Behavior of combined fly ash/slag-based geopolymers when exposed to high temperatures

The high temperature performance up to 800◦C of combined fly ash (FA) and slag geopolymers at\ud the ratio of 100, 65/35, 50/50, 35/65 and 100% (wt-%) is presented in this paper. Geopolymers are\ud alternative novel binders to conventional Portland cement and are generally believed to provide superior\ud fire resistant properties due to their ceramic-like characteristics. This paper presents new data on the\ud behavior of geopolymers made with combined FA/slag mentioned previously, which were mixed with\ud alkaline materials with molecular silicate modulus (Ms=SiO2/Na2O) of 0, 0.5, 1.0, 1.5 and 2.0 with\ud sodium (Na) dosages of 4 and 8 (wt-%). Altogether 60 mixes were made yielding compressive strengths\ud between 3 and 83MPa. Behavior of the material to high temperatures was investigated by exposing\ud the specimens to 800◦C and testing for compressive strengths. It was found that as the initial strength\ud increases, the residual strength exponentially decreased. The compressive stress versus strain relationships\ud showed that the ductility of the specimens decreased as the initial strength increased. The ability of the\ud materials with high ductility (i.e. less brittleness) to accommodate thermal incompatibilities arising from\ud uneven temperatures arising during heating is concluded to be the major factor contributing to the reduced\ud strength losses