Chloride diffusion study of coral concrete in a marine environment

Using the distribution of free chloride concentration (C-f) and total chloride concentration (C-t) measured by different grades and species of coral concrete (CPC) soaking in sea water, the chloride binding capacity (R), surface free chloride concentration (C-s) and apparent chloride diffusion coefficients (D-a) of CPC were calculated. Then, the influence of curing age and exposure time on the durability of chloride in coral concrete were discussed, and the superior of magnesium sulfate cement (MSC) in resisting chorine salt erosion were verified. The results indicated that the CPC R values increased whereas the C-s values decreased with the extension of the curing age. The relationship between the exposure time and Cs followed an exponential form; however, its growth rate was considerably lower than that of ordinary concrete (OPC) due to its high water absorbability. Furthermore, the decreasing relationship between D-a and the exposure time conformed to the power function. The CPC D-a exposed for 10-25 a under a laboratory-simulated marine environment was 88.9-99.1% lower than that in an actual marine environment. The D-a of CPC was 0.5-6.6 times higher than that of any other type of concrete but decreased more quickly with the exposure time. After studying the CPC chloride diffusion parameters C-f, C-t, R, C-s and D-a, the advantages of MSC against the erosion due to chloride salt were fully demonstrated. Hence, for a CPC structure under an actual marine environment, extending the moisture curing age or using MSC will improve its ability to resist chloride diffusion, reduce the speed of chloride intrusion and prolong the service life of the structure. (C) 2016 Elsevier Ltd. All rights reserved.