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) 2 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 Na 2 O/slag ratios. Particles of Mg(OH) 2 do not chemically react within these cements. Instead, Mg(OH) 2 acts as a filler accelerating the hardening of sodium carbonate activated slags. Although increased Mg(OH) 2 replacement reduced the compressive strength of these cements, pastes with 50 wt% Mg(OH) 2 still reached strengths of ∼21 MPa. The chemical and mechanical characteristics of sodium carbonate activated slag/Mg(OH) 2 cements makes them a potentially suitable matrix for encapsulation of high loadings of Mg(OH) 2 -bearing wastes such as Magnox sludge. Novel cements can contain up to 50 wt% Mg(OH) 2 , offering a new route to immobilisation of this nuclear waste constituent.