Expanded polystyrene (EPS) foam concrete is attractive for lightweight building applications, yet its practical use is often limited by weak EPS-cement interfacial bonding, which promotes interfacial debonding and crack propagation and thereby compromises mechanical performance. Although nano-SiO2 (NS) has been reported to improve EPS-cement compatibility, the interfacial strengthening mechanism is still not fully clarified across scales, especially the molecular-level interactions that govern the formation of a robust interfacial transition zone (ITZ). Herein, EPS particles were modified with NS and a multi-scale framework (macro tests, micro-characterization, and molecular dynamics (MD) simulations) was employed to establish a mechanistic linkage between interfacial chemistry/structure and macroscopic performance. The results show that an optimal NS dosage of 9% (by cement mass) increases the 28-day compressive strength and flexural strength of EPS concrete by up to 18.3% and 11.2%, respectively, compared with the unmodified system. SEM, XRD, and FTIR collectively indicate a denser interfacial microstructure, increased hydration-product accumulation near the EPS surface, refined interfacial porosity, and the occurrence of condensation-related reactions involving NS. MD simulations further reveal that NS facilitates the formation of molecular bridges between EPS and C-S-H through hydrogen bonding and ionic interactions, which enhances interfacial adhesion and contributes to improved ITZ thermal stability. This study provides a cross-scale mechanistic understanding for designing high-performance EPS foam concrete via targeted interfacial engineering. MD simulations further suggest that NS enhances interfacial bonding by increasing the occurrence of hydrogen-bond networks and ionic associations at the EPS/C-S-H interface, as evidenced by the intensified interaction-related distributions and peaks in the simulation outputs.

Carbon fiber reinforced concrete (CFRC) faces significant challenges in simultaneously enhancing mechanical performance and interface bonding. Conventional modification methods often improve certain properties while limiting others. In this study, a combined modification using nanosilica (NS) and polyvinylpyrrolidone (PVP) was employed. A multi-scale approach integrating macroscopic tests-including compressive, flexural, shear, and freeze-thaw experiments-microstructural characterization, and molecular dynamics (MD) simulations was adopted to investigate the modification mechanisms. Results show that the combined modification markedly enhances compressive, flexural, and shear strengths, as well as resistance to freeze-thaw cycles. NS improves matrix stability, while PVP strengthens the interface through hydrogen bonds between its carbonyl groups (-C--O) and C-S-H hydroxyl groups (-OH), enhancing interfacial ductility. MD simulations further reveal that NS densifies and reconstructs the matrix-side interface, while PVP promotes crack suppression and energy absorption under high strain, significantly improving fracture toughness and load-bearing capacity. These findings demonstrate that NS and PVP combined modification effectively enhances CFRC performance, providing a theoretical basis for developing high-performance cement-based composites.

To address poor rheology, pumping challenges, and interfacial instability during pipe-jacking through sandy-spoil, this study develops a sodium polyacrylate (PAA)-modified bentonite slurry and establishes an integrated macro-micro-nano multiscale analytical framework. At the macroscopic level, an orthogonal design systematically evaluates fluid loss, Su's funnel viscosity, bleeding rate, and friction coefficient; the results indicate that 12-14% bentonite with 0.3-0.4% PAA simultaneously achieves low fluid loss, near-zero bleeding, and pronounced friction reduction while keeping viscosity within the pumpable range. At the microscopic level, TEM reveals a transition from a dense, agglomerated state to a flexible, lubricated state; PAA forms a coating layer and lubricating film that enhance particle dispersion and flow, strengthen thixotropic recovery, and thereby optimize structural stability and rheological performance. At the nanoscale, MD elucidates a cooperative interfacial mechanism: PAA and water assemble on mineral surfaces into a stable hydrated/lubricating layer, where weak interactions strengthen particle-water-polymer coupling, accounting for the macroscopic improvements in friction reduction and stability. Overall, PAA modification enables coordinated "lubrication-water retention-interface stabilization," providing experimental evidence and mechanistic support for optimizing pipe-jacking slurry formulations.

