Experimental Study On Mechanical Properties Of Ultra High Toughness Fiber Reinforced Concrete

Ultra high toughness fiber reinforced concrete is a kind of Engineering cement-based composite material,which is called UHTCC(ultra-high toughness cement-based composites)in the United States.The material has higher toughness,stronger crack control ability and extensibility.In this paper,the basic mechanical properties and production cost of UHTCC are mainly considered.Three kinds of toughened fibers are used,and the effects of three kinds of fiber length,three kinds of fiber diameter and five kinds of fiber content on the basic properties and mechanical properties of UHTCC are considered.27 kinds of mix proportions are designed and tested,and the preparation process is improved,The optimum range of raw material parameters and dosage was selected,and the experiment was designed based on the optimum mix proportion range to further explore its chloride ion permeability resistance and axial tensile strength.The main contents and conclusions are summarized as follows(1)In this paper,the fiber reinforced mechanism of UHTCC and the role of various materials in the matrix are analyzed.27 kinds of mix proportion are designed and tested.The optimal mix proportion range is obtained,and the mixing sequence is improved in the experimental process.(2)The basic mechanical properties of 27 groups of UHTCC specimens were tested.Based on the values of compressive strength,flexural strength and flexural compression ratio,it is suggested that 8mm fiber should be selected when UHTCC is tested,and the volume fraction of fiber should be 2%.The maximum particle size of sand should not be more than 0.6 mm,the sand binder ratio should not be more than 0.7,not less than 0.3,and the sand binder ratio should be about 0.5.The content of fly ash should not exceed65% of the total mass of cementitious materials.The ratio of water to binder should not exceed 0.35,and it should be about 0.3.The performance of domestic PVA UHTCC fiber concrete is lower than that of PP UHTCC fiber concrete,and its price is 4 times of that of PP fiber.Compared with pp-uhtcc,the properties of pva-uhtcc made in Japan are improved by 10% ～ 25%,but the price is 8 times of PP fiber,so it is suggested to use domestic modified PP fiber for preparation.(3)The results show that different fiber content has a great influence on the chloride ion penetration resistance of pp-uhtcc at 56 d age.When the fiber content changes from1% to 3%,the electrical flux decreases by 10.8% to 14.8%,and the chloride ion penetration resistance increases significantly;When the fiber content increases from 1%to 2%,the axial tensile strength of pp-uhtcc is increased by 248%-391% compared with that of ordinary concrete,and the phenomenon of multi crack failure is shown in the test process.Pp-uhtcc no longer has typical brittle failure characteristics.