Structure Of Agent Research Articles

The role of crystalline admixtures in the long-term healing process of fiber-reinforced cementitious composites (FRCC)

Crystalline admixtures (CΑs), categorized as permeability-reducing admixtures according to ACI-212, are additives serving in the construction industry for decades and have recently been used as self-healing promoters. Although substantive research has been done on concretes' durability properties and healing efficiency at the macroscopic level, limited information was available regarding its microstructural features and chemical properties. Therefore, this paper aimed to analyze fiber-reinforced cementitious composites (FRCC) with polypropylene fibers (PP) in the long-term healing process. Initially, an analysis of the CAs raw materials was carried out. Then, the concrete compositions' physicomechanical properties were tested. For the healing analysis, specimens were pre-cracked after 28-days with an estimated crack width between 50 and 500 μm. The specimens were cured in three healing conditions: seawater immersion at 20 °C, immersed in tap water at 20 °C, and wet/dry cycles. The healing rate was evaluated based on the crack closure, recovery of compressive strength, and sealing efficiency through water absorption. An almost perfect surface healing was observed for specimens immersed in seawater and tap water. At the same time, the wet/dry condition proved to be insufficient for both CAs types. The analysis of the healing material highlighted significant differences in the agent's structure at the surface and inside the crack. Also, the influence of other compounds, such as Mg, during the hydration of C3S to the healing agents has been analyzed, indicating M-S-H compounds, magnesium calcite, and brucite according to SEM and XRD analysis.

Hydrothermal Transformation of Titanate Scrolled Nanosheets to Anatase over a Wide pH Range and Contribution of Triethanolamine and Oleic Acid to Control the Morphology.

Mild hydrothermal conditions used for the treatment of titanate scrolled nanosheets (SNSs) suspensions (140 °C, 72 h) resulted in a large variety of anatase TiO2 anisotropic nano-objects depending on the studied parameters: influence of the medium pH and the presence or not of structuring agents (SAs). The present work shows that such a hydrothermal treatment of the SNSs, whatever the pH, resulted in the formation of single-crystalline anatase nanoneedles (NNs) with a specific crystal-elongation direction and a pH-dependent morphological anisotropy with aspect ratios (ARs) from 1 to 8. The SNSs suspensions were prepared by the conventional ultrabasic treatment of TiO2 with NaOH, followed by washing with HNO3 to different pH values. The crystal size of the anatase TiO2 obtained from this hydrothermal treatment increased with the pH of the suspensions, from 15 nm nanoparticles (NPs; AR = 1) at pH 2.2 to 500 nm NNs (AR = 8) at a pH 10.8 with a long axis systematically along the anatase [001] direction. Triethanol amine and oleic acid were used as SAs. Their respective influence, when acting on their own, had little influence on the control of the size, shape, or polydispersity of the NNs. However, their concomitant use provided a much better control of not only the size and polydispersity, which was strongly reduced, but also on (i) the shape and morphology giving rise to a controlled access to well-defined nanorods as opposed to nanoneedles and (ii) the crystal phase purity eliminating the few percent brookite still visible in the X-ray diffraction patterns of samples prepared in SA-free conditions. This approach offers an on-demand control over the production of anatase morphologies with defined aspect ratios.

Interfacial properties of regenerated cellulose fiber/polystyrene composite materials. Effect of the coupling agent's structure on the micromechanical behavior

AbstractThe interfacial properties of polystyrene/regenerate cellulose fiber composite materials are characterized using micromechanical tests such as the single fiber fragmentation and microbond (“microdrop test”). The cellulose fibers were grafted with different copolymers of different chemical structures as well as different molar masses ranging from 300 to 18,000 (ASA, jeffisocyanate, commercial poly)styrene‐co‐maleic anhydride and “home‐made” poly(styrene‐co‐TMI). The two polystyrene based copolymers have been shown to be miscible with polystyrene. It was found that the higher improvement of the interfacial shear strength was obtained when the fiber is grafted with the higher molecular weight, i.e., the poly(styrene‐co‐TMI).