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Open AccessArticle

Alkalinity and Its Consequences for the Performance of Steel-Reinforced Geopolymer Materials

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Dental Prosthetics and Materials Science, Leipzig University, 04275 Leipzig, Germany
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Else Kooi Lab., Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, 2628 CT Delft, The Netherlands
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Chemistry Department, Faculty of Science, Zagazig University, Zagazig 44519, Egypt
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Institute of Mineralogy, Crystallography and Materials Science, Leipzig University, 04275 Leipzig, Germany
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Institute of Concrete Structures and Building Materials, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
*
Author to whom correspondence should be addressed.
Academic Editor: William Skene
Molecules 2020, 25(10), 2359; https://doi.org/10.3390/molecules25102359
Received: 8 April 2020 / Revised: 23 April 2020 / Accepted: 15 May 2020 / Published: 19 May 2020
(This article belongs to the Special Issue Advances in Alkali-Activated Materials)
This paper investigates the development of the alkalinity and its impact on carbon steel reinforcement embedded in alkali-activated fly ashes (AAFA) and alkali-activated fly ashes with ten percentage mass (wt%) of blast furnace slag (AAFAS)-based materials (geopolymer–GP). The pH analysis of eluates indicates a remarkable decrease of alkalinity in AAFA and AAFAS in the first hours of the geopolymerization process. Phenolphthalein solution and pore solution tests on concretes also show a sharp decrease of alkalinity with increased Ca content in the binder due to carbonation. Micro X-ray computer tomography (µXCT) and electrochemical techniques indicate that the changed pH in the GP systems was accompanied by a decrease in the corrosion rates of steel reinforcement when compared to ordinary Portland cement (OPC) systems. In contrast to calcite and vaterite, which were detected in OPC and AAFAS after a carbonation process, only sodium carbonate natron was determined at lower levels in AAFA by X-ray diffraction (XRD). View Full-Text
Keywords: geopolymer concrete; alkalinity; micro X-ray computer tomography (µXCT); steel reinforcement corrosion geopolymer concrete; alkalinity; micro X-ray computer tomography (µXCT); steel reinforcement corrosion
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MDPI and ACS Style

Koenig, A.; Mahmoud, H.; Baehre, O.; Dehn, F. Alkalinity and Its Consequences for the Performance of Steel-Reinforced Geopolymer Materials. Molecules 2020, 25, 2359.

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