Cellulose nanofibres mitigate chloride ion ingress in cement-based systems

Abstract

This study pioneers the use of cellulose nanofibres (CNF) as a means to restricting the chloride-ion ingress in cement based systems. Three CNF variants, differing in their carboxylate content from 0.13 to 1.13 mmol/g of the nanofibre, were introduced to paste and mortar mixtures alike, at up to 1.2% by volume fraction of the dry nanofibre. The reference mixture was a plain system, prepared with CSA Type GU Portland cement. The ingress of chloride ions was investigated per the Rapid Chloride Penetration Test (ASTM C1202) and further assessed by colorimetry. Companion studies were conducted to measure changes to the air-void network and the pH environment within. The results demonstrate that adding CNF significantly impedes chloride-ion penetration, most likely due to a lower porosity in the 10 nm–140 nm range. Higher amounts of carboxyl groups, [COOH], uniformly led to higher CNF efficiency, both for easy workability and for restricting the chloride ingress. So that, for 0.50% fibre volume fraction, and the CNF variant grafted with 1.13 mmol of carboxylate/g, the mortar witnessed a 50% drop in the measured electrical charge as well as in the depth of chloride penetration. The study indicates that the [COOH] groups scavenge the soluble calcium cations Ca2+, from the aqueous phase of the cement paste without, however, altering the pH therein.