Study On Crack And Freeze-thaw Resistance Of Hybrid Fibers Reinforced High Performance Concrete

Currently, high performance concrete (HPC) is used more and more widely in civil engineering, and researchers show interest in properties of HPC. In this paper, several experiments are undertaken to analyze the influence of different types of fiber on free shrinkage (0-45 days) of HPC, steel-polypropylene (steel-PP) hybrid fibers on early age (0-20 hours) restrained shrinkage cracking of HPC, and steel-PP hybrid fibers on compressive strength, splitting tensile strength and flexural toughness of HPC exposed to 200 freezing and thawing cycles (FTC).According to DBV, free shrinkage test was performed. Result of free shrinkage test indicates that the effect of steel fiber on free shrinkage of HPC is limited, and the effect of glass fiber or polypropylene fiber (PP) fiber is poor. Compared with result of free shrinkage of HPC, modified ACI 209 model, CEB90 model, Sakata model, GZ model, GL model can be used to forecast free shrinkage of HPC, and B3 model can't be used to.Plate test was carried out for restrained shrinkage cracking under indoor condition and outdoor condition. Measurement of temperature, humidity and wind speed was performed during the experiment. Result of test shows that, crack resistance of HPC can be improved by single type of steel fiber or PP fiber. Because steel-PP hybrid fiber can control crack at different scale and different cracking stage, steel-PP hybrid fibers behave better than single type of steel fiber or PP fiber on crack resistance of HPC. The curing of HPC in 6 hours after casting should be emphasized. The pattern of cracks will be decided by direction of wind: when the direction of wind is fixed, cross-shaped cracks will appear; when the direction of wind is movable, cracks in parallel with wind will appear.Result of compressive strength and splitting tensile test of HPC before and after rapid freezing and thawing test addresses that, compressive strength of HPC is more sensitive to FTC than splitting tensile strength; steel fiber or PP fiber enhances compressive strength of HPC exposed to FTC. The result of flexural toughness test indicates that, steel-PP hybrid fibers improve toughness of HPC within full range of deflection. The optimum fiber content varies with the type of hybrid fibers, and excessive fiber may affact toughness and the resistance to FTC of fiber reinforced concrete. FTC impair toughness of fiber reinforced concrete, and the loss of toughness of hybrid fibers reinforced concrete is lower than that of...