Study On Alkali Resistance Of Synthetic Fiber

Compared with ordinary concrete,fiber concrete has superior physical and mechanical properties,and the stability of fiber in concrete is the key to the role of fiber concrete.The interior of the concrete is an alkaline environment,which requires that the fibers to be incorporated should have good alkali resistance,especially the synthetic fibers that have developed rapidly in recent years.Therefore,it is particularly important to study the application properties of different synthetic fibers in cement coagulation,especially alkali resistance and mechanical properties,which is of great significance for promoting the promotion and application of fibers in civil engineering.In this paper,polypropylene fiber(PP),polyacrylonitrile fiber(PAN),polyvinyl alcohol fiber(PVA)and polyoxymethylene fiber(POM)were used as research objects,the synthetic fiber i5 alkali treated with a NaOH solution,a reference cement supernatant,a silica fiime-reference cement supernatant,and a mixed solution.The alkali resistance of the fiber monofilament was studied by the fiber swelling ratio and the breaking strength retention rate.The fiber corrosion mechanism was investigated by combining the microscopic topography and chemical structure changes,and four kinds of synthetic fibers were summarized.The alkali resistance is strong and weak,which provides reference for the synthetic fiber for cement concrete in actual engineering.The strength retention rate is the standard,the comparative analysis fiber is immersed in the NaOH solution and soaked in the reference cement supernatant and mixed solution.The corresponding relationship of post-aging time provides a reference for estimating the effective service life of synthetic fibers in cement substrates and complex alkali environments.In addition,four kinds of synthetic fiber cement mortar strength tests were carried out,and the flexural strength and compressive strength of the mortar reflected the reinforcing effect of the fiber on the cement substrate and the corrosion resistance of the fiber in the cement alkali environment,and combined with the alkali solution soaking test results,comprehensive evaluation of the alkali resistance of synthetic fibers.After the relevant experiments and analysis,the following main conclusions are drawn:After high temperature NaOH solution(pH=14)immersion for 6h,the strength retention of the four synthetic fibers was about 95%,indicating that the synthetic fiber has good alkali resistance.As time increases,the fiber exhibits a gradual increase in swelling rate and a gradual decrease in strength.When the temperature and solution concentration increase,the fiber strength loss is large,corrosion by solution is relatively serious,and alkali resistance is reduced,but four kinds of there is a certain difference in alkali resistance between synthetic fibers,showing different trends in mechanical changes.The microscopic study found that the alkali solution corroded the four kinds of synthetic fibers is a process of corrosion from the outside to the inside.The change of the fiber surface is closely related to the mechanical properties of the fiber,but the overall structure of the fiber after immersion remains unchanged.The test results of the benchmark cement supernatant and the mixed solution after soaking are most similar to the immersion test results of pH=14,indicating that the pH=14 NaOH solution is the closest to the cement concrete pore solution environment.When the strength retention rate is close to the same,the four kinds of synthetic fibers are immersed in the pH=14 NaOH solution for 6h,which is equivalent to the reference cement supernatant immersion for 28d.With the prolonged treatment time,the fiber can find the corresponding time node after soaking in the two alkaline solutions,according to the overall change rule,the long-term performance of the synthetic fiber in the concrete alkali environment can be inferredComparing the flexural strength and compressive strength of synthetic fiber cement mortar and benchmark cement mortar of different curing ages,it is found that the synthetic fiber has certain crack resistance to the cement substrate,which can effectively improve the flexural strength of the specimen.However,the effect on the compressive strength is not obvious.The results of the strength test of synthetic fiber cement mortar are highly consistent with the results of the soaking test of alkali solution,that is,the synthetic fiber has good alkali resistance,especially the POM fiber has the best alkali resistance in the four synthetic fibers,and can be applied to the properties.In cement concrete with alkaline environment,this can only consider the strength of about one year.After one year,the fiber strength is weakened and the reinforcing effect on the cement substrate is lost.