Mechanical Properties Of PVA Fiber/Cement-matrix Interface And Their Effects On Tensile Properties Of SHCC

Strain hardening cement-based composites(SHCC)is a type of cement-based composite with ultra-high tensile ductility.The difference in raw materials and preparation process may result in different mechanical properties of SHCC.In this paper the mechanical properties of PVA fiber / cement matrix interface have been investigated at first aiming to analyze the influence mechanisms of material components and preparation methods on the strain hardening behavior and multiple cracking of SHCC.A model to predict mechanical properties of SHCC is established which is helpful for preparation of SHCC.The main conclusions are drawn up as follows:(1)The effect of PVA fiber / cement matrix on the mechanical properties of PVA fiber / cement matrix was studied by single fiber pull-out test.It was shown that the increase in oil agent content coating on the surface of fiber made fiber pull out from the matrix easy.Steam curing improved the interface bond properties between PVA fiber and cement matrix.At the same time,the interface bond strength and interface fracture energy showed an upward trend with increasing curing age.(2)The relationship between the applied stress and crack opening displacement(COD)of SHCC with single crack was studied by uniaxial tensile test on prefabricated notched SHCC specimens.The influence of curing age and curing methods on the relation of stress and COD was also discussed.With the increase of age,the first crack strength increased obviously,but the maximum bridge stress didn't increase obviously.With the increase of curing age,fibers showed greater ability to hinder the opening of crack.With the same curing age,the maximum bridging stress of specimens cured in the steam condition was larger than that cured in the standard curing condition.(3)The relationship between tensile stress and crack opening displacement(COD)of SHCC was deduced by definition of fiber fracture domain and pull-out domain.The formula to predict first crack strength,ultimate tensile strength and ultimate tensile strain of SHCC was obtained.According to the mechanical parameters obtained from the single fiber pull-out test,the theoretical predict results showed that the first crack strength and ultimate tensile strength were consistent with the experimental results,but the ultimate tensile strain had a certain deviation in comparison with the experimental results.