基于无损测试的新老混凝土抗冻融性能表征方法

Characterization method of freeze-thaw durability for new-to-old concrete based on nondestructive test

分析了基于相对动弹模量下降40%的抗冻融性能表征方法不能适应于新老混凝土的物理机制。通过采用超声波速来量测动弹模量,借助试验分析冻融过程中新老混凝土不同方向超声波速的变化规律,提出了能反映黏结面冻融损伤的指标和新老混凝土抗冻融性能表征方法。结果表明:动弹模量的不合理量测和定义是导致其在新老混凝土抗冻融性能表征方面不能适用的原因;平行于黏结面方向的超声波速损失近似线性规律,而垂直于黏结面方向的超声波速损失则呈现显著的三阶段特征;两个方向上超声波速损失率的差值,其曲线上的拐点表示了黏结面的抗冻融极限,通过与新老混凝土黏结面的劈拉强度试验结果对比,表明该方法能够准确地描述新老混凝土抗冻融性能。

In this paper,the physical mechanism that the characterization method of freeze-thaw durability by 40%decline in the relative dynamic elastic modulus( DEM) cannot be applicable for new-to-old concrete is investigated;through measuring ultrasonic velocity in different directions,the variation of DEM of new-to-old concrete within the freezing and thawing process was measured,and a new presentation of freeze-thaw durability,is proposed for new-toold concrete. The results show that: unreasonable measurement and definition of DEM lead to its inapplicability to characterize the freeze-thaw durability of the new-to-old concrete interface. The loss of velocity by ultrasonic test parallel to the interface is approximately linear,and the loss of velocity normal to the interface shows a significant feature of three stages. Inflexion points on the curve of Dr,which is the difference of velocity loss rates normal and parallel to the interface,indicates the performance limit of interface when subjected to freezing and thawing. The measured free-thaw durablity is compared with test result of splitting tensile and it is satisfied, showing the applicability of the characterization method.