The Study On Preparing Composite Cementitious Materials With Low-alkalinity Steel Slag

As a by-product of the iron and steel industry,the utilization rate of steel slag is low.This severely affects the sustainable development of the iron and steel industry.In this paper,the low-alkalinity steel slag from a certain iron and steel group was researched.The morphology of the mineral facies in this steel slag was identified by SEM and optical microscope.The mineral compositions were analyzed by XRD.The results showed that The main minerals of this steel slag is CMS,RO phase,C₃MS₂ and a small quantity of Ca(OH)₂,CaCO₃ and f-CaO.Because the main mineral facies liking CMS,RO phase and C₃MS₂ have no cementing property and the quantity of C₂S and C₂F which have cementing peoperties is small,the activity of this slag is poor. Besides,due to the water-cooling process to the steel slag,some active substances were hydratied which leading to the loss of activity.In order to improve the activity and soundness of steel slag and explore a technical way to resource recycling steel slag largely,steel slag,slag and ultra-fine fly ash(which have the mean grain size of 5.51μm) were mixed with to make a composite powder.The soundness of this composite powder is inspected.When the composite powder replaced the cement with different adding,the relationship between the packing density and the particle grading was investigated wirh the aid of compressible packing model.The working regularity between the packing density and the mechanical properties of cementitious materials is inspected.Taking it as a guide,the mix proportion was determined and the concrete added with the composite powder was tested.The mechanical properties and water demond of concrete were tested.It was found that after added with some siliceous materials such as slag and ultra-fine fly ash,the soundness of steel slag was obviously improved.When a certain amount of cement is replaced by the composite powder of steel slag-GBFS-ultra-fine fly ash,the pack density of the cement was enhanced to a certain extent.The higher the proportion of ultra-fine fly ash was,the greater pack density was obtained.When the water to binder ratio was lower,there was a good correlationship between the pack density and the compressive strength.When the water to binder ratio went to higher, the chemical properties of raw materials have a greater impact on the compressive strength of paste.The greater the amount of slag powder was,the higher compressive strength was achived.The results of preparing concrete with the composite powder detected that as a complex mixture of minerals to replace the 50%～80%of the 425 ordinary portland cement,the composite powder meet the cause of preparing C30 concrete.The early strength of concrete was lower,but the growth was much greater later.Improving the fineness of steel slag mixed in the compsite powder caused the concrete strength rise at every age.With the same the slump,the water demand of the concrete with composite powder was less than the blank sample and the performance was better.