Enhancing the durability of cross-laminated timber (CLT) with boron treatment in ground-contact conditions

Cross-laminated timber (CLT) is gaining popularity as a sustainable engineered wood product due to its excellent structural properties. However, its susceptibility to biological degradation in high-moisture environments, especially in ground-contact applications, raises concerns regarding long-term durability. This study investigated the performance of CLT impregnated with Tar & imath;mBor, a boron-based wood preservative, over a six-month outdoor ground-contact exposure period. Three-layer CLT made of timber impregnated with different retention levels of boron were produced using a polyurethane adhesive system. Mechanical and biological resistance properties were evaluated using both destructive and non-destructive testing methods, including modulus of rupture (MOR), modulus of elasticity (MOE), shear strength, and screw withdrawal resistance (SWR). The results indicate that while boron treatment enhances biological resistance, it also leads to reductions in mechanical properties, particularly at higher retention levels. Additionally, significant differences in boron leaching were observed between above-ground and below-ground sections, with below-ground samples exhibiting severe depletion. Regression analysis demonstrated strong correlations between non-destructive and destructive test methods, providing insights into predictive durability assessment. The findings contribute to developing improved preservative strategies for CLT, ensuring its suitability for long-term use in exterior and foundation applications.