Glycine wet carbonation of recycled concrete aggregate for vaterite formation, ITZ enhancement, and improved recycled concrete performance

Document Type

Article

Publication Date

7-15-2026

Abstract

Recycled concrete aggregate (RCA) is commonly limited by a weak interfacial transition zone (ITZ) associated with residual mortar and high interfacial porosity. This study proposes a glycine wet carbonation strategy to improve the interfacial microstructure of RCA through the formation of a vaterite carbonation layer. Quantitative X-ray diffraction, scanning electron microscopy, and carbonation depth measurements collectively confirmed the development of a thin vaterite and calcite layer surrounding the aggregate, with glycine carbonated samples exhibiting a greater carbonation depth of approximately 332 μm, indicating localized interfacial modification. This carbonated surface layer strengthened the original ITZ and improved aggregate integrity. More importantly, when incorporated into concrete, the vaterite carbonation layer partially transformed and dissolved during hydration, supplying reactive calcium that promoted the formation of a denser ITZ between RCA and the new cement matrix. Nanoindentation and pore structure analysis confirmed interfacial densification and pore refinement, with Gaussian mixture model deconvolution showing that approximately 60% of the ITZ phase fraction in the glycine carbonated RCA paste corresponded to HD C-S-H with an elastic modulus of about 31.7 GPa. As a result of this ITZ strengthen, recycled concrete containing glycine carbonated RCA exhibited enhanced mechanical properties, including a 13.82% increase in compressive strength, together with improved resistance to chloride ingress and freeze–thaw. Beyond these performance benefits, glycine carbonation of RCA promotes CO2 sequestration, facilitates the beneficial reuse of recycled aggregates, reduces dependence on natural aggregate resources, and enhances durability.

Publication Title

Journal of Building Engineering

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