Development of an Alcali-Silica-Reaction (ASR) Performance Test Method for Fly Ash Concrete – Variation of Pre-storage Time and Determination of Criteria

Project Number 329

Experiences with fly ash as concrete addition over many years have shown that fly ash can successfully be used to avoid damage to concrete by alkali silica reaction (ASR). The alkalis in the binder react with silicates in the alkali-sensitive aggregate and form a gel whose volume steadily increases leading to damage of the microstructure. The use of fly ash in the binder lowers the total alkali content of the concrete and additionally alkalis are incorporated in the reaction products of the fly ash.

Previous investigations have led to the use of fly ash in concrete with ASR sensitive aggregate under certain conditions. Up to now susceptibility to ASR has been tested in a fog chamber at 40 °C. The test is approved, but it requires a long period up to one year.

With the revision of the Alkali Guideline by the German Committee of Reinforced Concrete (DAfStb), a performance test has been introduced as an alternative test method which is being increasingly used in practice. This method uses a higher temperature of 60 °C, thus shortening the testing time. However, investigations show that the effect of fly ash is not adequately assessed with this method. This can lead to restrictions of the application of fly ash concrete if only this performance test is used as criterion.

The present research aims at the determination of robust assessment criteria for the effectiveness of concretes containing fly ash and alkali-sensitive aggregate when tested with the proposed 60°C performance test according to the Alkali Guideline. In particular, the effect of the pre-storage of the specimens will be evaluated. In addition to that, experiences with this new performance test will be gained and a data base for fly ash concrete is build up.

Starting in October 2009 and finishing in September 2011, the project is carried out by the Institute for Building Materials and Construction at the Technical University of Munich under the direction of Prof. Detlef Heinz. It is technically supervised by the Technical Committee Power Plant By-products. The project is assigned to the VGB research programme "Waste Management of Coal-fired Power Plants and Waste Incineration Plants" (ERKOM).