Interfacial bond behavior between wood chip concrete and engineered timber glued by various adhesives

Abstract

This paper investigated the interfacial bond behavior between wood chip concrete (WCC) and engineered timber (i.e. Cross Laminated Timber (CLT) or Laminated Veneer Lumber (LVL)) intended for adhesively-bonded timber-concrete composite (TCC) panel system application. The WCC was produced by replacing 15% volume of the coarse aggregates with beech wood chips to reduce self-weight and improve the thermal insulation of concrete. Five WCC and five plain concrete (PC) cylinders were tested under axial compression to obtain the compression properties. Pull-off tests of adhesives were conducted to examine the adhesive strength of four typical constructional adhesives, including epoxy, Phenol-Resorcinol-Formaldehyde (PRF), Polyurethane (PUR) and Urea-formaldehyde (UF). Afterwards, engineered timber (CLT and LVL) and WCC blocks were bonded by these four type adhesives for shear test. The shear strengths of timber-WCC blocks were measured and were discussed with respect to failure modes associated with adhesive features. Fracture surfaces across the glue line were examined under an optical microscope and a scanning electron microscope (SEM) to identify the adhesive forms on wood fibers. The compression test results showed that the WCC remained most of the compressive strength (i.e. 92.5%) with a slight decrease in density (i.e. 4.1% reduction) compared with the PC. In the pull-off test, epoxy showed significantly better adhesive strength compared to other adhesives, while PUR failed due to the incomplete curing caused by the lack of moisture at the surface of steel dolly used for the pull-off test. Among the double-bonded shear tests, the PUR performed best for both LVL and CLT blocks.