Fiber reinforced dry-mix shotcrete with metakaolin

Both material and fiber rebounds in shotcrete are high, and the use of an appropriate mineral admixture is known to alleviate the problem. However, the exact influence of the particle size gradation and shape on the rebound and the ultimate mechanical properties of shotcrete are poorly understood. In the same context, high reactivity metakaolin (HRM), which has shown a great deal of promise in cast concrete, has not been investigated in shotcrete. This study is divided into two parts: in the first part, the effectiveness of four mineral admixtures ¯ fly ash, silica fume, HRM and carbon black ¯ with varying particle size gradations and shapes was investigated from a rebound reduction point of view. In the second part, HRM and silica fume were compared on the basis of the hardened mechanical properties with special emphasis on flexural toughness in the presence of fiber reinforcement. It was found that so far as rebound reduction is concerned, particle size of the mineral admixture is a more governing factor than its shape. Silica fume, due to its ultra-fine particle size, is superior to HRM in reducing rebound, but a blend of silica fume and HRM achieves better overall properties