Carbonation of concrete made with dredged marine sand and its effect on chloride binding

• Interaction between DMS chloride in concrete and concrete carbonation was studied.
• Chloride ions introduced by DMS can reduce the porosity of cement paste.
• Carbonation can improve free Cl− concentration in DMS concrete.
• Initial total Cl− concentration of DMS concrete is very important to steel bar corrosion.

River sand (RS) has been overly exploited to meet demand in the construction industry, particularly in China. Chloride salt in dredged marine sand (DMS) is the primary concern that limits the use of DMS in reinforced-concrete (RC) structures. This paper developed an interaction model between the carbonation behaviour and chloride ions in DMS concrete compared with RS concrete. In this research, the test results indicated that the chloride ions introduced by DMS can reduce 20–50% carbonation of the DMS concretes. A higher carbonation resistance can reduce the possibility of steel bar corrosion in the concrete. The process of concrete carbonation can alter the state of chloride ions in the concrete and their concentrations. During the carbonation process, the bound chloride ions would become free, and their concentration in carbonated concrete could increase by up to 200% compared to that of uncarbonated concrete when the chloride ion concentration was less than 3% by cement mass. Therefore, the effect of carbonation on chloride ions must be considered with respect to the durability when DMS concrete is designed for use in RC structures.