Journal article
Fluorescence Microscopic Investigations of the Retarding Effect of Superplasticizers in Cementitious Systems of UHPC

Publication Details
Arend, J.; Wetzel, A.; Middendorf, B.
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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 e ects 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, a ects 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 di erent polymers
and the correlation to the retarding e ect of superplasticizers, especially concerning the presence of
silica fume, which is indispensable for ultra-high performance concrete (UHPC).

Last updated on 2021-04-05 at 16:41