Study On Interface Control And Properties Of Domestic Polyvinyl Alcohol Fiber-engineered Cementitious Composites

Polyvinyl Alcohol Fiber-Engineered Cementitious Composites?PVA-ECC?have been extensively studied and applied for its excellent strain hardening and multiple cracking behavior.However,most of the fiber used to prepare PVA-ECC are produced in Japan at present.Because the surface of the fiber in Japan is modified with special oils,the interface between the fiber and cementitious matrix is optimized.PVA-ECC exhibits excellent strain hardening and multiple cracking behavior.One of the most important problems is the high price of Japanese fiber,which limits PVA-ECC applications.The price of domestic PVA fiber is cheaper than that of the Japanese fiber.However,since the surface of domestic PVA fiber has not been modified,therefore PVA fiber exhibit high degree of hydrophilicity.Furthermore the chemical debonding energy between the fiber and cementitious matrix is too high,which results in the fiber rupture with in the cementitious matrix,ultimately reducing the strain-hardening and multiple cracking behavior.In order to solve this problem,the surface modification of domestic PVA fiber was carried out to adjust the interface between PVA fiber and cementitious matrix to improve the toughness of PVA-ECC.The main contents of this paper are as follows:?1?Surface modification of domestic PVA fiber was carried out with silicone oil emulsion with concentration of 1wt%,7wt%and 13wt%and waterborne epoxy resin emulsion with concentration of 0.2wt%,0.5wt%and 1wt%.The surface morphology of pristine PVA fiber and PVA fiber was characterized by scanning electron microscope.The SEM results showed that the pristine PVA fiber had many grooves along the length,whereas after modification the surface is covered by the coating formed by the modifier and which confirms that the surface modifier was deposited on the fiber surface.?2?Single fiber pullout tests were carried out using the pristine PVA fiber,PVA fiber modified by different concentrations of silicone oil emulsion and waterborne epoxy resin emulsion.The effects of different surface modifier and concentrations on the interfacial properties between PVA fiber and cementitious matrix were studied.The results showed that the chemical debonding energy between the cementitious matrix and pristine PVA fiber was high,hence resulting in fiber rupture during pullout.For the surface modified PVA fiber,the slip process occured after the chemical debonding.For both silicone oil emulsion and waterborne epoxy resin emulsion,with the increase in emulsion concentration,the chemical debonding energy,frictional strength and slip hardening coefficient all showed a decreasing trend.?3?Three point flexural tests were carried out by using pristine PVA fiber,silicone oil emulsion modified PVA fiber and waterborne epoxy resin emulsion modified PVA fiber.The effects of different surface modifiers and concentrations on the flexural properties of PVA-ECC were analyzed.Generally,with the increase in emulsion concentrations,for both silicone oil emulsion and waterborne epoxy resin emulsion,the ultimate flexural deflection,ultimate flexural strength and number of cracks all increase first and then decrease.The test results showed that the ultimate flexural deflection,ultimate flexural strength and number of cracks for pristine PVA fiber specimens,measured as 0.621mm,3.993MPa and 4 respectively,were comparatively lowest.Furthermore,the crack spacing was found to be 30mm which was highest than the modified fiber specimens.The 7wt%concentration of silicone oil emulsion and 0.5wt%concentration of waterborne epoxy resin emulsion showed the best flexural performance as compared with other concentrations among their counterparts.The ultimate flexural deflection,ultimate flexural strength and number of cracks were recorded as 2.219 mm,5.404 MPa and 17 for samples with7wt%concentration of silicone oil emulsion and 2.589 mm,5.024 MPa and 12 for samples with0.5wt%concentration of waterborne epoxy resin emulsion.In addition,the crack spacing values,found to be lowest among their respective concentrations,were measured as 7.06 mm and 10 mm for 7wt%concentration of silicone oil emulsion and 0.5wt%concentration of waterborne epoxy resin emulsion respectively.The flexural toughness was evaluated by ASTM C1080-97 standard.The toughness index results also initially showed increasing and then decreasing trend with the increase of emulsion concentrations.The 7wt%concentration of silicone oil emulsion and 0.5wt%concentration of waterborne epoxy resin emulsion demonstrated the maximum toughness index values of 140.982 for I₆₀ and 104.003 for I₅₀ respectively.However,for pristine PVA fiber,the thoughness index was recorded as 29.954 for I₃₀,which is comparatively lower than that of the modified fiber.In this experiment,PVA fiber modified with silicone oil emulsion is more conducive to the flexural toughness of PVA-ECC than PVA fiber modified with waterborne epoxy resin emulsion.?4?Uniaxial tensile tests were carried out by using pristine PVA fiber,silicone oil modified PVA fiber and waterborne epoxy resin emulsion modified PVA fiber.The effects of different fiber modifiers and concentrations on the tensile properties of PVA-ECC were analyzed.Generally,with the increase in emulsion concentrations,for both silicone oil emulsion and waterborne epoxy resin emulsion,the ultimate tensile strain,ultimate tensile strength and number of cracks all increase first and then decrease.The test results showed that the ultimate tensile strain,ultimate tensile strength and number of cracks for pristine PVA fiber specimens,measured as 0.449%,2.018MPa and 1 respectively,were comparatively lowest.Furthermore,the crack spacing was found to be80mm which is highest than the modified fiber specimens.The 7wt%concentration of silicone oil emulsion and 0.5wt%concentration of waterborne epoxy resin emulsion showed the best tensile performance as compared with other concentrations among their counterparts,exhibits excellent strain hardening and multiple cracking behavior.The ultimate strain,ultimate strength and number of cracks were recorded as 1.406%,3.131MPa and 38 for samples with 7wt%concentration of silicone oil emulsion and 0.637%,2.774MPa and 11 for samples with 0.5wt%concentration of waterborne epoxy resin emulsion.In addition,the crack spacing values,found to be lowest among their respective concentrations,were measured as 2.11mm and 7.27mm for 7wt%concentration of silicone oil emulsion and 0.5wt%concentration of waterborne epoxy resin emulsion respectively.In this experiment,PVA fiber modified with silicone oil emulsion is more conducive to strain hardening and multiple cracking properties of PVA-ECC than PVA fiber modified with waterborne epoxy resin emulsion.