydrogen-bond network as the Al/Si ratio increases, indirectly influencing ion migration and hydration stability. Electronegativity and interaction energy analyses show that Al incorporation increases the electronegativity of oxygen atoms in the framework, strengthening electrostatic attraction to Ca2+, thus reducing the free energy and mobility of Ca2+. High-Al/Si CASH systems demonstrate more stable energy profiles and stronger Ca2+ binding, indicating enhanced thermodynamic stability under prolonged aqueous exposure. These findings highlight the potential of Al incorporation in improving the durability of cement-based materials in aqueous environments.

Fiber-reinforced composite coatings (FRCCs) are promising for marine protection, but insufficient adhesion at both the fiber/resin and resin/metal interfaces continues to limit their long-term durability. In this work, FRCCs were prepared by electrospinning poly(vinylidene fluoride) (PVDF) nanofibers modified with myristic-acid functionalized kaolin onto epoxy (EP), polyurethane (PU), and fluorocarbon (FC) pre-coated steel. Multiscale characterization (SEM, EIS, mechanical testing, salt spray testing, electromagnetic flux monitoring, and molecular dynamics simulations) revealed that variations in both fiber/resin and resin/metal interfacial adhesion mechanisms accounted for the distinct performance of the three systems. EP-based coatings displayed strong adhesion at the metal interface but limited long-term durability, PU-based coatings showed balanced impact resistance and anticorrosion performance, whereas FC-based coatings offered superior long-term anticorrosion durability but relatively weaker mechanical robustness. An electromagnetic flux method developed in this study captured permeability-driven changes associated with Fe to FeO transformation and tracked interfacial delamination at the coating/metal interface in real time, with signal evolution consistent with EIS data trends and a detection time below 10 s. Molecular dynamics simulations (MDS) further demonstrated that hydrogen bonding dominates fiber/resin adhesion, with PVDF/PU interfaces exhibiting the strongest bonding, followed by PVDF/ EP and PVDF/FC, consistent with experimental observations. These findings highlight the dual interfacial mechanism that govern coating durability and provide a framework for the rational design of next-generation FRCCs for marine applications.

The disposal of red mud (RM), a hazardous byproduct of alumina production, poses a significant environmental risk due to the leaching of heavy metals and alkalis. Conventional encapsulation in cementitious materials often fails as water ingress remobilizes contaminants. Here, we transform RM from a hazardous waste into a key functional component to create a robust, bulk-superhydrophobic foamed concrete. RM's multi-scale particles are utilized to construct a hierarchical surface roughness, which in synergy with low-surface-energy polymers (polydimethylsiloxane and calcium stearate), imparts three-dimensional water repellency to the entire porous matrix. The addition of red mud successfully induced a superhydrophobic state, with the water contact angle reaching up to 156 degrees and the sliding angle reaching a minimum of 6 degrees. This physical barrier proved highly effective, suppressing the leaching of hazardous heavy metals (As, Cr, Pb) and alkaline components (Na) by 60%- 90%. Crucially, aggressive TCLP tests on powdered samples confirmed the material's bulk-hydrophobicity, with Na leaching reduced by 76.5%. While the hydrophobic agents alone caused a severe strength reduction (from 2.73 MPa to 1.1 MPa), the dual function of red mud effectively compensated for this loss. By acting as both a rheological modifier that stabilized the foam network and a micro-filler that densified the hardened matrix, red mud restored the compressive strength to levels comparable to the control specimens without hydrophobic agents. By engineering intrinsic water repellency, this work convert an environmental liability into a highperformance, durable, and safe construction material, offering a new pathway for the circular economy.

This study comprehensively investigates the synergistic effects of nano-silica (NS) dosages (0-5 wt%) and metakaolin (MK) substitution rates (15-21 wt%) on the hydration, mechanical performance, and microstructure of limestone calcined clay cement (LC3) pastes by experiments. Results demonstrate that NS accelerates early hydration via nucleation effects and pozzolanic reactions, while MK optimizes the formation of C-(A)-S-H gel and carboaluminate phases. An optimal combination of 3 % NS and 18 % MK increased 28-day compressive strength by 34 % and reduced median pore diameter by 30 % compared with unmodified LC3. Isothermal calorimetry revealed that NS advances silicate and aluminate reaction peaks, whereas excessive NS (5 %) may hinder hydration due to particle agglomeration. Microstructural analysis confirmed that NS refines pore structure and promotes densification, while MK stabilizes ettringite to monocarbonate conversion. The findings of this study contribute to a better understanding of the synergistic effects of NS and MK on the modification of LC3, providing a basis for an in-depth insight into their regulatory mechanisms on LC3.

