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 5–8 % 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.

In this work, the effects of cellulose nanofibrils (CNFs) on workability, hydration reaction, microstructure, early age shrinkage, fracture properties, flexural strength, and compressive strength of cement paste were investigated. Six batches with variable CNF concentrations with the same water-to-cement (w/c) ratio (0.35) were tested. Flow table test showed a reduction in the workability as CNF dosage increased. Isothermal calorimetry (IC) tests showed that after 3 days, degree of hydration (DOH) improved up to 8% because of the addition of CNFs. Thermogravimetric analysis (TGA) tests at 7 and 28 days showed no significant changes in DOH for all pastes. After 7 days, mixture with 0.15% CNF resulted in up to 31% improvement in compressive strength. For 0.09% CNF addition, cement paste showed 26% increase in compressive strength after 28 days. Tests revealed that adding a small quantity of CNF (0.06%) along with entraining 0.05 extra water reduces autogenous shrinkage by 49% at a cement paste with w/c = 0.30. For interpreting the results, a tunnels, reservoirs, and bridges (TR&B) model is proposed. This model suggests that, as proposed by others, CNFs can modify microstructure by providing tunnels for transporting water to unhydrated cement grain. Because of their hydrophilicity, CNFs retain water and work as reservoirs (internal curing), which explains the improvement in properties at low w/c ratios. Significant increases in fracture energy (up to 60%) and flexural strength (up to 116%) suggest that CNFs are an effective toughening mechanism, acting as bridges that increase the energy required for crack propagation.