The Research On The (Salt) Frost Resistance And Fracture Properties After (Salt) Freeze-thaw Cycles Of PVA-ECC With Pre-crack

In recent years, as people pay more attention to the high performance concrete and fiber concrete, research has entered a stage of rapid development. The last two decades, researchers at home and abroad have done a lot of research work on the performance of polyvinyl alcohol fiber reinforced cementitious composites(PVA-ECC), and try to apply in road engineering. The research focused on the theoretical analysis, mechanical properties, shrinkage cracking and durability, while the research of fracture toughness and fracture properties after freeze-thaw cycles of PVA-ECC are rarely involved.This paper mainly studies the impact of fly ash content, pre-crack height and different freeze-thaw environment to the frost resistance of PVA-ECC, after which will study the fracture performance of the specimen after freeze-thaw cycle, and simulate the crack propagation of PVA-ECC.The main research contents and conclusions are as follows:1.The frost resistance research will use rapid freezing and thawing test method, the PVA-ECC specimens were placed in fresh water and 3% sodium chloride solution, measured the mass loss rate and ultrasonic relative dynamic elastic modulus loss rate and analysis the frost resistance of PVA-ECC. The results showed that frost resistance of PVA-ECC in freshwater is good, and the destruction of salt solution for PVA-ECC is greater.2.Doing three-point bending fracture tests of the PVA-ECC specimens after freeze-thaw cycles, by measuring the peak load, load-crack mouth opening displacement(P-CMOD), deflection and load-strain data to analysis the fracture properties of PVAECC after freeze-thaw cycles. The results showed that the bearing capacity and deformation capacity of PVA-ECC will decrease with the increase of the number of freeze-thaw cycles, and the number of fractures also decreased.3.Through use the first inflection point of load-strain curves of full-bridge strain gauge can get the initial cracking load of PVA-ECC, and through the second inflection point can obtain the load of PVA-ECC multiple cracking ending. The results show that this method to determine the initiation load have a higher degree of accuracy.4.Using initial fracture toughness ini ICK, multiple cracking fracture toughness c ICK and unstable fracture toughness un ICK(3K fracture criteria) to evaluate the fracture toughness of PVA-ECC. And use JIC-JIF criteria to calculate fracture properties of PVA-ECC. PVA-ECC has a high fracture toughness and fracture energy by calculated.5.Using XFEM method to simulate the crack propagation of PVA-ECC and the stress situations under cyclic load. Respectively simulating the loading method of displacement load, cyclic load, to obtain the crack propagation path, stress cloud and P-CMOD curves of model, and to do comparison with experimental data. The results show that this method can effectively simulate the crack open expansion process of strain hardening materials.The research of PVE-ECC in this paper has important practical significance and broad prospect of engineering application for the correct evaluation of fracture properties after freeze-thaw cycles, and solve practical problems in cold areas of concrete pavement salt freeze damage and fracture damage.