Investigation on chloride releasing from coral aggregates to cement paste in coral aggregate concrete

Abstract

Coral aggregate concrete (CAC) is one of the most commonly used building materials in construction on marine islands, but the chlorides contained in the coral aggregates (CA) could affect the durability of CAC with steel bars embedded. In this paper, an analytical solution for the diffusion of chlorides from CA into the cement paste in CAC was derivated and the model was established. Studies on chloride releasing behaviours in CAC through an experimental setup of CAC interface specimens with five mixes were conducted. From the analytical model, the chloride diffusion coefficient DCl can be obtained and, different from other reported chloride diffusion coefficient from harden specimen, this coefficient could be the only factor that describes the chloride transport in CAC from the mixing stage. The chloride releasing rate αCl from CA was also calculated and quantified. The results show that the chloride release rate from CA decayed with time and significant chloride release occurred in the first 30 days from the mixture of raw materials, the released amount of chlorides from CA was positively correlated to the average pore size of cement pastes, and the chloride diffusion coefficient of CA in this study was 2–3 magnitudes higher than that of hardened cement paste.