In-situ microscopic investigations of the interaction of admixtures and solid surfaces in cementitious systems

如果不使用有机外加剂，矿物基高性能材料的生产是不可能的。这些混凝土和砂浆的应用日益多样化以及辅助胶凝材料数量的不断增加，需要有机外加剂更高的专业化和效率。超增塑剂，如聚羧酸醚，是具有低水/胶比的混凝土如超高性能混凝土（UHPC）所必需的。水泥基体系中使用的另一种有机外加剂是可再分散聚合物粉末（RP）。例如，它们用于瓷砖粘合剂砂浆中，以改善硬化砂浆的机械性能。特别是对于改善非多孔表面的粘附性，将RP添加到胶凝材料中是有效的。然而，这些RP也用于水泥基粘合剂中，用于连接纤维增强UHPC的结构元件，特别是改善对钢纤维的粘附性，这是申请人的部门中进行的当前研究项目的一部分。对于这两个例子，有机混合物和矿物或金属表面的相互作用是至关重要的。这两种类型的有机外加剂的作用机制已经在一般情况下进行了研究，但没有在现场的方法进行详细分析的矿物或金属表面和有机外加剂的相互作用存在。该项目的目的是使用荧光显微镜开发这种原位方法，这在生物学等其他学科中是众所周知的。 在常规显微镜方法中，通常看不到外加剂。因此，混合物分子将被荧光染料染色，使其在荧光显微镜下可见。在胶凝材料中，pH值、离子浓度、外加剂浓度和固体表面性质等参数是至关重要的，因此会发生变化。为了验证该方法，将依赖于这些环境影响因素的外加剂分布与常用方法的结果和相关砂浆的宏观性能进行比较。这种新的原位方法允许对新的外加剂-粘结剂组合的相互作用进行研究，从而能够预测宏观性能。本文将通过上述两个应用实例对荧光显微镜法进行开发和验证：1.根据环境的不同，将现场分析高效减水剂在不同矿物表面上的吸附。研究结果将与相关砂浆的流变性能相关联。2.通过单根钢纤维的拉拔试验，考察了RP对矿物胶粘剂粘接强度的改善作用。通过荧光显微镜，RP在钢纤维界面处的分布将被分析，并与宏观拉拔试验进行比较。

The production of mineral based high performance materials is not possible without the use of organic admixtures. The increasing diversity of application of these concretes and mortars and the rising number of supplementary cementitious materials necessitates a higher specialization and efficiency of the organic admixtures. Superplasticizers, like polycarboxylate ethers, are necessary for concretes with a low water/binder ratio like ultra-high performance concrete (UHPC). Another organic admixtures used in cement based systems is redispersible polymer powder (RP). For instance, they are used in tile adhesive mortars to improve the mechanical properties of the hardened mortar. Especially for improving the adherence on non-porous surfaces, adding RP to cementitious materials is effective. Though, these RP are also used in cement based adhesives for joining structural elements of fibre-reinforced UHPC especially improving the adherence to the steel-fibres, which is part of a current research project conducted in the department of the applicants. For both examples the interaction of organic admixture and mineral or metallic surfaces is crucial. The mechanisms of action of both types of organic admixtures were already investigated in general, but no in-situ-method for detailed analyses of the interaction of mineral or metallic surfaces and organic admixtures exists. The aim of this project is a development of such an in-situ-method using fluorescence microscopy, which is well known from other disciplines like biology. Admixtures are usually not visible in conventional microscopic methods. Therefore, the admixture molecules will be stained with a fluorescing dye making them visible in fluorescence microscopy. In cementitious materials, the parameters pH value, ion concentration, concentration of admixture and character of solid surface are crucial and thus will be varied. For validation of this method, the distribution of admixtures in dependency of those environmental influencing factor will be compared to the results of common methods and macroscopic properties of related mortars. This novel in-situ-method allows investigations on the interaction of new admixture-binder-combinations enabling the prediction of macroscopic properties. This fluorescence microscopic method will be developed and validated with this two above mentioned application examples: 1. In dependency on the environment the adsorption of superplasticizers on different mineral surfaces will be analysed in situ. The results will be correlated to rheological properties of related mortar. 2. The improving properties of RP on adhesion strength of mineral adhesives will be tested by pullout-tests of single steel fibres. By fluorescence microscopy the distribution of RP at the interface to the steel fibre will be analysed and compared to the macroscopic pullout tests.