Mechanochemical dry ice treatment enhances carbon sequestration and performance in slag-based geopolymers

Under the dual-carbon framework, carbon sequestration technologies and low-carbon cementitious materials, such as geopolymers, have become critical strategies for reducing carbon emissions in the construction sector. This study proposes a mechanochemical-carbon sequestration (MC-CS) technique, which simultaneously processes geopolymer precursors and a solid carbon source (dry ice), and systematically evaluates its effects on slag powder and slag-based geopolymer (SBG) mortar. Results show MC-CS treatment promotes the formation of a carbonate layer on the slag surface, enhancing carbon sequestration capacity and retarding early hydration reaction of geopolymers, thereby improving flowability and extending setting time. The synergistic interaction between hydration and carbonation reactions significantly enhances strength and durability of the geopolymer. Excessive treatment, however, causes the carbonate layer to detach, reducing carbon sequestration efficiency and suppressing later-stage reactions. The study demonstrates 30 min of MC-CS treatment enabled SBG mortar to achieve the highest carbon uptake (3.6%), the most favorable fresh and mechanical properties. Carbon sequestration efficiency is improved by mechanochemical-carbon sequestration (MC-CS) technology. After 30 min of MC-CS treatment, the overall performance of the geopolymer is improved. A synergistic interaction mechanism between carbonation and hydration products in geopolymers is proposed.