To improve the interfacial compatibility between sisal fibers (SiF) and the cementitious matrix, a composite modification strategy using the silane coupling agent KH550 and nano-SiO2 (NS) was adopted. The optimum dosage and strengthening mechanism were investigated through macroscopic tests, microstructural characterization, and molecular dynamics simulations. The results showed that, when the KH550 dosage was 4 wt% of SiF, together with 3.0 wt% NS by mass of cement and 1.5 vol% SiF, the composite reached the highest compressive and flexural strengths, which were 7.2% and 10.7% higher than those of the unmodified SiF group, respectively. Experimental characterization and molecular dynamics analysis indicated that the enhancement was associated with the combined action of KH550 and NS. KH550 improved the fiber-matrix interface through chemical bridging and interfacial regulation, while NS contributed to matrix refinement through its pozzolanic activity and filling effect. The molecular dynamics results provided qualitative atomic-scale support, showing a more favorable interaction environment, a stronger hydrogen-bonding network, and more evident atomic-scale distribution overlap in the modified system. Overall, the KH550/NS composite modification improved both the matrix compactness and the interfacial performance of sisal fiber-reinforced concrete, providing a useful basis for the optimization and design of this material.

To address the gap in interface modification of carbon fiber-reinforced concrete (CFRC), this study compares the effects of ethylene-vinyl acetate (EVA) and silane coupling agent (SCA). Both modifiers significantly enhance the interfacial bonding between carbon fibers (CF) and the cementitious matrix, improving the overall mechanical performance of CFRC. Macroscopic tests show increased compressive, shear, and flexural strengths. SEM reveals that SCA leads to a denser interfacial microstructure, while XRD and FTIR analyses confirm its role in promoting cement hydration. Molecular dynamics simulations indicate that EVA enhances bonding mainly through hydrogen bonding and ionic interactions, whereas SCA further forms robust Si-O-Si ionic bonds, contributing to superior interfacial strength. This multiscale study not only clarifies the mechanisms of CFRC enhancement but also offers a framework for optimizing interface engineering in high-performance fiber-reinforced cementitious composites.

Rubberized concrete is a novel green building material that enhances many features when rubber particles are incorporated into cement mortar, simultaneously yielding economic benefits through the recycling of waste tires. This study applies styrene–butadiene latex (SBL) for toughening treatment. The investigation delves into the mechanism by which SBL improves the interface between rubber and cement, encompassing macroscopic mechanical properties, microscopic structural characteristics, and nano-scale interfacial interactions. Macroscopic mechanical tests reveal a significant increase in flexural strength, shear strength, and compressive strength of the composite concrete upon the introduction of SBL and rubber. Specifically, the compressive strength improved by 8.8%, shear strength by 13.7%, and flexural strength by 18.9% at 28 days. Through electron microscopy observation of corresponding polymer cement concrete sections, observations reveal that SBL reinforces both interfaces and elucidates its bonding impact at the micro-level interface. Molecular dynamics (MD) modeling of SBL/rubber/CSH is employed at the nanoscale to compute and examine the local structure, dynamic behavior, and binding energy of the interface. The findings indicate that SBL mitigates interface impacts, enhances interface hydrogen bonds, van der Waals interactions, Ca−H coordination bonds, and stability, consequently improving interfacial adhesion and fortifying the feeble interface bonding between organic polymers (rubber) and inorganic silicates (CSH).

Carbon fiber reinforced concrete (CFRC) often suffers from weak bonding between its cement matrix and carbon fibers (CF) because the fibers have an inert surface.To overcome this limitation, we introduce phenylpropyl emulsion (SAE) as an interfacial modifier and examine its strengthening mechanism through macroscopic and microscopic experiments and multiscale simulations using discrete element and molecular dynamics methods. Macroscopic experiments show that both CF and SAE significantly improve the mechanical properties of CFRC, although the effectiveness of SAE depends on its dosage. Specifically, a 4

