Application And Performance Of Steel Slag In Autoclaved Aerated Concrete Blocks

Steel slag is solid waste generated during the steel making process.If the steel slag cannot be effectively treated,it will not only occupy a large amount of land but also cause environmental pollution.In recent years,in response to the basic policy of the state to protect the environment,the rational use of steel slag has received more and more attention.In this paper,steel slag was applied to autoclaved aerated concrete,and two systems were studied:steel slag-sand aerated concrete and steel slag-ash aerated concrete.In the steel slag-sand system,the effects of different ratios of raw materials,different kinds of activators and the amount of gas generating agent on the strength and dry density of concrete blocks were studied.The main mineral composition and microscopic morphology were studied by X-ray diffractometer,infrared spectrometer,scanning electron microscope and differential thermal analyzer.In the steel slag-fly ash aerated concrete block system,the best ratio of steel slag and fly ash was studied.The above microscopic test method also used to observe its main mineral composition and microscopic morphology.Finally,the hydration heat release behavior of the best proportion concrete block in the two systems was studied by hydration calorimetry.The main contents of this paper are as follows:(1)XRD analysis of experimental raw material steel slag and fly ash was carried out.The results show that the main components of steel slag are C2S,C3S,C2F and RO phase.The main mineral components in fly ash are mainly mullite phase and quartz phase.The raw materials such as steel slag were subjected to particle size analysis and testing.(2)The strength of steel slag mortar after autoclaving can reach the strength of 28 days under normal temperature curing.The autoclave can increase the early strength of the steel slag.By studying the influence of different raw materials on the strength and dry density of concrete block,the best mix ratio of steel slag-sand aerated concrete block test is as follows:the amount of steel slag is 40%,the amount of river sand is 40%,The amount of cement admixture is 12%,the amount of lime is 6%,the amount of gypsum is 2%,the amount of aluminum powder is 630g/m3,and the strength of the block is relatively high,reaching 3.23 MPa.Then carried out a series of micro test analysis,The results show:Ca(OH)2 in the concrete block has completely reacted under autoclaved conditions.The main hydration products of concrete blocks are tobe mullite and xonotlite,they are the source of strength for concrete blocks.The total mass loss of the block after heating for a long time was 16.83%.The heat resistance of concrete blocks is general.(3)The addition of the activator increased the strength of the steel slag-sand aerated concrete block to some extent.The addition of sodium silicate(Na2SiO4)had the best excitation effect on the autoclaved aerated concrete,and its strength reached the highest.There is no significant change in the hydration products of concrete blocks with different activators.The hydration products all produced tobe mullite,C-S-H gel,and SiO2 and inert phase RO phase which did not participate in the reaction,and the degree of hydration was different.(4)When the steel slag content is about 40%,the strength of the steel slag-fly ash aerated concrete block is optimal.From the results of XRD and SEM analysis,the suitable calcium to silicon ratio is the main factor for the formation of hydration product tobe mullite.The proper amount of steel slag and fly ash can optimize the hydration product composition of the concrete block.It can be obtained from the TG/DSC curve analysis that 40%of the steel slag has the largest amount of hydration products and the largest mass loss.(5)The heat release and heat release rate of steel slag-fly ash aerated concrete block are lower than the heat release rate and heat release rate of steel slag-sand aerated concrete.Due to the lower heat release of steel slag-fly ash aerated concrete,it is more suitable for the preparation of mass concrete.It is not easy to cause structural instability caused by heat release of concrete.Figure[39]Table[16]Reference[90]...