Physico‐mechanical characteristics of hydrating tetracalcium aluminoferrite system at low water: Solid ratios

Tetracalcium aluminoferrite (C 4 AF) mixed with gypsum in amounts of 0, 5, 10, 20 and 30% was hydrated at 25 or 80°C, either as discs (formed at pressures of 140 and 690 MPa to obtain an effective water:solid ratio of 0.08 and 0.13, respectively) or in powder form at water:cement ratios of 0.5 and 1.0. Hydration products formed at periods ranging from a few minutes to 7 days were identified and estimated. The sequence of hydrate formation and the accompanying length changes were also determined. The formation of hexagonal hydrate, cubic hydrate, ettringite, low sulphoaluminate series and their interconversions was primarily dependent on gypsum content, temperature, and initial water:solid (w/s) ratio. The study indicates that ettringite need not necessarily be a precursor of the formation of low sulphoaluminate hydrate when hydration is carried out at a very low w/s ratio at 80°C. The microhardness and porosity characteristics of the hydrated products were compared after 2 days of hydration. The relative contribution of low sulphoaluminate, ettringite, and other hydrated phases on strength development were assessed.