Experimental Study On Durability Of Fiber Reinforced High Strength Concrete

With the rapid development of China’s infrastructure industry,high-strength concrete has more applications in large special projects because of its high compressive strength and small deformation,but it has the disadvantages of poor toughness and easy cracking.The harmful substances will invade the concrete from cracks,make the concrete material can not match the high durability in the actual special and bad environment,and lead to the durability problems such as premature occurrence of aging disease in the structural engineering.Shorten the service life of the structure under the special environment.Adding fiber to concrete can help to overcome the inherent defects of high strength concrete.In recent years,the new basalt fiber and cellulose fiber are the materials with low production cost and green environmental protection,which play a positive role in promoting the engineering application of high strength concrete.The fiber high strength concrete prepared by them has high research value in the present situation of resource environment.At present,many researches have been carried out on the basic mechanical properties of fiber reinforced high-strength concrete,but there are still some shortcomings in durability.As one of the important performance indexes,durability is directly related to the reliability of structure.Engineering structure has good durability and can avoid many unnecessary economic losses and safety accidents.Therefore,in this paper,the cube compressive resistance,splitting tensile resistance,chloride ion penetration resistance and freezing resistance of basalt fiber and cellulose fiber high strength concrete were studied.The purpose is to provides a theoretical basis for the promotion of fiber reinforced high strength concrete,a new green material,and gives full play to its superior performance.The main contents of the study are as follows:(1)Cube compressive strength test and splitting tensile strength test of fiber high strength concrete.The effects of basalt fiber volume ratio,basalt fiber length and cellulose fiber volume ratio on the compressive strength of C60 high strength concrete were studied.The experimental results show that the effect of the two fibers on the compressive strength is not significant,but the effect on the splitting tensile strength is obvious.Basalt fiber is superior to cellulose fiber in improving tensile strength and toughness of high strength concrete.In this paper,the optimum fiber volume ratio of basalt fiber is 0.20%,the optimum fiber volume ratio of cellulose fiber is 0.15%.The effect of the fiber length of 18 mm basalt is better than that of 6 mm and 30 mm.(2)Resistance to chloride ion permeability(RCM)test of fiber reinforced high-strength concrete.Study the effects of basalt fiber volume ratio,basalt fiber length and cellulose fiber volume ratio on chloride ion diffusion coefficient of the C60 high strength concrete.The results show that,with the basalt fiber volume fraction and fiber length increased,the chloride diffusion coefficient of C60 high strength concrete significantly increased;cellulose fiber volume ratio increases,the chloride diffusion coefficient of C60 high strength concrete first decreased and then increased,the optimum volume ratio in this paper is about 0.10%;basalt fiber will deteriorate the resistance to chloride ion of high-strength concrete,the proper dosage of cellulose fibers can improve the resistance to chloride ion of high-strength concrete,and excessive amount of cellulose fiber will have a negative effect.(3)Freezing and thawing resistance test of the fiber reinforced high strength concrete.The freezing and thawing resistance of C60 basalt fiber high strength concrete with different fiber volume ratio and fiber length and C60 cellulose fiber high strength concrete with different fiber volume ratio were analyzed and evaluated.The experimental results show that adding fiber in high strength concrete can restrict the appearance damage degree of high strength concrete.Basalt fiber with length of 6 mm and 30 mm has limited effect on improving freezing and thawing resistance of C60 high strength concrete.The freezing and thawing resistance of C60 high strength concrete increases with the volume ratio of basalt fiber and cellulose fiber.The improvement degree of basalt fiber is much higher than that of cellulose fiber in the fiber volume ratio range of 0.10% to 0.20%.The damage model of concrete after freeze-thaw cycles is established and the curve fitting is carried out.The relationship between freeze-thaw damage degree and freeze-thaw cycle times of C60 fiber high strength concrete is presented.