Surface Modification For Interface Tailoring Of PVA Fiber Engineered Cementitious Composites

The increasing demand of novel structures with improved durability and performance as well as repair of existing structures with low cost have provided challenge to the engineers to fulfill the gap by using high performance construction materials.Concrete is one of the basic and widely used material for structural applications because of its binding properties,good ability to be molded in different shapes,high strength in hardened state and optimum cost.However,concrete is brittle in nature and has poor tensile strength and tensile strain properties.Recently,the addition of fibers as reinforcements has proven to be effective in overcoming the limitations of concrete brittle fracture.A new class of high-performance fiber reinforced cementitious composite,namely Engineered Cementitious Composites?ECC?reinforced with Polyvinyl alcohol?PVA?fibers,is characterized by strain-hardening,multiple-cracking and tight crack width.The distinctive behavior of strain-hardening cementitious composite?SHCC?is a combine result of subtle balance between different parameters.Such as reinforcing fibers and cementitious matrix material properties,interfacial bond,fiber distribution and orientation,matrix flaw size and its distribution are of an important concern in deciding the resulting properties of the cementitious composite.The comprehensive study of all the influencing parameters is complicated,although significant amount of literature is available regarding the theories of micro-mechanics and its effects on the composite performance,different experimental and numerical models are derived for experimentally characterizing the mechanical properties and theoretically verifying the results.However,the focus of present research work is on the tailoring of interfacial bond between domestic PVA fiber and the cementitious matrix.Due to the high cost of imported Japanese Kuralon PVA fibers,the practical applications of ECC are limited,especially in China.In the present study,different oiling agents are utilized to modify the local PVA fiber surface to achieve the optimum strain-hardening properties at comparatively lower cost.This research work investigates the effects of oiling treatments on the interfacial behavior between fiber and cementitious matrix and on composite properties.For this purpose,a direct single fiber pull-out method was utilized to study the interfacial behavior after PVA fiber surface treatment.The oil treatments have proven effective in modifying the fiber-matrix interface with the reduced chemical debonding energy?G_d?values of 50%to 85%in comparison to untreated PVA fiber.The composite flexural performance was studied using a three-point bending test.It was found that the flexural strength varies between 4.5 Mpa and 8.2 Mpa depending on the oiling treatment.The oiling treatments have shown increased toughness values and ASTM toughness index up to I₆₀by using 2%volume of fibers.In addition,the study on viscosity modifying admixture?VMA?under flexural and tensile test were studied to identify the robustness,finding the right proportion for the given cementitious mix.Three different methods ASTM,JSCE,and PCM were used to examine the flexural toughness of the cementitious composites.Based on the results of each standard of flexural toughness the limitations are also discussed.The results imply that within the specific quantity of VMA the influence of fiber reinforcement is increased and strain-hardening behavior is improved.However,exceeding the suggested ratio negatively effects the fiber dispersion and ultimately negatively influence overall composite property.Furthermore,the fiber-matrix interfacial properties were tailored to meet the micro-mechanics design based theoretical requirements for tensile strain-hardening and satu-rated multiple-cracking.The single fiber pull-out tests were conducted to study the interfacial behavior and tensile test was carried out to analyze the effects of treatment on the composite level.In addition,finite element analysis for single fiber pull-out behavior is also simulated.The FEA results showed good agreement to that of the experimental pull-out results.Moreover,the experimental results for tensile test suggest that the surface modified composite exhibit comparatively larger strain capacity.The oil treated PVA fiber uniaxial tensile test results demonstrated significant improvement in ultimate tensile strain capacity and ultimate tensile stress.In addition,the multiple saturated cracks with lower crack spacing was observed for the treated specimens in contrast to the control samples.Overall,the present study suggests that the surface modified domestic PVA fibers could be feasible to produce cost-effective SHCC.