Engineering high-performance cementitious matrices for improved projectile impact resistance with silane, micro fibrillated cellulose and fine calcined bauxite aggregate

Abstract

This experimental study evaluated the effectiveness of passive and active strategies in improving the projectile impact resistance of cementitious matrices. The principle of the passive approach is to reinforce the matrix by substituting weak Van de Waal's forces between hydration products with covalent bonds which have the orders of magnitude higher dissociation energy. A silane coupling agent (SCA) and micro fibrillated cellulose (MFC) were selected as the vehicles to engineering the bond scheme at the molecular scale by forming a covalently linked organic-inorganic hybrid. The mechanism of the active strategy is to aggravate damage to the projectile and thus leave less energy available for the penetration process. This is achieved by incorporating exceptionally hard calcined bauxite aggregates (CBA). Impact tests were conducted utilizing 8-mm-diameter conical-nosed steel projectiles at a designed velocity of 650 m/s. Damage was quantified by the depth of penetration (DOP) and equivalent crater diameter (ECD). Results indicated that the SCA and MFC modified matrices resulted in a 30% and 20% reduction in DOP, respectively. The crack intensity was decreased tremendously or even absent for the SCA and MFC modified matrices compared with the prominent cracks of the control radiated from the cratering region. Matrices incorporating fine CBA or siliceous aggregates led to a 55% and 38% smaller DOP, respectively. Crushing of aggregates and appreciable deformation, severe scratches, and significant mass loss of retrieved projectiles were observed. Matrices including fine CBA or siliceous aggregate maintained excellent integrity and drastically less severe cracking on the impact surface as well as the interior region compared with the control.