Influence of freeze–thaw cycles on apparent dynamic tensile strength, apparent dynamic fracture toughness and microstructure of concrete under impact loading

The freeze–thaw damage, particularly in cold region, occurs frequently when concrete structures lose their durability. In this study, the dynamic mechanical properties of concrete after 0, 50, 100, 150 cycles of freeze–thaw are investigated. The microstructure of concrete associated with freeze–thaw damage is observed by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) technologies. According to the experimental data, the influences of the freeze–thaw cycles and the loading rate on the dynamic mechanical properties are analysed, respectively. It is shown that the apparent dynamic splitting tensile strength and the apparent dynamic fracture toughness of the specimen both decrease with the increase of the freeze–thaw cycles and the loading rate. On the basis of MIP results, it is found that the porosity, the most probable pore size and the critical diameter of the concrete all increase with the increase of the cycles of freeze–thaw. The micrographs obtained from SEM illustrate that the development of cracks and the production of crystals are dominant performances reflecting the damage of concrete under freeze–thaw cycles. In addition, the freeze–thaw cycles can induce dissolution of the specimen, which benefits the growth of the crystal ettringite.