Utilization of industrial and demolition Waste: preparation and characterization of a novel carbonate paste

• A carbonate paste was proposed for simultaneous carbon sequestration and waste utilization. • Combined monitoring of pH and electrical conductivity revealed the dynamics of Mg²⁺ and Ca²⁺ during CO₂ dissolution in the paste. • Ca²⁺ flocculation on MgO micro-aggregate was observed and explained from electrochemical and colloidal chemistry perspectives. • Control of pore structure via W/C ratio, C/M ratio, and FA porosity is critical for optimizing CO 2 diffusion and carbonation efficiency. Landfilling industrial and demolition waste is an unstainable practice consuming land and posing environmental risks. To mitigate these challenges while promoting carbon reduction and resource efficiency, this study explores the CO 2 activation of industrial and demolition waste to produce a novel carbonated paste suitable for geotechnical and road applications. Magnesium slag (MS), fly ash (FA), and MgO were blended to form a reactive matrix, with recycled aggregate fines (RAF) as the structural skeleton to enhance carbon sequestration. Physical and mechanical properties were examined under carbonation curing, with standard curing as a reference. A 3-day carbonation process significantly activated MS, yielding a strength increase of up to 12.3 times compared to standard curing. Comprehensive chemical and physical properties and the reaction products were detected via pH measurements, conductivity assessments, quantitative X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy to shed light on the reaction mechanisms. The primary strength contributors in the paste were Nesquehonite, Dypingite, Magnesite, and Calcite, which formed through the carbonation reactions of MgO, MS, and RAF. The porous structure was found to be a key to the CO 2 diffusion and carbonation reaction; Water-to-cement ratio, calcium-to-magnesium ratio (MS:MgO) and the porous FA particles played critical roles in controlling the internal pore volume thus affecting the strength. These findings provide insights into the synergistic utilization of CO 2 and solid waste for future grean and low-carbon construction materials, offering a sustainable solution for carbon capture and waste valorization.