On Modified Pull-off Method Assessing Strength at Arbitrary Distance from Concrete Surface

(1)试验方法的建立1）从粗集料最大粒径与核心粒径的关系出发，分析了混凝土表面各距离处的拉脱抗拉强度的变化规律; 2）拉脱抗拉强度与抗压强度、劈裂抗拉强度、脉冲速度、3）明确了拔出抗拉强度预测抗压强度的准确性，并与上述无损检测方法进行了比较。(2)在各种混凝土强度评定中的应用1）采用不同配合比、不同龄期的试件，研究了不同拉脱距离下的拉脱抗拉强度特性，2）拉脱抗拉强度可用于评价混凝土与饰面材料之间的粘结强度等界面行为。采用透水模板时，混凝土表层抗拉强度随水灰比的降低而提高。(3)1）拔出拉伸强度可用于评估由于冻融作用在每个不同距离处的损坏程度。(4)修补施工方法的应用1）拉脱抗拉强度可用于评估弱端部分所需的切屑深度，以及修补后的界面行为，如粘结强度。

(1) Establishment of test method1) Variations of pull-off tensile strength at each different distance from concrete surface were analyzed in the relation between maximum size of coarse aggregate and the size of core.2) Relations of the pull-off tensile strength versus the compressive strength, splitting tensile strength, pulse velocity, rebound number and pin penetration depth were examined.3) The accuracy of prediction of compressive strength by the pull-off tensile strength was made clear and compared to those by above non-destructive testing methods.(2) Application for evaluating strength in various kinds of concrete1) Characteristics of pull-off tensile strength at each different distance were investigated using specimens with a variety of mix proportion, age of test, cement type and moisture content.2) Pull-off tensile strength was available to evaluate the interface behavior such as bond strength between concrete and finishing materials.3) Pull-off tensile strength in the surface layr of concrete increased with the lowering of water cement ratio by using permeable form.(3) Application for assessing the deterioration1) Pull-off tensile strength was available to evaluate the degree of damage at each different distance due to freeze-thaw action.(4) Application for repair construction method1) Pull-off tensile strength was available to evaluate the required chipping depth of weakend portion, and the interface behavior such as bond strength after repairing.