Immobilizing Cu2+ from copper tailings in cement is crucial, yet its atomic-scale mechanism remains poorly understood. Using ab initio metadynamics, we delineate the complete multi-step leaching pathway of Cu2+ from a C-S-H surface, characterized by two distinct energy barriers. Initial detachment involves a stepwise ligand exchange, with the first barrier primarily dictated by the rupture of the Cu-Osi covalent bond. A highly stable, singly-anchored intermediate (State C) is maintained by a novel “triple-lock” of secondary interactions: a direct H-bond, a water-mediated bridge, and Ca-Ow coordination. This robust anchoring significantly contributes to the higher second energy barrier for complete dissolution. Final desorption is governed by a compensatory mechanism where the hydrated ion reinforces internal stability as the “triple-lock” gradually weakens. Crucially, Cu2+ adopts a labile, four-coordinate geometry throughout, challenging previous rigid six-coordinate models and offering fundamental insights for designing environmentally robust cementitious materials.

Foam concrete (FC) is widely used in building envelopes in severe cold regions, but it frequently faces the combined degradation threat of low-temperature freeze-thaw (F-T) cycles and potential high temperatures during its service life. However, the coupled deterioration mechanisms remain largely unexplored. To address this gap, this paper focuses on a novel diatomaceous earth (DE)-metakaolin foam concrete and its microstructural and macroscopic performance. The results show that DE exhibits a significant water storage effect within the matrix, which easily triggers severe ice-water phase transitions during F-T cycles, generating destructive frost heave stresses. However, DE also acts as internal exhaust valves under high temperatures, effectively relieving the internal pressure caused by water vaporization. The D5M10 group, combining 5% DE and 10% MK, exhibits the optimal resistance to coupled high-low temperatures. After experiencing moderate damage from 25 F-T cycles and subsequent exposure to an extreme high temperature of 600 ℃, the residual compressive strength of the D5M10 group is successfully maintained at 4.1 MPa, demonstrating exceptional residual bearing toughness. The moderate F-T microcracks formed in the early stage can, in turn, promote vapor depressurization at high temperatures, thereby avoiding matrix spalling. This study provides crucial theoretical support for the long-life design of porous structures under complex thermodynamic conditions in severe cold regions.

Coupling durable passive shielding with damage-triggered self-healing is essential for protecting marine steel infrastructure. Herein, a bio-inspired Janus nanofibrous composite coating was constructed on carbon steel via a sequential electrospinning and spray-coating. The architecture integrates a steel-adjacent hydrophilic layer of polyurethane/benzotriazole (PU/BTA) core-shell nanotainers with an external superhydrophobic shield of fluorinated TiO2-modified epoxy. The resultant surface exhibits exceptional liquid repellency with a water contact angle of similar to 163 degrees and maintains superhydrophobicity even after 130 cycles (39 m) of sandpaper abrasion. Electrochemical tests confirm outstanding barrier protection with an initial low-frequency impedance modulus (|Z|(0.01 Hz)) exceeding 1.4 & times; 10(11) Omega & centerdot;cm(2). Upon mechanical damage, the core-shell nanofibers responsively release BTA, initiating a rapid self-healing that restores |Z|(0.01 Hz) from similar to 10(3) to similar to 10(5) Omega & centerdot;cm(2) within 6 h. Molecular dynamics simulations elucidate this dual-mode mechanism. First, the fluorinated surface shows weak water affinity, thereby discouraging electrolyte adhesion. Complementarily, released BTA undergoes strong spontaneous chemisorption on iron via Fe-N coordination, forming a compact passivation film that suppresses interfacial water diffusion by similar to 83%. This work establishes a robust "passive barrier + active repair" strategy, validated by macroscopic durability tests and molecular-level simulations, offering a promising solution for long-term marine corrosion protection.

Strain-hardening cementitious composites (SHCC) are a class of high-performance fiber-reinforced cementitious composites (HPFRCC) engineered to exhibit strain-hardening and multiple cracking under uniaxial tension. In practical engineering, SHCC members are subjected to sustained tensile loading over their service life, making time-dependent crack widening inevitable. This gives rise to two fundamental challenges: 1. establishing a quantitative observation scheme to characterize crack widening behavior, and 2. developing a predictive model for crack evolution over different loading durations. To address these issues, this study introduces novel loading devices and an imaging-based observation scheme to quantify single-fiber pullout and individual crack widening under sustained loading. Using macro-photography and digital image processing, the pullout and crack-widening responses under various load levels are quantitatively characterized. A time-dependent constitutive law for fiber pullout is established based on the observed two-stage pullout behavior. Furthermore, a two-parameter power-function model is proposed to predict crack widening under different sustained loads. Finally, a scale-linking framework is introduced to evaluate the time-dependent crack opening in SHCC under high sustained load levels.

