Enhancing the mechanica and durability properties of cement mortars by using alumina nanocoating on carbon nanofibers
Abstract
This thesis presents a comparative study on using nanocomposite of aluminum oxide (Al2O3) nanocoating on carbon nanofibers (CNFs) and bare CNFs for enhancing the cement mortars mechanical properties, durability under freeze-thaw conditions, and mitigating the drying shrinkage. Although CNFs work to bridge the cracks in cement and to improve the strength, their pristine surface is relatively inert. On the other hand, metals oxides nanomaterials have shown a remarkable surface reactivity, nevertheless, they offer less bridging role. Herein, we close the gap by combining the two parameters, the bridging, and the surface reactivity. This is done by fabricating porous Al2O3 nanocoating on carbon nanofibers denoted as, Al2O3/CNFs. The Al2O3 layer offers a certain degree of pozzolanas in a form of a nanofilm that possesses a high specific surface area of 274.3 m2/g. Several characterizations such as Transmission Electron Microscopy (TEM), Scanning electron microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) have been conducted to study the coating, mortar's microstructure, and elements mapping. Brunauer-Emmett-Teller and Barrett-Joyner-Halenda (BET-BJH) analysis was employed to detect the porosity, whereas Derivative thermal analysis- differential thermogravimetric (TGA-DTG) and X-ray powder diffraction (XRD) have been coupled to investigate the hydration mechanism. The Al2O3/CNFs samples with mass ratios of 0.125 percent, 0.25 percent, 0.5 percent of the cement were compared with bare CNFs with the same mass ratios of 0.125 percent, 0.25 percent, 0.5 percent, and with a plain sample as a reference. The compressive strength before and after freeze-thaw cycles of the Al2O3/CNFs-0.125 percent and CNFs-0.25 percent have shown the highest performance relative to the reference sample. The mass loss due to the freeze/thaw conditions was significantly reduced by addition of Al2O3/CNFs at different ratios comparing to composites that contain CNFs with different ratios and comparing to reference samples. The better performance was shown with the most reduction obtained for the Al2O3/CNFs-0.125 percent, Al2O3/CNFs-0.5 percent and CNFs-0.25 percent, respectively. In addition, the Al2O3/CNFs-0.125 percent and CNFs-0.25 percent have shown the least drying shrinkage. The results of this study demonstrated that the Al2O3 nanofilm along with CNFs improved the microstructure bridging, enhanced the hydration gel production, and refined the microstructure pores. All these favorable properties improved the overall mechanical properties, freeze-thaw durability, and drying shrinkage.
Degree
M.S.