Experimental Study On Axial Compression Of Hybrid Fiber Reinforced Cementitious Composites Columns

With the development of high-rise buildings,people have higher and higher requirements on the strength of concrete.However,although the higher strength of concrete is,the larger brittleness of concrete becomes.It is an inevitable trend to increase the toughness of concrete and make concrete develop towards the direction of high strength and low brittleness.In previous studies,steel tube,steel reinforcement,steel bone or fiber cloth are usually used to compound with concrete to improve the strength,toughness and other mechanical properties of concrete,and some progress has been made.Adding fiber into concrete is also one of the effective ways to improve the performance of concrete.A variety of fibers are mixed in the cementitious composites to compensate each other and have good performance.In this paper,a new viewpoint is put forward that hybrid fiber reinforced cementitious composites are used to restrain core plain concrete composite columns in the outer layer,so as to improve the strength,ductility and deformation properties of concrete.In this paper,a total of 27 circular composite column specimens are designed.There are several ways of grouping and comparison as follows: according to the thickness of the outer cementitious composites,it can be divided into 75 mm,62.5mm and 50 mm,each accounting for 1/3.According to the strength grade of the outer cementitious composites,it can be divided into C40,C70 and C90,each accounting for 1/3.According to the strength grade of core concrete,it can be divided into C50,C60 and C80,each accounting for 1/3.Through the axial compression test of composite column,the influence of the thickness,strength grade of the outer cementitious composites and the strength grade of the core concrete on the bearing capacity and deformation performance of the composite columns are analyzed.The axial compression test of hybrid fiber reinforced cementitious composite column shows that the addition of hybrid fibers can effectively improve the deformation performance of composite columns,prevent or delay the appearance of cracks on the surface of the specimen,and make the specimen maintain good integrity.Under the same strength grade of external hybrid fiber cement-based composite,the strength grade of core plain concrete remains unchanged and the outer cement is changed.The thicker the thickness of matrix composites,the less obvious the increase of peak load,and the more obvious the ductility.When the outer layer thickness of cementitious composites is thicker,more gentle decline,the corresponding curve ductility is better.Considering the overall performance and engineering practice,it is recommended to select a thickness of 62.5mm.For hybrid fiber cementitious composites,under the premise of meeting the strength requirements,when the core concrete strength is low,it is recommended to choose C70/C40,when the core strength is high,it is recommended to choose C40.For core concrete,it is recommended to select strength grade C50 on the premise of meeting the strength requirements.The ductility of the composite column is compared and analyzed.When the strength grade of the core concrete is the same,the peak strain basically shows an upward trend with the increase of the thickness of the outer cementitios composites.Based on the analysis of test data,the strength calculation formula of core concrete is obtained by fitting.The bearing capacity of outer layer mixed fiber ECC and core plain concrete was superimposed.And the calculated peak load is in good agreement with the test peak load.