Entrained air and freeze-thaw durability of concrete incorporating nano-fibrillated cellulose (NFC)

Abstract

NanoFibrillated Cellulose (NFC) has consistently proven effective at improving some key properties of cement-based materials. However, till date, the effects of the NFC on the freeze-thaw (F-T) durability of concrete has received little attention. This study aims to fill this gap by first evaluating the fresh, entrained air content of 0.65 and 0.40 water-cement ratio, Plain and Plain +0.1 % NFC concrete mixtures prepared with and without an Air Entrainment Admixture (AEA). Micro computed tomography scan (CT-Scan) was also utilized in investigating the effects of the NFC on the entrained air characteristics of hardened concrete specimens. Thereafter, water-saturation process, F-T durability via, changes in specimen mass, Relative Dynamic Modulus of Elasticity (RDME) were investigated, and strain accumulation was monitored until specimens failed or 300 F-T cycles were attained. Relative to Plain concrete mixtures, test results showed that entrained air content values of Plain +0.1 % NFC mixtures were lower, causing the effective void spacing to significantly increase. However, RDME and strain measurements indicated that F-T internal damage progression in NFC-modified concrete mixtures prepared without an AEA was considerably slower compared to corresponding Plain concrete mixtures. Moreover, the overall F-T performances of air-entrained, Plain and Plain +0.1 % NFC concrete specimens were comparable despite that the latter set of specimens had lower entrained air content, with wider entrained air void spacing. Besides impeding the saturation process of specimen, the NFC enhanced the strain capacity of concrete, and the significant contraction of specimen on exposure to cooling-temperatures was helpful in mitigating expansive F-T damage process. Therefore, for applications where strength reductions associated with air-entrained plain mixtures are undesirable, the NFC will be very beneficial for the production of high-strength and F-T durable concrete.