小骨料混凝土双K断裂参数的试验测定

双K断裂模型以起裂韧度和失稳韧度来描述混凝土裂缝扩展过程，《水工混凝土断裂试验规程》将双K断裂模型作为该规程的基本理论依据，并将该模型的双K断裂参数作为试验规程要求测定的基本断裂参数。为配合该规程的制定，本文进行了19个三点弯曲梁试件和25个楔入劈拉试件共43个试件的断裂试验，对小骨料混凝土双K断裂参数的起裂韧度和失稳韧度进行直接试验测定。所有试件均为同批浇注相同级配，最大骨料粒径为10mm，试验中采用了电阻应变片法作为确定起裂荷载的参考。结果表明，起裂荷载与最大荷载之比为0.67～0.71，起裂韧度与失稳韧度之比为0.45～0.50，变化较稳定；楔入劈拉试件高度大于等于400mm、三点弯曲梁试件高度大于等于200mm时，起裂韧度与失稳韧度基本为常数，但同组试件之间具有一定的离散性；两种试件形式的韧度值有一定的差异。根据本文试验数据计算得到的裂缝尖端开口位移临界值较断裂韧度参数更容易受到试件尺寸的影响，楔入劈拉试件高度大于600mm时，其值为0.056～0.070mm；三点弯曲梁试件高度大于300mm时，其值为0.040～0.047mm，比较稳定。

Experimental measurement of double-K fracture parameters of concrete with small size aggregate

The development process of cracking in concrete can be described by double-K model,which is adopted as the theoretical base of the Concrete Fracture Test Specification in Hydraulic Engineering(China).The parameters of the model are determined by experiments including three-point bending test of 19 specimens and wedge-splitting test of 43 specimens.The initial fracture toughness and unstable fractured toughness of the parameters are measured.The maximum size of the aggregate is 10mm.The initial cracking load is determined by means of resistance strain gauge.The results show that the ratio of load for initial cracking to maximum load is 0.67-0.71 and the ratio of initial fracture toughness to unstable fracture toughness is 0.45-0.50.The initial fracture toughness and unstable fracture toughness for wedge-splitting test specimens with height larger than 400mm and three-point bending specimens with height larger than 200mm are approximately equal to constants respectively.Some differences of toughness exist between the results of these two kinds of test.The critical crack tip displacement CTOD-c calculated according to the experimental data is 0.056-0.070mm for wedge-splitting test specimens and 0.040-0.047mm for three-point bending test specimens.