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%) to produce mortar samples. The heat of hydration and microstructural studies confirmed that none of the selected CNFs negatively affect the early-age cement hydration. Dynamic vapor sorption (DVS) isotherms revealed that the addition of CNFs 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 CNFs 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 both DCNF and LCNF-containing batches, the strength reductions were less than 20% due to the sulfate exposure. Moreover, the expansion due to the ASR of CNF-containing mortar bars was nearly 97% lower than the samples without CNFs after one year of exposure test. For all the tested parameters, LCNF-containing samples showed better performance compared to DCNF samples.