变温下SO_2^(-4)对水泥硬化浆体中Al^(3+)配位分布的影响

Effect of sulfate ions on distribution of Al^(3+) coordination in hardened cement pastes at variable temperature

基于大体积混凝土内部的温度变化,利用27 Al魔角旋转核磁共振(27 Al MAS NMR)结合去卷积技术,研究变温下SO2-4对水泥硬化浆体中Al 3+配位分布的影响。结果表明,变温的高温阶段促进AFt、TAH(third aluminum hydrate)和掺杂在C-S-H结构中(C-S-A-H)的四配位铝(Al[4])向AFm转化;降温阶段促进TAH生成,利于AFm和C-S-A-H中Al[4]向AFt转化;而变温后20℃常温不仅利于AFt向AFm转化,TAH向Al[4]转变,而且利于Al[4]进入高钙硅比(Ca/Si)C-S-H结构。在5%Na2SO4溶液中,SO2-4在侵蚀3d时首先对AFm侵蚀,对TAH和C-S-A-H中Al[4]侵蚀作用较小;变温过程的高温加快SO2-4对AFm和TAH的侵蚀,并且对C-S-A-H凝胶有脱铝作用;变温后20℃常温有利于C-S-H凝胶与硫酸根竞争Al[4],低Ca/Si的C-S-A-H凝胶具有较强的抗SO2-4脱铝能力。

Based on the temperature variation in the interior of mass concrete,the effect of sulfate ions on distri-bution of Al3＋ coordination in hardened cement pastes at variable temperature were investigated by 27 Al magic angle spinning （MAS）nuclear magnetic resonance（NMR）with deconvolution technique.The results indicated that the high temperature during the variable temperature process promoted ettringite （AFt）,third aluminum hydrate （TAH）and tetrahedral coordination Al3＋（Al[4]）incorporated in C-S-H structure transformed to mo-nosulphate （AFm）.And the decreasing temperature process promoted the formation of TAH,and was benefi-cial to the AFm and Al[4]transforming to the AFt.But the normal temperature of 20 ℃ was not only advanta-geous for transformation from AFt to AFm,and from TAH to Al[4],but also for Al[4]entering into the C-S-H structure with high Ca/Si.However,in 5% Na2 SO4 solution,firstly,the AFt was formed due to AFm at-tacked by the sulfate ions,and the effect of sulfate ions on the TAH and tetrahedral coordination Al3＋ in C-S-H structure was less at 3 d.The variation temperature speeded up the corrosion of sulfate ions for TAH and Al [4],and there was a dealuminization of the sulfate ions for C-S-A-H gels.Moreover,the normal temperature of 20 ℃ was beneficial to competition of C-S-H gels with sulfate ions for the Al[4],and the sulfate ions resist-ance of dealuminization of C-S-A-H gels with low Ca/Si was stronger.