To elucidate the mechanisms of microstructural changes in ultra-high-performance concrete (UHPC) under microwave exposure, this study characterizes the microstructure at multiple scales using a combination of microscopic experiments and molecular dynamics simulations. The hydration products, pore structure, morphology, and interface transition zone (ITZ) of UHPC specimens were analyzed using mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Molecular dynamics simulations were employed to investigate the uniaxial tensile behavior, free volume, and radial distribution of calcium silicate hydrate (C-S-H) gel, the primary hydration product. The results indicate that microwave curing significantly reduces the pore volume of specimens, with a daily average reduction of 0.15% in the early stages. This accelerated reduction in porosity effectively diminishes the number of high-risk pores. The hydration products formed under microwave curing exhibit higher density and enhanced internal pore optimization. Simulation findings suggest that the non-thermal effects of microwaves play a more significant role in the structural evolution. The molecular orientation of C-S-H changes after oscillation, leading to more ordered molecular arrangements. Mechanical oscillation also expels free volume from the crystal cells, promoting a more compact overall structure and increasing the tensile strength by up to 1 GPa.

In this study, a microencapsulated phase-change material (PCM) with an n-octadecane core and a fly ash cenosphere shell (ODE/FAC) was prepared and it was used to replace micro silica sand forming a novel kind of heat-stored engineered cementitious composite (HS-ECC). The influence of ODE/FAC content on the mechanical and thermal properties of the resulting HS-ECC was investigated. It turned out that the compressive strength, flexural strength, and tensile cracking strength of HS-ECC gradually decreased as the incorporation content of ODE/FAC increased, while the tensile strength and tensile strain capacity were enhanced. Moreover, the inclusion of ODE/FAC can obviously decrease the thermal conductivity of ECC, which indicates the elevated heat storage capacity. This work is significant because it provided new insights into the design of heat-stored ECC for synergistically improving the tensile properties and thermal energy storage performance.

Sulfate attack progressively degrades concrete stiffness and accelerates long-term creep. Existing creep models mainly address sound concrete and do not represent the spatial gradient of corrosion products within the interfacial transition zone (ITZ). This study develops a multi-scale homogenization framework, coupling phase evolution, layered ITZ corrosion, and viscoelastic creep. The ITZ is discretized into sub-layers, with corrosion degree decaying exponentially from the aggregate surface, and the decay coefficient is calibrated from measured sulfate concentration profiles. Phase volume fractions are updated with corrosion degree, and the effective elastic modulus is obtained using Mori–Tanaka homogenization. Creep compliance is then predicted with a Burgers model, whose parameters depend on the homogenized modulus and corrosion product content. The framework reproduces the non-monotonic evolution of elastic modulus under different sulfate concentrations, with a mean absolute percentage error below 10%. At a corrosion degree of 0.3, the predicted relative creep increment reaches approximately 11% at 365 days. The effects of temperature, loading age, and wet–dry cycles are also quantified. Sensitivity analyses identify the long-term creep modulus and corrosion product coefficient as the dominant parameters. The model provides a physically grounded tool for assessing the long-term deformation of sulfate-attacked concrete.