Influence of microenvironment evolution induced by calcium leaching in concrete under pressurized water conditions on chloride transport

Abstract The investigation into the influence of microenvironmental evolution, induced by calcium leaching on chloride transport in concrete in pressurized water environments, encompassed analysis of aspects such as the solid phase composition, microstructure characteristics, pH value distribution, free and total chloride concentrations using X‐ray diffraction (XRD), Thermogravimetric (TG), Mercury intrusion porosimetry (MIP), Scanning electron microscopy/Energy dispersive spectrometer (SEM/EDS), and titration tests. The results exhibit a weakening of the diffraction peaks of Ca(OH) 2 (CH) in the XRD spectra over time under hydraulic pressure. Throughout the calcium leaching procedure, there was an increase in the proportion of pores with diameters exceeding 100 nm. The pH distribution notably followed a pattern where it initially increased, then decreased, ultimately stabilizing at a distinct level. As exposure progressed from the surface to the interior of the concrete, hydroxide ions accumulated predominantly at 10–20 mm. According to the calcium leaching characteristics under pressurized water conditions, concrete can be sectioned into four zones. Specifically, there is a decrease in calcium ions and pH value in concrete Zone 1 near the exposure surface, indicative of a corresponding decrease in the chloride binding capacity. Concrete Zone 2 shows enrichment of hydroxide ions enhances Friedel's salt stability, while leached calcium amplifies the chloride adsorption of ≡SiOH. These effects collectively trigger an increase in both pH and chloride binding capacity.