Gypsum plastering mortars with Acacia dealbata biowaste additions: Effect of different fractions and contents on the relative humidity

Hemihydrate gypsum is a very eco-efficient binder. Gypsum plasters were commonly used in the past and should be still chosen nowadays for being an eco-efficient choice. However, their hygroscopicity and contribution to act as moisture buffer are not very high. The present study analyses the hygrothermal behaviour of mortars based on gypsum and modified with the addition of residual biomass of A. dealbata, an invasive species in Portugal. Five different fractions of the plant were tested as additions for mortars, at incorporation levels of 5% and 10% by volume, with the purpose of enhancing the moisture buffering of the plasters without jeopardizing other properties. The study found that the addition of A. dealbata increases their hygroscopic behaviour. In some cases (bark fraction) the Moisture Buffering Value of the reference mortar is triplicated, and the behaviour is comparable with high hygroscopic plasters as clay-based ones. However, biological colonization must be controlled.