Mix Design And Performance Optimization Of Strain Hardening Cementitious Composites

Cement-based composite is one of the most important building materials.However,it has the disadvantages of low tensile strength,weak deformation resistance and high brittleness applied in infrastructure construction.Therefore,the issue of how to improve the ductility,deformation resistance,safety and durability of cement-based composite has become more and more important.The strain hardening cement-based composite(SHCC)which is designed by the basic principles of micromechanics,fracture mechanics and statistics has ultra-high ductility and high strain hardening characteristics under tensile and shear loads,and the ultimate tensile strain can reach 3% at least.SHCC has been used in the United States,Japan,Europe and other places,signifying a wide range of application prospects.However,Many factors restricted the popularization and application of SHCC in China,such as the gradation of ordinary fine aggregate which is applied in SHCC,the unstable performance of SHCC,and the high cost of imported PVA fiber.In order to solve the above problems,the influence of the content and gradation of fine aggregate in SHCC matrix on the working performance of SHCC matrix was studied,and the effect of fine aggregate gradation and content on the strain hardening property of SHCC was discussed.The design method of SHCC mixture ratio based on fine aggregate gradation and dosage was put forward in this paper.Compared the effects of different PVA fibers on the mechanical properties of SHCC at different curing ages,and obtained the following conclusions:(1)With the increase of the mixing amount of fine silica powder(0%-40%),the slump flow of SHCC matrix decreased in turn.Considering the fluidity and agglomeration of the matrix,the optimum mixing amount of fine silica powder was 10%,and with the increase of the mixing amount of coarse silica powder(0%-27%),the slump flow of SHCC matrix decrease in turn.Regarding the fluidity and agglomeration of the matrix,the optimum mixing amount of coarse silica powder is 9%.(2)With the increase of the amount of fine aggregate(sand-binder ratio),the water binder ratio of matrix which is in optimum workability increases in turn.When the ratio of sand to binder rise from 0.36 to 0.84,the optimum water consumption increases from 0.32 to 0.41.The tensile strain of SHCC increases firstly and then decreases with the increase of sand-binder ratio.When the sand-binder ratio is 0.60,the tensile strain of SHCC reaches the maximum value.The optimum mixture ratio of SHCC is as follows: cement: fly ash: fine aggregate: water: water reducing agent: PVA fiber=1: 2: 0.6: 0.355: 0.0036: 2vol%.(3)With the increase of curing age(7d-90d),the strain hardening performance of SHCC prepared by three PVA fibers are firstly increase and then decrease.The strain hardening performance decrease obviously in 56 days and 90 days,and the strain hardening performance of K-SHCC is better than the strain hardening performance of the CW-SHCC and WW-strain.(4)With the increase of mixing amount of methyl silicone oil(0%-4%),the limit tensile strain of SHCC improve,the number of cracking fracture increases,the residual crack width decrease,the strain hardening phenomenon of the SHCC become significant,However,the ultimate tensile stress decreases,the flexural strength and compressive strength decreases,and the mechanical properties of SHCC reduce.the flexural strength and compressive strength decrease,the fracture toughness property improve of the SHCC matrix.At the same time,the dispersion coefficient of fiber increases.Adding the dosage of the methyl silicone oil improve the toughness of SHCC matrix and the dispersible uniformity of fiber.The interfacial properties of fiber/matrix improve.The ductility of SHCC improves,and the strength of the SHCC reduces.When comprehensive considering the performance of ductility and strength,the optimum content of methyl silicone oil is 2%.