Experimental Study On Mechanical Properties Of ECC

ECC is short for engineering cement-based Composite.Unlike fiber concrete,which usually achieves specific properties only by adjusting the fiber content,ECC is a high-performance material with excellent properties of high toughness,high ductility,tensile resistance and crack control,guided by the concepts of fracture mechanics and micromechanics and designed for the interface of fiber,matrix and fiber matrix.When subjected to uniaxial tension,the ultimate tensile strain can reach more than 3%(about150~300 times of concrete)stably,and the ultimate crack width is within 0.1mm.The cracks are fine and dense,which improves the characteristics of wide and sparse cracks of concrete and can greatly improve the durability of the structure.However,ECC,as a kind of high performance composite material,has not yet formed a unified specification and the basic mechanical properties of ECC test methods are not unified standards.Based on the above problems,this paper conducted a series of studies on the basic mechanical properties of ECC through experiments.The main contents are summarized as follows:1.Through the compression performance test of ECC cube,prism and cylinder,the influence of fly ash content,water-binder ratio,PVA volume rate and size effect on ECC compression performance was explored;According to the test results,the conversion relations between axial compressive strength,static compressive modulus and cube compressive strength are established.According to the stress-strain test curve,the stress-strain relationship is simplified and the constitutive equation is given.2.Through the direct tensile test of ECC specimens,the influence of fly ash content,water-binder ratio and PVA volume rate on the tensile performance of ECC was explored.In this paper,the development of strain-hardening and crack in tensile process is described reasonably,the stress-strain relationship of ECC material is simplified reasonably according to tensile stress-strain test curve,and the corresponding tensile constitutive equation is given.3.Through the four-point bending test of ECC specimen,the cracking characteristics of multi-crack in four-point bending of thin plate were described reasonably,and the whole curve of bending load-deflection was analyzed,the main factors affecting the bending strength were studied,and the bending toughness index method was used to evaluate the four-point bending toughness of thin plate.4.Finally,based on the test results of mechanical indexes of ECC in three aspectsof compressive performance,tensile performance and bending performance,the optimal mix ratio of ECC was determined through comprehensive comparative analysis,providing a basis for the future structural design and engineering application of ECC.