Study on the effect of CaCO3 whiskers on carbonized self-healing cracks of cement paste: Application in CCUS cementing

•CaCO3 whiskers improve the compressive strength of the CCUS well cement paste.•CaCO3 whiskers improve the carbonation self-healing performance of cement paste.•CaCO3 whiskers accelerate the self-healing of cement paste cracks. The cracking damage of the CCUS downhole cement sheath is inevitable. In this study, a high concentration of CO2 reacted with the CaCO3 whiskers to induce CaCO3 deposition so as to improve the self-healing performance of the cement paste cracks. The characterization techniques such as compressive strength meter, μ-CT, X-ray diffractometer (XRD), thermogravimetric analyzer (TG) and environmental scanning electron microscope (ESEM) were used to study the effect of the CaCO3 whiskers on the self-healing performance of cement. The compressive strength growth of the cement pastes with and without the incorporation of the CaCO3 whiskers after carbonation self-healing reaction for 28 days was 1133% and 960%, respectively. The analysis of the crack volume of the cement pastes before and after carbonization by μ-CT revealed that the self-healing rate of the crack volume of the cement paste mixed with the CaCO3 whiskers was 55.24%, which was 18.32% higher than the system without any CaCO3 whiskers. In addition, the XRD and TG analyses demonstrated that the content of Ca(OH)2 in the cracks of the CaCO3 whisker cement decreased on increasing the carbonization time, which indicated that the CaCO3 whisker cement had a high extent of Ca(OH)2 involved in the carbonization reaction. Further, the ESEM results confirmed that the surface of the incorporated CaCO3 whiskers became rough, and the carbonized product (calcite) filled the cracks and pores, thus, making the cement paste cracks self-healing.