Carbon conversion technology for performance improvement and environmental benefits of ultra-high-performance concrete containing slag

An increasing number of countries worldwide are setting goals for carbon neutrality. To achieve these goals as quickly as possible, the concrete industry needs to adopt new technological innovations. In this study, carbon conversion technology was used to convert gaseous carbon dioxide into a nano-calcium carbonate that was added to ultra-high-performance concrete (UHPC) containing slag, and the macroscopic and microscopic properties and sustainability of the UHPC were investigated. The compressive strength, ultrasonic pulse velocity, and surface resistivity of the UHPC were tested at 1, 3, 7, 28, and 90 days. The microstructure of UHPC was characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Finally, the CO2 emissions of UHPC were calculated and analyzed. The experimental results showed that the addition of nano-calcium carbonate (NC) can effectively improve the compressive strength, ultrasonic pulse velocity, and surface resistivity of UHPC. The heat of hydration, XRD, and TGA experiments showed that the presence of NC significantly accelerated the initial hydration rate of the UHPC. In addition, in the early stage of hydration (1 d), more hydration products can be clearly observed in the TEM and SEM images of the NC-containing samples. Finally, the combined compressive strength, surface resistivity, and CO2 emission calculation analysis revealed that the addition of NC significantly improved the mechanical properties, durability performance, and sustainability of UHPC. This indicates that the application of carbon conversion technology in the field of concrete has good prospects, which can help achieve carbon neutrality more quickly