Engineered Cementitious Composites (ECC) are high performance fiber reinforced cementitious composites that can lead to higher ductility and narrower crack width than quasi-brittle concrete, which leads to a lower permeability and better durability. However, existing permeability prediction methods, which primarily rely on surface crack width, can introduce significant inaccuracies. This study proposes a crack modeling scheme capable of capturing the complex roughness characteristics of ECC cracks for improved permeability prediction. The similarity between generated and actual cracks was validated through geometric parameters, wavelet analysis, and permeation simulation, and the robustness of the proposed method was also evaluated. The proposed approach yields water flow predictions that are more accurate than those obtained using the Poiseuille law. Overall, this method provides an effective framework for representing complex rough cracks in permeability prediction.

Tricalcium silicate (C3S) hydration is critically influenced by grain boundaries surface (GB), whose atomic-level role in reactivity is unclear. Our multiscale simulations reveal GB ' structural disorder creates highly reactive sites via electronic activation: high electrostatic potential, weakened Ca-O bonds, and confined frontier orbitals. Metadynamics shows GB offer a kinetically superior dissolution pathway with significantly lower energy barriers than crystalline planes (CP). Unbiased MD confirms spontaneous Ca2+ dissolution at GBs within nanoseconds, while CP remain inert. These findings provide an atom-to-continuum understanding of how GB enhance C3S hydration, informing next-generation cement design.

A multifunctional acrylic coating integrates a mussel-inspired compound (AMPY) and a disulfide-based dynamic agent (DSDA) for the reinforced protection of cement-based materials. AMPY drives the formation of a multi-scale hydrogen-bonding network, elevating interfacial adhesion strength to 4.76 MPa. DSDA facilitates dynamic network reconstruction, enabling rapid self-healing under thermal or photothermal stimulation with a 93.8% adhesion recovery rate. Molecular dynamics simulations clarify the localized roles of these components. AMPY-functionalized chains preferentially accumulate at the C–S–H surface to maximize interfacial affinity, whereas dynamic disulfide bonds govern chain mobility and network rearrangement during the healing process. Durability evaluations demonstrate a 74.1% reduction in chloride migration (4.21 × 10−12 m2/s) and a significant suppression of carbonation depth (4.8 mm versus 28.4 mm for the reference after 90 days). Aggregation-induced emission (AIE) behavior in AMPY enables a visual damage-warning function, allowing for defect detection and real-time monitoring of the healing process. This dual-dynamic architecture provides a versatile strategy for high-performance protective coatings in long-term concrete infrastructure.

Introduction Glass fiber reinforced cement is utilized in construction field.Interfacial modification with coupling agents and functional polymers represents a critical strategy to enhance interfacial bonding.However,molecular mechanisms remain insufficient.In this study,molecular dynamics were used to evaluate interfacial responses of C-S-H/glass fiber modified with KH-570 and poly(vinylpyrrolidone-co-acrylic acid)(PVP-co-PAA).The results demonstrated that KH-570 induced marginal increase,while PVP-co-PAA led to remarkable enhancement.The analyses of coordination number,bond lifetime decay decoded interfacial bonding networks before and after modification.This study could reveal the distinct failure pathways and molecular mechanisms of interfacial bonding. Methods All the MD simulations were performed based on a package named LAMMPS.Firstly,all the systems were relaxed under NVT ensemble last for 5 ns,with timestep 1 fs and 300 K.Temperature control was achieved by Nose-Hoover thermostat and damping parameter 0.1 ps.The bottom Ca layers of C-S-H were fixed throughout the simulation to prevent model rotation.An additional 2 ns relaxation was conducted and trajectories were recorded every 1 ps.During the shear simulations,spring forces were applied on atoms located at the top of SiO2 slab. Results and discussion The molecular dynamics(MD)simulations are employed to evaluate shear mechanical properties of C-S-H/SiO2,C-S-H/KH-570 and C-S-H/PVP-co-PAA interfaces.The molecular mechanisms of interfacial modification are thoroughly revealed via analyzing the types and dynamic behaviors of interfacial bonding networks.During dynamic failure,PVP-co-PAA exhibits a distinct behavior compared with rigid SiO2.Flexible polymer networks undergo conformational changes,leading to an increased shear displacement.The density analyses of bonding networks indicates that interfacial bonding networks can reorganize from OS 2iO—Ca—OC-S-H into OKH-570/OPVP-co-PAA—Ca—OC-S-H.Moreover,interfacial failure is decided by ionic bonding of OS 2iO/OKH-570/OPVP-co-PAA—Ca.The coordination number follows an increasing order of OS 2iO

