Study On Preparation And Mechanism Of One-part Alkali-activated Slag Cementitious Material With Quicklime,slaked Lime And Sodium Carbonate

At present,the NaOH and water glass were commonly used in the researches of alkali-activated slag(AAS)cementitious material at home and abroad.Although the AAS prepared by NaOH and water glass has excellent strength,there are many problems such as quick setting time,severe shrinkage,complicated preparation and high cost etc.The one-part AAS cementitious material with quicklime,slaked lime and sodium carbonate as activator is expect to has the advantages of longer setting time,smaller shrinkage,better cracking resistance and lower cost etc,which needs further study.With NH(NaOH)as control group,the activators of CNC(quicklime＋sodium carbonate,1:1 in molar),CHNC(slaked lime＋sodium carbonate,1:1 in molar)and CCHNC(quicklime+slaked lime+sodium carbonate,0.5:0.5:1 in molar)were used to mak:e one-part alkali-activated slag cementitious material.The dosage(4%,5%,6%and 7%,namely the mass ratio between NaOH generated in the reaction of CNC,CHNC and CCHNC and the total of activator and slag)of each type ac tivators were changed to take study on the apparent pore solution pH,setting time of paste and fluidity,strength(compressive and bending strength),autogenous shrinkage of mortar.The type,quantity,morphology and pore structure of hydration products were studied by using XRD,TG-DSC,MIP and ESEM-EDS,and the hydration mechanism was revealed.The main conclusions were as follows:1.The apparent pore solution pH of paste is NH>CHNC>CCHNC>CNC under the same dosage of activators,and the CO32-ions in CNC,CHNC and CCHNC play a role of delaying setting time and decreasing fluidity loss rate of mortar.Therefore,the setting time is NH<CHNC<CCHNC<CNC and the fluidity loss rate of mortar is NH>CHNC>CCHNC>CNC..2.The apparent pore solution pH of paste is invers-ely proportional to setting time and directly proportional to fluidity loss rate of mortar.Under the same type activator,the apparent pore solution pH of paste increases,the setting time be shortened and the fluidity loss rate of mortar increases with the increase of activator dosage.3.On the mortar compressive strength at 56 d,when the activator dosage is low,the quantity of C-S-H is small and when the activator dosage is low,there are amount of micro-cracks in C-S-H.All of the compressive strength of NH,CNC,CCHNC and CHNC increase first and then decrease with the increase of activator dosage,and the optimal activator dosage of each groups are 5%,6%,5%and 4%.All the apparent pore solution pH of paste corresponding to above groups are between 12.70 and 13.10 in the first 41 h age,which is beneficial for the formation of AAS with excellent strength.4.Under the activator dosage of 5%,the nominal crystal-gel ratio is NH<CHNC<CNC<CCHNC,and the autogenous shrinkage is NH>CHNC>CNC>CCHNC.For the activator of CCHNC,the quantity ratio of calcite crystal and C-S-H increases and then decreases with the increase of activator dosage(namely the nominal crystal-gel ratio increases first and then decreases),and the autogenous shrinkage decreases first and then increases.The nominal crystal-gel ratio is biggest and the autogenous shrinkage is smallest when the activator dosage is 50%in CCHNC.