The effect of stake dimension on the field performance of two hardwoods with different durability classes

Abstract

Timber diversity is associated with virtually all types of wood structures for various end-uses including bridges and railway-sleepers. Some timbers resist bio-degradation and are termed naturally durable. Wood durability is influenced by numerous extrinsic and intrinsic factors; however, knowledge is scant about the role stake dimension plays. Therefore, the field performance of replicates of four dimensions (500 × 50 × 25; 250 × 25 × 12.5; 125 × 12.5 × 6.25; and 62.5 × 6.25 × 3.13 mm) from two commercially important hardwoods ( Milicia excelsa and Sterculia rhinopetala) of different durabilities (i.e., high and moderate, respectively) was investigated for 5 years using the graveyard method with non-durable Ceiba pentandra as a control. Durability parameters assessed were visual durability ratings, hardness, and mass losses. C. pentandra usually performed worst in all parameters. Generally, a steady increase exists in degradation from the thickest stakes (500 × 50 × 25 mm) to the thinnest (62.5 × 6.25 × 3.13 mm). Thus, the greater the stake dimension, the smaller its visual durability rating, mass and hardness losses (i.e. more durable). However, few discrepancies occurred, as the thinnest stakes were often buried deep in the soil, decreasing their chances of getting attacked. M. excelsa remained harder and more durable for stakes of all dimensions (especially the thickest) than those of S. rhinopetala. However, the thinnest M. excelsa stakes unexpectedly recorded mean mass loss of 4.9%, compared with 2.1% for S. rhinopetala. The study shows wood dimension significantly affects its durability, which would inform timber engineers about their wood dimension choices for appropriate end-uses.