3D printed cementitious materials are subjected to environmental drying from a very early age as it does not have any formwork protection. In this paper, we present a novel methodology using a rheometer for measuring the shrinkage strains in such stiff cement-based materials from the onset of processing. In this approach, cylindrical samples are placed between parallel plates attached to the rheometer and continuous monitoring of shrinkage strain is made possible by using a constant normal force protocol. Using this protocol, shrinkage strain was measured in samples subjected to external drying and protected from drying and also on samples with and without shrinkage reducing agent. It was found that the incorporation of about 3 wt% shrinkage reducing agent significantly reduces the early-age shrinkage strain. The effect of early-age drying induced microstructural changes was investigated in this study using mercury intrusion porosimetry, loss on ignition and electrical resistivity measurements. When subjected to early age drying, the porosity of the samples was found to increase significantly and the assessment of chemically bound water revealed that the degree of hydration was not uniform, but varied as a gradient with the minimal values at the drying surface.

中文翻译：

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评估塑性收缩的流变方法以及早期干燥对水泥基材料微观结构的影响

3D 打印的水泥材料由于没有任何模板保护，因此从很小的时候起就受到环境干燥的影响。在本文中，我们提出了一种使用流变仪的新颖方法，用于测量这种坚硬的水泥基材料从加工开始时的收缩应变。在这种方法中，圆柱形样品放置在连接到流变仪的平行板之间，并且通过使用恒定法向力协议可以连续监测收缩应变。使用该方案，测量经过外部干燥和防止干燥的样品以及含有和不含有减缩剂的样品的收缩应变。发现掺入约3wt％的减缩剂显着降低了早期收缩应变。本研究使用压汞孔隙率测定法、烧失量和电阻率测量来研究早期干燥引起的微观结构变化的影响。当进行早期干燥时，发现样品的孔隙率显着增加，并且化学结合水的评估表明水合程度并不均匀，而是以干燥表面处的最小值呈梯度变化。