Long-Term Performance of Wood–Cement Composites: Stabilization Versus Degradation Driven by Waste Type

The valorization of wood waste in cement-based materials offers a promising path toward reducing the environmental footprint of the construction sector. While short-term properties of wood–cement composites have been studied, their long-term durability remains a critical uncertainty for practical application. This study investigates the long-term mechanical behavior of Portland-cement mortars incorporating 5% by mass of four types of wood waste: spruce, oak, beech, and oriented strand board (OSB). Specimens were subjected to flexural and compressive tests after 28 days and approximately 242 days of curing under natural laboratory conditions to assess the evolution of their properties. The results demonstrate that the long-term performance is highly dependent on the wood type. Composites with spruce sawdust, oak, beech, and OSB exhibited remarkable stability, with strength variations generally within ±8% over the extended period, supporting a scenario of matrix stabilization. In contrast, mortar with spruce shavings suffered a significant strength reduction of approximately 25%, indicating susceptibility to degradation, likely due to its high-water demand and porous resulting matrix. All wood-composite mortars showed a substantial density reduction of 20–36% compared to the reference. The findings confirm that OSB and oak waste provide the best overall performance, combining higher initial strength with excellent long-term stability. This research concludes that carefully selected wood waste can produce durable, lightweight cement composites viable for non-structural applications, thereby supporting the integration of circular economy principles in sustainable construction. Unlike previous studies that primarily assessed short-term strength, this paper provides one of the few comparative long-term assessments under natural curing conditions, highlighting the stabilization–degradation mechanisms across wood types.