Abstract The rheology of modern Portland cement (PC) concrete critically depends on the correct dosage of gypsum (calcium sulfate hydrate) to control the hydration of the most reactive phase - tricalcium aluminate (C3A). The underlying physio-chemical mechanism, however, remains unsolved mainly due to the lack of high-spatial-resolved and chemistry-sensitive characterization of the C3A dissolution frontier. Here, we fill this gap by integrating synchrotron-radiation based crystallographic, photon-energy-dependent spectroscopic and high-resolution morphological studies of the C3A hydration product layer. We propose that ettringite (6CaO·Al2O3·SO3·32H2O) is the only hydration product after the initial reaction period and before complete gypsum dissolution. We quantify the 2D and 3D morphology of the ettringite network, e.g. the packing density of ettringite at various surface locations and the surface dissolution heterogeneity. Our results show no trace of a rate-controlling diffusion barrier. We expect our work to have significant impact on modeling the kinetics and morphological evolution of PC hydration.

中文翻译：

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石膏存在下铝酸三钙水合的同步加速器 X 射线纳米断层扫描和光谱显微研究

摘要 现代硅酸盐水泥 (PC) 混凝土的流变性关键取决于石膏（水合硫酸钙）的正确用量，以控制最具反应性的相 - 铝酸三钙 (C3A) 的水化。然而，潜在的物理化学机制仍未解决，主要是由于缺乏对 C3A 溶解前沿的高空间分辨率和化学敏感性表征。在这里，我们通过整合基于同步辐射的晶体学、光子能量相关光谱和 C3A 水合产物层的高分辨率形态研究来填补这一空白。我们认为钙矾石 (6CaO·Al2O3·SO3·32H2O) 是初始反应期之后和石膏完全溶解之前的唯一水合产物。我们量化钙矾石网络的 2D 和 3D 形态，例如 钙矾石在不同表面位置的堆积密度和表面溶解不均匀性。我们的结果显示没有任何控制速率的扩散屏障的痕迹。我们希望我们的工作对模拟 PC 水合的动力学和形态演变产生重大影响。