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Open AccessArticle

Investigation of the Incompatibilities of Cement and Superplasticizers and Their Influence on the Rheological Behavior

1
Department of civil engineering, Building Materials and Construction Chemistry, Technische Universität Berlin, 13355 Berlin, Germany
2
Department of Geography and Geosciences, GeoZentrum Nordbayern, Friedrich-Alexander-University, 91054 Erlangen, Germany
*
Author to whom correspondence should be addressed.
Materials 2020, 13(4), 977; https://doi.org/10.3390/ma13040977
Received: 2 December 2019 / Revised: 7 February 2020 / Accepted: 18 February 2020 / Published: 21 February 2020
(This article belongs to the Special Issue Rheology of Reactive, Multiscale, Multiphase Construction Materials)
The rheological behavior of cement paste and the improvement of its flowability takes center stage in many research projects. An improved flowability can be achieved by the addition of superplasticizers (SP), such as polycarboxylate ethers (PCE). In order to be able to use these PCEs effectively and in a variety of ways and to make them resistant to changes in the environment, it is crucial to understand the influence of SPs on cement hydration. For that reason, the topic of this paper was the incompatibility of a specific SP and an ordinary Portland cement (OPC). The incompatible behavior was analyzed using rheological tests, such as the spread flow test and penetration test, and the behavior was compared by means of an ultrasound technique and explained by the phase content measured by in-situ X-ray diffraction (XRD) the heat evolution measured by calorimetry, and scanning electron microscope (SEM) images. We showed that the addition of the SP in a high dosage led to a prevention of the passivation of the most reactive and aluminum-containing clinker phases, aluminate and brownmillerite. This induced the aluminate reaction to take place in the initial period and led to an immediate stiffening of the cement paste and, therefore, to the complete loss of workability. The results showed that in addition to the ettringite, which began to form directly after water addition, hemicarbonate precipitated. The fast stiffening of the paste could be prevented by delayed addition of the SP or by additional gypsum. This fast stiffening was not desirable for SPs, but in other fields, for example, 3D printing, this undesirable interaction could be used to improve the properties of printable mortar. View Full-Text
Keywords: rheology; incompatibility of superplasticizer; hydration; spread flow test; penetration; in-situ XRD; calorimetry; ultrasound; SEM rheology; incompatibility of superplasticizer; hydration; spread flow test; penetration; in-situ XRD; calorimetry; ultrasound; SEM
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MDPI and ACS Style

Pott, U.; Jakob, C.; Jansen, D.; Neubauer, J.; Stephan, D. Investigation of the Incompatibilities of Cement and Superplasticizers and Their Influence on the Rheological Behavior. Materials 2020, 13, 977.

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