In this paper, calcium carbonate (CaCO3) whisker as a fiber reinforcement is mixed with steel and PVA fiber to form a multiscale hybrid fiber reinforced cementitious composites (MHFRCC). ASTM standard and post-crack strength techniques are performed to evaluate the mechanical properties of MHFRCC. The 1.25 % long steel fiber, 0.55 % short PVA fiber and 2.0 % CaCO3 whisker specimens showed the best flexural behavior before L/600 deflection. However, 1.5 % long steel fiber, 0.4 % long PVA fiber and 1.0 % CaCO3 whisker specimens presented better crack resistance after L/600 deflection. It is revealed that flexural parameters increase as comprehensive reinforcing index increase. The result showed that the CaCO3 whisker and short PVA fiber provided crack resistance effect at micro-scale and mainly play a dominate role in inhibiting micro-cracking. However, long steel fiber and long PVA fiber showed a better bridging effect of macro cracks at a large deflection.
Nowadays researchers are developing a new hybrid fiber reinforced cement-based composites (HyFRCC). The new HyFRCC can restrain micro-cracking, improves compressive and flexural performance of beams by addition of calcium carbonate (CaCO 3 ) whisker, polyvinyl alcohol (PVA) fiber and steel fiber. In this work, a mix optimization procedure is shown for multi-scale HyFRCC, with steel, PVA fiber and CaCO 3 whisker. The new HyFRCC is explored with addition of coarse sand to further improve its mechanical properties. Additionally, the flexural performance of beam and slabs has been investigated to optimize sand gradation and fiber combination in new HyFRCC. The compressive strength, flexural strength, flexural behavior, flexural toughness, equivalent flexural strength and deflection-hardening behavior of beams and slabs are improved with optimized content of sand gradation, fibers and CaCO 3 whisker. The HyFRCC slab with 1.5% steel fiber, 0.4% PVA fiber, 1% CaCO 3 whisker and optimized coarse sand showed overall best properties. Citation/Citar como: Cao, M.; Li, L.; Khan, M. (2018) Effect of hybrid fibers, calcium carbonate whisker and coarse sand on mechanical properties of cement-based composites. Mater. Construcc. 68 [330], e156 https://doi.org/10.3989/ mc.2018.01717 RESUMEN:Effecto de fibras híbridas, filamentos de carbonato cálcico y arena gruesa en las propiedades mecánicas de cementos compuestos. En la actualidad se están desarrollando nuevos cementos compuestos reforzados con fibras híbridas (HyFRCC, por sus siglas en inglés). Estos nuevos cementos HyFRCC pueden impedir la microfisuración y aumentar la resistencia a compresión y flexotracción de las vigas, mediante la incorporación de filamentos de carbonato cálcico (CaCO 3 ), fibras de alcohol polivinílico (PVA) y fibras de acero. En este trabajo se plantea un procedimiento para optimizar la proporción de fibras (de acero y de PVA) y filamentos (de CaCO 3 ) en un nuevo HyFRCC. Se investiga la influencia de la arena gruesa en sus propiedades mecánicas, además de la resistencia a flexotracción de vigas y forjados a fin de adecuar la granulometría de la arena y la combinación de fibras en el nuevo material. Un buen ajuste entre el contenido y la granulometría de la arena y la proporción de las fibras y de los filamentos de CaCO 3 permite: incrementar la resistencia tanto a compresión como a flexotracción, la tenacidad a flexotracción y la resistencia a flexotracción equivalente; perfeccionar el comportamiento a flexión; y reducir la flecha de vigas y forjados endurecidos. La mezcla que mejores resultados arroja en conjunto contiene 1,5 % de fibras de acero, 0,4 % de fibras de PVA, 1 % de filamentos de CaCO 3 y arena gruesa optimizada. PALABRAS CLAVE: Composite; Microfisuras; Carbonato cálcico; Resistencias a compresión; Resistencias a flexión ORCID ID: M. Cao
The pea aphid, Acyrthosiphon pisum, has an incomplete immune system compared to those of other insect species; some conserved components and pathways in other species are missing in its genome. As a core component of the insect immune system, prophenoloxidase (PPO) genes are retained in the pea aphid. Early studies have also shown the presence of phenoloxidase activity in specific tissues or cells in the pea aphid and suggested its involvement in response to immune challenges. In this study, we knocked down the expression of PPO genes in the pea aphid using double-stranded RNA-based interference, and quantitative PCR analysis and an enzyme activity assay confirmed our success in the PPO gene knockdown. In bacterial and fungal infection experiments, we observed that the knockdown of PPO resulted in more live bacterial cells and fungal spores in the body of the aphids and higher mortality of the aphids after infection. Our study provides evidence supporting a critical role of PPO in the defence of the pea aphid.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.