Effect of nanocellulose on early hydration and microstructure of cement paste under low and high water-cement ratios

The early hydration and microstructure of cement paste with nanocellulose (CNC) at low and high water-cement ratios (0.3 and 0.5) was investigated coupled with isothermal calorimetry (IC), scanning electron microscopy (SEM), and X-ray diffraction (XRD). IC results showed that at both water-cement ratios, CNC prolonged the ending time of the induction period and acceleration period and reduced the main exothermic peak to inhibit early hydration. The inhibition effect became more significant with the increase of CNC dosage. XRD results showed that CNC inhibited the formation of ettringite and portlandite, and SEM images also confirmed that CNC delayed the formation and deposition of early hydration products. Interestingly, the inhibition effects of CNC on early hydration exotherms and hydration products at low and high water-cement ratios were different. At a water-cement ratio of 0.3, CNC inhibited the cumulative hydration heat of cement paste until 120 h. In the presence of CNC, porous microstructures were formed later, and the appearance of needle-like C-S-H gels was also delayed. At a water-cement ratio of 0.5, the inhibition effect of CNC gradually disappeared with increasing hydration time. After 24 h of hydrating, the needle-like C-S-H gels appeared first in CNC-cement paste, and the early-formed structure was also denser than pure cement paste. Additionally, the different influence reasons of CNC on early hydration under high and low water-cement ratios were explained from the perspective of charge adsorption and free water content.