Low-Energy,Low CO2-Emitting Cements Produced from Coal Combustion By-Products and Red Mud

摘要

Over the past 35 years or so,energy conserving or“low-energy”cements have beenstudied.The research presented herein studied the production and performance ofcalcium sulfoaluminate(CSA)cement,particularly that containing C2S(“belite”),termedCSAB,and CSA with calcium aluminoferrite,termed CSFAB.These cements areproduced at lower temperatures than Portland cement and require less energy to mill.Furthermore,they require less limestone in the raw mix than Portland cement,so thereare less CO2 emissions.However CSA cement requires a high-alumina raw materialsuch as bauxite which is very expensive.The aim of this study was to formulate CSFABcement using fluidized bed combustion(FBC)ash and red mud as raw materials and aminimum amount of bauxite.Mortar specimens were prepared from the CSFAB cementsfor compressive strength and dimensional stability testing.Several CSFAB cements were fabricated using lime,bauxite,FBC ash and red mud.Itwas possible to lower the proportion of bauxite in the raw mix by inclusion of red mudand produce a clinker comprising mainly iron-rich C4AF,C4A3S,and C2S.Goodcompressive strength and expansion results were achieved on a CSFAB clinker thatwas formulated with 17%FBC ash and 15%red mud,and which was milled with 30%FGD gypsum.This cement developed strength mainly from the formation of ettringitefrom the reaction of C4A3S,gypsum and water.The aluminoferrite and belite did notreact appreciably even after 3 months hydration.Cement chemistry notation:C=CaO S=SiO2 S’=SO3A=Al2O3 F=Fe2O3 H=H2O