Static yield stress is crucial for concrete, especially for 3D printed concrete, as it determines whether the bottom layer can support the load of the subsequent layers or withstand any potential impulses. A better understanding of the evolution of the static yield stress and its changing mechanism is therefore needed. Under the assumption that hydrate formation follows fractal patterns, this work proposes a model for simulating static yield stress that links the hydration process and bridging possibility. To validate the model, parameters were first obtained from the BNG (Boundary Nucleation Growth) equation fitted with calorimetry data, and the relation of associated hydration rates to sound speed variation rate was analyzed. Results showed that the proposed model predicts well the static yield stress obtained with a penetration test, under varying water-cement ratios and accelerator conditions. The fitted parameter β was found to correlate with size and morphology of the hydration products, suggesting that the model can not only simulate the static yield stress, but also capture the structural build-up information. Furthermore, the decrease in fractal-related β implies that more compact hydrates are formed during hydration.

中文翻译：

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水泥水化初期水泥浆体静屈服应力演变及结构堆积的建模与试验研究


静态屈服应力对于混凝土至关重要，尤其是对于 3D 打印混凝土，因为它决定了底层是否能够支撑后续层的负载或承受任何潜在的脉冲。因此，需要更好地了解静态屈服应力的演变及其变化机制。在水合物形成遵循分形模式的假设下，这项工作提出了一种模拟静态屈服应力的模型，该模型将水合过程和桥接可能性联系起来。为了验证该模型，首先从与量热数据拟合的 BNG（边界成核增长）方程中获得参数，并分析了相关水合率与声速变化率的关系。结果表明，所提出的模型可以很好地预测在不同水灰比和加速器条件下通过渗透试验获得的静态屈服应力。发现拟合参数 β 与水化产物的大小和形态相关，表明该模型不仅可以模拟静态屈服应力，还可以捕获结构堆积信息。此外，分形相关β的减少意味着在水合过程中会形成更致密的水合物。