Modified gypsum compounds: An ecological–economical choice to improve traditional plasters

An investigation was performed on the improvement of properties for commercial hemihydrate by means of low additions of granulated blast furnace slag and pozzolanas like silica fume or fly ash. Results after 180 days for pastes cured under water at 20 °C showed that it is possible to triplicate the compressive strength of plain plaster. The reaction mechanism can be summarized by the total reaction of the hemihydrate in the first 24 h, followed by the slower slag and pozzolanas hydration and interaction of the sulfates with aluminium to form ettringite. Excellent dimensional stability and low density was also observed.

► We studied hemihydrate–slag–pozzolanas pastes with improved performance than plasters.
► The main hydration products are gypsum, ettringite and C–S–H.
► Density is slightly higher than pure plasters but strength is almost triplicate.
► Silica fume additions translate in excellent dimensional stability after 180 days.