Research On Mechanical Properties Of Strain-hardening Cement-based Composites

Strain-harding cementitious composite(SHCC) is one branch of the ductile Fiber Reinforced Concrete(FRC),and designed by micromechanism it has high toughness and durability. Compared to normal concrete the difference is that SHCC can exhibit strain-harding performance after the first crack generated, which will generate multiple-cracks as response to different loads. Even though the deformation is very large, the crack width of SHCC can be kept at a small value.Because of its micro-cracking and high ductibility performance, SHCC represents a new kind of concrete materical and has a prodigious potential using value to solve durability corrosion problems.At present, the research to this composite material in our country is not started very long, although something has been learned about this material at theory and experiment , no relevant analysis model and theorical system have been built, so it is necessary to make a full system study on this material.In SHCC, Polyvinyl Alcohol (PVA) fiber is mainly used as reinforce material, and the mix proportion applied is obtained from many tests. In this series test study, first, the mechical indexs of SHCC are analyzed by tensile test, four-point bending test respectively to find the special law and the characteristic value, and then deal the data with referring to the rule of normal concrete. Second, all kinds of influent factors(mix proportions, sand sizes, fibers and admixtures)had been studied by tensile test, bending test, electronic microscope scanning test and mercury intrusion test, to make sure which condition is better. Meanwhile, the generation, number and width of cracks were also measured in details by crack width gage.As known form the experiments, when added fibers SHCC's toughess increased by several ten times and the strain was up to 3%; the crack width can be controlled in a small value , less than 100μm ; and the ultimate strain can reach 0.004, which is larger than normal concrete's 0.002;the antiflex strength is 2～3 times than the matrix. The best sand size is about 0.3mm; if too fine the workbilty of SHCC is not very good, otherwise too coarse the deformation capability is low. Fly ash and silicon ash can change the workbilty and enhance the toughness. For strength, the tensile strength increases while the compress strength is reduced highly, and it has a big relation with the mix composition. The most apparent character of SHCC is its typical multi-cracking and strain-harding performance. The fine cracks increase the toughness and reduce the penetration capability, which remedies the compress strength reduce. In a word, SHCC has high deformation, high durability and high capability to resist earthquake, so it has a potential value to use.