Admixtures for concrete and mortar with MgO-based binders: a review from RILEM TC 311-MBC

Magnesia-based cements are an emerging, potential low-CO 2 alternative to Portland cements. Admixtures, which control workability, setting and hardening are crucial for the application of these novel binders in mortar and concrete mixtures. However, research and development in this field are not yet well advanced. Working Group 4 of RILEM TC 311-MBC 'Magnesia-based binders in concrete' critically reviewed recent advances and further perspectives in the field of admixtures for magnesium silicate and magnesium carbonate cements and concretes, focused mainly on plasticizers, accelerators and retarders. Alkali phosphates are very efficient plasticizers, especially for magnesium silicate cements. Also, polycarboxylate ethers work, when rather high dosages are applied, despite that current products are designed for Portland cements. Furthermore, alkali phosphates act both as hardening accelerators and retarders, depending on the type of magnesia-based cements. Carbonates, silicates and organic salts, i.e. magnesium acetate, have been used as hardening accelerators, while certain metal cations and organic anions such as citrate and gluconate have been used as retarders. However, further research is needed to develop admixtures specifically for these two groups of magnesia-based cements which facilitate good workability and strength development.