| In actual engineering,the phenomenon of cracking and leakage of underground side walls is very common,which not only seriously affects the durability and bearing capacity of the structures,but also is difficult and expensive to repair.The commonly used construction material for underground side walls is concrete,and concrete has the characteristics of low tensile strength and poor deformability,which brings greater challenges to the anti-cracking and the anti-permeability of underground side walls.Engineered Cementitious Composites(ECC)is a new type of cement-based material with strong tensile strain ability,which can significantly improve the structural cracking caused by the brittleness of cement-based materials,and at the same time increase the material’s fracture energy.The excellent crack control ability of ECC is very conducive to the anti-cracking and the anti-permeability requirements of underground side walls.Traditional ECC uses polyvinyl alcohol(PVA)fiber,but PVA fiber is expensive,which is not conducive to large-scale use in engineering,and sisal fiber,as a kind of plant fiber,is environmentally friendly and has low cost.Therefore,this article replaces the PVA fiber in ECC with sisal fiber,aiming to redesign and develop a green and economical engineered cementitious composites that meets the basic mechanical and working performance requirements of underground side walls,and discuss the anti-cracking and anti-permeability effects of underground side walls using sisal fiber-ECC.The main research work and results of this paper are as follows:(1)This paper uses orthogonal test to optimize the mix ratio of sisal fiber-ECC.16 groups of sisal fiber-ECC with different mix ratios were obtained through the orthogonal test of 4 factors and 4 levels.The influence of water-binder ratio,sandbinder ratio,fly ash content and sisal fiber volume content on the compressive strength and bending strength of sisal fiber-ECC was explored;The working performance test and standard cube compressive strength test of the sisal fiber-ECC after optimization of mix ratio were carried out,which preliminarily analyzed the feasibility of using the sisal fiber-ECC after optimization of mix ratio in the actual underground side wall project.In addition,the axial tensile performance test of sisal fiber-ECC after optimization of mix ratio was carried out,and its tensile strength was measured to be2.42 MPa,which is not much different from that of concrete,but it has a good tensile stress level retention rate after cracking.(2)Based on ANSYS,using a modeling method that has been verified by actual engineering,the crack resistance of the underground side wall using optimized sisal fiber-ECC under temperature load is studied.The crack resistance of the underground side wall model using sisal fiber-ECC and the model using ordinary concrete is compared,and it is proved that the optimized sisal fiber-ECC can reduce the cracking risk of the underground side wall.The finite element analysis shows that when the ambient temperature is low,the underground side wall will form a larger tensile stress due to the faster cooling rate,causing the underground side wall to crack,at this time,in order to reduce the risk of cracking of the underground side wall,a method of lowering the injection temperature can be adopted.(3)Carried out the capillary water absorption test of the hollow cylindrical specimen under the continuous compressive load.The influence of the continuous compressive stress level(Respectively 0%,10%,20%,30% and 40% of the ultimate bearing capacity)on the capillary water absorption performance of sisal fiber-ECC specimens is analyzed and compared with that of ordinary concrete specimens.The test results show that when the continuous compressive stress level is in the range of10%～30%,compared with ordinary concrete,the optimized sisal fiber-ECC can block water transmission and maintain a lower capillary water absorption and water absorption.For underground side walls,when the continuous compressive stress level is 10%～30%,the use of optimized sisal fiber-ECC as a pouring material can achieve a better impermeability effect. |
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