Effect Of Mineral Admixture And Carbonization Curing On Performance Of Magnesium Oxysulfate Cement

To reduce environmental pollution induced by the production of Portland cement-based building materials and eliminate the release of solid wastes from industry,this paper will firstly apply both CO2 curing and mineral admixtures in magnesium oxysulfate(MOS)cement.By the way of utilization of solid waste and low-carbon cementitious material,reduce energy consumption and carbon emissions and protect the environment.As a new type of inorganic binders,the MOS cement produced by the light-burned magnesium oxide and magnesium sulfate solution,which with a lower environmental pollution,lower cost for equipment and related manufacture processes and energy consumption than Portland cement due to the main content which its lower calcination temperature than OPC.Besides,the MOS cement achieved many advantageous properties such as high cohesiveness in light-weight panels,low thermal conductivity and no potential for corrosion of reinforcing steel,etc.Nevertheless,the low mechanical strength,poor water resistance and the large drying shrinkage limits the development and application scope of MOS cement.In this paper,pulverized fuel ash(PFA)and ground granulated blast-furnace slag(GGBS)were added to replace Mg O at variable levels of 10%,20%,and 30% by mass of Mg O,respectively,in MOS cement.The results show that the decreasing rate of compressive strength became higher with the more addition of these two mineral admixtures;the incorporation of PFA or GGBS could significantly improve the water resistance of MOS cement.For specimens incorporated by 30% of GGBS,the strength retention coefficient after 28 days of water immersion reached 84.2%.The drying shrinkage decreased with the increase introduction of mineral admixture.Mixtures containing 30% of PFA presented the lowest drying shrinkage of MOS cement which was decreased by 23.3%.Either early or late CO2 curing improved the water resistance and volume stability of MOS cement pastes in this study.However,it is interesting to notice that the specimens received early CO2 curing had a lower strength as compared to the one with late CO2 curing.Finally,the effects of mineral admixtures and CO2 curing on the mechanical properties,water resistance and shrinkage of magnesium oxysulfate cement were studied.It can be noticed that the incorporation of mineral admixture can obviously prevented the compressive strength decrease tendency induced by CO2 curing.Beside,the mineral admixture can further improve the water resistance and reduce the drying shrinkage of MOS cement under CO2 curing.The main hydration product of MOS cement is needle-like 5·1·7 and the M-S-H gel can be induced by the pozzolanic reaction of PFA or GGBS.CO2 curing could further accelerate the formation of amorphous substances in mixtures containing PFA or GGBS.What's more formed the crystal of basic magnesium carbonate at the same time.Therefore,the coupling effect of PFA or GGBS as partial substitution of magnesium oxide(Mg O)and CO2 curing treatment provides a potential method to manufacture MOS cement with higher durability and low drying shrinkage.