Research On Low Temperature Synthesis Of Calcium Sulphoaluminate Cement From Industrial Waste

In this paper,coal gangue,steel slag and other industrial waste as main raw materials,research on the high iron,low iron and non iron system of the CaO-SiO₂-Al₂O₃-SO₃-Fe₂O₃ system.Using a new process of hydrothermal synthesis-low temperature calcination,calcium sulphoaluminate cement clinker was compounded.The hydrothermal synthesis products,cement clinker minerals and hydration products were analyzed by X-ray diffraction,the microscopic morphology of hydrated samples was observed by scanning electron microscopy.The f-CaO content of clinker,compressive strength,chemically combined water content and Ca?OH?2 content of hardened samples were determined.The effect of hydrothermal temperature on the composition of hydrothermal precursors was studied,the results showed:In CaO-Si O₂-Al₂O₃-SO₃ system,the main composition of 80 ? hydrothermal precursors are Ca6Al₂?OH?12?SO₄?3·26H2O and Ca?OH?2,and also CSH gel generate;in Ca O-Si O₂-Al₂O₃-SO₃-Fe₂O₃?low iron?s y s t e m,t h e c o m p o s i t i o n o f 9 5 ? h y d r o t h e r m a l p r e c u r s o r a r e AFt?Ca6Al₂?OH?12?SO₄?3·26H2O,Ca6Fe₂?OH?12?SO₄?3·26H2O?,hydrated garnet?Ca3Al₂?SiO₄??OH?8,Ca3AlFe?SiO₄??OH?8?,AFm?Ca4Al₂SO10·12H2O,Ca4Fe₂SO10·12H2O?,Ca?OH?2 and a large amount of CSH gel,in Ca O-Si O₂-Al₂O₃-SO₃-Fe₂O₃?high iron?system,the composition of 130 ? hydrothermal precursors are A F m,h y d r a t e d g a r n e t a n d C S H?I?.The effect of calcination temperature on the mineral phase of calcined product was studied,the results showed:In CaO-SiO₂-Al₂O₃-SO₃ system and CaO-SiO₂-Al₂O₃-SO₃-Fe₂O₃?low iron?system,when the calcination temperature is900¹100 ?,the main phase of calcined samples is C5S2$,?-C2 S,CaSO₄,CaO and C12A7,as well as a small amount of calcium sulphoaluminate generate;in CaO-SiO₂-Al₂O₃-SO₃-Fe₂O₃?high iron?system,at 750 ?,the main phases of calcined samples are CaSO₄,C5S2$,C12A7 and CaO,as well as a small amoun of C4A3$,C4A3-x Fx$ and ?-C2 S,when the calcination temperature is 950 ?,the formationof C4A3$,C4A3-xFx$ and ?-C2 S is increased,when the calcination temperature is1050 ?,the main phase is C4A3$,C4A3-xFx$ and ?-C2 S.The effect of gypsum content on the mechanical properties of CaO-SiO₂-Al₂O₃-SO₃-Fe₂O₃?high iron?system?respectively use slag and calcined coal gangue as main raw materials?cement was studied,the results showed:In the presence of a proper amount of gypsum,calcium sulphoaluminate can be hydrated to form three sulfur type calcium aluminate hydrate,when the gypsum content is 13%,hydration for1 d,the 1 d compressive strength of cement,respectively,compared with the same age period of clinker compressive strength increased by 31.6% and 31.6%;the 28 d compressive strength of cement than the same age clinker compressive strength increased by 64.7% and 57.0%.The microstructure of 28 d hardened slurry was observed by scanning electron microscopy,a large number of CSH gels can be seen,AFt growth integrity,was long fiber,aspect ratio can reach 200³00,intertwined into a network structure.In the sintering process of sulphoaluminate cement clinker for CaO-SiO₂-Al₂O₃-SO₃-Fe₂O₃?high iron?system.The mainly composition of 130?hydrothermal precursors are AFm,hydrated garnet and CSH?I?,free water,interlayer water and combined water of them are gradually removed.Firstly,AFm dehydrated to C3A·CaSO₄,hydrated garnet dehydrates to C12A7,Ca?OH?2 and SiO₂,CSH?I?decomposes to ?-C2 S.The temperature continues to rise,Ca?OH?2 dehydration of CaO,C3A·CaSO₄ decomposes to C12A7,CaSO₄ and CaO,CaSO₄ and ?-C2 S generate C5S2$,C5S2$ will decompose at high temperatures.Finally,CaO and SiO₂ generate?-C2 S,C12A7and CaSO₄ form C4A3$,Fe partially replace Al to form C4A3-xFx$.Due to numerous mesophase appear at 750 ?,1050 ? completely complete synthesis of calcium sulphoaluminate cement minerals,result in the synthesis temperature of clinker is lower than the common sulphoaluminate minerals 150²50 ?.