In this study, a two-step carbonation method is developed to control the formation of calcium carbonate (Cc) polymorphs on the surface of recycled hardened cement paste (RHCP) without the use of chemical additives. In the first step, RHCP undergoes semi-dry carbonation under controlled humidity conditions, followed by wet carbonation at various temperatures in the second step. The results show that vaterite and aragonite are stabilized during the wet carbonation process, forming primarily on the surface of RHCP particles. The stabilization of the metastable Cc phases is driven by the synergistic effect of existing Cc seeds in the RHCP and the reaction temperature. A temperature range of 9–48 °C promotes the formation of vaterite, while higher temperatures (60–90 °C) lead to its dissolution. The calcite seeds present in RHCP do not enhance the formation of vaterite and aragonite during wet carbonation. This method offers a potential practical approach for valorizing concrete waste while capturing CO₂ from the atmosphere.

中文翻译：

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稳定再生水泥浆颗粒表面的亚稳态碳酸钙多晶型物：一种无化学添加剂的两步碳化方法


在本研究中，开发了一种两步碳化方法，以控制再生硬化水泥浆 （RHCP） 表面碳酸钙 （Cc） 多晶型物的形成，而无需使用化学添加剂。第一步，RHCP 在受控湿度条件下进行半干碳化，然后在第二步中在不同温度下进行湿碳化。结果表明，vaterite 和 Aragonite 在湿式碳化过程中稳定，主要在 RHCP 颗粒表面形成。亚稳 Cc 相的稳定是由 RHCP 中现有 Cc 晶种和反应温度的协同效应驱动的。9-48 °C 的温度范围会促进 Vaterite 的形成，而较高的温度 （60-90 °C） 会导致其溶解。RHCP 中存在的方解石种子不会增强湿碳化过程中 vaterite 和文石的形成。这种方法提供了一种潜在的实用方法，可以在从大气中捕获 CO₂ 的同时对混凝土废料进行估值。