Traditional concrete struggles to enhance both the overall mechanical properties and the interface bonding strength of carbon fiber reinforced concrete (CFRC), while conventional modification methods may limit the improvement of other critical properties. To overcome the limitations in CFRC's interface bonding strength and mechanical properties, this study introduces water-based epoxy resin (WEP) to improve both. The dual role of WEP in enhancing interface bonding and overall mechanical performance is explored through multi-scale analysis. The optimal formulation was identified through macro-mechanical experiments, showing that WEP significantly improves the overall mechanical performance of CFRC. At a 4 % WEP incorporation ratio, the compressive strength of modified CFRC increases by 8 %, while the flexural strength improves by 29 % compared to the unmodified CFRC. Microscopic analysis shows that WEP forms a dense three-dimensional network at the cement matrix and CF interface, promoting the formation of additional C-S-H gel and creating an "anchoring" effect that strengthens interface bonding. Molecular dynamics (MD) analysis reveals that pretreated CF and WEP enhance the interface bonding strength between CF and the cement matrix through strong and weak hydrogen bonds, as well as ionic interactions, leading to a stable bonding structure. This study offers new insights into improving the mechanical performance of CFRC and highlights the potential of WEP as an eco-friendly polymer modifier for enhancing the mechanical properties of composite materials.

This study investigates the deformation characteristics of silt-lightweight soil reinforced with expanded polystyrene (EPS) beads of varying sizes. Silt-lightweight soil is engineered to address geotechnical challenges in soft ground conditions. A series of laboratory one-dimensional consolidation tests were conducted to evaluate the effects of EPS bead size and cement content on soil deformation behavior under incremental and continuous loading. The results show that EPS particle size significantly influences volumetric deformation. As the EPS particle size increases from 3 to 4 mm, the proportion of volume change attributed to EPS deformation decreases from approximately 80

To enhance the reuse of construction waste in structural materials and improve the interfacial transition zone (ITZ) in recycled concrete (RC), this study employed two modification strategies and conducted a multiscale analysis to compare the effects of combined Nano-SiO2 (NS)/ethylene-vinyl acetate copolymer (EVA) modification and EVA-only modification on the mechanical properties, hydration characteristics, and microstructure of RC. The aim was to better overcome the interface defects in recycled concrete through synergistic modification. Experimental results show that the incorporation of EVA and NS significantly improves the mechanical properties of RC, with the combined modification outperforming the single modification. Specifically, when EVA content is 5% and NS is 2%, the 28-day compressive, shear, and flexural strengths of concrete increased by 15.7%, 17.6%, and 18.5%, respectively. Microscopic tests, including scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR), revealed that the cement matrix became denser, the porosity decreased, and the content of hydrated calcium silicate (C-S-H) increased. Molecular dynamics (MD) simulations indicate that EVA-only modification enhances interfacial bonding through hydrogen and ionic bonds, while the combined modification further strengthens the interface by forming additional Si-O-Si bonds, thereby improving the overall cohesion between the new and old concrete.

Traditional concrete exhibits limited effectiveness in enhancing the fiber-matrix interface in carbon fiber reinforced concrete (CFRC). In this work, KH560 was employed to modify the surface of carbon fibers (CF), aiming to improve their bonding interaction with the cement matrix. The enhancement mechanism was investigated using a multi-scale analytical approach, with particular emphasis on interfacial adhesion and overall mechanical performance. Macro-scale mechanical testing revealed that, at a CF content of 0.6

The toughening effect of vinyl acetate (EVA) on carbon fiber reinforced concrete (CFRC) was studied by multi-scale analysis. EVA has excellent bonding properties and elasticity, which can improve the weak interface bond between carbon fiber and cement matrix, which is a key factor limiting the mechanical properties of CFRC. In this study, the synergistic effect of EVA and carbon fiber in concrete was explored by means of macroscopic mechanical test, microscopic SEM and FTIR observation, and nanoscale molecular dynamics (MD) simulation. The compressive and flexural strength test results show that EVA significantly improves the toughness and durability of CFRC, especially when the EVA content is 9%. SEM analysis showed that the interface bonding between CF and cement matrix was improved, while FTIR analysis showed that EVA delayed hydration and promoted the formation of a denser C-S-H gel structure. MD simulations further confirmed that EVA enhances hydrogen bonding at the CF/cement interface, resulting in stronger bonding and better mechanical properties. This multi-scale analysis provides EVA's comprehensive understanding of the mechanisms behind the toughening effect of CFRC, providing valuable insights for future applications in civil engineering.

