This study explores a novel beneficial utilization of CO₂ in ordinary Portland cement (OPC) based concrete. In existing studies, CO₂ is mainly added into concrete through accelerated carbonation of fresh or hardened concrete, which is limited by the low diffusion of CO₂ into the concrete. In addition, a high CO₂ concentrated environment is needed to carbonate the concrete, making the existing methods only applicable to pre-cast concrete. Aiming to eliminate these limitations in the existing methods, this study proposes to directly add gaseous CO₂ into fresh concrete mix as an admixture through a two-step mixing approach, pre-carbonation method. In this method, CO₂ is first absorbed into a slurry of calcium-rich cementitious material in the first step, and then blended with the rest ingredients to produce concrete in the second step. This method can in-situ produce nano to sub-micro CaCO₃ particles in fresh concrete, providing extra heterogenous nucleation sites for the hydration of OPC. Therefore, the hydration of OPC can be greatly improved, as evidenced by the calorimetry testing result. The addition of CO₂ also produces more ettringite in the produced mortar, as revealed by X-Ray Diffraction and Thermogravimetric analysis. As a result, the overall volume of the hydration products of the OPC is increased, leading to denser microstructure of the mortar samples. For these reasons, the compressive strength of the cement mortar samples can be significantly improved by the proposed method.

这项研究探索了普通硅酸盐水泥（OPC）基混凝土中CO ₂的新型有益利用。在现有的研究中，CO ₂主要通过新鲜或硬化混凝土的加速碳化而被添加到混凝土中，这受CO ₂扩散到混凝土中的程度低的限制。另外，需要高浓度的CO ₂浓缩环境以使混凝土碳酸化，使得现有方法仅适用于预制混凝土。为了消除现有方法中的这些限制，本研究建议通过两步混合方法（预碳化法）直接将气态CO ₂作为掺合料添加到新拌混凝土中。在这种方法中，CO ₂在第一步中，首先将其吸收到富含钙的胶凝材料的浆料中，然后在第二步中将其与其余成分混合以生产混凝土。这种方法可以在新鲜混凝土中原位产生纳米至亚微米级的CaCO ₃颗粒，从而为OPC的水合作用提供了额外的异质形核位点。因此，量热测试结果证明，可以大大改善OPC的水合作用。添加CO ₂X射线衍射和热重分析表明，在砂浆中还会产生更多的钙矾石。结果，OPC的水合产物的总体积增加，导致砂浆样品的致密的微观结构。由于这些原因，所提出的方法可以显着提高水泥砂浆样品的抗压强度。