Effect of gypsum on early hydration of amorphous C12A7 and its mechanism
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摘要: 为推动非晶态C12A7在早强快凝工程材料中的高效应用,洞悉二水石膏对非晶态C12A7的影响作用机理,本文采用X射线衍射、微量热分析、扫描电子显微镜等测试手段研究了二水石膏对非晶态C12A7早期水化性能的影响。结果表明,适量二水石膏会延缓非晶态C12A7的水化进程,即随着二水石膏掺量增大,非晶态C12A7达到第一个水化放热峰的时间延迟,第二个放热峰值降低,放热峰持续时间延长;水化24 h时,二水石膏掺量为50 % 的试样水化放热总量最大,水化活性最高。在本实验的二水石膏掺量范围内,所有试样的水化产物均以钙矾石AFt和氢氧化铝AH3为主,二水石膏掺量和水化龄期可改变钙矾石的生成量和形貌特性,进而影响浆体的抗压强度。在相同水化龄期内,随着二水石膏掺量的增加,试样的抗压强度均呈先增后降趋势;本实验中最佳二水石膏掺量为50 %,其在水化龄期24 h、72 h和168 h时的抗压强度均为最高。Abstract: In order to promote the efficient application of amorphous C12A7 in early strength and rapid setting engineering materials, and understand the interaction mechanism between gypsum and amorphous C12A7, the influence of gypsum on the early hydration of amorphous C12A7 was studied by X-ray diffraction, scanning electron microscopy and isothermal calorimetry. The results show that proper dosage of gypsum can retard the hydration of amorphous C12A7, with the increasing dosage of gypsum, the time of the first exothermic peak is retarded, the second exothermic peak of hydration is reduced, and the duration of exothermic peak is prolonged; After 24 hours hydration, the accumulate heat of hydration of the sample with 50 % gypsum are the highest. In the experiment, ettringite and AH3 gel are the main hydration products. The content of gypsum and hydration ages can change the morphology of ettringite, and affect the compressive strength of the sample. At the same age, with the increase of the dosage of gypsum, the compressive strength of the hydrated pastes increases from 33 % to 50 % and then decreases from 50 % to 64 %. Amorphous C12A7 with 50 % gypsum system has the highest strength at day 1, day 3 and day 7.
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Key words:
- gypsum /
- amorphous C12A7 /
- hydration products /
- ettringite /
- strength
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表 1 非晶态C12A7的主要化学成分质量分数
Table 1. The oxide composition of amorphous C12A7
% SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O 3.02 50.57 0.36 43.60 0.68 0.10 0.22 表 2 二水石膏的主要化学成分质量分数
Table 2. The oxide composition of gypsum
% CaO SO3 Na2O Crystal water 32.60 46.37 0.12 20.2 表 3 非晶态C12A7和二水石膏质量分数
Table 3. The mass percent of amorphous C12A7 and gypsum in system
% 试样 非晶态C12A7 二水石膏 C1 67 33 C2 62 38 C3 58 42 C4 54 46 C5 50 50 C6 46 54 C7 36 64 -
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