高碱性介质中高效减水剂与模型粉的相互作用

R. Flatt, Y. F. Houst, P. Bowen, H. Hofmann, J. Widmer, U. Sulser, U. Mäder, T. A. Bürge
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引用次数: 43

摘要

摘要:人们普遍认为,高效减水剂在水泥颗粒上的吸附是决定混凝土流变性的关键因素。为了避免与水泥水化有关的问题,经常在非反应性模型粉上研究高效减水剂的吸附。然而,为了使模型系统保持尽可能接近水泥,表面应该具有相似的电荷和相似的化学性质。此外,溶液的pH值应接近水化水泥的pH值(约12.5)。在这些条件下,水泥已被证明具有带正电的表面。本研究使用的模型粉末为Mg(OH) 2和死烧MgO,其标称等电点分别为12.0和12.4,化学性质与Ca(OH) 2和CaO相似。研究了该模型悬浮液的表面电荷与加入高效减水剂的关系。这些药物要么是市售的,要么是目前正在开发的,从强离子到弱离子不等。测定了两种结构相似但离子基间距不同的聚合物高效减水剂在pH为12和11.3、温度为10 ~ 40℃时对MgO和Mg(OH) 2的吸附等温线。结果表明,低离子聚合物对氧化镁的吸附具有很强的温度依赖性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Interaction of Superplasticizers with Model Powders in a Highly Alkaline Medium
Synopsis: It is broadly recognized that the adsorption of superplasticizers on cement particles is a key factor in determining the rheology of concrete. In order to avoid the problems linked to the hydration of cement, the adsorption of superplasticizers is often studied on unreactive model powders. However, in order for the model system to remain as close as possible to cement, the surface should have a similar charge and a similar chemical nature. Furthermore, the pH of the solution should be close to that of the hydrating cement (about 12.5). Under these conditions, cement has been shown to have a positively charged surface. The model powders used in this study were Mg(OH) 2 and dead burnt MgO, which have nominal isoelectric points of 12.0 and 12.4 respectively, and which are chemically similar to Ca(OH) 2 and CaO. The surface charge of such model suspensions was studied as a function of added superplasticizer. These were either commercially available or currently under development, ranging from strongly to very weakly ionic. Adsorption isotherms for two polymeric superplasticizers, with similar structures but with different ionic group spacing, have been measured for both MgO and Mg(OH) 2 at pH 12 and 11.3 respectively and between 10 and 40°C. Results showed a strong temperature dependence for the adsorption of the less ionic polymer on MgO.
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