Concrete fracture process zone characteristics

This study is essentially an extension of prior research on the fracture mechanics of concrete conducted at UW. By experimental observations as described in literature reviews, the effects of stress concentrations introduced by holes in concrete can be ignored at one scale but not at a large scale. This research is to find a model that will give us some information about that scale for high strength and light weight concrete. Externally applied stress fields are introduced into the crack line wedge loaded double cantilever beam specimens to further identify whether the previously developed tri-linear fracture process zone model is material dependent for normal concretes. If a stress singularity is found at crack tip in more brittle concretes such as high strength and light weight concretes, this research will have direct effect on the concrete design approaches used in today's practice. If there is no stress singularity existing at a crack tip, a material dependent cracking model for concrete will help us to better understand concretes and provide information for reinforced concrete cracking behaviors under service load conditions.; Test variables included in this research are the effect of stress fields caused by externally applied lateral loads on the fracture process zone model, the changes in fracture process zone model due to changes in coarse aggregate weight and size, the specimen sizes, the fine aggregate distribution, and the properties of cement matrix and bond strength between ingredients with the addition of Silica Fume to the regular concrete. The experimental results are analyzed in depth and corresponding fracture process zone models for each test series are derived through an extensive trial and error procedure. lt was found that the overall stress state in concrete does not have any influence on fracture process zone model. Significant variations were observed in fracture parameters and mechanical properties of Silica Fume concrete. The fine aggregate distribution introduced into Silica Fume concrete was found not to affect the aggregate interlock bridging strength as observed in regular concrete. The combined use of Silica Fume and Solite in concrete significantly changed in aggregate interlock bridging strength in numerical tri-linear fracture process zone models. The importance of each fracture parameter of fracture process zone models on the fracture behavior is identified.