Abstract:The effects of different fly ash contents on chloride ion content, chloride ion binding capacity and capillary water absorption properties of coral aggregate concrete(CAC) was investigated. In addition, the hydration products, theoretical total pore volume and bound water content in CAC were analyzed by X ray diffraction(XRD) and thermogravimetry(TG DTG). The results indicate that the total chloride ion content increases with curing age. At early ages, the total chloride ion content in CAC containing fly ash is lower than that without fly ash; however, it increases at later ages. The change in the free chloride ion content with curing age is just opposite. The addition of fly ash improves the chloride binding capacity of CAC. Fly ash has little effect on the capillary water absorption of CAC for 28d; however, it can significantly reduce the absorbed water and sorptivity at 60days. Adding 20% fly ash decreased the secondary sorptivity of CAC for 28d and 60d by 61% and 154%. Fly ash has little influence on the types of hydration products formed, but it can reduce the content of Ca(OH)2 in CAC and lead to Friedels salt.