Shrinkage mitigation of alkali-activated slag with natural cellulose fibres

Abstract

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.

Comparison of liquid absorption-release of superabsorbent polymers in alkali-activated slag and Portland cement systems: An NMR study combined with additional methods

“…To reduce shrinkage, some chemical admixtures or synthetic mineral admixtures, such as expansion agents [11][12][13] or shrinkage reducing agents [14][15][16], are introduced into the AAS system. In recent years, some researchers also used natural cellulose fibres [17], lightweight aggregates [18], or recycled aggregates [9] as internal curing agents to mitigate the shrinkage of the AAS system. These latter internal curing agent materials are regarded as a water reservoir, which can compensate for the consumption of free water during the AAS hydration process and reduce the capillary stress of the hardened structure, thereby reducing shrinkage.…”

Feasibility of Preparing Steel Slag–Ground Granulated Blast Furnace Slag Cementitious Materials: Synergistic Hydration, Fresh, and Hardened Properties

“…Moreover, with the increase in steel slag content in SGM, there is a slight prolongation of the initial setting time. Some scholars believe that this can be due to the lower solubility of steel slag compared to GBFS [61][62][63][64]. The presence of a large number of inert components, primarily in the form of the RO phase in steel slag, reduces the content of active components.…”

“…The presence of a large number of inert components, primarily in the form of the RO phase in steel slag, reduces the content of active components. These inert components also do not dissolve in an alkaline environment [61][62][63][64][65][66][67][68].…”

Effect of Modified Cow Dung Fibers on Strength and Autogenous Shrinkage of Alkali-Activated Slag Mortar

“…Based on these characteristics, the research and utilization of natural fibers in alkali-activated materials are of great significance, especially in regions that lack fiber resources. Brakat and Zhang [12] indicated that the incorporation of natural cellulose fibers alleviated the autogenous shrinkage of AAS pastes by 35-67%. According to Wongsa et al [13], the addition of sisal or coconut fibers to alkali-activated fly ash mortar enhanced the tensile and flexural strength of the mortar, similar to what glass fiber does.…”