Damage constitutive model of RAC under triaxial compression based on weibull distribution function

Fly ash (FA) and ground blast furnace slag (GGBS) can be used to densify the pore structure of recycled aggregate concrete (RAC). However, there remains a lack of deep exploration into the effects of confining pressure and mineral admixtures on RAC's crack formation and damage analysis. This study thus focused on investigating the combined impact of the replacement rate of recycled coarse aggregate (RCA), FA, and GGBS contents on the damage mechanisms of RAC under varying stress conditions by microscopic tests and triaxial compression tests. Results identified that increasing confining pressures enhance the peak stress, peak strain, and elastic modulus of RAC, with shear cracks predominating under triaxial compression. Whereas higher the replacement rate of RCA reduced the mechanical performance of RAC, incorporating 20 % FA and 20 % GGBS can significantly enhance its strength and modulus. Electron microscopy (ESEM) images proved that the incorporation of FA and GGBS lead to a denser internal structure compared to that of RAC without mineral admixtures. The constructed damage constitutive model agreed well with experimental data of this study and literatures, showing slower increases in damage variables (D) under triaxial stress compared to uniaxial compression. Model parameters indicated that increasing confining pressure decreased parameter m and increased F0, resulting in flatter post-peak stress-strain curves, and RAC incorporated with 20 % FA and 20 % GGBS had smaller m value under different stress states. These findings provide valuable insights for applying mineral-admixed RAC in diverse engineering scenarios, offering a robust reference for optimizing RAC formulations with FA and GGBS in practical applications.