Abstract

During the last century, cement has developed into the most important building material in the world, and it is responsible for ~7% of all man-made CO2 emissions. Various measures have been proposed or implemented to reduce the carbon footprint of the cement industry such as improving the energy efficiency, use of renewable energy, and carbon capture and storage technologies. The development of novel cements-also termed as “sustainable” or “green” cements has also been considered. Two promising sustainable cements are alkali-activated slag cements (AAS) and MgO-based cements. However, AAS suffers from large drying shrinkage and the use the caustic alkalis. In addition, previous studies demonstrated that the characteristics of MgO have a significant impact on the properties of the MgO-based cements. The current study dedicates to develop novel reactive MgO-based cements with supplementary cementitious materials and to explore the role of reactive MgO in AAS cements. In the first section, a thorough characterisation of 14 commercial reactive MgOs was performed, based on which the MgOs were grouped into 3 categories. Then two novel MgO-based cements, namely, reactive MgO-microsilica cement and reactive MgO-slag cement were studied in terms of their mechanical and hydration properties. The hydration mechanisms between reactive MgO and microsilica/slag were proposed based on various analytical techniques such as XRD , TGA, SEM /EDS. In addition, the effect of the characteristics of MgO on the performance of the cement pastes was discussed. In the last section, three reactive MgO-based ternary cement systems, namely, reactive MgO-CaO-slag, reactive MgO-waterglass-slag and reactive MgO-sodium carbonate-slag cement, were investigated in terms of their mechanical, drying shrinkage and hydration properties. The effect of the reactivity and content of MgO on the performance and hydration products of the AAS was discussed.