Research On The Permeability Of Hybrid Fiber Reinforced Concrete With PP Macro-fiber And PP Micro-fiber

With the widespread application of the reinforced concrete structure in the global scope,the durability of the problems have attracted the attention of researchers all over the world,rebar corrosion has been identified as one of the main reasons leading to premature failure of the reinforced concrete structure,and the chloride ion corrosion is mainly caused by the culprit.Looking at the current domestic and international research on chloride ion permeability of concrete,polypropylene fiber on permeability of concrete is greatly improved.However,most of the research focuses on single-doped PP micro-fiber.PP micro-fiber can restrain shrinkage crack and micro crack of concrete.PP macro-fiber can restrain the dry shrinkage crack of concrete after hardening.Both can suppress cracks on different scales.A good hybrid effect can be formed under proper fiber content and doping ratio.With the support of "Research on key Technologies of Zhuhai connection Tunnel Construction of Hong Kong-Zhuhai-Macao Bridge"(Grant No,2500000124),the natural immersion method is used to simulate the chloride environment in the underwater area of the ocean.The resistance of coarse and fine hybrid polypropylene fiber reinforced concrete to chloride ion penetration is studied.The main work and research results are as follows:(1)Study on resistance of hybrid fiber reinforced concrete to chloride ion penetration.The transport properties of hybrid polypropylene fiber reinforced concrete(PP)in marine underwater area(long term immersion)were studied by laboratory natural immersion method under three kinds of water cement ratio and four kinds of fiber content.The main conclusions are as follows.1 There are two factors of interaction between water-cement ratio and the content of mixed fiber.Under different water-cement ratio,the optimal mixing fiber content is different for the anti-chloride ion penetration.The decrease of the diffusion coefficient of chlorine ion in C30 concrete is greater than that of C35 and C40.2 The effect of hybrid fiber on chloride ion penetration resistance of concrete is complex.The apparent chloride diffusion coefficient of C30 concrete decreases at first and then increases with the increase of hybrid fiber content,C35,The apparent chloride diffusion coefficient of C40 concrete increases at first and then decreases with the increaseof hybrid fiber content.The content of hybrid fiber has no significant effect on the time attenuation factor m of chloride diffusion coefficient and the accumulation rate k of chloride ion characterized by surface chloride ion.(2)Life prediction of hybrid fiber reinforced concrete.The durable life of concrete is predicted by establishing chloride ion diffusion model and based on reliability theory.The sensitivity of structural life to the thickness of protective layer,time attenuation coefficient,surface chloride ion concentration and chloride ion diffusion coefficient decreases in turn,but the addition of hybrid fiber is more effective than increasing the thickness of protective layer of concrete structure.After adding 0.7% hybrid fiber,the durability of concrete is significantly improved when the ratio of water to cement is 0.7%.(3)Effect and mechanism analysis of coarse and fine hybrid polypropylene fiber.According to the expression,other literature data and the comparison between chloride ion diffusion coefficient and effective porosity,it can be seen that polypropylene crude fiber can optimize harmful pores and multiple harmful pores with larger pore size than polypropylene fine fiber.The smaller the ratio of water to cement is,the less harmful pores and more harmful pores of concrete itself,and the more likely the pore structure of concrete is to deteriorate because of the fact that polypropylene fine fiber increases the weak interface and increases the harmful pores.The smaller the water-cement ratio is,the smaller the doping ratio of polypropylene fine fiber is.Hybrid effect of hybrid fiber for C35 and C40 concrete It is not very ideal.When the total amount of fiber doping is 0.7%,the optimum doping ratio is more than 6%.(4)The selection of the best hybrid fiber content.The compressive strength of the specimen at different immersion time and the parameters related to the resistance to chloride ion penetration were compared,and the service life of the specimen was referred to at the same time.In the underwater environment of the ocean,the optimum content of hybrid fiber is 0.7%.The concrete has good mechanical properties and resistance to chloride ion penetration.