Study the Effects of Nano-Silica on Crack Toughness of High Performance Concretebase on Double-K Model

To reflect the different period of fracture process in concrete, two fracture parameters ini KIc , un KIc were introduced in the double-K model.Where ini KIc is the initial toughness, un KIc is theunstable toughness. They are considered as the standard to assess the propagationof cracks in concrete. The initial crack toughness is defined as the material's ability to resist cracks propagation. The unstabletoughness is used to assess the propagation stability of cracks. The article studies the effects of nano-silica on the toughness of highperformance concrete. High performance concrete using nano-silica with ratesof 0%, 0.5%, 1.5% will be tested by a mechanic fracture method based on the recommendation of RILEM. The results obtained will be used to analyze and calculate the fracture toughness according to the double-K model.