Effects of cellulose nanofiber gels on the chloride ingress and freeze/thaw properties of cement paste

The issues of freeze/thaw and chloride ingress pose key durability concerns for concrete materials. This study investigated the effects of cellulose nanofiber (CNF) gels on cement paste's freeze/thaw durability and chloride ingress. Paste specimens were created by replacing water in the mixture with nitro-oxidized CNF suspensions, which form hydrogels in the presence of metal ions (e.g., Na⁺, Ca²⁺) in the pore solution. Three different CNF sources at concentrations of 1 % or 2 % by mass of water were studied. It was found that specimens containing CNF suspensions exhibited improved freeze/thaw resistance characteristics when compared to specimens without CNF suspensions. In addition, transmission X-ray microscopy was used to determine diffusion coefficients, and it was found that specimens containing CNF suspensions had lower or comparable diffusion coefficients compared to those without CNF suspensions. For instance, after 14 days of ponding, the CP specimen exhibited a diffusion coefficient of 0.39 × 10⁻¹² m² s^–1, while specimens with CNF-1 and CNF-3 had values of 0.16 × 10⁻¹² m² s^–1 and 0.33 × 10⁻¹² m² s^–1, respectively, corresponding to approximately 59 % and 15 % lower than the value of CP. However, CNF suspensions prepared from different feedstocks did not yield similar results, so further study is required to establish what CNF characteristics are necessary to yield maximum benefit.