Yoneyama Akira, Choi Heesup, Inoue Masumi, Kim Jihoon, Lim Myungkwan, Sudoh Yuhji
Department of Civil and Environmental Engineering, Kitami Institute of Technology, Hokkaido 090-8507, Japan.
Faculty of Environmental Technology, Muroran Institute of Technology, Hokkaido 090-8585, Japan.
Materials (Basel). 2021 Feb 20;14(4):1006. doi: 10.3390/ma14041006.
Recently, there has been increased use of calcium-nitrite and calcium-nitrate as the main components of chloride- and alkali-free anti-freezing agents to promote concrete hydration in cold weather concreting. As the amount of nitrite/nitrate-based accelerators increases, the hydration of tricalcium aluminate (CA phase) and tricalcium silicate (CS phase) in cement is accelerated, thereby improving the early strength of cement and effectively preventing initial frost damage. Nitrite/nitrate-based accelerators are used in larger amounts than usual in low temperature areas below -10 °C. However, the correlation between the hydration process and strength development in concrete containing considerable nitrite/nitrate-based accelerators remains to be clearly identified. In this study, the hydrate composition (via X-ray diffraction and nuclear magnetic resonance), pore structures (via mercury intrusion porosimetry), and crystal form (via scanning electron microscopy) were determined, and investigations were performed to elucidate the effect of nitrite/nitrate-based accelerators on the initial strength development and hydrate formation of cement. Nitrite/nitrate-AFm (aluminate-ferret-monosulfate; AFm) was produced in addition to ettringite at the initial stage of hydration of cement by adding a nitrite/nitrate-based accelerator. The amount of the hydrates was attributed to an increase in the absolute amounts of NO and NO ions reacting with AlO in the tricalcium aluminate (CA phase). Further, by effectively filling the pores, it greatly contributed to the enhancement of the strength of the hardened cement product, and the degree of the contribution tended to increase with the amount of addition. On the other hand, in addition to the occurrence of cracks due to the release of a large amount of heat of hydration, the amount of expansion and contraction may increase, and it is considered necessary to adjust the amount used for each concrete work.
最近，亚硝酸钙和硝酸钙作为无氯无碱防冻剂的主要成分，在寒冷天气混凝土施工中促进混凝土水化的应用越来越多。随着亚硝酸盐/硝酸盐类早强剂用量的增加，水泥中铝酸三钙（CA相）和硅酸三钙（CS相）的水化加速，从而提高了水泥的早期强度，并有效防止了初期冻害。在低于-10°C的低温地区，亚硝酸盐/硝酸盐类早强剂的用量比平时更大。然而，含有大量亚硝酸盐/硝酸盐类早强剂的混凝土中水化过程与强度发展之间的相关性仍有待明确。在本研究中，测定了水合物组成（通过X射线衍射和核磁共振）、孔隙结构（通过压汞法）和晶体形态（通过扫描电子显微镜），并进行了研究以阐明亚硝酸盐/硝酸盐类早强剂对水泥初始强度发展和水合物形成的影响。通过添加亚硝酸盐/硝酸盐类早强剂，在水泥水化初期除了生成钙矾石外，还生成了亚硝酸盐/硝酸盐-AFm（铝酸铁单硫酸盐；AFm）。水合物的量归因于与铝酸三钙（CA相）中的AlO反应的NO和NO离子绝对量的增加。此外，通过有效填充孔隙，它对硬化水泥制品强度的提高有很大贡献，且贡献程度往往随添加量的增加而增加。另一方面，除了由于大量水化热释放而出现裂缝外，膨胀和收缩量可能会增加，因此认为有必要针对每项混凝土工程调整用量。
