Characterisation of reactive magnesia and sodium carbonate-activated fly ash/slag paste blends

A system of alkali-activated fly ash (FA)/slag (AAFS) mixtures as a clinkerless cement was investigated with different dosages of Na2CO3, as a sustainable activator. The effect of incorporating various proportions of reactive magnesia (MgO) was also examined. Mechanical, mineralogical, and microstructural characterisation of the cement pastes was carried out using the unconfined compressive strength, X-ray diffraction, thermogravimetric analysis, infrared spectroscopy and scanning electron microscopy. It was found that the strength of Na2CO3 activated FA/slag mixtures generally increased with time and the Na2CO3 dosage. The hydration products were mainly C–(N)–A–S–H gel of low-crystallinity, which is rich in Al and may have included Na in its structure, and hydrotalcite-like phases. Adding reactive MgO in the mixes showed an accelerating effect on the hydration rate as suggested by the isothermal calorimetry data. Additionally, findings revealed variations on the strength of the pastes and the chemical compositions of the hydration products by introducing reactive MgO into the mixtures. ; The financial support of the PhD scholarship for the first author from the Yousef Jameel Foundation and Cambridge Overseas Trust are gratefully acknowledged. ; This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.conbuildmat.2015.06.015