Laboratory synthesis of C3S on the kilogram scale

An optimized process using amorphous silica for efficient C3S synthesis in the laboratory is reported: an estimated production capacity of ~2 kg C3S within a week is possible. Amorphous silica (fumed silica) was used as raw material and inter-ground with CaCO3 and water for C3S synthesis, the dried raw mixture has sufficient green strength to be self-supporting, which allows large cylinders to be placed in Platinum crucibles. The mineral composition of the sintered sample was quantified with X-ray powder diffraction using Rietveld analysis. C3S with <0.4 wt% of free CaO was sintered at a shortened residence time (≤5 h) when temperatures ≥1550 °C. The efficiency of the C3S synthesis was dramatically enhanced because of 1) increased burnability of the raw mix due to amorphous silica and very fine CaCO3 particles after grinding, 2) simplified sample preparation process avoiding pressing discs and 3) improved capacities of the crucible and furnace.