Study On Binding Properties Of Modified Slag Cement In Preparation Of Both Sintering-free Bricks Of Respective Muck & Phosphogypsum

Muck and phosphogypsum are the two largest types of solid wastes produced in the currently domestic urbanization and its industrialization.If these solid wastes are not properly been disposal,their accumulation will not only occupy the land,harm the environment,but also have great potential safety risks.In this paper,some solid wastes with potential hydration activity(such as blast furnace slag,abbreviated as BFS,and fly ash)were used as the main raw material to prepare the cementing materials(CM)with high efficiency cementation to grains of muck and phosphogypsum,respectively.The PO52.5(or PO 42.5)cement was used as the alkaline activator for CM.Two kinds of CM specimens were the modified slag cement(MSC)and the phosphogypsum binding cement(PBC),and the MSC was mixed with muck to prepare specimens of sinter-free muck brick and the PBC was mixed with phosphogypsum to prepare specimens of sinter-free phosphogypsum brick by high pressure compression molding method,respectively.The mechanical properties and micro-morphology of resulting specimens of MSC,sinter-free muck brick and sinter-free phosphogypsum brick were characterized by means of using electronic universal testing machine and scanning electron microscope(SEM),systematically.The MSC specimens were prepared using the powders of BFS,PO 52.5 cement,and the excitant which mainly consisted of gypsum as their raw materials.In the preparation and characterization of the resulting MSC specimens,it was found that the compressive strength,flexural strength,and softening coefficients of the MSC mortar specimens were increased at first and then decreased with the increase of the adding content of PO 52.5cement,and they were reached to the maximum values for the resulting specimen with the content of PO 52.5 cement being 24%.The maximum values of the 28 d compressive strength,28 d flexural strength and the softening coefficient for the resulting mortar specimen were 42.4 MPa,10.1 MPa,and 0.93,respectively.The initial setting time and p H value of the resulting MSC paste specimens were also increased with the increase of adding content of PO 52.5 cement.The specimen with the PO 52.5 cement content being28% had the the initial setting time of 232 min and the p H value of 28 days being 13.11.And in the preparation and characterization of the specimens of sinter-free muck brick using MSC as their binding materials,it was found that both the compressive strength and softening coefficient of the specimens were decreased with the decrease of the mass ratio of MSC to muck as the molding pressure being the 10 MPa.Among all the prepared specimens,the resulting brick specimen with the mass ratio of MSC to muck being 1:4 had the 28 d compressive strength being 15.8MPa and the softening coefficient being 0.8,which met the relevant standard requirements in JC/T 422-2007(Sinter-Free Waste Tailings Brick).In addition,the resulting specimens with a mass ratios of MSC to muck being 1:4,1:6,and 1:8 had improved compressive strength after 15 times of dry-wet cycle.In the preparation and characterization of the specimens of sinter-free phosphogypsum brick with PBC as binding materials(which mainly comprised of fly ash,BFS,and PO 42.5 cement),it was found that the compressive strength and softening coefficient of resulting specimens of the free-sinter phosphogypsum brick were increased with the increase of the mass ratio of PBC to phosphogypsum as the molding pressure being 10 MPa.The resulting specimen with mass ratio of PBC to phosphogypsum being1:1 had the 28 d compressive strength being 26.5 MPa and the softening coefficient being0.9.As the mass ratio of PBC to phosphogypsum being 1:1,the compressive strength of the resulting specimens were increased with the elevation of molding pressure.The 28 d compressive strength of the resulting specimen with molding pressure of 10 MPa was increased by 48.6% as compared to that with molding pressure of 5 MPa.However as the molding pressure was higher than 10 MPa,the increase of compressive strength for the resulting specimens were slowly with its increase,and when the molding pressure was raised from 15 MPa to 20 MPa,the 28 d compressive strength of the specimen was only increased by 10.6%.