Effect of elevated temperatures on the performance of metakaolin geopolymer cement Incorporated by cement kiln dust

The aim of the present work was to study the influence of elevated temperatures on the thermal behavior of geopolymer cements based on the incorporation of metakaolin with cement kiln dust. Geopolymer composites were synthesized by partially substituted metakaolin (MK) with 0, 20, 30 and 40 wt% of cement kiln dust (CKD). The mixture of liquid sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) was used as alkaline activator solution with fixed ratio 2.5 and the concentration of sodium hydroxide was 10 Molar. The obtained geopolymer specimens were cured in water at ambient temperature (25°C) for 28 days and then subjected to various elevated temperatures 200°C, 400°C, 600°C and 800°C for 1hour. Geopolymer cements were characterized before and after temperature exposure via visual appearance, X-ray diffraction (XRD), Fourier Transform infrared spectrometry (FTIR) and the compressive strength test. Some selected samples were investigated by using thermo gravimetric analysis (TGA/DTG).The results show that, all geopolymer specimens loss their compressive strength from ambient temperature to 400°C, this is due to the escape of moisture and dehydroxylation of aluminosilicate gel from the geopolymer matrix. However, geopolymer samples gained strength upon heating to 600°C as a result of further polymerization of unreacted silicate species. At 800°C, the geopolymer mix with 20% CKD retained highest strength and thermal stability than other mixes due to viscous sintering process which induced crack healing thus enhanced the mechanical properties of geopolymer under high temperature. This suggests that geopolymer paste that contains 80%MK and 20% CKD can withstand high temperature as well as very suitable for refractory and fire resistance applications.Keywords