干燥引起的初始缺陷对混凝土宏观性能的影响

Influences of Initial Defects Caused by Drying on Macroscopic Performance of Concrete

将制备的混凝土试件分别标养3,7,28d(试件编号记为SC3,SC7和SC28)后置于干燥环境(21℃,相对湿度37%)中,在不同试验龄期测试上述3种试件的力学性能、抗冻性能和抗氯离子渗透性.基于弹性波波速来定量表征由干燥引起的混凝土初始缺陷程度,并结合微裂纹密度、扫描电镜(SEM)、压汞试验等微观分析技术探讨了混凝土初始缺陷的内在机理.结果表明:虽然SC3和SC7系列试件的28d抗压强度、劈拉强度与SC28系列试件无明显差别,但在90d龄期时SC3系列试件的抗压强度、劈拉强度较SC28系列试件降低11%和13%,SC7系列试件的抗压强度、劈拉强度比SC28系列试件分别降低7%和6%;SC3和SC7系列试件的28,90d龄期抗冻性能和抗氯离子渗透性均明显低于SC28系列试件;混凝土的干燥初始缺陷与其孔径分布、微裂纹密度有关,SC3系列试件的有害/多害孔含量和微裂纹密度最高,SC7系列试件次之,SC28系列试件最低.

Concrete specimens were stored in dry environment(21℃and the relative humidity is 37%)after being normally cured for 3,7,28 d(SC3,SC7 and SC28),respectively.Mechanical properties,frost resistance and chloride penetration resistance were tested at different ages.Furthermore,the elastic wave velocity was employed to quantitatively characterize the levels of drying initial defects and microstructural analyses were also carried out to reveal the generating mechanism of the drying initial defects.Results show that the 90 d compressive strength/splitting-tensile strength of SC3 and SC7 series decrease by 11%/13%,7%/6%as compared to that of SC28,respectively,although the 28 d compressive strength/splitting-tensile strength of SC3 and SC7 are not significantly different from those of SC28.The frost resistance and chloride ion permeability resistance of SC3/SC7 are significantly lower than those of SC28.Microstructural analyses revealed that drying initial defects in concrete are related to the microstructure of hydration products,content of harmful pores and microcrack density in the mortar matrix affected by drying.