Development of a performance test to determine the sulfate resistance of concrete

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2022). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022
The resistance of concrete against sulfate attack is often investigated by laboratory test methods on mortar specimens using expansion measurements. In rare cases, strength loss is measured by flexural or tensile strength tests. The objective of this work was the development of a new performance test method that takes into account both the chemical and physical resistance of a given concrete mix to sulfate attack. Statistical design of experiments was used to investigate the significance and accelerating effect of various relevant parameters, such as binder type, storage temperature, type and concentration of sulfate solution, and concrete composition, on the residual tensile strength ft of ASTM C307-03 briquet specimens. To evaluate the sulfate resistance of different concretes, the tensile strength was normalized, i.e., it was related to the tensile strength of the same-aged, unstressed concrete. For this purpose, the fib Model Code's maturity formula was adapted. It was demonstrated that it can be used to predict the tensile strength of an undamaged concrete ftm during the test period with sufficient accuracy. As a result, a test procedure was described, which is based on testing the relative tensile strength and considers all relevant parameters. Tests on 23 concretes with different cements and cement-fly ash combinations were used to establish threshold values for the reliable evaluation of sulfate resistance. Accordingly, a high sulfate resistance is given if the relative tensile strength of the concrete does not fall below a value of 0.70 after 273 days of sulfate storage. Furthermore, two criteria for test termination can be defined after 182 days of storage. If the concretes exhibit a relative tensile strength of > 0.85, then it can be assumed that the proposed threshold value of ft/ftm ≥ 0.70 is met also after 273 days of storage, and thus a high sulfate resistance of the concrete is given. If the concretes have a relative tensile strength of ft/ftm < 0.70, then their sulfate resistance is classified as low. In the modified SVA method commonly used for approval tests in Germany, tests with moderate sulfate concentration currently have to be carried out for two years. The new method is able to evaluate the sulfate resistance of concrete in a much shorter period of time under realistic environmental conditions.
Published by RWTH Aachen University, Aachen