Multiphase carbonation engineering of RCA via CO₂-enriched cement slurry treatment: Mechanistic insights into carbonation efficiency and asphalt pavement performance enhancement

[Geoengineering News]

https://www.sciencedirect.com/science/article/abs/pii/S0950061825038735

Authors: Xiaotong Du, Kui Hu, Jiahao Zhang, Jia Li, Giuseppe Carlo Marano, Tingyi Zhang

23 September 2025

https://doi.org/10.1016/j.conbuildmat.2025.143722

Highlights

•The multiphase carbonation engineering treatment enhances the surface properties of RCA.

•CO₂-induced calcium carbonate precipitation reshapes the microstructure of RCA.

•The carbonation process improves the interfacial adhesion between RCA and asphalt.

•The treatment offers environmental benefits through CO₂ sequestration and reduced carbon emissions.

Abstract

The growing demand for sustainable pavement materials necessitates innovative approaches to enhance recycled concrete aggregates (RCA), whose surface defects critically undermine asphalt bonding performance. Given its high porosity and loosely bound structure, calcium silicate hydrate (C-S-H) is identified as the primary factor undermining RCA performance and thus the key target of modification. This study proposes a CO2-enriched cement slurry treatment under ambient conditions to engineer the RCA microstructure through controlled carbonation of C-S-H. The treatment integrates three mechanistic pathways: hydration-induced hardening of unhydrated cement phases, carbonation curing of setting slurry, and targeted carbonation of residual microstructural pores on the RCA surface. The multiscale validation combines microstructural characterization, macroscale experiments, and molecular dynamics simulations to elucidate the interfacial mechanisms, complemented by a life cycle assessment. Results confirm the high efficiency of this multiphase carbonation strategy, achieving a 13.37 % reduction in RCA water absorption, 1.62 MPa bond strength enhancement, and 40.33 % increased Marshall stability. Nanoscale characterization reveals calcium carbonate precipitation reducing average pore diameter. Molecular dynamics confirms the interfacial binding energy between asphalt and RCA increased by 24.65 % and 28.99 % under dry and wet conditions. The number of hydrogen bonds formed between water molecules and the RCA surface decreases by 151, indicating enhanced moisture resistance and a reduced potential for water migration at the interface. Environmental analysis based on life cycle assessment demonstrates a substantial reduction in global warming potential and particulate emissions. This efficient carbonation approach converts construction waste into high-performance pavement materials while maximizing environmental benefits.

Source: ScienceDirect