Effectiveness of Polycarboxylate Superplasticizers in Ultra-High Strength Concrete: The Importance of PCE Compatibility with Silica Fume
Effectiveness of Polycarboxylate Superplasticizers in Ultra-High Strength Concrete: The Importance of PCE Compatibility with Silica Fume
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DOI：
10.3151/jact.7.5
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发表时间：
2009-02-01
影响因子：
2
通讯作者：
Sieber, Roland
中科院分区：
文献类型：
--
作者：
Plank, Johann;Schroefl, Christof;Sieber, Roland
合成了甲基丙烯酸酯以及基于烯丙基醚的聚羧酸酯(PCE)，以增塑水/水泥比为0.22的水泥和硅粉的浆体。研究发现，甲基丙烯酸酯共聚物可以很好地分散水泥，而烯丙醚共聚物对于硅粉的分散效果更佳。机理研究表明，在水泥孔隙溶液中，硅粉的表面电荷通过将 Ca2+ 吸附到二氧化硅表面上带负电的硅烷醇盐基团上而变为正电荷。这样，聚羧酸酯共聚物就会吸附并分散硅粉颗粒。因此，在水泥-硅粉浆料中测试了两种共聚物的混合物。这些共混物提供比仅使用一种聚合物明显更好的分散性。显然，水化水泥（这里主要是钙矾石）和硅粉的表面在化学成分上有很大不同。因此，需要具有不同分子结构的 PCE 来与这些表面上存在的钙原子提供最大程度的配位。
Methacrylate ester as well as allylether based polycarboxylates (PCEs) were synthesized to plasticize pastes of cement and silica fume having a water/cement ratio of 0.22. Methacrylate ester copolymers were found to disperse cement well, whereas allylether copolymers are more effective with silica fume. Mechanistic investigations revealed that in cement pore solution, the surface charge of silica fume becomes positive by adsorption of Ca2+ onto negatively charged si-lanolate groups present on the silica surface. This way, polycarboxylate copolymers adsorb to and disperse silica fume grains. Thus, mixtures of both copolymers were tested in cement-silica fume pastes. These blends provide significantly better dispersion than using only one polymer. Apparently, the surfaces of hydrating cement (here mainly ettringite) and silica fume are quite different with respect to their chemical composition. Therefore, PCEs with different molecular architectures are required to provide maximum coordination with calcium atoms present on these surfaces.