Free water plays a crucial role in the hydration process of β-calcium sulfate hemihydrate (β-HH) based plaster. To further understand the hydration mechanism of β-HH, this study monitored water consumption and pore structure evolution of plaster prepared by different water/β-HH (W/H) ratios using low-field NMR. The hydration characteristics were jointly analyzed using X-ray diffraction (XRD), thermogravimetric (TG), and isothermal calorimetry. In addition, the pore structure of the plaster was characterized by BET and MIP. Results indicated that during early hydration (0–10 min), free water migrated from macropores to micropores in β-HH samples. The specific surface area and free water content of β-HH based plaster decreased during rapid hydration period. It is also found that increasing the W/H ratio accelerated free water consumption but resulted in larger pore diameter. Furthermore, signal intensity and transverse relaxation time were found to be exponentially related (y = Ae + y) to the CaSO∙2HO crystal content, hydration degree, and heat release. These correlations suggest that low-field NMR correlated well with other measurements and could be viable method to characterize the plaster hydration process.

中文翻译：

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基于低场核磁共振的β-半水硫酸钙水化特性及机理分析

游离水在β-半水硫酸钙(β-HH)基石膏的水化过程中起着至关重要的作用。为了进一步了解 β-HH 的水化机理，本研究使用低场核磁共振监测了不同水/β-HH (W/H) 比例制备的石膏的耗水量和孔隙结构演变。使用 X 射线衍射 (XRD)、热重 (TG) 和等温量热法联合分析水化特性。此外，还通过BET和MIP对石膏的孔结构进行了表征。结果表明，在早期水合过程中（0-10 分钟），游离水从 β-HH 样品的大孔迁移到微孔。 β-HH基石膏的比表面积和游离水含量在快速水化期间下降。研究还发现，增加W/H比会加速自由水的消耗，但会导致孔径变大。此外，信号强度和横向弛豫时间与 CaSO·2HO 晶体含量、水合度和放热呈指数关系 (y = Ae + y)。这些相关性表明低场核磁共振与其他测量结果相关性良好，并且可能是表征石膏水化过程的可行方法。