Cellulose nano- and micro-fibers as air lime carbonation accelerators: FTIR analysis of the carbonation kinetics

Air lime mortars are reemerging as an alternative sustainable material for construction and restoration of built heritage. However, their widespread use is still limited by the long hardening times, via carbonation, and limited early strength. A possible sustainable strategy to accelerate the carbonation process and early strength development of these mortars is using natural organic additives, such as submicrometric cellulose fibers. In this study, the effect of three cellulose additives on the carbonation kinetics of air lime mortars is presented. Furthermore, the effect of the cellulose time of addition on the carbonation process was evaluated. Additives were included both during the slaking process and to a hydrated lime paste. Results show that the cellulose fibers accelerate the carbonation of air lime mortars, particularly in the case of micro-cellulose and of micronized CitroCell cellulose sourced from citrus processing waste. When additives are included during slaking, their acceleration effect on carbonation is enhanced. These outcomes suggest that the addition of cellulose additives can enhance both the rate and depth of carbonation, potentially improving the performance and durability of the mortars. It should be considered and further investigated that additivation during slaking might be advantageous not only for cellulose but also for other kind of additives.