Study On The Thermal-mechanical Response Of Concrete With Different Humidity Under Microwave Irradiation

The effectively separation of mortar and aggregate is the key issue for high-quality aggregate recovery.Microwave-assisted concrete aggregate recycling is a new green technology,with low pollution and energy generated during the heating process.As an excellent microwave absorbing material,moisture plays an important role in the microwave heating process.It is of great significance to investigate the influence of moisture content on the microwave crushing concrete technology.In this paper,theoretical analysis,experimental research and numerical simulation are employed to study the temperature rise law,heating effect,microstructure evolution and mechanical damage of concrete under microwave irradiation.Compared with traditional heating method,the mechanism of low-temperature concrete damage under microwave irradiation was studied.This research can provide the reference for the further development of microwave-assisted concrete recycling technology.The research contents are as follows:(1)Based on the mechanism of microwave heating concrete,the coupling analysis of heat transfer field,electromagnetic field,mechanical field and mass transfer field was realized through COMSOL Multiphysics to explore the thermal-mechanical characteristics of concrete in microwave field.The characteristics of microwave selective heating and the dielectric properties difference of aggregate and mortar lead to the distribution of hot and cold partitioning inside.Temperature and stress gradients were formed at the interface between aggregate and mortar.(2)The thermal effect of concrete with different humidity under microwave irradiation was explored.The temperature rise law of concrete with different moisture content in microwave field were obtained.The influence of moisture content on the heating effect of concrete was discussed.Research shows that when the moisture content and microwave power were relatively high,the concrete test block can be broken quickly at a lower temperature quickly,The damage form is the crystal fracture,aggregate and mortar separation interface is obvious,with less mortar phase adhered.(3)The influence of microwave power and moisture content on the mechanical properties of concrete in microwave field was explored.Based on the microwave irradiation system,through the uniaxial compression experiments,the influence of microwave power and moisture on concrete strength weakening was analyzed.The mechanism of concrete low-temperature damage under microwave irradiation was illustrated.Increase the microwave input power or moisture content can significantly increase the rate of crack expansion within the concrete,leading to larger concrete strength reduction.(4)Compared with the conventional heating method and microwave heating method,with the help of theoretical analysis and experimental test,the thermal failure law,temperature rise characteristics,and microstructure evolution of concrete samples under different heating conditions were analyzed.Based on the comparative test of saturated concrete and dry concrete specimens,the influence of moisture on concrete heating efficiency and aggregate separation effect was discussed.Compared with the conventional heating method,the microwave assisted of the aggregate and mortar interface separation was more effective.