An Investigation on the Effects of Cellulose Nano-Fibrils (CNF) on the Performance of Cement Paste and Concrete (2)
Publication Name: Advances in Civil Engineering Materials
Publication URL: https://www.astm.org/acem20180048.html
Cellulose nanofibrils (CNFs) have the potential to enhance cement and concrete properties because of the way they change both how water is distributed during mixing and how they modify the hydration process. In this work, the effects of CNFs on certain properties of cement paste and concrete were investigated. For the cement paste, workability, shrinkage properties, and compressive strength were investigated. In the cement paste study, 32 batches with variable CNF concentrations in 4 groups with different water-to-cement (w/c) ratios (0.35, 0.40, 0.45, and 0.50) were prepared and tested. Two rheological tests were performed; one used an ammeter to measure torque versus rotational speed, and a second used a standard flow table. Both tests showed a decrease in the workability of cement pastes that was due to the increase in CNF volume for all pastes, which suggests that CNF retains mix water in the fresh state. Thus, the water held in the CNF is not available during initial mixing of the cement paste. The results of the free shrinkage tests for all 32 cement pastes were collected for up to 90 days. Additional results showed that at a low w/c ratio (0.35), adding a small quantity of CNF (0.05 %) can reduce free shrinkage by 13 %. In compressive strength tests, a small dosage of CNF (0.05 %) improved compressive strength (up to 28 %), but higher dosages reduced strength. Results suggest that CNF has a good potential to be considered as a new natural plant-based internal curing agent in cement paste and concrete. For the concrete specimens, the primary focus was on workability effects and compressive strength. In the concrete study, twelve batches with different CNF volumes were prepared, and the corresponding slump results were measured. Results showed that to preserve the slump values, extra water content of 5Ð8 % should be added for every 0.1 % of CNF incorporated in the concrete mixture. Based on compressive strength tests, it has been shown that CNF is the weakest link in concrete microstructures and controls the compressive strength.