Durability Of Fiber Reinforced Concrete In Dry And Wet Sulfate Environment

The durability of concrete structures is one of the important research directions in the field of civil engineering.Sulfate erosion of concrete is a common durability problem.Structural damage caused by durability failure will cause huge economic loss and great social impact.Therefore,it is of great theoretical significance and engineering application value to study the durability of concrete under sulfate erosion environment.Is given priority to with experimental research,this paper studies the fiber reinforced concrete under sulfate wet environment of sulfate erosion resistance,the indoor accelerated system of sulfate erosion,namely the dry-wet circulation mechanism of soak 1 day,natural 2 hours to dry,drying in the drying oven（80±5℃）22 hours,as a cycle,cycle for 2 days.Thus,over a period of 300 days,a total of 150cycles of wet and dry cycle.At the same time,in order to compare with the dry and wet cycle,the long-term immersion test was also carried out.And on this basis,we studied the compressive strength of concrete under different erosion times,quality of relative dynamic elastic modulus,loss and damage of macro performance appearance,nuclear magnetic resonance research of mesoscopic structure and the microstructure changes through SEM test,analyzes the different dosage of fly ash and bentonite,different solution and erosion under the system of sulfate erosion effects on fiber concrete durability.In addition,the damage mechanism of fiber reinforced concrete was analyzed by combining macroscopic test,nuclear magnetic resonance test and SEM scanning results.Generally,the first stage of sulfate erosion of fiber concrete is the compaction of the internal pores of concrete,which is caused by the chemical reaction of ettringite produced by the continuous hydration of concrete and the physical crystallization of sulfate filling the internal pores of concrete,which is manifested as the increase of mass and the increase of compressive strength.In the second stage,cracks are generated inside the concrete,chemical corrosion is continuously aggravated,more and more corrosion products are produced,crystal expansion continues,internal cracks are expanded,the compressive strength of fiber concrete is reduced,the quality is still increasing,and the relative dynamic elastic modulus is decreased.The third stage is the continuous aggravation of corrosion,fiber concrete test block surface and edge around the phenomenon of falling off,this stage of fiber concrete indicators have decreased.The results also show that increasing the content of fly ash can accelerate the corrosion of sulfate on fiber reinforced concrete,while increasing the content of bentonite can slow the corrosion of sulfate on fiber reinforced concrete.Na₂SO₄solution corroded the fastest,MgSO₄ solution corroded the second,H₂O solution corroded the slowest,and sulfate dry and wet circulation environment can accelerate the corrosion of fiber concrete,but long-term immersion environment has little influence on the corrosion of fiber concrete.