Influence of CaO-based expansive agent on chloride penetration resistance of marine concrete

Abstract

CaO-based expansive agent (CEA) is a high performance expansive agent, which can well compensate for the shrinkage of concrete. However, due to micro-cracks caused by excessive expansion and poor chemical stability and gelling property of additional Ca(OH)2 (expansion product), durability of marine concrete may deteriorate. Therefore, the application of CEA in marine concrete is controversial. In this study, the autogenous deformation, compressive strength, and chloride penetration resistance of marine concretes containing various dosages of CEA were determined, and the influence mechanism of CEA on the chloride penetration resistance was further explored. The results showed that the addition of CEA increased the expansion deformation, chloride diffusion coefficient, and chloride penetration depth and decreased the compressive strength of marine concrete. In addition, as the dosage of CEA increased, porosity increased and chloride binding capacity decreased. Further discussion indicated that the addition of CEA increased the volume of large capillary pore with diameter between 400 and 5000 nm, and decreased the chloride binding capacity due to the increase in the SO3 content, both of which led to the decrease in chloride penetration resistance of marine concrete. However, when the dosage of CEA was not more than 6%, adding CEA can well compensate for the autogenous shrinkage and improve the crack resistance of marine concrete without a relatively small loss of compressive strength (≤8.7%). In addition, for the marine concretes containing CEA, the chloride diffusion coefficients were very small (<1 × 10-12 m2/s). Therefore, adding no more than 6% CEA, marine concrete had good crack resistance and chloride penetration resistance. Hopefully, the outcomes of this research can provide guidance for the application of CEA in marine concrete.