The experimental determination of double-K fracture parameters of concrete under water pressure

The main purpose of this paper is to experimentally determine the fracture parameter of concrete under water pressure. Wedge splitting fracture geometry is used. Similar to the work by Brhuwiler and Saouma, in order to obtain the true load-crack mouth opening displacement curve ( P-CMOD) , cycle loading-unloading of water pressure is carried out. At the stage of loading and unloading of water pressure, two different loading modes are used. One is constant crack mouth opening displacement (CMOD )-controlling loading mode. Another is constant load P-controlling loading mode. For the former 11 specimens are tested while for the latter 7 specimens are tested. In the tests, to monitor the initial cracking load and measure crack length, electric-resistance strain gauges are used and strategically arranged on surface of specimens. Then, from the measured data, the double- K fracture parameters proposed by Xu and Reinhardt, i.e., the initial fracture toughness https://www.w3.org/1998/Math/MathML" display="inline"> K Ic ini and unstable fracture toughness https://www.w3.org/1998/Math/MathML" display="inline"> K Ic un are experimentally determined. The results indicate that, compared to constant CMOD loading mode, for constant P loading mode the operation is easy. Therefore, it is more applicable for common lab. The results also show that the cycle loading of water pressure accelerates the development of crack and hence results in a sharp decrease in the maximum load. However, water pressure has little effect of on the initial cracking load.