Considering the long-term working performance of recycled concrete (RC) members, there is a need to compensate for the performance deficiencies of RC. In this study, the mechanical properties of RC were improved by two different modification methods, and the reinforcement effects of RC modified by Silane Coupling Agent (KH560)/Ethylene vinyl acetate copolymer (EVA) and RC modified by EVA alone were compared and analyzed. The effects of separate modification and co-modification on RC were analyzed through multi-scale methods in terms of macro-mechanical properties, microstructure, chemical composition and molecular mechanism, respectively. The results of macroscopic mechanical experiments showed that the compressive and shear strength of EVA/KH560 synergistic modification is higher than that of EVA alone. Scanning Electron Microscope (SEM) data showed that the surface density of the old and new concrete interfaces was higher under EVA/KH560 co-modification. X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) data showed that more cement gel will be produced under EVA/KH560 synergistic modification. Molecular dynamics (MD) simulations show that EVA single modification can produce hydrogen and ionic bonds at the interface of old and new concrete, while EVA/KH560 synergistic modification not only produces them, but also forms a stable Si-O-Si chemical bond.

As a green concrete material, rubber granules have the potential to significantly reduce the environmental pollution caused by discarded tires. However, the compatibility between cementitious surfaces and rubber particles is limited, leading to a reduction in the mechanical properties of concrete. The purpose of this study is to enhance the mechanical characteristics of rubber concrete mortar by using the ethylene-vinyl acetate copolymer (EVA). The results show that the compressive and flexural strengths of cement mortar are reduced when EVA is added to macro-mechanical studies. However, increasing the amount of EVA will gradually lead to an improvement in the flexural strength, shear strength, and toughness index of the cement mortar. Microscopic experiments, such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), demonstrate that the addition of EVA retards the hydration process of cement. Furthermore, as the amount of EVA increases, a membrane-like structure is formed on the surface of the cementitious matrix, enhancing the overall bond strength of the concrete. Molecular dynamics simulation results indicate that EVA primarily diminishes the interfacial effect by augmenting the inter-interfacial binding capacity through Ca-O ionic bonding and hydrogen bonding.

Considering the long-term working performance of the waste concrete building elements, this study used 3-Glycidoxypropyltrimethoxysilane (KH560) and Polyvinyl alcohol (PVA) fibers to modify the recycled concrete (RC) with the aim of improving the mechanical and long-term properties of RC. In this study, the mechanical properties of recycled coarse aggregate (RCA) concrete before and after modification were systematically investigated. The macroscale results showed that KH560 compensates for the reduced compressive strength of RCA concrete due to PVA fibers. The synergistic effect of PVA and KH560 substantially increased the flexural and shear strength of RCA concrete, with a maximum increase of 22.6% in flexural strength when the RCA substitution rate was 80%. The results of three microscopic tests (SEM / FTIR/XRD) revealed that KH560 increased the content of cement gel, which then optimized the internal pore structure of RCA concrete. The chemical reaction between KH560 and cement produced SiKH560-OKH560-SiCSH. At the nano -scale, computational analysis methods in atomistic modeling techniques were employed to model PVA fibers, cement and KH560, and the dynamic and static simulation results of the model were combined to discover a consistent SiKH560-OKH560-SiCSH chemical bond between KH560/CSH and both old and new CSH, Additionally, the findings revealed the coexistence hydrogen and ionic bonds. KH560 improves the interaction between PVA fibers and cement by forming numerous hydrogen bonds, and resolves the weak interface between the new and old cement through stable chemical bonds.

This study examines the dynamic shear strength properties of expanded polystyrene lightweight soil (EPS LWS) samples through dynamic triaxial tests, focusing on the effects of EPS bead content, cement concentration, and confining pressure. The results indicate that increasing the cement content positively correlates with the dynamic strength of EPS LWS due to the formation of reticulate cement hydrates that bond soil particles. When the cement content is below 10

