The practical implementation of accelerated carbonation for recycled waste concrete is impeded by sluggish carbonation efficiency. In contrast to previous carbonation enhancement schemes using high-pressure gas and/or complex pre-/post-processing, this study introduces a novel semi-wet carbonation method that achieves high-efficiency carbonation of recycled concrete aggregates (RCA) in a practically simple way. A noteworthy carbonation degree of 10.6 % was achieved within 30 min at room temperature and ambient pressure, which enhanced the RCA by reducing the water absorption rate and porosity by 3.6 % and 20 % respectively. The formed CaCO is primarily in calcite form with poorer crystallinity and smaller grain size and the formed silica gel features a lower polymerization degree compared with those formed in wet carbonation. It is due to that the carbonation reactions for the semi-wet scenario happen at the spatially confined water film of the solid-liquid interface. Moreover, the addition of sodium bicarbonate significantly accelerated the semi-wet carbonation, which is due to the weak alkaline environment lowering the CO speciation free energy as revealed by reactive molecular dynamics simulations. The proposed semi-wet carbonation method provides a promising way of pushing industrial CO capture and utilization.

中文翻译：

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半湿环境中再生混凝土骨料的加速碳化：一种有前途的二氧化碳利用技术

再生废混凝土加速碳化的实际实施因碳化效率低下而受到阻碍。与之前使用高压气体和/或复杂的前/后处理的碳化强化方案相比，本研究引入了一种新颖的半湿碳化方法，该方法以实际简单的方式实现了再生混凝土骨料（RCA）的高效碳化方式。在室温和环境压力下，在 30 分钟内达到了 10.6% 的显着碳酸化度，这通过将吸水率和孔隙率分别降低了 3.6% 和 20% 来增强了 RCA。形成的CaCO主要为方解石形式，结晶度较差，粒径较小，形成的硅胶与湿式碳酸化形成的硅胶相比，聚合度较低。这是因为半湿场景的碳酸化反应发生在固液界面的空间限制的水膜处。此外，反应分子动力学模拟表明，碳酸氢钠的添加显着加速了半湿碳酸化，这是由于弱碱性环境降低了CO形态自由能。所提出的半湿碳酸化方法为推动工业二氧化碳捕获和利用提供了一种有前景的方法。