Effect of cement kiln dust on geopolymer composition and its resistance to sulfate attack

Abstract

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. CKD could provide the necessary environment to activate geopolymer materials depending on water-soluble alkalis and sulfate compounds. Materials used in this investigation are ground granulated blast furnace slag (water cooled slag (WCS)), air cooled slag, CKD, and calcined kaolin. Calcinations process was done by kaolin firing at 750 C for 3 h. 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 WCS-geopolymer formation and activation using 2% NaOH along with 25% CKD results in best enhancement in mechanical as well as microstructural characteristics. Activation of metakaolin by 50% CKD has the lowest mechanical properties due to calcium deficiency that bind geopolymer matrix. Effect of 5% magnesium sulfate on WCS and metakaolin activated by CKD results in an enhancement in their mechanical properties up to 3 months, while subjected to a strength loss up to 6 months.