Research On The Volume Stability Of Steel Slag And Hydration Process Intensification

Physical and chemical analysis and utilization research in autoclaved building materials was made for the fine steel slag powder,which come from certain steel slag pile in Tangshan.The results showed that the main mineral phases of the steel slag are tricalcium silicate(C3S),dicalcium silicate(C2S),RO phase(soild solution of magnesium oxide,ferrous oxide and manganese oxide.etc),free calcium oxide(f-CaO)and some kirschsteinite,tricalcium,etc.and its alkalinity coefficient is 2.35.If the dosage of steel slag powder(non modification)is over 9%,it will be crack when mixed with tailings and cement to produce autoclaved block.The modification of steel slag is conducted by mechanical grinding.The results showed that it is favorable to the strength of autoclaved test specimen while the grinding fineness increased at first.Then if the fineness further increasing,more free oxides will be exposed,resulting the poor system stability and the autoclaved block crack.The wet-curing treatment was used to increase the volume stability of autoclaved system.The results showed that the appropriate pre-curing condition is ‘block curing’,i.e.curing after molded.And the curing regime is 70 ℃& 6 h.The appropriate ratio of steel slag,tailings and cement is 24:70:6,and the compressive strength value of the autoclaved block is 15.8 MPa.It was realized stability treatment in the process of curing stage in autoclaved process.The chemical modification was used to improve the volume stability of steel slag fine powder.It confirmed that the appropriate single modifier can be sodium hexametaphosphate 3%,or sodium dihydrogen phosphate 7%,or water glass 7%(based on steel slag).The compressive strength values of the autoclaved blocks in such cases are above 12 MPa.The appropriate composite modifier is sodium hexametaphosphate 3% and sodium citrate 3% with ratio of steel slag,tailings and cement being 28:67:5,and the compressive strength value of the autoclaved block is 21.7 MPa.The synergistic effect of pre-curing and chemical modification was studied systematically.The results showed that the appropriate synergistic scheme is sodium citrate 2%(based on steel slag)& 70 ℃& 6 h.The results showed that the f-CaO was dispelled almost 80% in the process of pre-curing and the stability of steel slag was improved significantly.Meanwhile,using of sodium citrate can not only inhibit hydration of active component of steel slag and cement in pre-curing process,but also effectivelystimulate the activity of steel slag in autoclaved process.The hydration in the autoclaved process was intensified.When the appropriate ratio of steel slag,tailings and cement is45:51:4 and the sodium citrate is 2%(based on steel slag),the compressive strength value of the autoclaved block is upto 32.8 MPa.The hydration characteristics of steel slag were analyzed by measuring its chemically combined water and free-CaO and by using X-ray spectrometer.For the autoclave process of high volume steel slag contained system,sodium citrate is not only the retarder for hydration of dicalcium silicate and tricalcium silicate in the process of the steel slag modification,but also the activator in autoclave process.The hydration process was intensified by the synergistic effect of mechanical grinding,hygrothermal treatment and sodium citrate.The autoclaved process can accelerate the hydration of active component,make C-S-H gel transform to desired cementing material as dicalcium silicate hydrate.The compressive strength value of the autoclaved block is thus improved.