Published online by Cambridge University Press: 21 February 2011
Calcium sulfoaluminate, 4CaO • 3Al2O3 • SO3, forms the basis of a new class of structural cements. Microstructural examination of commercial clinker is not easy because it is quite friable. However, backscattered imaging of impregnated clinker is successful and reveals an unusual pattern. The clinker has a sponge-like texture connecting better-sintered, denser regions. The microstructure is, however, very similar between regions of differing density. Irregular to equant, well-shaped crystals of 4CaO • 3Al2O3 • SO3 are enclosed in a matrix composed mainly of Ca2SiO4 together with a little titanium-rich, ferrite-like phase. The minor phases occluded within ferrite include oxide phases one of which concentrates Pb and Bi; the other, Cr, Fe and Ni. Other minor oxide phases in the matrix include lime, periclase, gehlenite and calcium sulfosilicate and probably bredigite. The crystal chemistry and elemental analyses of the individual phases are presented.