The relatively low hydration rate of calcium aluminate cement (CAC) at 15–35 °C leads to retarded setting time and reduced production efficiency of CAC-bonded castables. To accelerate the hydration rate of CAC within this temperature range, the present work proposes the fabrication of nano-hydrates acting as seeds by pre-hydration of CAC in suspensions. CAC powders are dispersed in water with water-to-solid ratio of 4.5 and stirred for varying durations at 25 °C to achieve different pre-hydration degrees. Then the pre-hydrated CAC suspensions replace a small part of cement in the pastes. The influence of the CAC suspensions addition on the hydration heat release and strength development of fresh CAC pastes at 25 °C is investigated. The results indicate that nano-scale hydrates CAH and AH form on the surface of pre-hydrated CAC particles in the suspensions and grow rapidly with the extension of stirring duration. The presence of nano-scale hydrates in the pre-hydrated CAC suspensions is found to shorten the induction period of CAC hydration and thus be beneficial to the accelerated hardening of CAC pastes. The pre-hydrated CAC suspension stirred for 3.5 h has the most significant effect on enhancing early strength of the CAC pastes. At this stage, the pre-hydrated CAC within the suspension is in the accelerated period, and has just begun to precipitate large amounts of nano-scale CAH and AH acting as seeds to catalyze the hydration and refine the pore structure of CAC pastes.

中文翻译：

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预水合 CAC 悬浮液对 CAC 糊剂水合行为的影响


铝酸钙水泥（CAC）在 15-35 °C 时的水化速率相对较低，导致 CAC 粘结浇注料的凝结时间延迟并降低生产效率。为了加快 CAC 在此温度范围内的水合速率，目前的工作提出通过悬浮液中的 CAC 预水合来制造纳米水合物作为种子。将CAC粉末分散在水固比为4.5的水中，并在25℃下搅拌不同的时间，以达到不同的预水化程度。然后，预水合的 CAC 悬浮液取代了浆体中的一小部分水泥。研究了 CAC 悬浮液的添加对 25 °C 下新鲜 CAC 糊剂水合放热和强度发展的影响。结果表明，悬浮液中预水合CAC颗粒表面形成纳米级水合物CAH和AH，并随着搅拌时间的延长而迅速生长。研究发现，预水合CAC悬浮液中纳米级水合物的存在可以缩短CAC水化的诱导期，从而有利于CAC糊剂的加速硬化。搅拌3.5小时的预水合CAC悬浮液对于增强CAC糊剂的早期强度具有最显着的效果。此阶段，悬浮液中预水化的CAC处于加速期，刚刚开始析出大量的纳米级CAH和AH作为晶种，催化水化并细化CAC浆体的孔结构。