Blast furnace slag-Mg(OH) cements activated by sodium carbonate.

The structural evolution of a sodium carbonate activated slag cement blended with varying quantities of Mg(OH) was assessed. The main reaction products of these blended cements were a calcium-sodium aluminosilicate hydrate type gel, an Mg-Al layered double hydroxide with a hydrotalcite type structure, calcite, and a hydrous calcium aluminate phase (tentatively identified as a carbonate-containing AFm structure), in proportions which varied with NaO/slag ratios. Particles of Mg(OH) do not chemically react within these cements. Instead, Mg(OH) acts as a filler accelerating the hardening of sodium carbonate activated slags. Although increased Mg(OH) replacement reduced the compressive strength of these cements, pastes with 50 wt% Mg(OH) still reached strengths of ∼21 MPa. The chemical and mechanical characteristics of sodium carbonate activated slag/Mg(OH) cements makes them a potentially suitable matrix for encapsulation of high loadings of Mg(OH)-bearing wastes such as Magnox sludge.