Development of adequate test methods for the early evaluation of fresh concrete for a target-oriented production

Project duration: November 2020 to April 2023

The aim of this research project is to develop test methods suitable for construction sites for evaluating the surface workability of fresh concrete. In particular, the properties of fresh concrete relevant for subsequent surface treatment are to be made assessable. At the same time, corresponding performance/acceptance criteria are to be defined for these test methods. The project is to be based directly on orienting studies carried out as part of a DBV 302 research project sponsored by the Deutscher Beton- und Bautechnikverein e.V. and conducted by the Chair of Building Materials Technology at the Ruhr University in Bochum. In these studies, promising approaches to the practical evaluation of the rheological properties of mortars and concretes with regard to appropriate surface treatment emerged, which are now to be consolidated in order to find their way into practice.

In practice, it is sometimes found that fresh concrete surfaces cannot be properly finished after installation, even though the consistency of the concrete on delivery corresponded to the specifications made in advance. This mainly affects floor slabs and floor slabs where the concrete surface is to be finished by mechanical smoothing. Concretes that turn out to be critical for this purpose usually exhibit a very high "stickiness". It is known from various studies that superplasticizers based on PCE can lead to such behavior. However, products that promote such behavior cannot be defined in principle, since the "stickiness" of a mortar is also influenced by the respective cement or cement paste, and thus the combination of binder and superplasticizer has to be considered. Furthermore, the rheological behavior can also be influenced by different temperatures. Concretes with increased "stickiness" thus significantly complicate subsequent processing / finishing of concrete surfaces or even make it impossible. In order to avoid such negative effects, a corresponding check of this property already at the acceptance of the concrete would be extremely helpful. To date, there are no adequate test methods and associated performance criteria for this.

Acknowledgements

The Chair of Building Materials Technology would like to thank the German Concrete and Construction Technology Association (Deutscher Beton- und Bautechnik-Verein e. V.), the Federation of Industrial Research Associations "Otto von Guericke" e. V. (AiF) and the Federal Ministry of Economics and Climate Protection for their funding and support. Special thanks also go to the project-supporting committee and all partners involved for the excellent, scientifically very exciting and humanly very pleasant cooperation.