Study on carbonation resistance and chloride ion distribution after carbonation of alkali-activated raw sea sand slag mortar

Driven by the scarcity of river sand and accompanying environmental concerns, sea sand is emerging as an alternative material. However, the durability of construction products can be jeopardized by chloride ions in raw sea sand. Alkali-activated cementitious materials possess high chloride binding capacity, alleviating some of these risks. But its carbonation resistance is weaker. In alkali-activated sea sand slag (AASS) mortars, the interaction effects and mechanisms of carbonation and chloride ions are still unclear. To address this, our study investigates the effects of alkali equivalent and sea sand substitution rates on carbonation resistance and chloride ion distribution in AASS mortar. Mortar specimens were prepared with varying alkali equivalents (4-6%) and sea sand substitution rates (0-100%), followed by mechanical strength, carbonation depth, chloride ion distribution, and microstructure. Our results reveal that higher alkali equivalents improve mechanical performance and carbonation resistance. Although the presence of shells in sea sand slightly reduces strength, an optimal substitution rate of 30% refines pore structure and thereby enhances durability. Conversely, higher sea sand substitution negatively affects resistance due to poor gradation. Increased alkali equivalent slightly escalated peak chloride concentration, whereas higher sea sand amplified the concentration gradient, expediting chloride transport. Through TG and MIP analyses, optimal resistance was verified at 5% alkali equivalent and 30% sea sand substitution. In conclusion, appropriate sea sand incorporation can improve AASS mortar durability, making sea sand a feasible alternative material.