Comparative Evaluation of Gypsum-Based Plasters with Pistachio Shells for Eco-Sustainable Building

Agri-food waste represents a serious problem that can be overcome by converting it into added-value material for the production of plasters for green building; in fact, it can be used as a reinforcement additive in the building material industry. In this study, the performance of gypsum-based plasters with pistachio shell additives was evaluated. Before being used as additives for gypsum-based plasters, pistachio shells were ground at three different grain sizes in order to verify how grain size influences the performance of the material. Tests were then carried out on all the produced mortars to evaluate their chemical and physical characteristics, and interesting results regarding the mechanical resistance of some of the produced materials were obtained. The results showed that the addition of pistachio shells improved mechanical performance in all cases and that the best mechanical performance and water absorption by capillarity were achieved with the 0.5–2 mm pistachio grain size, while the best thermal conductivity was achieved with the 2–4 mm grain size. Summarizing, the best results were obtained with a pistachio shell granulometry of 0.5–2 mm, sand, and a water/gypsum ratio of 0.86–0.74.