钢纤维掺量和配筋率对UHPC轴拉性能和开裂行为的影响

Effect of steel fiber content and reinforcement ratio on tensile properties and cracking behavior of UHPC

超高性能混凝土(UHPC)因物理力学性能优异而被广泛用作结构的加强层或保护层,但2%~3%的典型纤维体积掺量带来的高昂成本仍阻碍着其进一步推广应用。相较于典型纤维掺量UHPC,低纤维掺量UHPC材料成本更低,且具有改善配筋UHPC延性的潜力。为探究低纤维掺量配筋UHPC的轴拉性能和开裂行为,通过轴向拉伸试验测试了10组共30个试件的拉伸响应,并采用图像识别算法定量评估了试件内部的纤维分布特征,基于试验结果分析了配筋率和纤维掺量对配筋UHPC延性、承载能力和开裂行为的影响。研究结果表明:0.5%纤维体积掺量UHPC的延性随配筋率增大近似线性增加,但改变配筋率对2.0%纤维体积掺量UHPC的延性影响有限;配筋UHPC达到拉伸承载力时UHPC和钢筋的应力受配筋率和纤维掺量配比影响,计算拉伸承载力时需予以考虑;配置钢筋可显著提升0.5%纤维体积掺量UHPC控制最大裂缝宽度的能力,但对2.0%纤维体积掺量UHPC控制最大裂缝宽度的能力影响不大;改变配筋率对配筋UHPC最大裂缝宽度的影响较小;将纤维体积掺量从2.0%降低至0.5%后,除控制最大裂缝宽度的能力略有降低外,配筋UHPC的其他轴拉性能基本未见退化。

Ultra-high performance concrete(UHPC)is widely used as a reinforcing or protective layer for structures due to its excellent physical and mechanical properties,but the high cost due to typical fiber content of 2%to 3%hinders its further application.Compared to UHPC with typical fiber content,UHPC with low fiber content has a lower material cost and has the potential to improve the ductility of reinforced UHPC.To understand fully the tensile mechanical properties and cracking behavior of rebar-reinforced UHPC with low fiber content and to evaluate the effect of changing the reinforcement ratio,in this paper,the tensile responses of a total of 30 specimens in 10 groups were tested by direct tensile tests,the effects of reinforcement ratio and fiber content on the ductility,tensile load-bearing capacity,and cracking behavior of the reinforced UHPC were analyzed,and the characteristics of fiber distribution inside the specimens were quantitatively evaluated based on the image recognition.The results show that the ductility of UHPC with 0.5%fiber content increases approximately linearly with the increase of reinforcement ratio,but altering the reinforcement ratio has a limited effect on the ductility of UHPC with 2.0%fiber content.When the reinforced UHPC reaches the tensile load-bearing capacity,the stresses of UHPC and steel rebar are affected by the combination of reinforcement ratio and fiber content,which need to be considered when calculating the tensile load-bearing capacity.Adding rebars significantly improves the ability of UHPC with 0.5%fiber content to control the maximum crack width,but has no significant effect on the ability of UHPC with 2.0%fiber content to control maximum crack width.Changing the reinforcement ratio has less effect on the maximum crack width of reinforced UHPC.After reducing the fiber content from 2.0%to 0.5%,the other axial tensile properties of the reinforced UHPC are not basically degraded,except for a slight reduction in the ability to control the maximum crack width.