Ming Xing, Si Wen, Yu Qinglu, Sun Zhaoyang, Qiu Guotao, Cao Mingli, Li Yunjian, Li Zongjin
Faculty of Innovation Engineering, Macau University of Science and Technology, Avenida Wai Long, Taipa, Macao SAR, China.
School of Civil Engineering, Dalian University of Technology, Dalian, China.
Nat Commun. 2024 Apr 4;15(1):2929. doi: 10.1038/s41467-024-47164-0.
Portland cement (PC) is ubiquitously used in construction for centuries, yet the elucidation of its early-age hydration remains a challenge. Understanding the initial hydration progress of tricalcium aluminate (CA) at molecular scale is thus crucial for tackling this challenge as it exhibits a proclivity for early-stage hydration and plays a pivotal role in structural build-up of cement colloids. Herein, we implement a series of ab-initio calculations to probe the intricate molecular interactions of CA during its initial hydration process. The CA surface exhibits remarkable chemical activity in promoting water dissociation, which in turn facilitates the gradual desorption of Ca ions through a metal-proton exchange reaction. The dissolution pathways and free energies of these Ca ions follow the ligand-exchange mechanism with multiple sequential reactions to form the ultimate products where Ca ions adopt fivefold or sixfold coordination. Finally, these Ca complexes reprecipitate on the remaining Al-rich layer through the interface-coupled dissolution-reprecipitation mechanism, demonstrating dynamically stable inner-sphere adsorption states. The above results are helpful in unmasking the early-age hydration of PC and advancing the rational design of cement-based materials through the bottom-up approach.
几个世纪以来，波特兰水泥（PC）在建筑中被广泛使用，然而，阐明其早期水化过程仍然是一项挑战。因此，在分子尺度上理解铝酸三钙（CA）的初始水化过程对于应对这一挑战至关重要，因为它表现出早期水化的倾向，并且在水泥胶体的结构形成中起着关键作用。在此，我们进行了一系列从头算计算，以探究CA在其初始水化过程中的复杂分子相互作用。CA表面在促进水离解方面表现出显著的化学活性，这反过来又通过金属-质子交换反应促进Ca离子的逐步解吸。这些Ca离子的溶解途径和自由能遵循配体交换机制，通过多个连续反应形成最终产物，其中Ca离子采用五配位或六配位。最后，这些Ca配合物通过界面耦合溶解-再沉淀机制在剩余的富铝层上再沉淀，表现出动态稳定的内球吸附状态。上述结果有助于揭示PC的早期水化过程，并通过自下而上的方法推进水泥基材料的合理设计。
