To promote the application of carbonated recycled concrete powder (CRP), it is vital to thoroughly understand the performance of recycled concrete powder (RP) during the carbonation process. This paper presents an experimental study on the multiscale microstructure evolution of CRP and its chemical reactivity development during gas-solid carbonation. The phase transformation, nanostructure and reactivity evolution were investigated using thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ²⁹Si nuclear magnetic resonance (NMR) and zeta potential test. Scanning electron microscope and energy-dispersive spectroscopy (SEM-EDS), transmission electron microscope (TEM) and Brunauer-Emmett-Teller (BET) were employed to study the microstructural characteristics. Results indicate that portlandite, ettringite, and unhydrated clinker were carbonated into CaCO₃ and alumina gel within 1d, while the C-S-H subsequently underwent decalcification, yielding silica gel and nano CaCO₃. Regarding microstructure, calcium redistributes during carbonation, and silica phase undergoes polymerization from a nanoscale point of view. The CaCO₃ derived from portlandite firstly formed and refine the pores, followed by the outward distribution of later-generated silica gel and nano calcium carbonate from C-S-H due to space limitations within the particle. The initially formed CaCO₃ can chemically absorb Ca²⁺ in cement paste to facilitate the nucleation and growth of C-S-H, while the highly reactive silica gel obtained in later stage can further promote the formation of C-S-H. This study provides theoretical and technological support to improve the efficiency of carbonation processes and advance their engineering applications.

中文翻译：

---

气固碳化作用下再生混凝土细粉的多尺度微观结构和反应性演变


为了推广碳酸再生混凝土粉 （CRP） 的应用，彻底了解再生混凝土粉 （RP） 在碳化过程中的性能至关重要。本文对 CRP 的多尺度微观结构演变及其在气固碳化过程中的化学反应性发展进行了实验研究。使用热重分析 （TGA）、X 射线衍射 （XRD）、傅里叶变换红外光谱 （FTIR）、²⁹Si 核磁共振 （NMR） 和 zeta 电位测试研究了相变、纳米结构和反应性演变。采用扫描电子显微镜和能量色散光谱 （SEM-EDS） 、透射电子显微镜 （TEM） 和 Brunauer-Emmett-Teller （BET） 研究微观结构特征。结果表明，硅酸盐、钙矾石和未水合熟料在 1 d 内碳酸化成 CaCO₃ 和氧化铝凝胶，而 C-S-H 随后发生脱钙，产生硅胶和纳米 CaCO₃。关于微观结构，钙在碳化过程中重新分布，而二氧化硅相从纳米级角度来看发生聚合。从硅酸盐衍生的 CaCO₃ 首先形成并细化孔隙，然后由于颗粒内的空间限制，后来生成的硅胶和纳米碳酸钙从 C-S-H 向外分布。最初形成的 CaCO₃ 可以通过化学方式吸收水泥浆中的 Ca²⁺，以促进 C-S-H 的成核和生长，而后期获得的高活性硅胶可以进一步促进 C-S-H 的形成。 本研究为提高碳酸化过程的效率并推进其工程应用提供了理论和技术支持。