钢纤维对UHPC拉伸性能及其拔出行为的影响

Effect of Steel Fibers on Tensile Properties of Ultra-high Performance Concrete and Its Pullout Behavior

采用单轴拉伸试验和单丝拉拔试验探究了钢纤维形状、长度与直径对超高性能混凝土(UHPC)拉伸性能及钢纤维拔出行为的影响,并结合部分单丝拉拔试验样品的钢纤维表面形貌和钢纤维基体界面的扫描电子显微镜(SEM)观察结果,对前述影响进行了合理解释.结果表明:掺有端钩型钢纤维的UHPC拉伸性能和钢纤维单丝拉拔性能普遍优于同直径同长度的平直型钢纤维,端钩型钢纤维的锚固力是导致其拉伸全应力应变曲线出现“屈服段”和拉拔载荷位移曲线出现平台期的原因;无论平直型还是端钩型钢纤维,当钢纤维直径相同时,UHPC的初裂强度随钢纤维长度增加而呈先增大后减小趋势,当钢纤维长度为16 mm时获得最优UHPC拉伸性能与钢纤维单丝拉拔性能;随着钢纤维直径的增加,掺有相同长度端钩型钢纤维的UHPC拉伸性能与钢纤维单丝拉拔性能逐渐变差,原因在于随着钢纤维直径的增加,钢纤维基体界面出现泌水,导致混凝土局部孔隙增多,结构疏松.

Effect of type,length and diameter of steel fibers on the tensile properties of ultra-high performance concrete(UHPC)and its pullout behavior were investigated through the uni-axial tensile test and single fiber pullout test.It can be explained by scanning electron microscope(SEM)results of fiber surface and interfacial transition zone(ITZ).The results show that the tensile properties and pullout behavior of UHPC with end-hooked fiber are better than that of UHPC with straight fiber.Compared to straight fiber,better bonding properties of ITZ between end-hooked fiber and matrix contributes to the“yield period”in tensile stress-strain curve and platform period of pullout curve.For both type of steel fiber of the same diameter,the elastic tensile strength increases at first and then decreases as fiber length increases.The optimum tensile property and pullout behavior are gained at the length of 16 mm.For UHPC with end-hooked fibers at the same length,the tensile property and pullout behavior declines,due to increasing parosity and bleeding in ITZ at a large diameter.