粉煤灰抑制ASR的机制

Mechanism of Fly Ash on ASR

本文研究粉煤灰对ASR的抑制作用。测定了不同粉煤灰掺量砂浆棒膨胀率、水泥石中Ca(OH)2含量以及主要水化产物C-S-H凝胶的微观结构和化学组成,并对粉煤灰抑制ASR的机制进行探讨。结果表明:随粉煤灰掺量增加,其对ASR具有显著的抑制效果。水泥石中Ca(OH)2含量不断减少,二次反应生成大量低n(Ca)/n(Si)的C-S-H凝胶。随n(Ca)/n(Si)降低,C-S-H凝胶中固溶了大量的Al,凝胶的固碱能力增强,从而使混凝土孔溶液中的有效碱大大减少,减轻了ASR程度。凝胶的固碱能力增强除了因n(Ca)/n(Si)降低,使C-S-H凝胶的固碱能力增强之外。还可能因为Al3+代替Si4+形成[AlO4]5-四面体,由于Al3+比Si4+少一价,引起电价不平衡,系统带负电,因此碱离子更容易进入C-S-H凝胶中,减少了碱与活性集料反应的机会。

This paper studied the effect of fly ash on ASR. The expansion rate of mortar bars, the content of Ca（OH）2 at 80 ℃ in simulated alkali solution for 91 days and the microstructure and chemical composition of C-S-H gel were measured. The mechanism of fly ash on ASR was also discussed. The results showed that fly ash had strongly preventive effect on controlling ASR and the content of Ca（OH）2 decreased with increasing of fly ash. Ca（ OH）2 reacted with fly ash to produce more low Ca/Si molar ratio C-S-H gel. With the decreasing of Ca/Si molar ratio, more Al appeared in C-S-H, and more Na ＋ and K ＋ ions bond in C-S-H gel. Thereby a reduction in the amount of soluble alkali available for ASR appeared. The reason that C-S-H gel with low Ca/Si molar ratio could bind more alkali is not only for the low Ca/Si molar ratio, but also for much alumina in fly ash, Al can be introduced into tetrahedral sites for Si leading to a negative charge on the C-S-H. The charge may be balanced by inclusion of alkali, （Na^＋ , K^＋ ） ＋ Al^3＋ = Si^4＋ .