PVA fiber reinforced cementitious composites are becoming more and more popular. Due to the difference in physical and chemical properties of the materials, there is a problem of weak interfacial properties between PVA and cement. In order to solve this problem, this study adopts the means of pretreatment of PVA fibers with silane coupler KH560 (KH560), and the strengthening mechanism of KH560 is systematically investigated by means of multi-scale analysis. From the macroscopic test data, it was found that the flexural strength of PVA fiber concrete at 28 days was enhanced by 16% maximally when the PVA fiber content was 0.9%. A series of microscopic tests (Scanning Electron Microscope-SEM, X-ray Diffraction- XRD, Fourier Transform Infrared Spectrometer-FTIR) characterizing the interfacial properties of the KH560-modified material revealed the reason why the pretreated PVA could be better embedded in the cementitious base. Because the addition of KH560 not only generates more gel material and increases the tightness of the interfacial structure between the fiber and the cementitious base, but also reacts with the cement to produce Si-O-Si chemical bonds. A molecular model of PVA and a gel model of calcium silicate hydrate (C-S-H), the main product of cement, were constructed using the method of molecular dynamics (MD) simulation technique. The interaction between fibers and C-S-H was found to be not only mechanical occlusion, but also unstable hydrogen and ionic bonds between PVA molecules and C-S-H. The Si-O-Si bond is very important. In summary, the strengthening mechanism of KH560 and PVA synergistically on concrete is summarized by the analysis of different scales. It also provides theoretical and experimental support for the application of KH560 and PVA fibers in composite materials.

Amphiphilic Silane coupling agent (SCA) improves the weak bond between the two phases of rubber and hydration products, fills the interfacial gaps and effectively repairs the interfacial defects between rubber and hydration products. The addition of PVA fibers mainly improves the cracking performance and durability of concrete. However, most of the studies addressing this issue have been limited to phenomenology, ignoring the mechanism of action at the atomic structure level. Therefore, this study investigates the strengthening mechanism of the interfacial properties of KH-560 coupling agent-reinforced PVA fiber-rubber concrete from the multi-scale analysis of macro-mechanical properties, micro and fine structure, chemical composition and nano-optical level. Based on the results of macro-mechanical tests, it was found that the KH-560 coupling agent could improve the compressive, flexural and shear strength of PVA-rubber concrete, so that the damage morphology also changed from brittle damage to plastic damage, and the compressive strength of concrete was slightly reduced due to the addition of PVA, but the durability and cracking resistance were enhanced. XRD (X-ray diffraction), FT-IR (Fourier transform infrared spectroscopy) and SEM (scanning electron microscopy) tests observed the presence of some gels and polymers that filled the interfacial slits and effectively repaired the interfacial defects. The two-phase interface was simulated by molecular dynamics at the nano level, and it was found that KH560 molecules could be closely connected with C-S-H gel collectively through Si-O-Si chemical bonding, and KH560 molecular bonds were unevenly distributed between the C-S-H and rubber interfaces, while the addition of modifier KH560 and PVA fibers caused more hydrogen and ionic bonds at the interface, which enhanced the interfacial interaction energy. Systematic experiments were conducted on PVA fiber-rubber soil materials before and after SCA modification under macroscopic, microscopic, fine and nano-level multi-scale analyses, which ultimately lead to the design and performance improvement of SCA modification of PVA-rubber cement-based materials in a multi-scale framework. The graphic summary is shown in Figure 1.

This study employs PVA fibers to improve the performance of rubber concrete and silane coupling agent to change the incompatibility between rubber and cement in order to weaken the issue of a weak interfacial transition zone between rubber and cement foundation (KH570). The results showed that 1.5% content of KH570 modified 15% content of rubber-1.5% content of PVA fiber with the best effect. KH570 was identified using XRD, FTIR, and SEM characteristics. It was discovered that KH570 experienced a dehydration condensation reaction with free or adsorbed water in the cement, which helped to maintain the integrity between the cement matrix and the rubber. It strengthened the bond between the cement, the rubber, and the PVA fibers and enhanced the cement's capacity to encapsulate the rubber. Finally, molecular dynamics simulations reveal that cement and rubber are connected by Si-O-Si and molecules appear to be cross-distributed, increasing interfacial compatibility and reducing interfacial effects. It can be clearly observed in the interfacial bonding mechanism that KH570 is mainly a C-S-H matrix with parallel or perpendicular connections at the tail end.