Cohesive Zone Modeling Of Fracture Of Sustainable And Functionally Graded Concrete

There is a constant demand from the industry to provide better, more situation dependent construction materials; materials which are able to satisfy strength requirements while also able to accommodate other design requirements such as ductility, fracture resistance, thermal resistance/insulation, etc. Functionally graded materials (FGMs) are one such material. This study investigates the fracture process of sustainable concrete, fiber reinforced concrete, and of functionally graded concrete slabs. Both two-dimensional and three-dimensional problems are analyzed. The primary focus of the thesis is on sustainable, functionally graded concrete slabs, emphasizing the computational/mechanical aspects of fracture. A model of the slabs is developed; which incorporates a variety of cohesive zone models (CZMs) into an implicit, nonlinear finite element scheme. Intrinsic cohesive zone elements, with traction-separation relationships defined along the crack surface, are utilized to simulate mode I fracture of the slabs. Based on the load to crack mouth opening displacement (CMOD) relationships of the slab, one is able to optimize concrete properties and placement to reach predefined goals. A parametric study is conducted on the fracture parameters of the slab; the results of which show that the variations in the CZMs have a direct correlation with the overall behaviour of the slab. Additionally, in conducting the experiments for the slabs, a new fracture test for concrete is developed. The attractive feature of the test is that it uses a specimen geometry which is easily obtained from in-situ concrete in the field. Technology exists which allows us to extract cylindrical cores from concrete structures at relative ease. This study proposes a specimen geometry which can easily be developed from these cylindrical cores called the disk-shaped compact tension (DCT) specimen. A series of experiments are conducted on the specimen, and computational simulations are carried out. A parametric study is done; the results of which, show that the specimen geometry is able to predict the mode I fracture properties of concrete, with both virgin and recycled aggregates, with relative accuracy and ease.