Cement-based materials are susceptible to internal cracks during service, leading to a reduction in their durability. Microcapsules can effectively self-repair cracks in cement-based materials. In this study, novel electromagnetic-induced rupture microcapsules (DWMs) were prepared by using the melt dispersion method with Fe₃O₄ nano-particles/polyethylene wax as the shell and epoxy resin as the repairing agent. The core fraction, compactness, particle size distribution, morphology, and chemical structure of DWMs were characterized. DWMs were subsequently incorporated into the mortar to measure the pore size distribution, compressive strength recovery, and maximum amplitudes of the pre-damaged mortar after self-repairing. DWMs were also evaluated for their ability to self-repair cracks on mortar surfaces. The results showed that the core fraction, remaining weight (30 days), and mean size of DWMs were 72.5%, 97.6 g, and 220 μm, respectively. SEM showed that the DWMs were regular spherical with a rough surface and could form a good bond with cement matrix. FTIR indicated that the epoxy resin was successfully encapsulated in the Fe₃O₄ nano-particles/polyethylene wax. After 15 days of self-repairing, the harmful pore ratio, compressive strength recovery, and maximum amplitude of the pre-damaged mortars were 48.97%, 91.9%, and 24.03 mV, respectively. The mortar with an initial crack width of 0.4–0.5 mm was self-repaired within 7 days. This indicated that the incorporation of DWMs can improve the self-repair ability of the mortar. This work is expected to provide new insights to address the mechanism of microcapsule rupture in self-repairing cement-based materials.

Compared to natural aggregates, recycled concrete aggregates (RCAs) which are derived from construction and demolition (C&D) waste exhibit inferior properties, such as lower density and higher water absorption. Accelerated carbonation was an effective approach to enhance the properties of RCA. This study conducted a comparative analysis on the property enhancement of both coarse recycled concrete aggregate (CRCA) and fine recycled concrete aggregate (FRCA) by utilizing four carbonation approaches: conventional carbonation, CH spraying with conventional carbonation, wet carbonation, and two-step wet carbonation. Scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), X-ray diffraction (XRD) analysis, and CO₂ uptake comparison were used to investigate the microstructural properties of the RCA. Furthermore, we also evaluated the compressive strength of mortar specimens with four different replacement ratios and the density and water absorption values of different carbonation-treated aggregates. The experimental findings revealed the following: (1) All of the accelerated carbonation approaches were more effective for FRCA than CRCA due to a higher adhered mortar content. (2) The pretreatment of CH spray provided external Ca²⁺ which improved the carbonation efficiency and therefore significantly enhanced the property of FRCA. (3) Liquid–solid phase carbonation achieved higher carbonation efficiency in the inner pore areas of the adhered mortar, resulting in a high CO₂ uptake and microstructure densification compared with conventional gas–solid phase carbonation.

To improve the comprehensive performance of pervious concrete, the properties of pervious concrete in different paste–aggregate ratios were subjected to both early CO₂ curing and uncarbonated curing conditions. The mechanical properties, water permeability, porosity, and chemical composition of pervious concrete under two curing conditions were investigated and compared. The effects of CO₂ curing on the properties of pervious concrete with different paste–aggregate ratios were derived. Through mechanical experiments, it was revealed that early CO₂ curing can enhance the mechanical strength of pervious concrete by about 15–18%. Meanwhile, with the increase in the paste–aggregate ratio, the improvement effect induced by early CO₂ curing became more significant. The water resistance of carbonated concrete was not significantly reduced. And with the increase in the paste–aggregate ratio, the carbonation degree of pervious concrete was reduced; the differences in porosity and water resistance became less significant when the paste–aggregate ratio exceeded 0.39. Micro-structural analysis shows that the early CO₂ curing reduced both total porosity and the volume of micropores with a pore diameter of less than 40 nm, while it increased the volume of pores with a diameter of more than 40 nm. This is also the main reason that the strength of pervious concrete under early CO₂ curing is higher than that without CO₂ curing. The effect of varying paste–aggregate ratio and curing methods adds to the limited knowledge of the performance of pervious concrete.

Purpose: This paper aims to study the influence of NaNO₂ on the chemical composition of passivation film. Design/methodology/approach: X-ray photoelectron spectroscopy and X-ray diffraction were selected to determine the composition of passivation film of steel bars in mortar. The specimens were exposed to the chloride solution, carbonation environment and the coupling effects of chloride solution and carbonation. The chemical composition and micro structures at 0 and 5 nm from the outer surface of the passivation film of steel bars were analyzed. Findings: Results showed that the nitrite inhibitor improved the forming rate of the passivation film and increased the mass ratio of Fe₃O₄ to FeOOH on the surface of steel bars. The component of Fe₃O₄ at 5 nm of the steel passivation film was more than that at 0 nm. Sodium ferrite in the pore solution was easily hydrolyzed and then FeOOH was formed. Therefore, due to the nitrite inhibitor, a “double layer structure” of the passivation film was formed to prevent steels bars from corrosion. Originality/value: This is original work and may help the researchers further understand the mechanism of rust resistance by nitrite inhibitor.