Study On Durability Of Polypropylene Fiber Concrete In Chloride Environment

As the improvement to ordinary concrete, Polypropylene fiber reinforced concrete wasused widely in major projects with its excellent crack resistance and resistance to deformationcapacity. PPF concrete will also withstand the erosion of various corrosive media as thecommon concrete in its service process, so its durability failure cannot be avoided. Chlorideion penetration and steel corrosion are the main aspects to the durability of concrete structurein chloride environment.Steel corrosion due to chloride ion penetration is the importantreason to cause the durability of concrete failure. To study the durability of PPF concrete, thetransportation model of chloride into PPF concrete under the different chloride environmenthas a very important significance.This thesis carried out the study on durability of polypropylene fiber reinforced concretein four chloride environment, which contain marine underwater zone, marine tidal zone,marine cold zone, marine tidal zone in cold region. The transport processes of chloride intoPPF concrete were discussed, and the diffusion models of chloride in PPF concrete wereestablished. The content includes:The drying method and SEM test were carried out to study the microstructure of PPFconcrete. The test showed that the pore structure of PPF concrete turn to be better with theeffective porosity reduced when the Polypropylene fiber was from0to0.1%, but when thecontent increased from0.1%to0.5%, the pore structure of concrete turn to be worse.According to the theoretical analysis and experimental results, the calculation method of theporosity of PPF concrete was established which lay the foundations for the predicting modelof chloride diffusion.The diffusion properties of chloride in different volume of PPF concrete wereinvestigated by using long-term immersion method and alternation of wet-dry method to simulate marine underwater region and marine tidal region respectively. Due to the presenceof convection and pore like "ink tank-tube" micro-structure, there is a peak of chloride ion inthe distance from the specimen surface. Compared with the long-term immersion, bothchloride properties have the same peak concentration.Accelerated frost-salt test was used to simulate marine cold zone. The results showedthat the PP fiber can reduce the mass loss while increase the relative dynamic elastic modulus,relative splitting tensile strength. Due to the presence of convection and desalination, there isa peak of chloride ion in the distance from the specimen surface. The chloride diffusioncoefficient decayed with salt-freeze cycles, and increased with the volume of fiber. Therelationship between the peak chloride content and freeze-thaw damage was established byintroducing the concrete freeze-thaw damage variable, and also established the relationshipbetween chloride diffusion coefficient and freeze-thaw damage.The experiment of dry-wet cycles and salt-freeze cycles working together was used tosimulate marine tidal zone in cold region. Compared with the dry-wet cycles and salt-freezecycles, both environments accelerated the deposition of peak chloride ions, there is a peak ofchloride ion in the distance from the specimen surface. The chloride diffusion coefficientdecayed with the number of combined cycle, and increased with the volume of fiber.Finally, based on Fick’s second law and the analysis for the fiber volume andfreeze-thaw damage, the chloride diffusion models under different chloride environment wereestablished respectively according to test data. The model is reasonable according toexperimental verification, which provides theory basis for durability life prediction of PPFconcrete structures in chloride corrosion environment.