Mechanical properties and microstructure of cellulose nanocrystal modified cement pastes subject to chloride erosion

Cellulose nanocrystal (CNC) is promising as a green and environmentally friendly nanomaterial, with potential as an additive to enhance the resistance of cement-based composites to chloride ion erosion. This study aims to investigate the effects of CNC on the resistance of cement pastes to chloride ion erosion from the perspective of mechanical properties and microstructure. The macroscopic mechanical properties analysis of CNC modified cement pastes shows that the optimal CNC content is different under different water-cement ratios. For water-cement ratios of 0.3 and 0.5, the optimal CNC content is 0.1 % and 0.2 %, respectively. The compressive strength, splitting tensile strength and flexural strength of cement pastes are increased by 18.8–22.14 %, 19.4 %–26.38 % and 32 %–44.67 %, respectively after adding the corresponding optimal CNC into cement pastes with 0.3 and 0.5 water-cement ratio. In addition, the use of CNC reduces the mechanical strength loss rate of cement pastes caused by chloride ion erosion. After 90 days of chloride ion erosion, 0.1 % CNC reduces the mechanical strength loss rate of cement pastes by 3.14 %–9.31 % at a water-cement ratio of 0.3, and 0.2 % CNC reduces the mechanical strength loss rate of cement pastes by 5 %–7.32 % at a water-cement ratio of 0.5. The use of CNC significantly improves the mechanical properties of cement pastes before and after chloride ion erosion. The isothermal calorimetry (IC) test, X-ray diffraction (XRD) test, mercury intrusion porosimetry (MIP) test, and fourier transformation infrared spectroscopy (FTIR) test show that the main reason is that the addition of CNC promotes the hydration reaction of cement particles and enhances the degree of cement hydration in the later stage, thereby reducing the porosity, average pore diameter and most probable pore diameter of cement pastes. The reduction of strength loss of cement pastes after chloride ion erosion caused by CNC may be due to the fact that CNC effectively alleviates the increase of macropore proportion, average pore diameter and most probable pore diameter caused by chloride erosion. This study emphasizes the improvement of cement pastes performance by CNC in the chloride environment. It highlights the great potential of CNC as an anti-chloride ion erosion additive to improve the life of infrastructure eroded by chloride ions, which is consistent with the demand for sustainable green construction.