Preparation of cellulose fibre-sheets and its impact on pore connectivity of cement paste during early hydration

Abstract

This study was aimed at evaluating the size and microstructure of cellulose fibres modified via ultrafine ball-milling methods and investigated the effects of these fibres on the rheological properties, compressive strength, hydration behaviour, and pore structure of cement paste in the early stage of hydration by scanning electron microscopy (SEM), isothermal calorimetry, X-ray diffraction (XRD), and thermogravimetric analysis (TG), low-field nuclear magnetic resonance (LF NMR) and electrical resistivity. The results showed that the ultrafine ball-milling method with a velocity of 500 r/min effectively produced cellulose fibre-sheets (CFS) by rupturing intermolecular hydrogen bonds. And their microstructure was transformed from a “fibrous structure” to a “fibre-sheet structure”, which improved the rheological properties and early compressive strength of cement by bridging effect between the cement particles, hydration products, and CFS. Meanwhile, CFS provided more nucleation sites for hydration products accelerating the early hydration rate without changing the structure of hydration products. Compared to pure cement paste, the cumulative heat released from the CFS-cement paste with 0.3% CFS increased by 14%, reaching 113.34 J/g over 20 h. Besides, CFS altered hydration product distribution and increased product content, thus rapidly decreasing the pore connectivity of cement paste. Hydrating for 12 h, the cement paste containing 0.3% CFS had a reduction in pore connectivity from 0.25 to 0.07, which decreased by 72% in contrast with that of pure cement paste.