不同养护条件下混杂钢纤维超高性能混凝土的早龄期力学性能及开裂特性

Mechanical Properties and Cracking Characteristics of UHPC with Hybrid Steel Fibers at Early Age under Different Curing Conditions

结合烧失量与单轴拉、压实验,研究了空气及热水(1 d,60℃热水+2 d空气)养护条件下混杂钢纤维超高性能混凝土(UHPC)试件的3 d龄期水化程度与力学性能,同时利用数字图像相关技术与光学显微镜对拉伸试件表面的开裂特性进行了表征,并通过扫描电子显微镜对其微观结构进行了分析。结果表明:与空气养护相比,热水养护加快了UHPC基体的水化反应进程,温度的升高是促进水化反应的主要因素;热水养护UHPC试件的初裂、抗拉及抗压强度明显提高,但其拉伸应变性能的变化并不明显;试件的最大裂缝宽度总体上有所降低;基体变得更加致密,纤维与基体的界面粘结也更强。随着纤维掺量的增加,UHPC的拉伸应变有所提高,总体积掺量为2.5%(长、短纤维比例分别为1.25:1.25,1.5:1.0)试件的拉伸应变均超过了2×10^(-3);混掺1.5%(体积分数)长纤维与1.0%短纤维试件在热水养护下产生了较多宽度小于50μm的微裂缝。DIC技术获得的理论应变与单轴拉伸实测应变之间具有较好的吻合度。

The hydration degree and mechanical properties of ultra-high performance concrete(UHPC)specimens with hybrid steel fibers cured in air and hot water(1 d,60℃hot water+2 d air),respectively,were investigated via ignition loss tests and uniaxial tensile and compressive tests.Also,the surface cracking characteristics of tensile specimens were characterized by digital image correlation technique and optical microscopy,and the microstructures were analyzed by scanning electron microscopy.The results show that compared with the results obtained in air curing,hot water curing accelerates the hydration reaction progress of the UHPC matrix,and an increase in temperature mainly contributes to the promotion of hydration reaction,thus improving the initial cracking,tensile and compressive strength of the UHPC specimens in hot water curing.However,the tensile strain capacity changes slightly.In general,the maximum crack width of the specimen decreases,the matrix becomes denser,and the interface bonding between the fibers and the matrix is stronger.The tensile strain of UHPC increases with the increase of fiber content,in which the tensile strains of the specimens with 2.5%(volume fraction)of fibers(a ratio of long fibers to short fibers is 1.25:1.25 and 1.5:1.0,respectively)are more than 2×10^(–3),the specimen with 1.5%long fibers and 1.0%short fibers produces more tensile cracks with the width of<50μm in hot water curing.The uniaxial tensile strains predicted by DIC are in reasonable agreement with the strains measured.