Experimental investigation on chloride transport in semi-buried concrete exposed to seawater wet-dry cycles in coastal soil environment

The issue of ocean corrosion in coastal areas, particularly in concrete structures partially buried in the soil has attracted wide attention has garnered attention due to the unique challenges it presents. This study investigates the enhanced chloride ions intrusion in concrete due to bidirectional unsaturated gradients between the parts buried in soil and those exposed to the air. A 90-day chloride salt erosion experiment was conducted on both fully buried and semi-buried concrete across five different soil environments to analyze the transport properties of chloride ions. Drilling powder sampling and the detection of free chloride ion content in the concrete specimens were performed at intervals of 30, 60, and 90 days. The results indicate that the chloride ions in semi-buried concrete exhibit bidirectional unsaturated migration toward the air-exposed end, leading to significantly peak chloride ion concentrations at the air-exposed end compared to those subjected to wet-dry cycles in a pure salt solution. Specifically, after a 90-day cycle, the total chloride contents at the air-exposed end of semi-buried concrete in pure sandy soil, 50% clay soil, and pure clay soil increased by 68.8%, 43.1%, and 16.4%, respectively. Soils with lower permeability intensified the vertical unsaturation gradient within the concrete, accelerating chloride ion migration towards the exposed end and resulting in higher accumulation at elevated positions. The research work underscores the critical impact of bi-directional unsaturated transport on concrete durability in coastal environments and calls for a deeper understanding of its applications for corrosion prevention.