Damage Constitutive Model and Acoustic Emission Characteristics of Recycled Composite Micropowder Concrete under Coupling of Freeze–Thaw Cycles and Bending Load

In order to study the damage evolution characteristics of recycled composite micropowder concrete (RCMC) under the coupling of freeze–thaw cycles and bending load and establish a damage constitutive model, a test of the coupling of freeze–thaw cycles and bending load and a damaged layer test were carried out first, and the modified damaged layer thickness was used as the standard to evaluate the damage degree of RCMC in an environment in which freeze–thaw cycles and bending load are coupled. Second, the axial compression test and acoustic emission test were carried out. Based on the acoustic emission amplitude, the damage variable of RCMC under axial compression was characterized, and the axial compression damage model was established. Finally, combined with the damage factor in an environment with a coupling of freeze–thaw cycles and bending load, the damage constitutive model of RCMC under axial compression and coupling of freeze–thaw cycles and bending load is established. The results show that with increased freeze–thaw cycles and bending load, the stress–strain curve of RCMC gradually tends to be flat, the peak point moves to the right, the initial damage degree increases, and the brittleness is significant. The acoustic emission amplitude, energy, and ringing count of RCMC are closely related to its damage development, mechanical properties, and stress–strain curve. After correction, the accuracy of damage degree evaluation in an environment of freeze–thaw cycles and bending load is significantly improved. The larger the initial damage degree, the smaller the correction coefficient. Based on the acoustic emission parameters, the damage constitutive model of RCMC under coupling of freeze–thaw cycles and bending load under axial compression is established. The calculated results are in good agreement with the experimental results.