Competitive adsorption between superplasticizer and retarder molecules on mineral binder surface
Competitive adsorption between superplasticizer and retarder molecules on mineral binder surface
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DOI：
10.1016/j.cemconres.2007.12.003
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发表时间：
2008-05-01
影响因子：
11.4
通讯作者：
Winter, Ch.
中科院分区：
文献类型：
--
作者：
Plank, J.;Winter, Ch.
在以普通波特兰水泥（OPC）、铝酸钙水泥（CAC）和硬石膏为三元粘结剂的自流平砂浆中，聚羧酸系高效减水剂（PC）与柠檬酸盐缓凝剂复配时无增塑作用，而与酒石酸盐复配时流动性良好。PC和柠檬酸盐之间的不相容性背后的机制进行了研究，通过吸附和zeta电位测量。此外，还比较了外加剂的阴离子电荷密度。吸附测量结果表明，在柠檬酸盐的存在下，PC吸附急剧下降到小于10%的剂量添加，这意味着完全失去了流动性的糊。然而，在酒石酸盐的存在下，PC吸附保持足够高以仍然提供良好的流动性。相反，酪蛋白生物聚合物的吸附受添加和阻滞剂类型的影响不大。因此，它与两种缓凝剂一起提供高流动性。钙离子阻滞剂复合物和PC的比阴离子电荷密度的比较揭示了它们的吸附行为和阴离子电荷密度之间的直接相关性。具有较高阴离子电荷密度的掺合物对粘结剂表面表现出较高的亲和力，因此更易于吸附。当存在几种外加剂时，只有在吸附具有较高阴离子电荷的外加剂后，仍存在阳离子表面电荷和足够的吸附面积时，具有较低阴离子电荷密度的分子才会吸附。通过增加PC分子的阴离子电荷密度，解决了自流平砂浆配方中PC与柠檬酸盐之间的不相容性问题。与酪蛋白类似，该改性PC的吸附不受阻滞剂分子的影响。(C)2007爱思唯尔有限公司保留所有权利。
In a self-levelling mortar based on the ternary binder system ordinary Portland cement (OPC), calcium aluminate cement (CAC) and anhydrite, a polycarboxylate-based superplasticizer (PC) showed no plasticizing effect in combination with citrate retarder while good flowability was observed with tartrate. The mechanism behind the incompatibility between PC and citrate was investigated by means of adsorption and zeta potential measurements. Also, anionic charge densities of the admixtures were compared. Adsorption measurements revealed that, in presence of citrate, PC adsorption drops dramatically to less than 10% of dosage added, implying a complete loss of fluidity in the paste. In presence of tartrate, however, PC adsorption remains high enough to still provide good flowability. In contrast, adsorption of casein biopolymer is not much affected by addition and type of retarder. Thus it provides high fluidity with both retarders. Comparison of specific anionic charge density of Ca2+ retarder complexes and PC reveals a direct correlation between their adsorption behaviour and anionic charge density. Admixtures with higher anionic charge density show higher affinity to the binder surface and thus adsorb preferredly. When several admixtures are present, molecules with lower anionic charge density will adsorb only if, after adsorption of the admixture with higher anionic charge, a cationic surface charge and enough adsorption area still exists. The incompatibility problem between PC and citrate in the self-levelling mortar formulation was solved by increasing the anionic charge density of the PC molecule. Similar to casein, adsorption of this modified PC is not much influenced by retarder molecules. (C) 2007 Elsevier Ltd. All rights reserved.