Effect of materials parameters on fracture parameters of concrete

ABSTRACT Master Thesis EFFECT OF MATERIALS PARAMETERS ON FRACTURE PARAMETERS OF CONCRETE Kürşat Esat ALYAMAÇ Fırat University Graduate School of Natural and Applied Sciences Department of Civil Engineering 2004, Page : 82 Applications of Linear Elastic Fracture Mechanics (LEFM) to concrete were initiated by Kaplan in 1961 and continued until Keşler and co-workers' study in 1972 in which it was concluded that LEFM was not valid for cementitious materials. This inapplicability of LEFM is due to the fracture process zone (FPZ) which is ignored by LEFM. For this reason, several investigators have developed non-linear fracture mechanics approaches to characterize FPZ. These approaches primarily involve the fictitious crack model, the crack band model, the two-parameter model (TPM), the effective crack model, the size effect model and the peak load method. Contrary to LEFM, in which a single fracture parameter is used such as the critical stress intensity factor, these models need at least two experimentally determined fracture parameters to characterize failure of concrete structures. A concrete structure fails according to TPM when the stress intensity factor Kj and the crack opening displacement CTOD reach their critical values, Ksk and CTODc. Experimental studies have shown that fracture parameters of concrete are particularly influenced by the four material parameters compressive strength, maximum aggregate size, water-cement ratio and aggregate type. It is noted that fracture parameters of concrete can also be affected by other material parameters such as type of cement, cement content. In this thesis study, all of the above material properties on the fracture parameters of concrete were investigated according to TPM. Finally, it was concluded that K"!c depends on the compressive strength of concrete while CTODc is strongly related to the internal structure of concrete. Keywords: Concrete, Fracture Mechanics, Two-parameter Model, Peak-load Method. X