Effect of metakaolin on the mechanical properties and pore characteristics of fiber-reinforced tailing recycled aggregate concrete

In this study, based on the fiber-reinforced tailing recycled aggregate concrete, the effects of the metakaolin (MK) content on the mechanical performance were investigated. The pore structures and strain development of concrete were obtained by nuclear magnetic resonance (NMR) and digital image correlation (DIC). In addition, the enhanced effects of MK on concrete matrix were further studied at the micro level. The results uncovered that MK addition significantly improved the cubic compressive strength, axial compressive strength, splitting tensile strength and peak strain. The best performance was obtained by the mix that contained 10% MK. The NMR results showed that MK substitution led to decreased numbers of pores and a coarsening of micropore structure of concrete. The harmless pores (pore radius range 0–0.2 μm) were the most important parameter affecting the compressive strength. The DIC results indicated that the presence of MK particles favored the dispersion of polypropylene fibers in the concrete matrix. Microscopically, the addition of MK promoted the hydration process of matrix, leading to enhanced bonding between fiber and matrix.