Future ready limes for the AAC industry

Lime is an essential raw material for the production of Autoclaved Aerated Concrete (AAC). Its functionality is triple in this application: The mineral phase giving rise to the mechanical strength of AAC (tobermorite) is formed by the reaction of quicklime (calcium oxide, CaO) with silica (silicon dioxide, SiO₂) under hydrothermal curing. Lime is also providing the alkaline conditions required for the formation of the hydrogen bubbles structuring the mineral foam. Finally, the exothermic hydration (“slaking”) reaction with water is providing the required energy input in the system. Lime is produced by the calcination of limestone (CaCO₃) releasing carbon dioxide (CO₂). Today's limes appreciated for the production of AAC are showing slow reactivity, with t₆₀ values typically higher than 8 and up to 16 min and more. Those limes are obtained by severe calcination, so‐called “hardburning,” which requires a higher amount of energy compared to standard high reactive limes, releasing more CO₂ accordingly. Seeking for improving the carbon footprint of its product portfolio, Lhoist investigates different pathways to produce limes suitable for the production of AAC. This paper presents new lime qualities under development, their slaking behavior, and impact on the typical AAC process steps. The new limes show smooth while modified slaking profiles. The use of such lime qualities will allow for a progressive shift from today's formulation technologies towards formulations with highly improved environmental profile.