A Study On The ?-? Mixed-mode Fracture Of Reactive Powder Concrete

Reactive powder concrete(RPC)is a kind of ultra high performance concrete,which has excellent properties,such as high durability,high strength and so on.Therefore,it has the extensive value in practical engineering.?-? mixed mode fracture is the most common mode of fracture in concrete structure,and the structure's safety and stability is determined by its fracture characteristics.For guiding the application of this new building materials,it is necessary that a comprehensive and objective research of RPC's mixed mode fracture performance is taken.Four-point-shear beam was used to test the ?-? mixed mode fracture behavior of RPC.The P-CMOD,P-CMSD and the load-displacement curves were measured.The characteristics of various types of curves and the failure modes of ?-? mixed mode fracture were analyzed.According to the characteristics of curves,the effect of steel fiber content,the ratio of crack and the initial crack location on the fracture behavior of?-? mixed mode was analyzed and summarized.According to the measured data,the cracking load and the ultimate load were determined.Furthermore,other fracture parameters were got,such as fracture energy,ductility index and G2/G1.The variation of fracture parameters is analyzed with the effect of steel fiber content,the ratio of crack and the initial crack location.Meanwhile,RPC's fracture parameters of the ?-? mixed mode and of the pure I mode were compared,with the effect of steel fiber content and the ratio of crack.Taken the softening constitutive model of the normal concrete as a reference,RPC's ?-? mixed mode fracture softening constitutive model was established.The tension softening curve and the shear stress transfer relationship were determined for establishing the softening constitutive model.Using the softening constitutive model of RPC,four point shear beams were simulated by the numerical analysis.Compared with experimental results and the numerical results,the unknown parameters in the model were obtained.Meanwhile,the established ?-? mixed mode fracture softening constitutive model was verified.The main results of this paper are as follows:1)increasing the amount of steel fiber can effectively improve the ?-? composite fracture properties of RPC.With the increase of dosage of steel fiber,transmission capacity and tensile stress at the crack tip is raised;but the steel fiber does not improve the fracture properties of composite type ?fracture in too much,not too much steel fiber to transfer shear stress at crack tip.2)the change of initial defect(fracture height ratio)in RPC structure will affect the fracture performance of ?-? composite structure.3)in RPC,the energy dissipation mechanism of ? type fracture and ? type fracture is different;crack opening is the main cause of ?-?composite fracture growth in materials.4)the established constitutive model of ?-?compound fracture softening can well...