Research On Alkaline-Chlorine Resistance Of Basalt Fiber And Effect Of Basalt Fiber Composites On Flexural Performance Of Concrete

Basalt fiber has a good property in resisting corrosion of Cl~-irons and avoid corrosion problems similar to steel fibers or steel rebars.Therefore,basalt fiber and its composites are well applied in offshore concrete structures.But there still exist some shortcomings:1)Alkaline-chlorine corrosion resistance of basalt fiber and its composites is rarely discussed;2)The flat shape is the main structure adopted by basalt minibar,resulting in the disadvantage of worse energy absorption capacity compared with special-shaped fibers such as hooked-end fibers;3)Basalt minibar has poorer ability to improve flexural performance of concrete compared to macro steel fiber,which means the purpose of equivalently replacing macro steel fiber with same fiber dosage can’t be achieved.In order to popularize the application of basalt fiber and its composites,this research concentrates on the alkaline-chlorine corrosion resistance of basalt fiber and its composites and effect of basalt fiber composites on flexural performance and crack morphology of concrete.The main contents and conclusions of this research are displayed as follows:(1)The accelerating corrosion tests of basalt fiber and its textile in alkaline and chlorine mixed solution were conducted.The alkaline-chlorine corrosion resistance of basalt fiber was discussed based on microscopic morphology,diameter change,elemental composition,molecular structure and corrosion mechanism.The alkaline-chlorine corrosion resistance of basalt fiber textile was discussed based on tensile strength retention,microscopic morphology and corrosion mechanism.Then the coupling effect of OH~-and Cl~-ions on corrosion resistance of basalt fiber and its textile was analyzed.The results show that the OH~-and Cl~-ions jointly destroy the Si-O bonds and Al-O bonds of basalt fiber and epoxy resin of basalt fiber textile.While the corraded basalt fiber textile is severely dispersed into monofilament basalt fibers.Therefore,the joint effect of alkali and chloride aggravates the corrosion process of basalt fiber and its textile.(2)The four-point bending tests of basalt fiber textile reinforced concrete thin plates were carried out and reinforcement coefficient E_cwas introduced to evaluate the strengthening effect of basalt fiber textile on flexural performance of concrete and study the influence of mesh type on flexural performance of fiber textile reinforced concrete.The results indicate that the energy consumption and the bond performance between fiber bundles and concrete matrix are more excellent with a smaller mesh size and more tensile fiber bundles.In addition,the warp and weft fiber bundles are mutually restrained.When fiber textile is slipping out of concrete matrix,the weft fiber bundles can limit the slippage of the warp fiber bundles,thereby improving the positive reinforcing effect of fiber textile on flexural performance of concrete.(3)The new-developed basalt minibar with helical structure has the advantages of high section stiffness,uniform distribution in concrete matrix and good durability.When basalt minibar is slipping out of concrete matrix,the helical structure exposes basalt minibar to a uniformly-distributed compressive force along fiber length and perpendicular to fiber surface,which helps to enhance the bond performance between fibers and concrete matrix.When fiber length and dosage are same and aspect ratios of macro fibers are similar to each other,the reinforcing effect of basalt minibar on flexural performance of concrete is worse than that of macro steel fiber.The reinforcing effect of basalt minibar on flexural performance of concrete is equivalent to that of macro steel fiber when the dosages of basalt minibar and macro steel fiber are 40kg/m~3and 20 kg/m~3,respectively.(4)The four-point bending tests of hybrid fiber reinforced concrete were carried out to evaluate the reinforcing effect of hybrid fiber on flexural performance of concrete based on first-peak strength,peak strength,residual flexural strength and energy absorption.The the laser scanning tests of concrete crack surface were conducted to evaluate roughness number R_N,fractal dimension F_N and standard deviation of z coordinateσ_zto ensure the most suitable parameter to symbolize crack surface morphology of concrete.The results demonstrate that the reinforcing effect of hybrid fiber on flexural performance of concrete is obviously more excellent than that of single-doped macro fibers.With the increasing of fiber dosage,roughness number R_N increases gradually and fractual dimension F_N has a small change,of which the difference between maximum value and minimum value is 3.9%.But there is no obvious pattern of standard deviation of z coordinateσ_z with the increasing of fiber dosage.As a result,roughness number R_N is the most suitable parameter to symbolize crack surface morphology of concrete.