Artificial precursor for alkaline cements

One of the main challenges for the future development of alkaline cements is the availability of precursors. Traditional precursors (such as coal FA and the BFS) have some limitations concerning quality and quantity (the long term supply is not guaranteed). The progressive closure of coal-fired power plants and changes in steel production in many countries exacerbate the problem. The present work addresses the challenge of fabricating an artificial precursor (via thermal treatment) with a chemical composition similar to a type- C fly ash (∼20 % CaO and SiO 2 /CaO≈ 3 and SiO 2 /Al 2 O 3 ≈ 3). Three temperatures of synthesis were tested: 1000 °C, 1100 °C and 1250 °C. The precursors obtained after thermal treatment of a mixture of chemicals were activated with a 8 M NaOH solution. The temperature of synthesis obviously affected the degree of vitrification. Nevertheless, it can be said that partially amorphous/vitreous precursors, were produced at 1000 °C, developing good mechanical performance. In all cases, compressive strengths above 20 MPa were obtained, after 1 day curing. In cements made with precursors synthesized at 1000 and 1100 °C (amorphous content <70 %), a (N,C)-A-S-H type gel was formed, as the main product of hydration. However, in those cements made with precursors synthesized at 1250 °C (amorphous content ≥99 %), a mixture of (N)–C-A-S-H and (N,C)-A-S-H gels were observed after the hydration process.