Reducing carbonation degradation and enabling CO2 sequestration in alkali-activated slag using cellulose nanofibers

Abstract

This study evaluated the role of cellulose nanofibers (CNF) in reducing the carbonation degradation of alkali-activated slag (AAS) samples. AAS samples prepared with different dosages of CNF (0 %, 0.10 %, and 0.80 % by weight of the binder) were exposed to natural and accelerated carbonation for up to 90 days. The effects of carbonation on the microstructure of AAS paste samples were monitored using FTIR, XRD, TGA, MIP, and BSE/SEM. It was observed that after 90 days of natural carbonation, the control batch exhibited a reduction in compressive strength, whereas the CNF batches showed an enhancement. Notably, the CNF-containing batches maintained consistent strength over time, with no reduction in strength. Similarly, after 90 days of accelerated carbonation, CNF 0.10 % and CNF 0.80 % showed an increase in compressive strength compared to the control batch. Despite this enhancement in compressive strength, microstructural studies indicated that the addition of CNF increased the extent of carbonation, leading to a higher amount of CaCO3 formation and C–S–H/C-A-S-H decalcification compared to the control batch. The beneficial effects of CNF on the strength despite increased C–A–S–H decalcification are attributed to their reinforcing effects and the ability to form composites with CaCO3.