ABSTRACT
As to the phase transformations, in blast furnace slag cement pastes increasing amounts of melilite [a solid solution of gehlenite (C2AS) and akermanite (C2MS2)] are formed as the amount of slag in the original cement increases, at the expense of /?-dicalcium silicate, which is formed in Portland cement pastes under similar conditions. In pastes made from cements that contain distinct amounts of fly ash, /?-dicalcium silicate is also the main final decomposition product. In parallel, quartz, which is a common constituent of fly ashes, tends to react at high temperatures with calcium oxide formed in the decomposition of portlandite, yielding additional amounts of dicalcium silicate and reducing the amount of free lime in the material. In pastes made from cements that contain natural pozzolanas, gehlenite (C2AS) may also be formed as a product of thermal decomposition, whereas wollastonite (CS) may be formed if silica fume has been added to the original mix.
