The origin, composition and early age hydration mechanisms of Austrian natural Portland cement

The chemical and mineralogical properties of cement residues and hydration products have been assessed in historical Portland cement mortars. Results indicate a long time of burning and residence and a slow cooling rate. C2AS, CS and under burned raw material residues suggest inhomogeneous heat distribution typical for shaft kilns. Additionally, minor amounts of $-C2S, C5S2$, C4A3$ and CaS refer to the burning of a pyrite-bearing marlstone and a brown coal used as a solid fuel. Monosulfoaluminate intermixed with monocarboaluminate predominantly concentrate in the inner hydration products confirming the absence of interground calcium sulfate as a retarding agent. The distribution of AFm phases suggests the dissolution of sulfur from the sulfur-bearing cement residues and subsequent carbonation in the later stage of hydration. The coarse grain size of the cement and the presumable application of a historical deactivation method resulted in the formation of high microporosity.