Use of alkali-activated binder as an alternative for bio-based materials manufacturing

Bio-based materials are being used increasingly widely in construction, owing to their favorable thermal and acoustic performances. The aim of this study is to assess the potential of an alkali-activated binder for the production of Compact Bio-based Blocks (CBB) based on flax shives, for use as thermal insulation in construction. A preliminary study was conducted on the formulation of alkali-activated binders using Granulated Blast Furnace Slag (GGBFS), Metakaolin (MK) and sodium silicate. Such binders are characterized by high compressive strength at a young age, and short setting times. The alkali-activated binders were mixed with flax shives in order to make up the CBBs. The study was carried out on mixture with two different dry apparent density values, with differing Shive/Binder ratios, and two different curing protocols. The parameters studied include the dry apparent density, compressive strength, thermal conductivity and moisture buffer value (MBV). The results indicate that the produced blocks exhibit a bulk density ranging from 360 to 520 kg/m³, a compressive strength between 0.5 and 1.1 MPa, a thermal conductivity varying between 0.11 and 0.13 W/(m.K), and an MBV value greater than 2 g/(m².%RH). Increasing the Shive/Binder ratio leads to higher intergranular porosity (i.e. the porosity between the particles). This results in reduced apparent density, compressive strength, and thermal conductivity, while enhancing moisture buffering capacity. A linear correlation was observed between thermal insulation and humidity-regulating capacity, ensuring comfortable conditions inside the building. Accelerated curing at 60 °C for a period of 24 h leads to rapid setting and improved mechanical strength in the completed CBBs. Owing to their short setting time and their capacity to develop strength at young ages, the alkali-activated binders produced in this study can be considered a promising alternative to replace the binders typically used in bio-based building blocks.