Roman cements — Belite cements calcined at low temperature

Roman cement was a major material used in the architecture of the nineteenth and early twentieth century across Europe, until it was displaced by Portland cement, and is absent from the palette of materials from which conservationists may now select. Calcination of cement-stones and marls from six sites in Poland, Austria and the UK has been conducted. The resulting mineralogy is dependant upon the characteristics of the original feedstock and the calcination temperatures. The principal hydraulic components are belites and amorphous aluminates. The stable belites in cements calcined at lower temperatures are largely α/ C2S while β C2S is stabilised as the calcination temperature is increased. Other components include uncalcined remnants, lime, brownmillerite and gehlenite. Optimum cements, assessed by compressive strength, were produced at relatively low temperatures, typically in the region of 750 °C. Two strength development profiles have been observed.