Compressive strength, static bending and specific gravity of chemically-treated stakes from three structural and general-purpose hardwoods

Abstract

Non-durable timbers, employed as substitutes for the over-exploited traditional species for structural applications, are chemically-treated to extend their service-lives. However, strength properties of treated woods are barely investigated, particularly for tropical species. Some physico-mechanical characteristics (e.g. compressive strength, static bending and specific gravity) of three commonly-preserved, structural timbers (Terminalia superba, Antiaris toxicaria and Celtis mildbraedii) were examined after treatment with an organic preservative (Erythrophleum suaveolens seed extract) and an inorganic type (Pyrinex 48EC) at 0.5 and 1 % concentrations. Treatment was through non-pressure (i.e., steeping) and pressure methods. Specific gravities (SGs) of the stakes (air-dried to 12–14 % mc) increased after impregnation. Chemical retention and SGs were greater for pressure-treated stakes at 1 % than by steeping at 0.5 %. Differences in SG between non-pressure treated stakes at 0.5 and 1 % were not significant (p T. superba > A. toxicaria. Compression and static bending strengths for control were greater than the treated. Stakes pressure-treated at greater retentions and concentration (i.e., 1 %) lost greater strength than those, which went through steeping at lower retention and concentration (i.e., 0.5 %). This implies that limitations in strength characteristics of chemically-treated wood need be properly addressed by wood and engineering industries in the design of standards for timber in construction.