Lignocellulose materials as lightweight aggregates (LWA) in mineral bonded composites are a promising renewable resources alternative to mineral-based LWA. However, it has been well-known for decades that they heavily impair hydration of normal Portland cement (NPC) due to dissolution of extractables, e.g. saccharide species. Accelerating chemicals have thus been established to boost the hydration reactions. To overcome any issues of a most favourable “cocktail” of accelerators and to replace Portland cement for environmental reasons, the study at hand opted for calcium sulfoaluminate (CSA) as the mineral binder basis. Their impact on the climate is less than that of Portland cement and their hydration reactivity is much intenser and quicker. Three major steps have been taken to explore the potential of lignocellulose lightweight concrete based on CSA (LLCC) as a sustainable construction and building material:
1. Variety of CSA-based binders: Four CSA-based binders have been explored for their hydration related to conventional NPC. Isothermal calorimetry in conjunction with p-XRD (and qualitative workability rating) revealed most favourable a CSA with 77 wt-% Ye’elimit, 11 wt-% Belite, followed by tricalcium aluminate and anhydrite.
2. Influence of various lignocellulose aggregates: Spruce chips, bark, and shives from bast fiber plants had originally been considered. Shives and spruce chips were used for LLCC generation after preliminary test series. Beyond “qualitative workability”, isothermal calorimetry, mechanical strength testing and final density served as complementary characterization methods. In sum, the shives resulted in slightly better overall properties than the spruce chips.
3. Modfication of lignocellulose aggregates: To reduce the necessary water amounts in compositions with enhanced organic proportions – for increasing strength at practically lowest density – various pre-conditioning modes were applied to the shives and the spruce chips. It has been found that modification towards reducing water uptake on the one hand and releasability of extractables are indeed most beneficial to create LLCC with optimized materials properties.
Finally, to address issues of closed-loop economy, a LLCC sample was crushed and the fraction with large (>1mm) lignocellulose particles implemented in an exemplary LLCC recipe. Mechanical testing results have revealed very beneficial properties, i.e. enhanced strength as compared to expectations derived from the (raw) density.
Conclusively, LLCC has a great potential as an environmentally friendly composite to replace lightweight concrete based on Portland cement with mineral LWA.