In 3D printed concrete (3DPC), the absence of formwork leads to increased shrinkage compared to traditional cast concrete which uses formwork. This increase in shrinkage is primarily due to the rapid evaporation of moisture during the early stages. Therefore, our research focused on how the initial water content and the exposed surface area affect the total shrinkage by varying water-to-cement ratio (w/c) and the surface-to-volume ratio (s/v). For 3DPC with high w/c, we used calcium formate (CaF) to improve its printability by increasing static yield stress. Dry environment makes the evaporation the predominant mode of water loss, significantly decelerating the hydration process in samples with fully exposed surfaces. At 28 d, the evaporated moisture in 3DPC is 2.8 times higher than the moisture consumed by hydration. A predictive model for the shrinkage properties of 3DPC has been developed by considering that 3DPC experiences both hydration and evaporation simultaneously from early stages on the basis of the water mass conservation principle. The predictions were found to align with actual shrinkage test results, as evidenced by quantitative analysis of parameters like internal RH, mass loss, degree of hydration, and porosity, thus validating the accuracy of the model.

中文翻译：

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具有不同水灰比和样本尺寸的 3D 打印混凝土的失水和收缩预测

与使用模板的传统浇注混凝土相比，3D 打印混凝土 (3DPC) 中没有模板会导致收缩增加。收缩率的增加主要是由于早期阶段水分的快速蒸发。因此，我们的研究重点是初始含水量和暴露表面积如何通过改变水灰比（w/c）和表面积与体积比（s/v）来影响总收缩。对于高 w/c 的 3DPC，我们使用甲酸钙 (CaF) 通过增加静态屈服应力来提高其印刷适性。干燥的环境使蒸发成为失水的主要方式，从而显着减缓表面完全暴露的样品的水合过程。 28 d时，3DPC中蒸发的水分是水合消耗的水分的2.8倍。根据水质量守恒原理，考虑到 3DPC 从早期阶段就同时经历水合和蒸发，开发了 3DPC 收缩特性的预测模型。通过对内部相对湿度、质量损失、水合程度和孔隙率等参数的定量分析，发现预测结果与实际收缩测试结果相符，从而验证了模型的准确性。