Gypsum Mortars with Acacia dealbata Biomass Waste Additions: Effect of Different Fractions and Contents

In recent decades, interest in the eco-efficiency of building materials has led to numerous research projects focused on the replacement of raw materials with mineral and biomass wastes, and on the production of mortars with low-energy-consuming binders, such as gypsum. In this context, five different fractions (bark, wood, branchlets, leaves, and flowers) of Acacia dealbata—an invasive species—were evaluated as fillers for premixed gypsum mortars, at 5% and 10% (vol.) addition levels and fixed water content. Although these biomass fractions had different bulk densities (>50% of variation), all the mortars were workable, although presenting different consistencies. As expected, dry density decreased with biomass addition, but, while mortars with addition at 5% presented a slight shrinkage, a slight expansion occurred with those with 10% addition. Generally, the mechanical properties decreased with the biomass additions even if this was not always proportional to the added content. The wood fraction showed the most positive mechanical results but flexural and compressive strengths of all the tested mortars were found to be higher than the lower standard limit, justifying further studies.