Rheology, Hydration, and Microstructure of Portland Cement Pastes Produced with Ground Açaí Fibers

Abstract

Açaí (Euterpe oleracea) is a Brazilian typical fruit that is enveloped by natural fibers. This work investigated the effect of incorporating ground açaí fibers (in natura and chemically treated with NaOH and HCl) in 5–10 wt.% replacement of Portland cement on the rheology, hydration, and microstructure of pastes. Rotational rheometry, isothermal calorimetry, X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) were performed to evaluate the cement pastes, in addition to SEM-EDS, FTIR, zeta potential, and XRD for fiber characterization. The results showed that the chemical treatment reduced the cellulose and lignin contents in açaí fibers while increasing its surface roughness. The addition of 5% of either fiber slightly increased the yield stress and viscosity of paste, while 10% addition drastically increased these properties, reaching yield stress and viscosity values respectively 40 and 8 times higher than those of plain paste. The incorporation of 5% in natura fibers delayed the cement hydration by about 2.5 days while 10% in natura fibers delayed it by over 160 h. The chemical treatment significantly reduced this retarding effect, leading to a 3 h delay when 5% treated fibers were incorporated. Overall, the combined NaOH/HCl treatment was effective for açaí fibers functionalization and these fibers can be used in cementitious composites.

Investigation of the Effect of Graphene Oxide on the Properties and Microstructure of Clay-Cement Composite Grouting Materials

“…This can be attributed to the fact that the flocculation structure of the slurry was destroyed and the slurry was continuously diluted under the action of shear stress; that is, the phenomenon of shear thinning occurred. This phenomenon indicates that the slurry had good thixotropic properties, and it had already been reported for other cement-based materials [ 36 ]. The apparent viscosity of the slurry increased rapidly with the increase in GO concentration, mainly because GO plays a role in connecting the flocculation structure and reduces the free water of a system, which leads to greater viscosity.…”

Influence of Ultrasonication of Functionalized Carbon Nanotubes on the Rheology, Hydration, and Compressive Strength of Portland Cement Pastes

“…This can be beneficial, since significant increases in yield stress and viscosity can reduce the flowability of cementitious composites. This can make it difficult for air bubbles to escape from the fresh mix, consequently increasing the porosity of the matrix [70]. Increases in compressive strength of cement pastes with CNT incorporation can generally be explained by the heterogeneous nucleation effect [39,53].…”

Effect of Ornamental Stone Waste Incorporation on the Rheology, Hydration, Microstructure, and CO2 Emissions of Ordinary Portland Cement

“…According to Jiang et al [45], significant increases in yield stress may hinder matrix compaction. Thus, this can increase the matrix porosity [46]. Therefore, OSW can improve the fresh properties of cement pastes.…”