Research On Size Effect Of Basic Mechanical Properties And Bending Toughness Of PVA-ECC

High ductility concrete(Engineered Cementitious Composite,ECC)has become a new milestone of advanced cement-based composite material,it is mainly by the micromechanics design,and it has obvious strain hardening characteristics.It is found that ECC with approximate 2% fiber volume can stability produce more close crack during the deformation process,and it has the remarkable performance of strain hardening,the ultimate tensile strain of ECC is about 3%~7%,corresponding to 150%~300% of ordinary concrete,and 30%~300% of ordinary fiber concrete.At present,among all kinds of ECC materials,the study of PVA-ECC is most widely,but most of them related to the experimental study was conducted based on the small size specimen,theory study about the content of the size effect is quite scarce.Therefore,in this paper,the cube compressive strength,splitting tensile strength,ultimate bending strength and equivalent bending toughness size effect of high ductility concrete are systematically measured and analyzed,which is helpful to understand the properties of ECC materials.It provides a theoretical basis for its engineering application.The main research contents and results are as follows:(1)Through the PVA-ECC cube compressive strength and splitting tensile strength size effect test,the fiber content and curing age on ECC material compressive strength size effect and the influence of splitting tensile strength size effect were studied.The results showed that there is a significant size effect on the compressive strength and the splitting tensile strength of PVA-ECC.Under the same fiber content,the longer the curing age,the greater the effect of PVA-ECC compressive strength and splitting tensile strength.Under the same curing age,the larger the fiber content,the smaller the size effect of PVA-ECC compressive strength and splitting tensile strength,the less obvious the size effect.(2)Through the PVA-ECC ultimate bending strength and equivalent bending toughness size effect test,the effect of fiber content and curing age on the size effect of the bending strength of ECC materials and the size effect of flexural toughness were studied.The results showed that there is a significant size effect on the flexural strength and the equivalent bending toughness of PVA-ECC.Under the same fiber content,the longer the curing age,the more significant the PVA-ECC ultimate flexural strength and equivalent flexural toughness size effect.In addition,with increasing fiber content,PVAECC ultimate bending strength and equivalent flexural toughness size effect degrees are gradually decreases,and it shows that adding fiber can improve the flexural strength and toughness of PVA-ECC size effect.(3)Through the PVA-ECC ultimate bending strength and equivalent flexural toughness size effect test data statistical analysis,the PVA-ECC ultimate bending strength and equivalent flexural toughness of random distribution and statistical characteristics were studied.The results showed that the PVA-ECC ultimate bending strength and equivalent flexural toughness size effect is related to strength and toughness statistical,its internal mechanism may be caused by the strength of the material randomness.(4)Through the PVA-ECC internal rising temperature test,from the point of view of temperature stress explain the PVA-ECC cube compressive strength、splitting tensile strength 、 ultimate bending strength and flexural toughness to produce the inner mechanism of the size effect,the results showed that the PVA-ECC basic mechanical properties and flexural toughness are related to the internal temperature stress of specimen,which may be caused by the variation of internal temperature stress of the ECC material.