Carbonation Properties and Pore Characteristics of Different Interfaces in Recycled Lump/Aggregate Concrete

Scientifically grasping the durability performance of the recycled lump/aggregate concrete (RLAC) is of great significance for promoting the engineering application of this type of concrete. In this paper, to reveal the carbonation properties of the stone-mortar interface and the new mortar-old mortar interface in RLAC, rapid carbonation tests of these two kinds of interfaces and the mortar matrix were carried out, and the porosity of the new mortar-old mortar interfacial transition zone was investigated through backscatter electron images. The results show that the carbonization depth of the interfacial transition zone is greater than that of the mortar matrix, and the closer to the interface, the greater the degree of carbonization, showing an obvious two-dimension carbonization superposition phenomenon. The interface carbonization depths of the stone-mortar specimens vary from 26 to 46 mm, while those of the mortar-mortar specimens are only 7～15 mm. As compared with the new mortar-old mortar interface, the carbonization depth of the stone-mortar interface is much greater, indicating the latter interface having a weaker carbonization resistance. The water-to-cement ratio of the new mortar has a great influence on the carbonation performance of the new mortar-old mortar interface, and the related reduction in carbonization depth is between 15% and 52%, while the water-to-cement ratio of the old mortar has no obvious effect on the carbonation performance of such interface. When the water-to-cement ratio of the new mortar is fixed, the porosity of the new mortar-old mortar interface is almost unchanged with the water-to-cement ratio of the old mortar. However, when the water-to-cement ratio of the old mortar is fixed, the porosity of such interface decreases greatly with the reducing of the water-to-cement ratio of the new mortar. There thus comes to the conclusion that, in practical engineering, the carbonation performance of the new mortar-old mortar interface can be effectively improved by controlling the water-to-cement ratio of the new mortar.