Improvement of the performance of recycled concrete powder-based artificial aggregates through the acceleration carbonation effect induced by polyethyleneimine admixture

Abstract

Abstract Manufactured sand, recycled concrete powder, and cement were used as raw materials to produce recycled concrete powder-based artificial aggregates (RCP-AA) via cold-bonding granulation technology. The effects of curing methods and polyethyleneimine (PEI) dosage on the macro performance and microstructure of RCP-AA were analyzed. The recycled concrete powder contains a small number of active substances that can react with CO₂ to form CaCO3, thereby enhancing the performance of the artificial aggregates. Additionally, the secondary and tertiary amine groups in PEI molecules react with CO₂ to promote the carbonation process and form carbonates. This process not only improves carbonation efficiency under milder conditions, reducing the dependence on high CO₂ concentrations and pressure, but also significantly enhances the microstructure and performance of the aggregates. The results showed that carbonation and PEI addition significantly increased aggregate density, reduced water absorption, and enhanced single particle strength by promoting CaCO3 formation and improving the microstructure. Specially, the water absorption of RCP-AA reduced from 13.9 % to 9.8 %, and the early strength reached 3.07 MPa at an 8 % PEI dosage. Microstructural characterization further confirmed the effects of carbonation, showing a reduction in Ca(OH)2 content, an increase in CaCO3 formation, significant pore structure optimization, and improved carbonation efficiency and structural uniformity. The maximum CaCO3 generation occurred within the PEI dosage range of 8–12 %, while a 16 % dosage hindered carbonation due to the formation of overly dense polymer films. Considering both performance and practical applicability, an 8 % PEI dosage was recommended as the optimal level for improving the structure and mechanical properties of RCP-AA. This study provides a theoretical foundation for the preparation and curing of sustainable building materials, with the proposed method not only enhancing material performance but also offering significant potential for promoting the application of low-carbon, green materials, thereby supporting the construction industry's environmental sustainability.