Study On The Influence Of Suspension Preheater Boiler Kiln Dust On The Performance Of Cement And Concrete

In this paper, the work extended towards the influence of suspension preheater boiler kilndust on the properties of cement and concrete combining with the actual production of DCcement plant. The significance level of the dust and other admixtures’ effects on cementperformance was studied, and influence of the dust and limestone on the cement performancewas comparatively studied. Besides, effects of the dust on the performance of grade32.5and42.5Composite Portland Cement were researched. Effect of suspension preheater boiler kilndust on the compatibility of cement and water reducer was also studied.The results show that when the cement is added with suspension preheater boiler kilndust, the water demand of normal consistency is natural, and the setting time meets therequirements of the national standard. The preparation of grade42.5Composite PortlandCement requires that the clinker and limestone amount should be controlled in about70%and3%, and the amount of the dust can be appropriately increased within the scope of the nationalstandard. While grade32.5Composite Portland Cement is prepared, the amount of the clinkerand limestone should be better controlled in about50%and8%, and the amount of the dustcan be appropriately increased within the scope of the national standard. Proper addition ofthe dust and limestone can decrease the water requirement of normal consistency, and shortenthe setting time. In the case of fly ash, slag powder, limestone and kiln dust being usedtogether, the mechanical properties at each age of cement reaches the maximum when theamount of kiln dust is5%. If the amount of kiln dust is larger (10%), the compressive strengthdecreases, but the flexural strength increases at early age and decreases at later period as theamount of limestone grows. Moderate suspension preheater boiler kiln dust can improve earlyand later strength of grade42.5Composite Portland Cement paste. For32.5CompositePortland Cement, the the dust can help to develop the early strength but go against thedevelopment of late strength. The fine SiO2particles from the dust can react with Ca(OH)2from the C3S and C2S hydration to form calcium silicate gel to improve the cement density. Inaddition, suspension preheater boiler kiln dust can promote the formation and growth ofhydrated calcium carboaluminate (hydrated calcium sulphoaluminates) at early hydration. The curve of the rate of hydration heat evolution moves forward and grows after adding thedust into the cement, which indicates that the dust can accelerate the process of cementhydration reaction.The compatibility of the cement and NSF water reducer is improved with a suitableamount of the dust, and the cement paste has a high initial fluidity, without bad phenomenasuch as bleeding isolation and coalescence. However, the cement has a poor compatibilitywith FAS and PC water reducers, which manifests as lower initial fluidity, bleeding isolationand coalescence phenomena obviously. Besides, adding limestone increases the initial fluidityof cement, and fluidity loss is decreased. Limestone is helpful for the compatibility of cementand NSF water reducer, whose effect is similar to the dust.NSF water reducer can make fresh mixed concrete’s workability good, and the initialslump becomes larger with increasing amount of the suspension preheater boiler kiln dust.Besides, when FAS water reducing agent is mixed, the dust can improve the cohesiveness offresh mixed concrete. When the cement deals with PC water reducer, the workability of freshmixed concrete becomes worse with increasing amount of the dust. So the water cement ratioand the dosage of water reducing agent should be controlled strictly. The compressivestrength shows a down tendency with increasing amount of the dust as the mineral admixture.Therefore, the amount of the dust should be controlled at5%from the aspects of mechanicalproperties and durability of concrete.