Multiscale strength formation mechanism and stress-strain behavior of alkali-activated metakaolin concrete considering the effect of alkaline solution/binder ratio

This study investigates the effect of alkaline solution/binder ratio (AL/B) on the strength formation mechanism and stress-strain behavior of alkali-activated metakaolin concrete (AAMK). Experiments are designed with seven different AL/B (0.55–0.85), and the effects of different AL/B on the macro-mechanical properties and microstructure of AAMK are analyzed by means of tests such as nuclear magnetic resonance (NMR), uniaxial compression, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results show that the pore size distribution of the specimens move to the left and the pore size decreases with the increase of AL/B. The peak stress and elastic modulus increase while the peak strain decreases, indicating the enhanced mechanical properties; the increase of AL/B promotes the formation of N-A-S-H gel, which increase the strength and elastic modulus of the concrete. Based on the analysis of statistical damage ontological model reveals the changes in the strength formation mechanism and stress-strain behavior of the material under different AL/B. It is found that the characteristic parameters (εa, εh, εb, and H) change with the increase of AL/B, which affects the deformation and damage process of the material. The research results of this article provide a theoretical basis for the application of metakaolin in concrete, as well as a new idea for the development of low-carbon concrete.