CT study on meso-crack propagation of gradient composite concrete subjected to sulfate erosion

Abstract

Gradient composite concrete (GCC) was prepared using the design principle of functionally gradient materials. The GCC comprised a main structural layer (made from ultrafine fly ash (UFA) concrete), an interfacial transition zone (ITZ) and a protective layer (made from high-performance mortar) from inside to outside. Industrial computed tomography (CT) was used to study internal meso-crack propagation in the GCC subjected to sulfate wetting–drying cycles. The results show that internal meso-cracks decrease with increasing UFA content in the main structural layer. In the GCC sample, quite serious erosion was found in the main structural layer, associated with the largest number of cracks, the protective layer suffered least erosion and the ITZ, created using interfacial embossing, showed stable performance. Based on mechanical property tests and analysis, more rapid rates of increase of internal crack area produced faster decreases in ultimate compressive strength and elastic modulus for the main structural layer concrete. In the GCC, the levels of decrease in ultimate compressive strength and elastic modulus were lower than those of the main structural layer concrete.