Research On Activation Methods Of Kaolinate Clay,Limestone And LC~3 Cement Performance

The carbon emissions of the cement industry are very large,and the development of lowcarbon cement technology meets the needs of the era of energy conservation and emission reduction.Limestone calcined clay cement（LC3）can reduce carbon emissions by about 30%,which is attracting attention at home and abroad,especially in some developing countries.This paper focuses on the activation methods of the two main raw materials（kaolinite and limestone）of LC3 cement,and further develops the energy-saving preparation technology of LC3 cement.It provides certain technical support for the development of LC3 cement.In this paper,the grinding process and grinding aid composition of limestone powder using mechanochemical method were studied.Based on the evaluation indexes of laser particle size and activity index,the optimal grinding aid composition and grinding process of mechanochemical activation kaolinite,as well as the optimal mineralizing agent composition and calcination process of thermochemical activation of kaolinite were studied.Taking rheology and mechanical properties as the evaluation indexes,the effects of different content of limestone powder,calcined kaolinite and gypsum on the properties of LC3 cement were studied.It determined the optimal composition of LC3 cement.The main influencing factors of mechanochemical grinding limestone are the grinding process and the composition of the grinding aid.Grinding process research mainly includes water-solid ratio,feeding amount,grinding time.results show that the higher the water-solid ratio,the poorer the grinding effect,and the grinding effect no longer changes significantly while the water-to-material ratio exceeds 1.0.The feeding amount depends on the capacity of the grinding jar,both high and small amount can affect the grinding efficiency.The longer the grinding time,the better the grinding effect,and when the grinding time exceeds 30 min,the grinding efficiency is reduced.Composite grinding aids are better than every single grinding aid.The optimal grinding aids are propylene glycol（PG）0.2%,triethanolamine（TEA）0.3%,triisopropanolamine（TIPA）0.4%,and sodium lignosulfonate（LS）0.6%.To the mechanochemical activation of kaolinite,kaolinite fineness and activity increase with the increase of grinding time,and fineness is related to activity.The optimal process for activating kaolinite by mechanochemical method is of water-solid ratio 1.0,feeding amount 1100 g,and grinding time 7 h.The single grinding aid sodium hexametaphosphate（SHMP）has the best grinding effect with the dosage of 1.0%,and its activation effect is better than the composite grinding aids.Thermochemical method of activating kaolinite mainly involves calcination process and mineralizing agent composition.The calcination process includes heating rate,peak temperature,constant temperature time and cooling method.The study showed that optimal conditions for activation of calcined clay is a heating rate of 20℃/min.When the heating rate is too fast or too slow,it will be detrimental to the activation effect.Kaolinite activation begins at 450℃,the activation effect is ihghest at 750℃,and kaolinite activation is reduced while exceeds 950℃.When the constant temperature time is lower than 120 min,the longer the constant temperature time,the better the activation effect.The kaolinite activation effect is not significantly improved after the constant temperature time is greater than 120 min.The fancooled kaolinite has a better activation effect than that of the furnace-cooled.The optimal calcination process for thermochemical activation of kaolin is heating rate 20℃/min,peak temperature 750℃,constant temperature 120 min,and fan cooling.The effect of composite mineralizing agent is better than that of every single mineralizing agent.The optimal composition of the mineralizing agent is sodium carbonate（Na2CO3）1.0%,potassium carbonate（K2CO3）3.0%,potassium acetate（CH2CO2K）3.0%,erbium nitrate（Er（NO3）3）2.0%.To the composition of LC3 cement,the results show that the cement contains 6.0%gypsum has good fluidity and mechanical properties.The limestone with fineness of 20～40μm and the content of 6.0%make the cement has highest mechanical properties as well as calcined kaolinite with fineness of 40～60 μm and the content of 22.0%.The optimal composition of LC3 cement is gypsum 6.0%,limestone 7.0%and calcined kaolinite 15.0%.The mechanical properties of LC3 cement are a litter better than ordinary Portland cement.