不同轴拉性能的超高性能混凝土圆环约束收缩性能

开展2种不同轴拉性能(高应变强化型和应变软化型)的超高性能混凝土(UHPC)的圆环约束收缩性能研究.首先对高应变强化型UHPC及应变软化型UHPC进行单轴拉伸试验及声发射实时损伤定位试验,得到不同龄期时(2,7,28,80 d) UHPC的轴拉应力-应变曲线及其拉伸损伤演化机制.随后对2种UHPC进行圆环约束试验,得到UHPC内钢环的压缩应变-龄期曲线.最后基于高应变强化型UHPC及应变软化型UHPC的轴拉性能(应变强化与否)、抗拉强度发展规律及拉伸损伤演化机制,分析2种UHPC的圆环约束收缩机理.研究结果表明:高应变强化型UH-PC的内钢环压缩应变-龄期曲线出现大量幅值小于10×10^-6的锯齿形波动,对应产生的微裂纹宽度小于0.01 mm,与裂缝测宽仪(精度为0.01 mm)在UHPC圆环试件上始终未检测到微裂纹的结论相一致;应变软化型UHPC的内钢环压缩应变随着龄期出现了4次较明显的瞬时突变(28×10^-6,53×10^-6,41×10^-6,18×10^-6),且裂缝测宽仪在UHPC表面检测到了4条微裂缝(0.035,0.050,0.040,0.020 mm),由于拉伸软化特性,后续在其他荷载作用下会导致裂缝持续扩展;高应变强化型UHPC的应变强化特性使其在约束状态下产生的拉应力以多点分布微裂纹(宽度小于0.01 mm)的形式逐步小幅释放,应变软化型UHPC在约束作用下产生的拉应力通过多缝开裂(宽度小于0.05 mm)的方式瞬时部分释放.

Restrained Shrinkage Behavior in Ring Test of Ultra High Performance Concrete with Different Tensile Properties

The restrained shrinkage behavior in ring tests of two kinds of ultra high performance concrete (UHPC) with different tensile properties (high strain hardening UHPC and strain softening UHPC) were studied. Firstly, the direct tensile test and acoustic emission damage localization test were conducted on the high strain hardening UHPC and strain softening UHPC to obtain their tensile stress-strain curves (2, 7, 28, 80 d) and tensile damage mechanisms. Secondly, ring tests were conducted on the two kinds of UHPCs to obtain the compressive strain of inner ring-age curves. Finally, based on the tensile properties (whether strain hardening or not), tensile strength development, and damage evolution mechanisms, the restrained shrinkage mechanisms were analyzed. The test results show that for high strain hardening UHPC, the compressive strain of the inner ring exhibits many jagged fluctuations with amplitudes less than 10×10^-6, corresponding to multiple microcracks with widths less than 0.01 mm, in accordance with the results of the crack width measuring instrument. For strain softening UHPC, the compressive strain of the inner ring undergoes instantaneous mutations four times (28×10^-6, 53×10^-6, 41×10^-6, 18×10^-6). The crack width measuring instrument detected four cracks (0.035, 0.05, 0.04, 0.02 mm) that propagated quickly under additional loading conditions owing to the tensile softening characteristic. In this study, the strain hardening characteristic of high strain hardening UHPC leads to the tensile stress caused by restraint to be released gradually and gently through multiple microcracks (less than 0.01 mm), while the tensile stress of strain softening UHPC caused by restraint is released instantaneously and partially through several cracks (less than 0.05 mm).