Comparison of the tensile behaviour enhancement of cement paste incorporated with μm- and mm-scale cellulose fibres at the early curing age

•Cellulose fibres can cause hydration inhibition, especially µm-scale fibre.•TGA-based chemically bound water in cellulose fibres needs to be calibrated.•Mm-scale cellulose fibre has a significant effect on enhancing tensile behaviour.•Fibre length plays a fundamental effect on the tensile properties of cement composites. In this work, one type of commonly used commercial cellulose fibre with lengths ranging from μm to mm is introduced into cement paste at concentrations of 0.1 wt% to 10 wt% to study its effect on enhancing tensile behaviour and microstructural evolution at the early curing stage. Significantly inhibited hydration due to cellulose fibre incorporation is revealed, and the degree of inhibition increases as the length of the cellulose fibres decreases. Additionally, the degree of hydration calculated by the TGA data of cellulose fibre-incorporated cement paste needs to be calibrated against the mass loss of cellulose fibres during heating because it cannot be directly deduced by the TGA data of pure cellulose fibres. Only mm-scale cellulose fibres significantly improve the post-peak ductility, whereas µm-scale cellulose fibres have a weak enhancement effect on the post-peak ductility. It is found that cellulose fibres at both the μm and mm scales can enhance the tensile strength at day 28. Regarding this type of commercial cellulose fibre, it is optimal to adopt the mm-scale cellulose fibres because of their significant effect on improving tensile behaviour.