The development of engineering materials that simultaneously achieve ultra-light weight and high damage tolerance remains a formidable challenge in the construction sector, as traditional cementitious materials are fundamentally shackled by a brittleness-density trade-off. To overcome this limitation, this work proposes a bio-inspired interpenetrating phase composite (IPC) architecture, unlike the traditional matrix-filler paradigm where functional phases are randomly dispersed, this study proposes a topological structure paradigm based on a co-continuous interpenetrating network. This rational topological design allows the composite to be fabricated by impregnating a polyvinyl alcohol (PVA) aerogel precursor into a rigid open-cell foam cement (FC) skeleton, followed by directional freezing and lyophilization. This hierarchical design effectively resolves the intrinsic processing instability of polymer aerogels, utilizing the inorganic framework as a rigid template to suppress volumetric shrinkage from >30% to <1%. Multi-scale characterization reveals a synergistic toughening mechanism driven by chemically engineered interfaces and geometric confinement. Consequently, the resulting FC-PVA composite exhibits an ultra-low density (0.2 g/cm(3)) yet demonstrates a pseudo-plastic constitutive response, withstanding compressive strains exceeding 90% without disintegration. The material achieves an exceptional ultimate densification strength of 49.54 MPa and a high toughness of 3.12 MJ/m(3), effectively decoupling density from ductility. Beyond mechanical resilience, the composite integrates multifunctionality, including a low thermal conductivity (0.070 W m(-1) K-1), broadband acoustic absorption (average coefficient of 0.313), and fire resistance where the skeletal protection prevents macroscopic collapse under extreme heat. This work provides a viable pathway for designing next-generation resilient, energy-efficient, and multifunctional building materials.

Clarifying the bonding configurations and failure mechanisms at the interface between cement hydration phases and cellulose is of significant importance for guiding the optimized preparation of concrete-wood and wood-derived material composites. In this study, molecular dynamics simulations were employed to investigate the atomic-level bonding interactions between the primary cement hydration products, calcium silicate hydrate (C-S-H), calcium hydroxide (CH), and ettringite (AFt), and Iβ cellulose, the principal structural component responsible for the mechanical strength of wood. The axial failure evolution at these interfaces was further examined. Results indicate that hydroxyl groups, water molecules, and ions on the surfaces of the hydration phases form a complex interaction network dominated by hydrogen bonds with the hydroxyl groups of Iβ cellulose, maintaining relative structural stability and providing the energetic basis for interfacial adhesion. Interaction energy analysis demonstrates that the interfacial adhesion strength follows the order C-S-H/Iβ cellulose > AFt/Iβ cellulose > CH/Iβ cellulose. Simulations of axial failure processes show that the C-S-H/Iβ cellulose and AFt/Iβ cellulose systems predominantly exhibit cohesive failure within the cellulose phase, whereas the CH/Iβ cellulose system, characterized by comparatively weaker adhesion, undergoes interfacial failure.

The rapid deterioration of concrete structures in marine environments necessitates the development of underwater repair materials with enhanced rheological properties, mechanical strength, and interfacial bonding performance. This study proposes a novel dual-epoxy-modified cement paste (SDEP), incorporating a selfsynthesized oil-based underwater epoxy resin and an anionic waterborne epoxy emulsion into a sulphoaluminate cement matrix. A robust gradient-phase transition interface was achieved by constructing a continuous interpenetrating polymer-inorganic network (IPN), effectively bridging the compatibility gap between organic and inorganic phases. A comprehensive experimental program, including flowability tests, washout resistance assessments, mechanical strength evaluations, interfacial bonding measurements, X-CT, SEM, and nanoindentation analysis, was conducted. The SDEP exhibited excellent underwater workability with a flow diameter of 235 mm, and the washout resistance improved greatly compared to unmodified cement paste. The flexural strength increased by 36.4 %, while the underwater interfacial bonding strength was enhanced by 175.2 %. Nanoindentation results further confirmed a significant increase in the elastic modulus of the interfacial transition zone, indicating improved microstructural integrity. This study demonstrates a novel and effective design strategy for underwater repair materials through organic-inorganic phase synergy. The proposed SDEP system offers strong application potential in the rapid repair of submerged concrete structures, particularly in marine and hydraulic engineering.

