Study on the early performance of alkali-activated slag-fly ash binders incorporating cellulose nanocrystals

This study investigated the impact of cellulose nanocrystals (CNCs) on the early mechanical properties and chemical shrinkage of alkali-activated slag-fly ash binders (AASFB). Various characterization techniques were employed to explore the relationships between hydration kinetics, mechanical properties, chemical shrinkage, and microstructure of AASFB. The experimental results indicate that the incorporation of an appropriate amount of CNCs delays the early hydration process, fundamentally suppressing the chemical shrinkage of AASFB. Mercury Intrusion Porosimetry (MIP) tests and Scanning Electron Microscope (SEM) results revealed that the formation of gel stacking orderly reduced the porosity of AASFB by 1.69%, leading to a denser microstructure. X-ray diffraction (XRD) and Thermogravimetry Analysis (TGA) results showed a reduction in the early formation of gel products, resulting in a slight decrease of 7.69% in early compressive strength. However, as the reaction progressed, the compressive strength of samples containing 0.1 wt.% CNCs significantly increased by 8.6 MPa in the later stages, 6.9 MPa more than the increase of the control group C0. The study concludes by proposing a hydration model for CNCs in AASFB, suggesting that an appropriate amount of CNCs can significantly improve the microstructure and reduce chemical shrinkage. Conversely, a large amount of CNCs may lead to agglomeration within the AASFB, compromising the effectiveness of the mechanism and increasing the risk of structural damage.