超高性能混凝土的自愈合及抗冻性能

Self-healing and frost resistance of ultra-high performance concrete

为研究带裂服役超高性能混凝土(UHPC)的自愈合及抗冻性能,对混杂钢纤维UHPC试件预加0.05%和0.1%两种应变损伤,置于水中养护28天自愈合后进行300次冻融循环试验。通过单轴拉伸性能、裂缝特征、质量损失及超声波脉冲速率(UPV)指标综合评价UHPC的自愈合及抗冻性能,并利用扫描电子显微镜和能谱仪(SEM-EDS)分析微观结构和愈合产物。结果表明:28天水养后,预损伤0.05%试件表现出较好的自愈合性能,抗拉强度、拉伸应变和应变能均高于参照试件,表面所有裂缝全部愈合;预损伤0.1%试件的拉伸性能低于参照试件,表面最大裂缝(宽度为69μm)并未完全愈合。300次冻融循环后,两种预损伤试件的初裂强度和抗拉强度均进一步增加,而拉伸应变和应变能均有所减小。相对质量与UPV的变化趋势能够很好地反映两种预损伤试件的再水化效应。SEM-EDS结果显示:距裂缝较近部位的纤维-基体粘结更牢固;裂缝表面的愈合产物主要为Ca(OH)_(2)和CaCO_(3),内侧主要为水化硅酸钙(C-S-H)凝胶。

In order to study the self-healing and frost resistance performance of cracked ultra-high performance concrete(UHPC)in service,UHPC specimens with hybrid steel fibers were pre-loaded to the tensile strain level of 0.05%and 0.1%,respectively,cured in water for 28 days and then used for performing 300 freezing and thawing cycles experiment.The indexes including uniaxial tensile property,characteristics of crack,mass and ultrasonic pulse velocity(UPV)were utilized to comprehensively evaluate the self-healing and frost resistance performance.Meanwhile scanning electronic microscope and energy disperse spectroscopy(SEM-EDS)were adopted to analyze microstructure and self-healing products.The results show that:after 28 days water-curing,the specimen with preloaded strain of 0.05%exhibits better self-healing,in which the tensile strength,tensile strain and strain energy are higher than those of the reference specimen,and all surface cracks close;The parameters of tensile properties of the specimens with pre-loaded strain of 0.1%are lower compared to the reference specimen,with a partially healed maximum crack(the width of 69μm).After 300 freezing and thawing cycles,the initial cracking strength and tensile strength of two types of pre-damaged specimens further increase,while both the tensile strain and strain energy show the decrease trend.The variation of relative mass and UPV can well reflect the secondary-hydration effect of two specimens.The results of SEM-EDS demonstrate that,the fiber-matrix bonding near crack is stronger;The healing products are mainly Ca(OH)_(2)and CaCO_(3)on the surface of crack,and calcium silicate hydrated(C-S-H)gel in the inner side of crack.