Effects of plasma-treated rock asphalt on the mechanical properties and microstructure of oil-well cement

In this study, natural rock asphalt with a high softening point was selected as an oil-well cement admixture. The effects of the asphalt, which was subjected to a low-temperature plasma treatment, on the mechanical properties and microstructure of the cement paste were investigated. The results show that the hydrophilicity of the surface of the rock asphalt, and the interfacial bonding between the asphalt and cement matrix were improved with the use of the low-temperature plasma technology. The addition of the treated rock asphalt reduced the compressive strength of the cement paste but improved its tensile strength. Triaxial stress-strain curves, obtained under static and multicycle loads, showed that the rock asphalt improved the toughness of the oil-well cement paste. The addition of the 3% rock asphalt obviously enhanced the mechanical deformability of the cement paste. The results of the scanning electron microscopy analysis showed that the rock asphalt can deflect cracks and prevent crack propagation. The ability to restrain crack propagation improved as the adhesion between the treated hydrophilic asphalt and matrix cement improved. The results of the nitrogen-adsorption tests and mercury-intrusion porosimetry tests showed that the incorporation of the rock asphalt reduced the number of harmful pores present within the cement composite. The results of the X-ray diffraction (XRD) and thermogravimetric (TG) analyses performed on the asphalt-cement composites showed that the asphalt slightly retards cement hydration.