RESEARCH ON DAMAGE OF RECYCLED CONCRETE UNDER FREEZE-THAW AND SULFATE

In many areas in China, concrete buildings are often exposed to ocean sail corrosion and freeze-thaw environments, which poses threats to the durability of buildings. Previous studies cannot fully consider the combined effects of salt corrosion environment and freeze-thaw environment, and the further systematic research on the mechanical properties and damage mechanism of concrete buildings is still lacking. Therefore, the cyclic coupling effect of sulfate corrosion and freeze-thaw is taken as the research background to achieve the purpose of providing effective data support for the durability of recycled concrete. Through the mechanical performance test, the corresponding change law of the compressive strength of recycled concrete and the sulfate corrosion time under the sulfate corrosion environment is obtained. By using the scanning electron microscope and mercury porosimeter to detect the microscopic morphology and pore structure of recycled concrete under sulfate corrosion and freeze-thaw environment, the microstructure of the recycled concrete under different freeze-thaw times and different corrosion times are obtained. The research results show that: based on the mechanical performance experiment of recycled concrete, the relationship between the mechanical performance parameters of mineral-blended recycled concrete under different freeze-thaw and different corrosion times is initially established. Through the microscopic test method of recycled concrete, the relationship between fine appearance structure and macroscopic properties of recycled concrete is obtained. In the mechanical performance test, under the condition of freeze-thaw 30-90 times, while the sulfate corrosion process of 30d to 300d, the compressive strength gradually increases from the average value of 58.6Mpa. However, after 300d corrosion, the compressive strength drops rapidly to an average value of 47.3Mpa, with an average decrease of 11.3%, indicating that under salt corrosion and freeze-thaw. its frost resistance and corrosion resistance are weakened. In the microscopic test of recycled concrete, the average pore size of the mixed recycled concrete after 300 days has increased by about 50nm compared with the value after 30 days. The pore structure of the concrete has become significantly worse under the action of freeze-thaw and salt corrosion.