Study On Properties And Microscopic Mechanism Of Steel Slag Aggregate Concrete Under Sulfate Attack

In the process of rapid urbanization,China consumes a lot of sand and stone aggregate,and the contradiction of sand and stone shortage is increasingly prominent.steelmaking will produce a large amount of steel slag resulting in serious pollution and waste of resources.Compared with natural gravel aggregate,steel slag has higher density and strength.Qualified stable steel slag can replace part of natural gravel aggregate to prepare steel slag aggregate concrete.At the same time,saline soil is widely distributed in western China,and concrete is often eroded by sulfate,so it is particularly important to study the durability of steel slag aggregate concrete under sulfate erosion.This paper presents and studies the substitution rate,erosion time and erosion concentration of steel slag In order to further improve the performance of the aggregate concrete of steel slag,the new modification scheme of steel slag is studied.The main work of this paper is as follows:(1)Steel slag aggregate stability was tested.The main chemical constituents of steel slag were analyzed under different aging time,and it was found that the content of free calcium oxide decreased with the aging time.(2)The evolution of macroscopic mechanical properties of slag aggregate concrete under sulphate erosion was studied.It was found that the compressive strength,mass loss and relative elastic modulus of slag aggregate concrete with substitution rates of 30%,60% and90% were higher than that of ordinary concrete under sulfate erosion.(3)The corrosion product and microstructure degradation mechanism of slag aggregate concrete under sulphate erosion were studied.Through XRD and SEM experiments,it was found that the cementite in steel-slag aggregate concrete has fewer pores,and the hydrating activity of steel-slag aggregate can promote the formation of cementite.With the increase of erosion time and solution concentration,the cementite in steel-slag aggregate concrete gradually changed from fine needle to long column and finally formed agglomeration clusters.Overall,the sample had the least internal damage when the replacement ratio of slag aggregate was 60%.(4)The steel slag is modified by using cement-fly ash slurry surface package to improve the stability of steel slag aggregate.The modified slurry of 0.3,0.5 and 0.6 is used to modify the steel slag.It is found that with the improvement of the water-cement ratio,the enclosing ability of the modified slurry to the steel slag is improved,and the adhesion is reduced.When the water-cement ratio is 0.5,it can not only effectively fill the pores on the surface of the steel slag,but also completely wrap the steel slag surface of the steel slag with certain adhesion.After the physical properties and stability test of modified steel slag,it is found that the density and water absorption rate of steel slag are reduced,the expansion rate of water immersion and pressure evaporation rate are reduced,and the stability of aggregate of modified steel slag is improved.(5)The evolution law of macroscopic mechanical properties of modified steel slag aggregate concrete under sulfate corrosion is studied.It is found that although the compressive strength of modified steel slag aggregate concrete is lower than that of steel slag aggregate concrete at 28 d of curing,it is still higher than that of ordinary concrete.After 56 d of erosion,the compressive strength of modified steel slag aggregate concrete is increased by5.7% compared with that of steel slag aggregate concrete,and the macroscopic mechanical properties are better than that of steel slag aggregate concrete,which can effectively slow down the erosion process and improve the erosion resistance.(6)The reinforcement mechanism of modified steel slag to aggregate concrete with steel slag is studied.Through XRD and SEM test,the hydration activity of the modified steel slag is reduced,the modified slurry effectively reduces the erosion solution into the steel slag aggregate,suppresses the corrosion reaction of the sulfate ion and the steel slag aggregate,and makes the quantity and density of expansion products generated around the modified steel slag aggregate are lower than that of the steel slag aggregate concrete.The modified steel slag aggregate concrete is well preserved compared with the microstructure,and the damage deterioration degree is low.