Experimental Study On The Influence Of Pouring Method And Reinforcement On The Axial Tensile Properties Of UHPC

Ultra high performance concrete(UHPC)is a high-performance civil engineering material continuously improved on the basis of ordinary concrete.It has a wide application prospect in the engineering field.Different from ordinary concrete,UHPC has excellent tensile properties,which have been deeply studied by many researchers.This paper summarizes the previous research results and obtains some influencing factors on the axial tensile performance of UHPC.Due to the limitation of UHPC’s own material,its uniaxial tensile test is not suitable,and there is no unified specification for UHPC tensile test.Therefore,based on the previous research,the UHPC direct tensile test and tensile auxiliary device are designed and completed.This paper aims to analyze some factors affecting the axial tensile performance of UHPC,so as to find an effective way to improve the axial tensile performance of UHPC.From the perspective of pouring method and reinforcement,and supplemented with the influence of fiber layer on the axial tensile performance of UHPC,the test groups with different variables are designed.The influence mechanism of steel fiber and reinforcement on the axial tensile properties of UHPC is discussed.It is considered that both steel fiber and reinforcement improve the axial tensile properties of UHPC by inhibiting the development of cracks at micro and macro levels in UHPC.Combined with the actual engineering situation,the influence of different pouring methods on the axial tensile performance of UHPC is studied,which provides ideas for the improvement of pouring methods of UHPC.The research contents of this paper mainly include three aspects:1)study the effects of different fiber types,fiber lengths and fiber content on the axial tensile properties of UHPC;2)the influence of different pouring methods on the axial tensile properties of UHPC and the variation law of the axial tensile properties of UHPC with different thickness under the same pouring method are studied;3)The effects of reinforcement and reinforcement ratio on the axial tensile properties of UHPC were studied.The main research results of this paper are as follows:(1)For the fiber type,the tensile property of UHPC obtained by adding end hook fiber is the best,but the end hook fiber will reduce the fluidity of UHPC and is not conducive to the pouring of UHPC.Straight round fiber can significantly improve the axial tensile properties of UHPC and has little effect on the fluidity of UHPC.Microwave textured fiber has the least improvement on the axial tensile performance of UHPC.For the fiber length,among the three kinds of straight and round fibers,20 mm fiber has a greater impact on the axial tensile performance of UHPC,but it will also have a significant impact on the fluidity of UHPC.13 mm fiber can significantly improve the axial tensile performance of UHPC while having a smaller impact on the fluidity of UHPC,and 6 mm fiber has the least impact on the axial tensile performance of UHPC.For the fiber content,with the increase of fiber content,the axial tensile properties of UHPC also increase,while the fluidity of UHPC decreases.(2)The mechanical properties of UHPC with different thickness poured by four pouring methods:random pouring,layered pouring,pouring at both ends and parallel pouring are analyzed.Layered pouring has the greatest improvement on the axial tensile performance of UHPC,and the improvement of the axial tensile performance of UHPC by pouring at both ends is not as good as random pouring and parallel pouring.The improvement of UHPC axial tensile performance by parallel pouring is better than random pouring and weaker than layered pouring.In the actual pouring in the future,layered pouring can be used to improve the axial tensile performance of UHPC.The thickness of UHPC will affect the axial tensile performance of UHPC.Except for layered pouring,the tensile performance of 30mm thick UHPC is stronger than that of 100mm thick UHPC.(3)Adding reinforcement to UHPC can effectively improve the axial tensile performance and post crack working performance of UHPC.With the increase of reinforcement ratio,the tensile properties of UHPC are also increasing.With the increase of reinforcement ratio,the contribution of UHPC to tensile performance will decrease.For the calculation of tensile capacity of reinforced UHPC,the synergy of steel fiber and reinforcement should be fully considered.