Chloride Ingress Resistance of Mortar Containing Pre-Wetted Porous Fine Aggregate Under the Combined Effects of Internal Curing and Ion Adsorption

Abstract

Chloride ingress is a critical durability concern for cement-based construction materials exposed to marine environments and other chloride-containing conditions, as it can accelerate material degradation and reduce service life. To improve the chloride ingress resistance of mortar containing pre-wetted porous fine aggregate, the effects of internal curing provided by the porous fine aggregate and ion adsorption by calcined layered double hydroxides (CLDHs) on mortar performance were investigated. Compressive strength, pore structure, water-soluble chloride profiles, X-ray diffraction (XRD), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS) were employed to analyze chloride transport and fixation in mortars with different porous fine aggregate replacement ratios and CLDHs contents. The results showed that the pre-wetted porous fine aggregate was beneficial to later-age strength development, which may be associated with its internal water storage and release characteristics, although its effect varied with the replacement ratio. At a replacement ratio of 10%, the pore structure of the mortar remained relatively stable, and the increase in water-soluble chloride content relative to the reference mortar was mainly confined to the near-surface region. By contrast, higher replacement ratios increased the total porosity and the proportions of larger pores and pore throats, thereby promoting chloride migration into the intermediate and deeper regions. CLDHs did not significantly improve the overall pore structure of the mortar, but may have reduced the water-soluble chloride content through structural reconstruction and interlayer fixation. Among the investigated mixtures, the mortar containing 3% CLDHs exhibited the lowest water-soluble chloride content at all tested depths. The pre-wetted porous fine aggregate primarily regulated the pore structure and chloride transport conditions, whereas CLDHs mainly reduced water-soluble chloride content and may contribute to chloride binding. Their combined contributions helped retard chloride migration into the mortar and improve its resistance to chloride ingress.