Abstract
In this study, carbon fibers (CFs) were used as toughening materials to improve the mechanical properties of cement stone. The surfaces of the CFs were treated with concentrated nitric acid and sodium hypochlorite to increase the interfacial adhesion between the CFs and the cement. The CFs subjected to surface treatment were evaluated by scanning electron microscopy and infrared analysis to find a significant increase in the number of oxygen-containing groups on the surface. The CFs subjected to surface treatment were added to the cement matrix. The effect of the modified CFs on the mechanical properties of the cement matrix was evaluated by testing the means of mechanical properties. The maximum tensile strength, maximum compressive strength, and ultimate strain of the enhanced cement stone of the CFs treated with sodium hypochlorite increased by 68.2%, 12.0%, and 4.4%, respectively. The maximum tensile strength, maximum compressive strength, and ultimate strain of the enhanced cement stone of the CFs treated with concentrated nitric acid increased by 72.7%, 14.7%, and 4.5%, respectively. The addition of CFs to the cement stone exerted no effect on the type of cement hydration products, as determined by infrared analysis and X-ray diffraction. The toughening mechanism of the modified CFs added to the cement stone was ultimately explored, and the bridging effect, deflection effect, and pull-out effect of cracks were evaluated.
Highlights
Oil-well cement stone may exhibit cracking under various external forces within a depth of several hundred or thousand meters underground
This study is aimed at determining the optimal amount of Carbon fibers (CFs) treated with concentrated nitric acid and sodium hypochlorite blended into cement stone
The FTIR spectra of the normal CF and the treated CF samples, except that of the CF treated with concentrated nitric acid, showed an absorption peak of -NO2 at 1384 cm-1 (Figure 1)
Summary
Oil-well cement stone may exhibit cracking under various external forces within a depth of several hundred or thousand meters underground. Carbon fibers (CFs) exhibit stable chemical properties and have a large aspect ratio; as such, CFs can efficiently transmit interfacial stress and inhibit the formation and development of cracks, enhancing the strength and durability of the cement stone [3,4,5]. Through Raman spectroscopy, XPS, FT-IR, and SEM, it is known that the surface roughness and functional group density of CFs were increased by oxyhydrogen plasma treatment. Kim et al [19] oxidized the surface of rayonbased activated CFs (ACF, KF-1500) with nitric acid and sulfuric acid, respectively. This study is aimed at determining the optimal amount of CFs treated with concentrated nitric acid and sodium hypochlorite blended into cement stone
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