Shrinkage mitigation of alkali-activated slag with natural cellulose fibres

Enhancing the properties and performance of green alternatives to ordinary Portland cement is now a significant challenge for many researchers. Alkali-activated slag (AAS) is a promising alternative because it has good durability and is both cost-effective and eco-friendly. However, high shrinkage limits the adoption of AAS. This paper investigates the potential of shrinkage mitigation in AAS paste by combining a low volume fraction of dry and water-saturated natural cellulose fibres (NCFs), which act as an internal curing agent, depending on their porous structure and hydrophilic properties, as well as fibre reinforcement to enhance the mechanical properties. Shrinkage, internal relative humidity (RH), strength and heat flow were tested; microstructural analysis was conducted as well, in order to illustrate the influence of NCFs on the AAS microstructure. The results show that NCFs effectively implement outstanding mitigation of AAS autogenous shrinkage and drying shrinkage by about 35–66·9% and 33·9–51·5%, respectively. Furthermore, the inclusion of NCFs can enhance the flexural and compressive strength by around 4·6–8·0% and 4·7–9·0%, respectively, when compared to the AAS paste. It was evident from the experiments that the evolution of internal RH, which is supposed to be responsible for the high AAS shrinkage, corresponded well to the development of AAS deformation.