Abstract In the production of concrete from cement powder and water, setting behavior of the slurry is determined by the formation of ettringite (Ca6Al2(OH)12 · (SO4)3 · 26 H2O) from tricalcium aluminate (Ca9Al6O18, abbreviated C3A) and gypsum (CaSO4 · 2 H2O). Due to the high reaction potential of cement and water, premature hydration can occur after unintentional exposure to moisture. Model binary mixtures of C3A and gypsum stored at 90% relative humidity and 35 °C produced ample amounts of ettringite, which subsequently reacted with atmospheric CO2 to CaCO3, Al(OH)3 and gypsum. Investigated were the two main polymorphs of tricalcium aluminate encountered in cement, pure, cubic C3A and orthorhombic C3A in which calcium is partially substituted by sodium or potassium. Alkali substituted C3A converted to ettringite faster and more completely than pure C3A. Ettringite from prehydration caused a seeding effect, which promotes crystal growth and accelerates bulk hydration of the C3A/gypsum mixtures. Set retarders commonly applied in cement were dissolved in the mixing water prior to hydration to investigate their ability to counteract this acceleration. Sodium gluconate merely delayed the crystal growth but does not prolong the hydration process overall. Potassium pyrophosphate retarded much more effectively by suppressing the seeding effect via removal of calcium ions from the hydration reaction.

中文翻译：

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老化对铝酸三钙 (C3A)/石膏混合物的水合作用和缓凝剂效果的影响

摘要 在用水泥粉和水生产混凝土时，浆料的凝结行为取决于铝酸三钙（Ca9Al6O18，缩写为 C3A）和石膏形成钙矾石（Ca6Al2(OH)12 · (SO4)3 · 26 H2O）。 (CaSO4·2H2O)。由于水泥和水的高反应潜力，意外接触水分后可能会发生过早水化。C3A 和石膏的模型二元混合物储存在 90% 的相对湿度和 35°C 下会产生大量钙矾石，随后与大气 CO2 反应生成 CaCO3、Al(OH)3 和石膏。研究了水泥中遇到的铝酸三钙的两种主要多晶型物，纯立方 C3A 和斜方晶 C3A，其中钙部分被钠或钾取代。碱取代的 C3A 比纯 C3A 更快和更完全地转化为钙矾石。预水合产生的钙矾石引起晶种效应，促进晶体生长并加速 C3A/石膏混合物的大量水合。水泥中常用的缓凝剂在水化之前溶解在混合水中，以研究它们抵消这种加速的能力。葡萄糖酸钠仅延迟晶体生长，但不会延长整体水合过程。焦磷酸钾通过从水合反应中去除钙离子来抑制晶种效应，从而更有效地阻滞。水泥中常用的缓凝剂在水化之前溶解在混合水中，以研究它们抵消这种加速的能力。葡萄糖酸钠仅延迟晶体生长，但不会延长整体水合过程。焦磷酸钾通过从水合反应中去除钙离子来抑制晶种效应，从而更有效地阻滞。水泥中常用的缓凝剂在水化之前溶解在混合水中，以研究它们抵消这种加速的能力。葡萄糖酸钠仅延迟晶体生长，但不会延长整体水合过程。焦磷酸钾通过从水合反应中去除钙离子来抑制晶种效应，从而更有效地阻滞。