Change in microstructure and compressive strength of alkali-activated slag paste at temperature exposure of 50°C

This paper presents a study on the evolution of strength and alteration microstructure of alkali-activated slag (AAS) pastes exposed to 50°C. Ground granulated blast furnace slag (GGBFS) was used as thestarting material to prepare slags pastes which were then activated with a range of activators. The preliminary results from the study of these pastes are presented. It was found that all the pastes show a significantlystrength loss after exposure to 50°C for 24 hours. This is independent on the activators used. The paste samples were further examined by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electronmicroscopy (SEM) and sorptivity tests. A hypothesis for strength loss is proposed based on the observations in change of microstructure. This hypothesis will be further validated by the study of the AAS pastesprepared by using phosphorus slags.

The properties of fly ash based geopolymer mortars made with dune sand

This paper reports the properties of fly ash based geopolymer mortars made with dune sand. The geopolymer mortars of different cation type, namely sodium based (Na), potassium based (K) and a mixed Na/K, were prepared with dune sand (DS) and river sand (RS). The corresponding geopolymer pastes were also prepared. A series of tests including compressive strength, modulus of elasticity, splitting tensile strength, microanalysis (using scanning electron microscopy), porosity (using mercury intrusion porosimetry), sorptivity and air void (using section analysis method) were carried out. The results showed a strong correlation between strength and porosity of geopolymeric materials. The addition of DS had influences on the chemical compositions and physical properties of geopolymer mortars. These influences were dependent on the type of cation. Based on the results of mechanical properties, DS can be utilised as the fine aggregate for the production of geopolymer based construction material.