Geopolymer as a multifunctional mineral binder to produce laminated veneer lumber: effect of various aluminosilicate powder types on panels and geopolymer binder features

Geopolymer was used as a multifunctional mineral binder to produce laminated veneer lumber (LVL). The main aim of the study was to characterize the various geopolymer binder formulations based on natural kaolin, metakaolin and silica fume. The effect of different combinations of aluminosilicate powder in geopolymer binder was characterized via FTIR, XRD and TGA analysis. The mechanical (shear, bending, and compression) and physical (thickness swelling and water absorption) properties of the LVL specimens were also evaluated. Results showed that characteristic bands attributed to the geopolymer binder were more pronounced with further replacement of kaolin with metakaolin and silica fume. The higher the metakaolin content, the greater the amorphous content of the reaction products. The mechanical properties of the LVL samples strongly depended on the unreacted components (Si and Al molecules) existing in the aluminosilicate powder as well as the Si/Al ratio in geopolymer binders. The content of unreacted components was reduced by decreasing of the kaolin content in the binder formulations. Furthermore, increasing of Si/Al ratio, via addition of silica fume, showed positive influence on kaolin-based binders, while it showed a slightly negative influence on metakaolin-based binders. Although metakaolin is more favored for geopolymer synthesis due to its better mechanical, chemical, thermal and durability properties, the combination of kaolin with metakaolin could enhance its characteristics to be used as an aluminosilicate source for geopolymer binder. Kaolin-based binders showed higher tendency to penetrate into the wood cell lumens compared to metakaolin-based binders.