Entwicklung und Applikation von kontinuierlichen Glasschutzschichten auf Betonoberflächen

• Development and application of continuous glass protection layers on concrete surfaces

Eiwen, Felix Tobias; Roos, Christian Hans-Georg (Thesis advisor); Raupach, Michael (Thesis advisor)

Aachen (2020, 2021)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020

Abstract

The production of cement is a resource-, energy- and cost-intensive process which is the main source of CO2 in the manufacture of concrete structures. When using concrete components such as sewage pipes, clarifiers or cooling towers, operators are looking for possibilities to protect these components from external influences in order to significantly extend their service life. The focus of this work is on the development and application of continuous glass protective layers on concrete. For this purpose, a semi-automatic application process was developed using a robot and a flame spraying system, in which various self-developed glasses as well as commercial glasses could be applied to concrete substrates to form well bonded and continuous protective layers. In order to apply an optimal glass layer on the concrete substrate, the application temperature of the glass must be in the viscosity range log"η" ("η" in dPa·s) = 2 to 4. For the glasses tested in this thesis, the application windows correspond to 1040 °C to 1214 °C and a concrete substrate preheating temperature of at least 250 °C. The glass layers were applied in a defined spray pattern at a distance of 8 or 10 cm to the substrate and robot speeds of 80 to 220 "mm" /"s" . Depending on the spraying parameters, glass layer thicknesses of approx. 1.17 mm per spraying run were applied. Such coatings achieve adhesion tensile values of > 1.0 MPa, which satisfies the constructional requirements of the potential fields of application. Irrespective of the type of glass applied, water-impermeable coatings could be applied to small surfaces using the flame spraying process, but cracks could occur as a result of the process. Such cracks are a critical point in the glass protective layer and must be sealed by subsequent treatments. When glass-concrete composites are used for waste water disposal, chemical requirements are demanded on the glass in addition to adhesion. The challenge is to develop a glass composition according to the phase-theoretical approach that is sufficiently resistant to the strongly alkaline environment on the concrete side (pH = 13.2) and at the same time resistant to the strong acid attack (pH = 1.5) on the waste water side. The glass compositions (ZEM glasses) from the CaO Al2O3 SiO2 system, developed after a selection of thermodynamic calculations and optimised by substituting CaO with MgO and/or ZnO, are characterised by an excellent chemical resistance in alkaline environments (maximum mass loss = 0.6 Ma. %) and their acid resistance has been improved compared to pure CAS glass compositions. In addition, such developed ZEM glasses can be used as additives in concrete production due to their good alkaline properties as well as low-cost raw material selection. This allows the cement content to be reduced without the need for technical restrictions on the concrete component. Although the chemical resistance of the developed ZEM glasses is five times better than untreated concrete, a comprehensive protection of the concrete against acid waste water cannot be guaranteed. In corrosion tests in synthetic buffer solution (pH = 1.5) these glasses showed a mass loss of 24 - 34 Ma. %. Improved protection can therefore be achieved by optimising the flame spraying process, as a multilayer system consisting of an alkali-resistant ZEM glass applied first and then an acid-resistant glass can be applied. The knowledge gained in this work can easily be applied to other glass types in order to determine the respective individual application windows and spraying parameters.

Institutions

• Division of Materials Science and Engineering [520000]
• Chair of Glass and Glass-ceramic [524210]