Multiscale experimental study on waste soil co-solidified by CO2 and industrial waste

With the rapid construction and iteration of urban infrastructure in China, substantial amounts of abandoned engineering waste soil have piled up, causing serious environmental pollution and resource waste. To achieve efficient solidification and resource utilization of engineering waste soil, this study examined the use of pure industrial waste residue, WZ01 as the primary solidifying agent and calcium carbide slag (CCR) as the alkaline activator, to reinforce the engineering waste soil. The introduction of carbon capture utilization and storage (CCUS) technology to achieve multiple goals including carbon sequestration and storage of CO2, as well as resource utilization of engineering and industrial waste, was also examined. The feasibility of CO2–CCR–WZ01 synergistic solidification of slag soil was studied using microscale unit cell model multiscale experiments. Unconfined compressive strength tests and CO2 absorption rate tests were conducted to analyze the effects of four factors on the carbonation process: carbonation time (Tc), carbonation temperature (Kc), carbon pressure (Pc), and CO2 concentration (Wc). To determine which of these factors had the best effect on CO2–CCR–WZ01 solidification engineering waste soil, we conducted various micro experiments, such as scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), to explore the micro evolution law of CO2–WZ01–CCR solidified soil and analyze the reaction mechanism of CO2–WZ01–CCR synergistic solidification technology. Finally, indoor model box tests were conducted to analyze the improvement of CO2–WZ01–CCR collaborative solidification technology on slag soil with respect to mechanical and physical properties. The feasibility of on-site construction of the CO2–WZ01–CCR collaborative solidification technology and its application prospects were evaluated from a multiscale perspective. The experimental results show that with an increase in Tc, qu gradually increases and growth rate gradually decreases. As Kc increases, qu gradually increases and the amplification rate gradually becomes faster; As Pc increases, qu shows a trend of first increasing and then decreasing; With an increase in Wc, qu gradually increases and growth rate gradually decreases. The best carbonization effect of engineering slag soil was achieved with Tc = 6 h, Kc = 60 °C, Pc = 600 kPa, and Wc = 50%. The main product generated by carbonization reaction is calcite, which is concentrated on the outer surface of the unit, whereas cementitious products such as C–A–H and C–S–H generated by solidification reaction are distributed in the middle of the unit. Through the synergistic effect of carbonization solidification reaction, the generated products can effectively fill the pores and improve the strength of the slag soil. Under the influence of CO2–CCR–WZ01, the permeability index of the carbonized soil was significantly reduced. The bearing capacity reached 700 kPa, and substantial improvements were observed in the basic physical properties of the soil. The CO2–CCR–WZ01 co-curing technology demonstrates high efficiency, low carbon emissions, and environmental sustainability. This indicates that the technology can significantly reinforce and improve engineering waste soil, making it a promising solution for the resource utilization of engineering residues. Studying CO2 carbonization technology provides research direction and academic support for the low-carbon development of geotechnical engineering, which is of great significance in achieving “Dual Carbon Goals”.