高应变强化超高性能混凝土的裂缝控制机理和研究

利用声发射无损探伤技术实时监测三种类型超高性能混凝土（Ultra High Performance Concrete, 简称UHPC）轴拉试验过程中内部损伤点的形成和演化过程，同时通过裂缝观测仪量测UHPC拉应变到达2000με时的缝宽。与低应变强化UHPC和应变软化UHPC相比，高应变强化UHPC具有高抗拉强度和“类金属”拉伸应变强化性能，在强化段区间内通过多点微裂纹均布开展的形式来平衡等量变形，表现出优异的裂缝宽度控制能力。气体渗透测试证明高应变强化UHPC抗气渗性能优异，且拉应变达到2000με后即刻卸载状态下的抗气渗性能仍要优于未受荷C50混凝土。基于高应变强化UHPC这些特性，将其应用于桥梁结构的高应力区或其他需要高抗裂性能的部位将是预应力混凝土之外的新方案，例如钢-UHPC轻型组合结构、斜拉桥的桥塔锚固区。

Study on crack control mechanism of strain-hardening ultra-high performance concrete

In this work, the formation and evolution of internal damage points in three types of ultra-high performance concretes (UHPC) during the direct tension testing process were monitored by acoustic emission (AE) analysis system. At the same time, the crack-width of UHPC was measured by the crack observer. Comparing with the strain-softening UHPC and low strain-hardening UHPC, the high strain-hardening UHPC has the performances of high tensile strength and ‘metal-like’ tensile strain-hardening. In the strain-hardening state of high strain-hardening UHPC, the equivalent deformation was equilibrated by the uniform propagation of multiple micro-cracks, exhibiting excellent control capability of crack width. The gas permeation test shows that the strain-hardening UHPC has excellent impermeability. In the unloading state after tensile strain reached 2000με, its impermeability was still better than that of C50 concrete without loading. In view of these characteristics, it is meaningful to use strain-hardening UHPC in the bridge construction with high risk of cracking, for example, in steel-UHPC composite bridge and cable-tower anchorage zone of cable-stayed bridge.