Performance of nanofibrillated cellulose (NFC) in accelerated alkali-silica reaction tests

This study investigates the influence of nanofibrillated cellulose (NFC) on cementitious matrices subjected to accelerated mortar bar testing (AMBT), used to assess alkali-silica reaction (ASR). Pastes and mortars with different NFC contents (0 %, 0.05 %, and 0.10 % by weight of cement) were analyzed. The specimens underwent 30 days of curing, followed by exposure to 1 N NaOH solution for 30 days at (80 ± 2) °C. Accelerated mortar bar tests were carried out according to NBR 15577 and ASTM C1260, while complementary characterization techniques included mechanical testing, X-ray diffraction (XRD), thermogravimetric analysis (TGA), BET nitrogen adsorption, and microscopic evaluation. The results demonstrate that NFC did not mitigate expansions associated with ASR under AMBT conditions. Before alkaline exposure, NFC provided significant mechanical benefits, increasing compressive and tensile strength by up to 42 % and 53 %, respectively, due to its physical reinforcing effect. However, these improvements were not sustained after exposure, as NFC degradation in the alkaline solution led to the formation of nanopores, reducing mechanical strength. BET analysis revealed nanopore formation consistent with NFC degradation, and complementary tests on NFC films confirmed its instability in NaOH environments. Overall, NFC enhances mechanical performance, but its degradation under AMBT conditions compromises durability and may mask its actual influence on ASR mitigation.