Experimental Study On Frost Resistance Of Steel-Polypropylene Hybrid Fiber Reinforced Concrete

Engineering practice and research shows that hybrid fiber can enhance the mechanical properities of concrete availably to bring good economic benefits compared with single fiber.Yet for now researches mainly focus on mechanical level,while the durability study is rarely to see,especially the frost resistance.Based on the existing research results,several experiments were undertaken to analyze the mechanical properties and frost resistance of steel-polypropylene hybrid fiber concrete.The main results are as follows:(1)The optimal ratio was obtained through orthogonal test.The result showed that steel fiber can significantly improve the mechanical properties of concrete,especially splitting tensile and flexural strength;polypropylene fiber had no obvious effect on the compressive strength of concrete however it improved concrete brittleness in some way.(2)The rapid freezing and thawing test of single fiber concrete was conducted and the data displayed that the mass loss was small whatever the polypropylene fiber content,and high dosage polypropylene fiber concrete had better frost resistance compared with the low one;the frost resistance of steel fiber concrete was between the low and high dosage polypropylene fiber concrete.(3)The rapid freezing and thawing test of hybrid fiber concrete was conducted and the results demonstrated that the pros and cons of frost resistance of hybrid fiber concrete was related to fiber content.The increase of steel fiber content can improve it’s frost resistance;the polypropylene fiber content had direct impact on its frost resistance;the increase of total fiber content can also improve it’s frost resistence.Low polypropylene fiber content and high steel fiber content,low steel fiber content and high polypropylene content tended to had lower mass loss and high residual strength after freezing,where the optimal ratio was S1.5P1,S2P1 and S0.5P3.Throughout the freezing and thawing process,the decline rate of compressive strength was faster than the splitting tensile strength;relative dynamic elastic modulus was not suitable for evaluating freezing and thawing damage of fiber concrete.(4)The flexural toughness of hybrid fiber concrete was evaluated according to ASTM C1018 standards,JSCE standards,CECS:13-2009 standards and PCS which addressed that the modified JCI index and PCS were more suitable for steelpolypropylene hybrid fiber concrete to evaluate it’s toughness while the tension and compression ratio was unfit.The post freezing flexural toughness had been studied which assayed that concrete behaved good flexural toughness in less than 200 freeze-thaw cycles whereas it’s flexural toughness sharply declined in more than 200 cycles.The incorporation of hybrid fiber can efficiently improve the concrete flexural toughness and the steel fiber content affected more significantly.