Effect of cement kiln dust on Geopolymer composition and its resistance to sulphate attack

Utilization of cement kiln dust (CKD) with its high alkali content in the activation of geopolymer specimens to create nonconventional cementitious binders was investigated. Relatively high alkaline content of CKD is predominant factor preventing its recycling in cement manufacture. It was observed that depending on the water-soluble alkalis and sulfate compounds, CKD could provide the necessary environment to activate geopolymer materials. Materials used in this investigation are ground granulated blast furnace slag (GGBFS), air cooled slag (ACS), cement kiln dust (CKD) and calcined kaolin. Calcinations process was done by kaolin firing at 750°C for 3 hours. Alkaline activation by 2% NaOH along with the added cement dust was studied as compared with that not activated by sodium hydroxide. Curing was performed at 38°C under 100% relative humidity. Results showed that 25% CKD is the optimum ratio for geopolymer formation and activation of ggbfs by 2% NaOH along with 25% CKD results in best enhancement in mechanical as well as microstructural characteristics. Activation of low iron metakaolin by 50% CKD and 2% NaOH has the lowest mechanical properties due to calcium deficiency that bind geopolymer matrix. Effect of 5% magnesium sulfate on alkali activated water cooled slag and metakaolin (high iron content) by cement kiln dust results in an enhancement in their mechanical properties up to three months, while subjected to a strength loss up to six months.