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纳米C-S-H对水泥水化、硬化浆体孔结构及混凝土强度的影响
作者:张朝阳1  3  熠1 孔祥明1  3 郝挺宇2 
单位:(1. 清华大学土木工程系 北京 100084 2. 中冶集团建筑研究总院 北京 100056  3. 清华大学城市轨道交通绿色与安全建造技术国家工程实验室 北京 100084) 
关键词:纳米水化硅酸钙 水化 孔结构 强度 成核效应 
分类号:TU528
出版年,卷(期):页码:2019,47(5):0-0
DOI:10.14062/j.issn.0454-5648.2019.05.07
摘要:

 通过水化热测试、化学结合水含量测试、X射线衍射分析、压汞测试及强度测试研究了合成的纳米水化硅酸钙(n-C-S-H) 对水泥水化过程、硬化水泥浆孔结构及混凝土强度的影响。结果表明:n-C-S-H显著加速了水泥早期水化,提升了水泥在12~24 h龄期的水化程度,从而显著提高混凝土12~24 h龄期的抗压强度,24 h以后对强度提升效果逐渐减小。3 d以后n-C-S-H对混凝土强度发展没有明显的促进作用,1.5%掺量下混凝土强度反而较空白样有所降低;加入n-C-S-H的硬化水泥浆在12 h~3 d龄期内相比空白水泥浆临界孔径降低,凝胶孔孔隙率提高,毛细孔孔隙率降低。n-C-S-H改变了C-S-H凝胶的生成方式,使其原本从水泥颗粒表面析出变为了从孔溶液中析出,显著减小了毛细孔孔隙率,同时增加了凝胶间孔的体积。这种多核生长的方式导致水化产物结构疏松,从而导致基体强度略微降低。因此,在相同水化程度时,掺有n-C-S-H的混凝土抗压强度略低于空白混凝土。

 Effects of synthesized nano hydrated calcium silicate (n-C-S-H) on cement hydration, pore structure of hardened cement pastes and concrete strength were investigated using isothermal calorimetry, non-evaporative water test, X-ray diffraction, mercury intrusion test and compressive strength tests. The results show that n-C-S-H accelerates the early hydration of cement, significantly increases the hydration degree of cement in the age of 12–24 h, and thereby significantly enhances the compressive strength of concrete in the age of 12–24 h. The strength enhancement effect gradually reduces after 24 h. After 3 days, the acceleration effect on cement hydration and the enhancement effect on compressive strength of concrete become unobvious and the addition of 1.5% n-C-S-H even leads to lower compressive strength in comparison with the blank concrete sample. Compared with blank cement paste, the capillary porosity and the threshold pore size of the hardened cement pastes with addition of n-C-S-H decreases in the age of 12 h–3 d, while the gel porosity increases. Meanwhile, the incorporation of n-C-S-H in cement pastes changes the generation mode of C-S-H gel, which makes a large amount of the hydration product of C-S-H growing from the added n-C-S-H particles, instead of the typical growth from the surface of cement grains due to the so-called heterogeneous nucleation. The massive growth of C-S-H from the added n-C-S-H nuclei leads to the decrease of capillary porosity and the increase of inter-gel porosity. This multi-cores growth model causes a looser structure of hydration product and, thus reduces the strength of the C-S-H matrix. Because of this reason, at the same hydration degree, the compressive strength of concrete mixed with n-C-S-H is slightly lower than that of the blank concrete.

 
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