Effects of water/cement ratio on properties and microstructure of PVA fiber reinforced cementitious composites

The water/cement ratios of 0.2, 0.4, and 0.65 were selected to form three types of polyvinyl alcohol (PVA) fiber reinforced cementitious composites. Three-point bending test was implemented to evaluate the effects of water/cement ratio on properties based on crack patterns and PVA fibers morphology in cracks; SEM micrographs of PVA fiber side surface, fibers' embedded and ruptured or pullouted ends in fracture surface were investigated to analyze PVA fiber-matrix interface microstructure at the micro level. Bending test results show that the number of cracks near mid-span site and that of pullouted PVA fibers in cracks increase significantly. Meanwhile, bending toughness value and the rate of improvement from crack strength to bending strength are improved with increasing water/cement ratio. Interface microstructure finds out that matrix structure becomes looser and interface bonding ability becomes lower with increasing water/cement ratio. Meanwhile, the PVA fibers morphology of bridging cracks changes from PVA fiber instant breakage to pullouted and slipped with slight abrasion surface, which significantly improve the rate of fiber reinforced and fiber toughening.