Study On Durability Of Fly Ash Slag Concrete With Cracks Under Sulfate-chloride Action

Fly ash slag is solid waste produced by coal combustion.Using fly ash slag as fine aggregate of concrete material can not only avoid resource consumption and noise harm caused by excavation and quarrying,but also realize resource utilization of solid waste.The existing technology has been able to produce fly ash slag concrete with mechanical properties similar to ordinary concrete.Concrete buildings located in coastal areas and saline-alkali zones are subjected to sulfate and chloride erosion,and concrete cracks under the action of load provide channels for the transmission of corrosive media in the concrete,leading to accelerated deterioration of concrete and significantly reduced structural service life.At present,there are few reports on the deterioration process of fly ash slag concrete with cracks in service.Based on this,the durability of fly ash slag concrete under sulfate-chloride erosion is studied in this paper.Taking ordinary concrete as reference,the ion erosion test of fly ash slag concrete with cracks under the dry and wet cycle condition was carried out to study the corrosion resistance and deterioration mechanism of single chloride ion,single sulfate ion,and sulfate ion and chloride ion combined action.The main research contents of this paper are as follows:(1)Taking mass loss rate and relative dynamic elastic modulus as indexes,the effects of concrete type(fly ash slag partially replacing mechanical sand)and the presence of chlorine salts on the sulfate resistance of concrete were analyzed.It is found that the mass loss rate and relative dynamic elastic modulus of pulverized ash concrete and ordinary concrete increase first and then decrease with time under single sulfate condition,and the change rate of the parameters of fly ash slag concrete is large at both stages.(2)Taking ion concentration as an indicator,the interaction of chloride ions and sulfate ions in the diffusion process of fly ash slag concrete under different crack widths was explored.It was found that the concentration of two types of ions in fly ash slag concrete with cracks in mixed solution was lower than that in single ion solution.(3)The type,content and formation process of the erosion products of fly ash slag concrete were measured by SEM and XRD to reveal the deterioration mechanism of fly ash slag concrete with cracks under the action of sulfate and chloride salts.It was found that the diffraction peak strength of AFt,Friedel salt and other corrosion products was low,indicating that chloride ions and sulfate ions had mutual inhibition effect.(4)Considering the influence coefficient K of fly ash slag and the deterioration coefficient f(w)reflecting the crack width,the chloride ion diffusion correction model of the cracked fly ash slag concrete is established.The chloride ion diffusion correction model of the cracked fly ash slag concrete fits well with the test data.The research can enrich the knowledge of concrete durability and has practical significance for expanding the application of solid waste in the field of building materials.