Utilization of Eucalyptus Pulp Fibers in Cementitious Materials
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While the use of eucalyptus fibers in the paper industry is common practice, their use in construction materials has only recently attracted considerable interest with increasing demand for alternative, renewable, and economical natural fibers. However, when compared to other types of plant-based fiber used in cementitious materials, eucalyptus fibers have received little attention in the scientific literature, largely due to their shorter length. This research examines the interaction of eucalyptus pulps with cement at early ages, which relates to their use as internal curing agents in cementitious materials, and demonstrates opportunities for their use to enhance mortar and concrete. The results from fiber characterization and internal curing measurements indicate that the internal curing efficiency of the pulps is related more strongly to their physical morphology than to their chemical composition and that fiber with a thicker cell wall are more favorable for internal curing applications. Results from in situ NMR/MRI measurements along with isothermal calorimetry measurements further demonstrate that such pulps release their free water in their lumen structure within 25 hours of hydration. Thus, for the hydration reaction beyond 25 hours, mostly free water in small cell wall pores and bound water in the cell wall are responsible for mitigation of self-desiccation of a cementitious matrix. Therefore, these results confirm that wood pulps having a thick cell wall are beneficial internal curing applications. Results from sorption measurements suggest that eucalyptus pulp behaves like a semi-permeable membrane, in which its selectivity depends on pH and initial ion concentration of the pore solution. Based on these results, it can be concluded that the key mechanisms controlling the migration of entrained water from eucalyptus pulps to hydrating cement paste are capillary draw, water vapor diffusion, and osmosis. Examining mortar properties demonstrates the performance of eucalyptus pulps to mitigate early-age cracking. It was found that eucalyptus pulps improve the restrained shrinkage behavior of mortar at early ages due to the combination of an increase of early tensile capacity, a reduction in elastic modulus, and an improvement in post-cracking toughness. Study of concrete properties also indicates that depending on curing conditions, eucalyptus pulps were found to increase the degree of improve hydration reaction by internal curing. Results also suggest that standard curing conditions potentially underestimate the performance of eucalyptus pulp concrete. Thus, it is recommended that curing and testing conditions be considered with care such that they reasonably represent field conditions and performance.