Fluorescence Microscopic Investigations of the Retarding Effect of Superplasticizers in Cementitious Systems of UHPC
Fluorescence Microscopic Investigations of the Retarding Effect of Superplasticizers in Cementitious Systems of UHPC
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DOI：
10.3390/ma13051057
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发表时间：
2020-03-01
期刊：
影响因子：
3.4
通讯作者：
Middendorf, Bernhard
中科院分区：
文献类型：
--
作者：
Arend, Johannes;Wetzel, Alexander;Middendorf, Bernhard
超塑化剂分子在水泥体系中颗粒表面的吸附是浆体和混凝土所需液化的一个非常重要的方面。这样，梳形聚合物屏蔽颗粒之间的吸引力并诱导良好分散的均匀悬浮液。这些外加剂允许使用细填料，甚至与少量的混合水结合使用，因此是现代高性能混凝土的基础。然而，吸附并不仅仅产生有益的效果：聚合物覆盖的颗粒表面，特别是熟料，被阻碍与水相互作用，从而延缓水合。这是早期强度较低的原因，并且对于某些应用非常不利。如今，已知聚合物的分子结构，例如链长和电荷密度，强烈地影响延迟。胶凝体系的复杂性和多样性是这一领域的研究相当经验和时间以及成本密集的主要原因。为了研究高效减水剂在各种系统中的原位吸附，应用了荧光显微镜方法：通过用荧光染料对聚合物进行染色，它们变得可定位并且吸附可量化。研究了分子结构对不同聚合物的吸附特性的影响，以及与高效减水剂缓凝效果的相关性，特别是与超高性能混凝土（UHPC）中不可缺少的硅灰的存在有关。
The adsorption of superplasticizer molecules to particle surfaces in cementitious systems is a very important aspect for the desired liquefaction of pastes and concretes. This way, the comb shaped polymers shield attractive forces between the particles and induce a well-dispersed, homogeneous suspension. These admixtures allow the usage of fine fillers even in combination with low amounts of mixing water, and thus, are the basis for modern high performance concretes. However, the adsorption does not cause beneficial effects only: The polymer covered particle surfaces, especially clinker, are hindered to interact with water, thus hydration is retarded. This is the reason for lower early strength and is very disadvantageous for certain applications. Today it is known that the molecular structure of the polymers, for instance the chain length and charge density, affects the retardation strongly. The complexity and diversity of cementitious systems is the main reason why research in this field is quite empiric and time as well as cost intensive. To investigate the adsorption of superplasticizers in various systems in-situ, a fluorescence microscopic approach was applied: By staining the polymers with fluorescent dye they become localizable and the adsorption quantifiable. This work shows the influence of molecular structure to adsorption characteristic of different polymers and the correlation to the retarding effect of superplasticizers, especially concerning the presence of silica fume, which is indispensable for ultra-high performance concrete (UHPC).