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Main Title: Investigation of the Incompatibilities of Cement and Superplasticizers and Their Influence on the Rheological Behavior
Author(s): Pott, Ursula
Jakob, Cordula
Jansen, Daniel
Neubauer, Jürgen
Stephan, Dietmar
Type: Article
Language Code: en
Abstract: 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.
Issue Date: 21-Feb-2020
Date Available: 28-Apr-2020
DDC Class: 660 Chemische Verfahrenstechnik
Subject(s): rheology
incompatibility of superplasticizer
spread flow test
in-situ XRD
Sponsor/Funder: DFG, 386869775, Rheologie wirksame Additive in Portlandzement-basierten Formulierungen - Von nano/mikro-skaligen Strukturen zu makroskopischen Eigenschaften -
DFG, 313773090, SPP 2005: Opus Fluidum Futurum - Rheologie reaktiver, multiskaliger, mehrphasiger Baustoffsysteme
DFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berlin
Journal Title: Materials
Publisher: MDPI
Publisher Place: Basel
Volume: 13
Issue: 4
Article Number: 977
Publisher DOI: 10.3390/ma13040977
EISSN: 1996-1944
Appears in Collections:FG Baustoffe und Bauchemie » Publications

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