Study on the evolution of pore structure of manufactured aggregate concrete under sulfate freeze-thaw based on nuclear magnetic resonance technology

There is a large temperature difference between day and night in the northwest region of China and there is a large amount of saline soil environment. Therefore, a large number of buildings in the northwest region are inevitably subjected to the coupling effect of sulfate and freeze-thaw, resulting in a large number of pores inside the structure and ultimately leading to its damage and failure. Nuclear magnetic resonance (NMR) was used to analyze the pore size distribution, porosity and other pore structure parameters of manufactured aggregate concrete under the coupling effect of sulfate and freeze-thaw, and the influences of sulfate concentration, freeze-thaw cycles and stone powder contents on the pore structure of manufactured aggregate concrete were explored. The results show that sulfate reduces the freeze-thaw deterioration rate of the mechanism aggregate concrete, and the deterioration effect is more significant with the increase of sulfate concentration. The porosity of manufactured aggregate concrete increases with the increase of freeze-thaw cycles. The porosity of mechanism aggregate concrete decreases first and then increases with the increase of stone powder content. It has the best pore structure when the content of stone powder is controlled at about 10wt%. In addition to ettringite and gypsum, there is also anhydrous mirabilite in the chemical erosion products under the coupling effect of sulfate freeze-thaw, but the low temperature inhibits the chemical erosion of sulfate and makes physical erosion dominant.