Study on the chloride ion transport mechanism of recycled mixed aggregate concrete based on evolution characteristics of pore structure

Abstract

• An interface model of RMA concrete considering pore structure characteristics was established. • The evolution characteristics of the microscopic pore structure for RMA concrete were studied. • The chloride ion transport mechanism of RMA concrete was studied based on microstructure parameters. The difference in pore structure characteristics is the fundamental reason that the chloride ion transport mechanism of recycled mixed aggregate (RMA) concrete is different from that of ordinary concrete. In this paper, the chloride ion penetration tests were performed on eight groups of specimens with different water-binder ratios (w/b) and coarse aggregate types. The specimens’ micromorphology, pore structure, fractal dimension, and microhardness were analyzed in detail. The results show that the pore structure of the specimen has an important influence on the chloride ion transfer process. With the increase in curing age, the porosity of new mortar (NM) and mortar attached to the surface of brick aggregate (BM) decreased, while the total fractal dimension increased, and the porosity of BM decreased more than that of NM. The brick aggregate is wrapped in a dense hydration layer, which prevents chloride ions from penetrating the brick aggregate to a certain extent. The anti-chloride ion transport performance of NM is weaker than that of BM due to the NM contains more capillary and large pores. Different pore size distribution ranges of the specimens have similar fractal characteristics. The fractal dimension first increases and then decreases with the change of the pore size range from small to large. The interface pore model of RMA concrete was established to provide a reasonable basis for further research on the durability of the specimens.