Studying the effect of thermal and acid exposure on alkali-activated slag geopolymer

This paper presents a study on thermal stability as well as acid resistance of geopolymer materials prepared from ground granulated blast furnace slag (GGBFS), air-cooled slag (ACS), silica fume (SF) and cement kiln dust (CKD) using 6% of equal mix from alkaline sodium hydroxide and sodium silicate activators. The addition of ACS, SF and CKD as partially replaced GGBFS is investigated so as to improve the mechanical and microstructural properties of the geopolymer mix. Compressive strength tests and scanning electron microscopy were utilised in these studies. Materials were prepared using water/binder of 0·30 at 38°C and 100% relative humidity (RH). Results showed that geopolymer materials prepared using alkali-activated slag exhibit large changes in compressive strength with increasing fired temperature from 300 to 1000°C and possess an enhancement in thermal stability as compared to concrete specimens. Replacement of GGBFS by 15% ACS resists thermal deterioration up to 1000°C. It was suggested to be suitably applied in refractory insulation applications as well as for production of concrete nuclear reactors. On the other hand, geopolymer mixes exhibit low stability when subjected to different concentrations of a mix of nitric and hydrochloric acid in equal parts (1:1). Current studies of geopolymer microstructure are focused on morphology as well as its relationship with compositions and mechanical properties.