Mechanical-thermal performance of gypsum mortars incorporating untreated and alkaline-functionalized pruning waste

This study investigates how the surface condition of pruning waste affects the mechanical-thermal performance of gypsum mortars. Gypsum was partially replaced by lignocellulosic pruning waste at 5%, 10% and 15% by volume, using either untreated waste (PW) or alkaline-functionalised waste (PWF). Fresh and dry bulk density, setting behaviour, Shore C hardness, flexural and compressive strength, water-related properties, thermal conductivity and reaction-to-fire behaviour were evaluated. Statistical analysis assessed the effects of replacement level, waste treatment and their interaction. Pruning-waste incorporation significantly modified mortar performance. Untreated PW progressively reduced dry bulk density, with a maximum decrease of approximately 4.5% at 15% replacement. Flexural strength decreased in all waste-containing mortars, while compressive strength declined with increasing replacement level. Alkaline functionalisation did not produce a statistically significant overall improvement in compressive strength, although G5PWF reached 20.70 ± 1.83 N/mm² and remained statistically comparable to the reference mortar. Thermal conductivity showed a non-linear response. The lowest value was obtained for G10PW (0.3840 ± 0.01 W/m·K), corresponding to a significant reduction of approximately 22.6% relative to the reference mortar. Replacement level, waste treatment and their interaction significantly affected thermal conductivity. No sustained flaming was observed during the non-combustibility test, although the results do not constitute a formal Euroclass classification. Overall, pruning-waste content and surface treatment provided different mechanical-thermal performance balances, supporting their use as design variables for tailoring gypsum-based construction materials.