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In this research, a new binder class for wood based composites, named geopolymer binder, was developed based on pozzolanic by-products (e.g. fly ash). Additionally, effects of different amounts of silica fume, as a replacement agent with other aluminosilicate components (e.g. fly ash and metakaolin), have been evaluated in the innovative binder. The Automated Bonding Evaluation System technique was used to characterize the bonding shear strength of the developed geopolymer binder. It was shown that the best shear strength for fly ash based binders was obtained by the lowest press temperature and longest pressing time. The addition of silica fume (from 20% up to 100%) significantly influenced the bonding shear strength in all binder types. Due to the chemical and mineralogical compositions, silica fume displays higher pozzolanic activity than metakaolin whereas fly ash shows lower strength in comparison to metakaolin. The silica fume (100%) based binder has also superior shear strength compared to those of conventional UF resin and other geopolymer binders. Bonding shear strength like that for UF resin was achieved by substituting only 20% silica fume in geopolymer binder compositions.

Geopolymer binders are an emerging class of mineral polymer that can be manufactured from natural raw materials and industrial byproducts containing high amounts of silica (Si) and alumina (Al) in mineral compositions. Various ratios of materials used for manufacturing geopolymer binder have been tested to evaluate the bonding performance of geopolymers with wood by means of tests performed on an automated bonding evaluation system (ABES). Tests with a binder based on sodium silicate water glass (Na 50T) are partly promising, which resulted only 10% lower shear strength than that based on urea formaldehyde. The binder characteristics were significantly influenced by changing the ratio of SiO2:M2O (M=Na or K) and the ratio solid content to chemical base in the water glass. Expectedly, increasing press temperatures and pressing times showed a positive correlation with the curing performance of geopolymer binder. It was also demonstrated that the binder properties can be changed in wide ranges to obtain binders which fulfill the minimum requirements set by industrial users.