Abstract Calcium aluminate cements are used for special applications but are nowadays banned for general structural purposes due to the calcium aluminate hydrate conversion, that has led, for concretes fabricated with high water contents, to building collapses. The stoichiometries of these conversion chemical reactions are relatively well established but the consequences in porosity, key to predict durability, were unknown. Here, we have used hard X-ray ptychographic nanotomography to study the hydration of CaAl2O4 at different temperatures and chiefly, at 4 °C and then at 50 °C to provoke conversion similar to field conditions. The mass densities of the resulting Al (OH)3 gels were 1.94, 1.98 and 2.23 g·cm−3, for samples hydrated at 4, 20 and 50 °C, respectively. These values are lower than that of gibbsite, 2.42 g·cm−3. Above all, this 3D imaging technique has allowed measuring the secondary water porosity developed in the conversion, which has an average pore dimension close to 140 nm.

中文翻译：

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通过 ptychographic 纳米断层扫描分析铝酸钙水泥转化率

摘要 铝酸钙水泥用于特殊应用，但由于铝酸钙水合物转化导致建筑倒塌，因此现在禁止用于一般结构用途。这些转化化学反应的化学计量已经相对完善，但孔隙率的后果（预测耐久性的关键）尚不清楚。在这里，我们使用硬 X 射线 ptychographic 纳米断层扫描来研究 CaAl2O4 在不同温度下的水合作用，主要是在 4°C 下，然后在 50°C 下引发类似于现场条件的转化。对于在 4、20 和 50 °C 下水合的样品，所得 Al (OH)3 凝胶的质量密度分别为 1.94、1.98 和 2.23 g·cm-3。这些值低于三水铝石的 2.42 g·cm-3。首先，