Deterioration analysis of seawater and coral sand concrete in simulated marine environment based on CT technique

Seawater and coral sand concrete (CSC) has great potential application value in marine development. To simulate the application of CSC in the marine environment, specimens were partially submerged in seawater. Increasing the concentration of the attack solution, temperature cycling, and humidity cycling were used to accelerate the deterioration of concrete. Based on computed tomography (CT) technique, volume deformation and mortar density were used to reflect the deterioration characteristics of CSC. By comparing the deterioration characteristics of CSC attacked by different solutions, the deterioration model for the non-submerged part of CSC attacked by seawater was studied. The research result showed: the volume stability of CSC was more significantly affected by sulfate attack, but less affected by sodium chloride attack. And the volume stability of CSC would also vary depending on the cations attacking the solution. The obvious high-density and low-density zones could be detected in the CSC attack by seawater. At the non-submerged part, the mortar density of CSC was significantly affected by sulfate attack, and this effect could enhance by magnesium ions in the higher height range. Three stages of the degradation process for the non-submerged part of CSC attacked by seawater were: 1) ion transport with capillary action; 2) ion redistribution with "wick action"; 3) formation of low-density zone due to high -concentration chemical attack. Moreover, the deterioration performance of CSC partially submerged in seawater were jointly determined by the chemical attack in cement paste and the salt crystal filling in coral sand.