Analysis on frost resistance and pore structure of phase change concrete modified by Nano-SiO2 under freeze-thaw cycles

To study the effect of nano-SiO2 on the frost resistance of phase change concrete, and to further explore the deterioration of its internal pore structure under the effect of freeze–thaw cycles, X-ray tomography was applied to the rapid freeze–thaw test for the study of frost resistance, and the pore structure of the modified concrete was reconstructed during the freeze–thaw cycles. By image processing and registration techniques, the change pattern of mesoscopic pore inside the phase change concrete modified by nano-SiO2 and the development and ductility characteristics of the pore structure in the interface transition zone were analyzed. The results showed that the admixture of nano-SiO2 and phase change materials could effectively improve the frost resistance of concrete. Frost resistance life was improved by at least 43 % and up to 71 %. Additionally, nanomaterials could constrain the change of pore structure inside the composite modified concrete and densify the interface transition zone. The ITZ porosity of ordinary concrete increased by 10.58 times after 150 freeze–thaw cycles, while the secondary modified phase change concrete with 10mPCMs/1.5NS only increased by 1.2 times.