A design method for determining fracture toughness and tensile strength pertinent to concrete sieving curve

The aggregate particle gradation of concrete, which is generally characterized by a sieving curve, is a critical factor affecting the formation of the core stress skeleton of concrete specimens. In this paper, a fracture size and boundary effect model that can describe the effect of aggregate gradation on crack propagation at the micro-level in concrete is developed. The critical points on the aggregate sieving curve are selected as the characteristic values of aggregate particles. The individualized calculation method of the fictitious crack growth length under peak load is pro-vided, while the corresponding design application method of the simplified value of the fictitious crack growth length is given. The micro-level explains the physical nature of the discontinuous and jumping expansion of concrete cracks caused by the different aggregate particle gradations. The formula of the novelty design method can link the aggregate particle gradation at the micro -level with the macroscopic fracture and strength parameters. Further, a simplified two-point method to determine the concrete fracture and strength parameters simultaneously by using only two different specimens has been proposed. The proposed model and design method are not limited to the type of specimens. The concrete parameters and structural failure prediction analysis can be carried out by using notched, un-notched, geometrically similar, as well as non -geometrically similar specimens.