UHPC的轴拉性能与裂缝宽度控制能力研究

Experimental study on crack width control ability of ultra-high performance concrete

为研究3种类型超高性能混凝土(ultra-high performance concrete,简称UHPC)的轴拉应力-应变曲线及其裂缝宽度控制能力,包括高应变强化UHPC、低应变强化UHPC和应变软化UHPC.采用轴拉试验方法测试狗骨头形试件,得到UHPC的轴拉应力-应变曲线和缝宽-应变曲线.试验结果表明:高应变强化UHPC和低应变强化UHPC的轴拉应力-应变曲线均包括弹性段、应变强化段和应变软化段,应变软化UHPC只有弹性段和应变软化段;UHPC应变强化段和应变软化段的转折点是裂缝缓慢扩展和迅速扩展的临界点;提高UHPC的极限拉伸应变,即延长其应变强化段,有助于提高其裂缝宽度控制能力;高应变强化UHPC拉伸应变在0.42%之前,其裂缝宽度均小于0.05 mm.对比C50混凝土(极限应变、极限强度分别为0.012%、2.3 MPa),高应变强化UHPC优异的裂缝宽度控制能力避免了结构设计中受正常使用状态裂缝宽度验算限制的影响,同时可在钢筋屈服前与其全程协同工作,这使得钢筋增强高应变强化UHPC在某些需要对裂缝宽度进行严格控制的结构类型中具有很高的应用价值.

The axial tensile stress-strain curves and crack width control ability of three types of ultra-high performance concrete （ UHPC） were investigated, including high strain-hardening UHPC, low strain-hardening UHPC and strain softening UHPC, respectively. The tensile stress-strain curves and crack width-strain curves of the UHPC were attained from tests on dog-bone shape specimens. The results show that the tensile stress-strain curves of high strain-hardening UHPC and low strain-hardening UHPC include three stages （elastic, strain hardening, strain softening）, while the strain softening UHPC has only elastic stage and softening stage. The turning point of strain hardening stage and strain-softening stage is the critical point of slow propagation and rapid expansion of the cracks. The ultimate tensile strain improvement of UHPC can improve the crack width control ability. When the tensile strain of high strain-hardening UHPC is below 0.42%, the crack width is less than 0. 05 mm. In comparison with C50 concrete （ ultimate strain and ultimate tensile strength are 0.012%and 2.3 MPa, respectively）, the impact of the crack width checking in serviceability limit state on high strain-hardening UHPC can be avoided by its excellent crack width control ability, and the high strain-hardening UHPC can work together with steel under tensile loading before steel yield. It is meaningful to use reinforced high strain-hardening UHPC in those structures with high demand of crack width control.