Influence of pozzolanic additives on hydration mechanisms of tricalcium silicate
Influence of pozzolanic additives on hydration mechanisms of tricalcium silicate
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DOI：
10.1111/jace.15518
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发表时间：
2018-08-01
影响因子：
3.9
通讯作者：
Kumar, Aditya
中科院分区：
文献类型：
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作者：
Lapeyre, Jonathan;Kumar, Aditya
火山灰矿物添加剂，如硅灰（SF）和偏高岭土（MK），被用来部分取代混凝土中的水泥。本研究通过大量的实验和模拟来阐明和对比SF和MK对水泥主要相硅酸三钙（三斜C3S）早期水化速率的影响。结果表明，在低替代水平（即10%）下，SF和MK通过填充效应加速了C3S的水化速率，即增强了主要水化产物（C-S-H：水合硅酸钙）在添加剂提供的额外表面上的非均相成核。SF的填充效果不如MK，因为SF的细颗粒聚集，导致其表面积明显减小（可达97%）。在较高的替代水平（即20%）下，当SF继续作为填充物时，MK允许C-S-H在其表面成核的倾向被大大抑制。MK填充效应的这种逆转归因于MK溶解释放的溶液中大量的铝酸盐[Al(OH)(4)(-)]离子，这些离子抑制了C-S-H成核的地形位点，阻碍了其随后的生长。结果还表明，在水化的前24小时，MK是优于SF的火山灰。然而，SF和MK的火山灰活性都是有限的，因此不会对C3S的早期水化动力学产生显著的改变。总的来说，这项研究的结果为填料的机制起源、SF和MK的火山灰效应以及它们对胶凝反应速率的影响提供了新的见解。
Pozzolanic mineral additives, such as silica fume (SF) and metakaolin (MK), are used to partially replace cement in concrete. This study employs extensive experimentation and simulations to elucidate and contrast the influence of SF and MK on the early age hydration rates of tricalcium silicate (triclinic C3S), the major phase in cement. Results show that at low replacement levels (i.e., 10%), both SF and MK accelerate C3S hydration rates via the filler effect, that is, enhanced heterogeneous nucleation of the main hydration product (C-S-H: calcium-silicate-hydrate) on the extra surfaces provided by the additive. The filler effect of SF is inferior to that of MK because of agglomeration of the fine particles of SF, which causes significant reduction (i.e., up to 97%) in its surface area. At higher replacement levels (i.e., 20%), while SF continues to serve as a filler, the propensity of MK to allow nucleation of C-S-H on its surface is substantially suppressed. This reversal in the filler effect of MK is attributed to the abundance of aluminate [Al(OH)(4)(-)] ions in the solutionreleased from the dissolution of MKwhich inhibit topographical sites for C-S-H nucleation and impede its subsequent growth. Results also show that in the first 24hours of hydration, MK is a superior pozzolan compared to SF. However, the pozzolanic activities of both SF and MK are limited and, thus, do not produce significant alterations in the early age hydration kinetics of C3S. Overall, the outcomes of this study provide novel insights into the mechanistic origins of the filler and pozzolanic effects of SF and MK, and their impact on cementitious reaction rates.