基于PVA纤维-基体界面性能分析水泥基材料的弯曲性能

Analysis on Bending Properties of PVA Fiber Reinforced Cementitious Composites Based on PVA Fiber-Matrix Interface Property

通过调整水胶比形成三种配比的聚乙烯醇纤维增强水泥基材料(PFRCC),应用单纤维拔出试验测定了PVA纤维-水泥基体界面参数(化学脱粘能Gd和摩擦粘结强度τ0),发现水胶比增加,界面性能参数Gd、τ0均降低;应用三点弯曲试验获得了材料的弯曲韧度和强度,基于PVA纤维-基体界面性能分析,并结合断裂面处PVA纤维宏观影像和微观的扫描电镜(SEM)影像,研究了界面性能对材料弯曲性能的影响。结果表明:低水胶比下由于裂缝处高的应力和界面处纤维与水泥基体高的化学粘结力使大量桥接裂缝的纤维瞬间断裂而失效,导致材料的弯曲韧度和从开裂到弯曲材料强度的增幅较小;中水胶比下裂缝处纤维脱粘后滑动并受摩擦粘结强度作用被严重刮削;高水胶比下裂缝处大量纤维由于界面处低的化学粘结力被拔出,而且拔出的纤维在滑动过程中由于低的摩擦粘结强度被轻微刮削,故桥接裂缝的纤维经历长的滑动,宏观上呈现出高的弯曲挠度特征,因而材料的弯曲韧度和强度的增加幅度显著提高。

Three types of polyvinyl alcohol(PVA)fiber reinforced cementitious composites(PFRCC)were produced by adjusting water/binder(w/b)ratio.A single fiber pullout test was utilized to measure interface parameter(chemical debonding energy G d and frictional bond strengthτ0)between PVA fiber and cementitious matrix and found that the values of G d andτ0 decrease when w/b increases.The values of bending toughness and strength of PFRCC was attained via three-point bending test.The effects of PVA fiber-matrix interface property on bending properties were evaluated based on interface analysis with the aid of the macro-image and SEM micrographs of PVA fibers morphology in the failure crack.The analysis results find out that a large number of fibers of the samples with low w/b in the final failure crack are instantly ruptured due to high strength in the crack and high chemical bond in the fiber-matrix interface,which leads to low bending toughness and low rate of improvement from crack strength to bending strength;the fibers of the samples with moderate w/b in the crack can debond and slide,but the morphology of the fibers are seriously scraped by frictional bond strength.While a large number of fibers of the samples with high w/b in the crack are pulled out due to low chemical bond and the pull-out fibers are slightly scraped during sliding by low frictional bond strength.Therefore,the bridging fibers experience longer slippage and the samples are characterized by high bending deflection on a macro level,which results in high bending toughness value and high rate of strength improvement.