The Effect of Water Absorption of Cross-Laminated Timber and Glue-Laminated Timber on Concrete Physical and Mechanical Properties

Abstract

This study examines the potential of coating the surfaces of cross-laminated timber (CLT) and glue-laminated timber (GLT) to evaluate the impact of moisture on the physical and mechanical properties of concrete in a timber-concrete composite slab. The C30/37 strength-class concrete was poured to simulate a timber-concrete composite slab on top of CLT and GLT samples. Natural oil (NO) and a flexible two-component waterproofing slurry (WPS) were applied to the timber surface to investigate the effects of water absorption and compare them with those of uncoated timber elements. The density, strength, and surface moisture of hardened concrete were measured in the laboratory after 3, 7, 14, and 28 days. Surface moisture and moisture at a 10 mm depth in the timber were also assessed at the same intervals. Prior to pouring the concrete, the timber surface was sprayed with water to simulate rain during on-site construction. The findings revealed that, among all surface treatments tested, the WPS coating was the most effective in limiting moisture migration, reducing water ingress by approximately 2.5 times in CLT and 2.4 times in GLT after three days. This demonstrates that WPS forms a significantly more effective moisture barrier than the alternative treatments. This reduction directly enhances concrete performance: strength increased by 9.4% (CLT) and 7.8% (GLT) compared to uncoated samples. The proposed solution offers practical benefits in overcoming many challenges related to precipitation and water ingress during construction. The study provides concrete evidence that moisture management strategies are essential for the wider adoption of timber–concrete composite systems in sustainable structural design.