Experimental Study On The Freeze-Thaw Damage Of PVA Fiber Concrete

Due to alternative variation of atmospheric temperature,concrete materials often suffer a certain degree of freezing and thawing damage in cold regions.This kind of damage is detrimental to mechanical properties,permeability and safe operation of the concrete structure,seriously affects its durability.Therefore the concrete structures usually have been destroyed before design service time.The results show that the decrease of durability and damage of concrete structure due to freeze-thaw cycle mainly lies in the emergence and development of cracks in concrete.Incorporation of the PVA fibers can effectively improve its crack resistance.With the development of economy and technology in china,PVA fiber as a kind of new building material has been favored by many researchers and gradually promoted owing to the advantages of high tensile strength,high elastic modulus,acid-proof alkali.But the study of PVA fiber concrete is still in the primary stage,and more focus on the physical and mechanical aspects,few report about its durability.Therefore,it is of great significance to study the freeze-thaw damage of PVA fiber concrete.Through the combination of freeze-thaw cycle,mechanical property and chloride ion permeability test,this paper launches research on the freeze-thaw damage of PVA fiber concrete with freeze-thaw cycle number and fiber content as factors.The main research work and conclusions are as follows:(1)By means of quick freeing and thawing test,ordinary concrete and PVA fiber concrete with the volume fraction of 0.05%,0.1%,and 0.2% about the change situation of surface configuration,mass loss and relative dynamic elasticity modulus after freeze-thaw cycles are compared and studies.The results show that the incorporation of PVA fiber can enhance the ability of surface erosion by frost and defrost,significantly reduce the decrease rate of the mass and relative elastic modulus after freezing and thawing cycle,improve the frost resistance and durability of concrete.The volume content of 0.1% PVA fiber concrete exhibits the strongest frost resistance.(2)The influence of freezing-thawing cycles on mechanical properties of PVA fiber concrete was studied based on analysis of compressive strength and three-point bending flexural strength.The research suggests the decay rate of compressive and flexural strength increase with the increasing of freeze-thaw cycles.The incorporation of PVA fiber can effectively inhibit the development of cracks in concrete due to freeze-thaw,and slow down the loss rate of compressive strength and flexural strength of concrete.It is worth noting that PVA fiber has a greater effect on flexural strength during freeze-thaw damage.(3)Chloride erosion test of PVA fiber concrete after different freeze-thaw cycles isconducted in order to investigate the influence of damage caused by freeze-thaw cycles on the chloride diffusion of concrete.The research results indicate that the effect of freeze-thaw cycle on the PVA fiber concrete diffusion rate of chloride ions is smaller than that of ordinary concrete.The chloride concentration and diffusion coefficients increase with increasing of freezing-thawing damage degree,So that the concrete resistance to chloride ion erosion ability is weaker.(4)From the theory of macro-damage,the damage evolution equation of PVA fiber concrete in different fiber content which based on the relationship between the probability distribution function of Weibull and the degree of damage is established with fitting to experiment data and estimating to the parameter.Through regression analysis,the relationship between the diffusion coefficient of chloride ion and the number of freeze-thaw cycles is established and the relational expression of the injury factor and the chloride ion diffusion coefficient is derived.