A method of manufacturing a hydratable cementitious material, which includes: a) providing at least one waste material containing calcium, silica, magnesium, aluminium, and/or iron; b) thermally treating each waste material to a first temperature such that surface water vapour present is substantially removed; and c) blending the treated waste material such that the resultant blend has a reactive oxide chemical/physical composition in the following range, by weight of the blend: Calcium Oxide 7.0 to 76% Alumina 0.1 to 30% Iron Oxide 0.4 to 19% Silica Oxide 1 to 36% Magnesia 0.1 to 2%. The resultant blend from step c) may subsequently be mixed with Portland cement.