Basalt Fiber Reinforced Polymer (BFRP) anchor bars offer several advantages including light weight, high tensile strength and good corrosion resistance, making them an ideal alternative to steel anchor bars in underground structures. This study through the pullout test of three 25 mm diameter fully threaded BFRP anchor bars and analysis using ABAQUS finite element software to investigate their anchorage performance and failure mechanisms. The experiment shows that the pullout capacity of BFRP anti-floating anchors exceed 400 kN, which meets the engineering design requirements for anti-floating. The axial stress of anchor bar is highest at the opening of hole and decreases rapidly with increasing depth. The depth of the axial stress transmission is approximately 2 L/3 (L is the anchorage length of the anchor bar). The shear stress initially increases rapidly along the anchorage depth, peaks near an anchorage depth of 0.75 m, and gradually decreases thereafter, with the peak shear stress increasing with higher load levels. The numerical simulation indicates that the bonding strength between the anchor bar and anchorage body multiple components during the pullout process, with the load transferring downwards from the opening-hole as the load increases, rather than being uniformly distributed throughout the entire anchorage length. Anchor bars with longer anchorage lengths exhibit a slower decay rate of axial stress and a deeper range of axial stress transfer, despite having the same diameter. The failure analysis has identified three failure mechanisms. The shear slip failure at the first interface is caused by a decrease in frictional force, mechanical bite force, and chemical adhesive force at the first interface under increasing load; the shear slip failure at the second interface is due to insufficient strength of the rock-soil mass. Anchor bar fracture failure originates from progressive fracture caused by localized stress concentration in the fiber bundles.

Chloride ion (Cl⁻) ingress significantly reduces the durability of reinforced concrete, particularly in marine environments, due to the high permeability of concrete pores. Concrete transportation inhibitors (CTIs) have emerged as a potential solution, yet their inhibition mechanisms remain unclear. In this study, molecular dynamics simulations and quantum chemical analyses are employed to elucidate the performance of surfactant-like CTIs. Results show that the enhancement of nanoscale interfacial tension (IFT) is central to reducing fluid transport. Among the tested structures, the Bola-type molecule with phosphonic acid head groups (B-PO32-) demonstrates the strongest adsorption to calcium silicate hydrate (C-S-H), low self-aggregation, and an enlarged interaction area with water. These properties allow B-PO32- to act as an effective nanoscale barrier to chloride penetration. This work provides a molecular-level framework for evaluating CTIs and offers design principles for next-generation concrete additives aimed at improving durability in aggressive environments.

Fluidity is a critical property of cement that significantly impacts the performance of cement paste in construction engineering. Fluidity is typically enhanced through the application of chemical additives (e.g., water-reducing agents). While chemical additives can enhance the fluidity and workability of cement, their drawbacks, such as cost and environmental impact, must be carefully considered. Most of the current research focuses on the use of chemical admixtures, while studies on physical alternatives remain limited. This study employs molecular dynamics (MD) simulation to propose an innovative strategy for improving the fluidity of cement slurry by applying an electric field, which acts as a physical water reducer. This research investigates the lubricating effect and underlying mechanism of the electric field on cement hydration product C-S-H particles at the nanoscale. This work demonstrates that increasing the electric field strength significantly reduces friction between cement particles, thereby improving fluidity when ions are present at the particle interface. Atomic-level structural analyses reveal that the electric field promotes a denser C-S-H structure and facilitates ion desorption from the C-S-H surface, which acts as a lubricant between particles. This study provides new insights into how an electric field can serve as a lubricant in cement systems, offering a promising approach to enhancing concrete fluidity without relying on chemical admixtures.

The preparation of self-healing anticorrosive coatings has garnered significant attention due to their ability to extend the service life of carbon steel and mitigate corrosion. In this paper, acrylate monomers were used to prepare acrylate copolymers through free radical polymerization. These copolymers demonstrate excellent sealing, adhesion (9.2 MPa), and hydrophobic properties(contact angle of 111.2 degrees). The incorporation of functional monomers leads to the formation of multiple hydrogen-bond networks, giving the coatings excellent self-healing capabilities. Microscale molecular dynamics simulations reveal that the number of hydrogen bonds in different copolymers affects their self-healing speed, with the healing rate increasing as the environmental temperature rises. After immersion in a 3.5 wt% NaCl solution for 504 h, the low-frequency impedance reached 2.04 x 107 Omega & sdot;cm2, which is four orders of magnitude higher than that of the control group. This polymer material is designed to create smart self-healing anticorrosive coatings with enhanced adhesion and hydrophobicity.