Role of delignified and lignin-containing cellulose nanofibers in enhancing durability performances of portland cement composites

This study investigates the effectiveness of cellulose nanofibers (CNF) in enhancing the long-term durability performance of ordinary portland cement (OPC) composites against sulfate attack and alkali-silica reaction (ASR). Two different types of cellulose nanofibers, namely lignin-containing cellulose nanofibers (LCNF) and delignified cellulose nanofibers (DCNF), were used in three different dosages (0.05%, 0.1%, and 0.3% by weight of the cement) to produce mortar samples. The heat of hydration and microstructural studies confirmed that none of the selected CNFs negatively affected the early-age cement hydration. Dynamic vapor sorption (DVS) isotherms revealed that the addition of CNF increased the amounts of C–S–H of the paste samples and therefore, resulted in the densification of the matrix. LCNF and DCNF-containing mortar samples were exposed to 5% MgSO₄ and 5% Na₂SO₄ for 6 months. The results showed that incorporating CNF improved the resistance of mortar against sulfate attack. Specifically, after 6 months of sulfate exposure, the compressive strengths of the control samples were reduced by nearly 50%. In the case of 0.3% DCNF and 0.3% LCNF-containing batches, the strength reductions were less than 20% after the same sulfate exposure duration. Moreover, the expansion due to the ASR of CNF-containing mortar bars was nearly 97% lower than the samples without CNF after one year of exposure test. For all the tested parameters, LCNF-containing samples showed better performance compared to DCNF-containing samples.