水灰比对PVA纤维增强水泥基复合材料性能和显微结构的影响

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

对3种不同水灰比(0.2,0.4,0.65)形成的聚乙烯醇(PVA)纤维增强水泥基材料,通过三点弯曲试验,结合表观裂缝形状和裂缝处PVA纤维形态,研究了水灰比对材料弯曲性能的影响;通过对断裂面处纤维表面、纤维嵌入端和纤维拉断或拔出端的SEM影像分析,从微观层面研究了水灰比对PVA纤维-基体界面显微结构的影响。弯曲试验结果表明:随着水灰比增加,跨中部位裂缝数量明显增加,裂缝处拔出的纤维数量增多而拉断的数量减少,材料的弯曲韧度和开裂强度到弯曲强度的增强幅度提高。界面显微结构表明:随着水灰比增加,基体结构由致密变疏松,界面粘结力减弱,桥接裂缝的PVA纤维状态由瞬间猝断转变为滑动拔出且表面有轻微刮削,纤维对材料增强增韧的效率显著提高。

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 puUouted ends in fracture surface were investi gated 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.