In Situ Test of Cohesive Strength on the Interface Zone between Mortar and Aggregate in Concrete

The interface zone in concrete is the weak link and its structures and properties are the key factors determining overall performance of concrete. In this paper, the cohesive strength on the interface zone is tested through the in- situ drawing test of the aggregate from the concretes of C15,C20, C25, C30,C35,C40. and the tensile strength and the shear strength on the interface zone are analyzed by the simple assumptions about the uniform drawing and well distributed stress on the interface. As a result, It’s showed that with the pebble size increased, normalized pull strength of low grade concrete has a tendency to increase, while high grade concrete is in the vicinity of 7% fluctuation; when pebble diameters are the same, with the concrete strength increases, the normalized pull-out strength decreases. As the particle size less than 30mm or more than 110mm, tensile strength seems to limit value. the macro pull strength is on the range of 4%—12% of concrete compressive strength.