Blast furnace slag-Mg(OH)2 cements activated by sodium carbonate

Abstract

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 Na₂O/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.