Influence of wetting-drying cycles on wood behaviour of coastal pedestrian walkways

Abstract

In the context of inspection and maintenance actions for beach walkways in the North of Portugal, some samples of wood used in their construction were collected – the Pinus sylvestris wood, widely applied in the country. The sustainability of the beach walkways over natural coastal areas is very dependent on their material durability. One of the main problems of the timber used to build those structures is its behavior under wet-drying cycles. For that reason, this work aimed to simulate the effects of weathering on the long-term bending behavior of pinewood. Weathering slab samples with two decades of service life and new, unused slabs were subjected to wetting–drying cycles and tested between each wetting or drying phase. As the bending test characterizes one of the most representative efforts in pedestrian boardwalk slabs, the bending module of rupture was used as an indicator to characterize the resistance of timber. Thus, in this study, the samples' density, dimensional stability, and mechanical strength were determined at the end of each batch of cycle repetitions. The tests were carried out before and after a set of wetting-drying cycles caused by immersion in water and placement into an oven at 80°C to simulate environmental exposure. Thus, it was intended to simulate the use in service through the realization of successive wetting-drying cycles in a laboratory environment and to evaluate its influence on the density, dimensional stability, and mechanical strength of the pine wood tested. The extreme conditions used in the laboratory pretend to accelerate the degradation of samples and simulate, in a relatively short period, what would need years to occur in service. The results showed that the wood that had never been in service is more susceptible to bending resistance variations with cycles than the one already in service. Thus, after a few wet-drying cycles, the wood without any service life tends to approximate, in terms of bending behavior, to the one with two decades of service. This indicates that the method used could satisfy the need to obtain predictions for long-time behavior in a relatively short period.