Avoidance of Alkali Reactions by Fly Ash - Examinations of Concretes During Long-term Storage

Project Number 344

Within an AiF Research Project (AiF No. 13605, VGB No. 245) the possibility to avoid a damaging alkali-silica reaction in concrete with alkali-sensitive aggregates by using fly ash as concrete addition was examined. It was proven that the exchange of cement by fly ash enables the production of concrete with alkali-sensitive aggregates without getting a damaging alkali reaction in concrete. The results of the research project were considered during the revision of the "Alkali Guideline" of the German Committee of Reinforced Concrete (DAfStb).

The concrete samples produced within this project are still stored in the Institute for Building Materials and Construction. These are approximately 60 concretes with different alkali-sensitive aggregates (gravel with opal sandstone/flint, material from the upper Rhine rift and greywacke) and combinations of binders with different additions. Within this projects these concretes shall be further stored in the fog chamber at 40 °C and 100 % r.F. as well as outside and shall be observed continuously. All concretes are constantly examined for cracking and stretching. Selected concretes will be investigated chemically in order to examine the composition of the pore solution and with microscopic investigations at thin sections.

The examinations of the samples stored outside or in the fog chamber are carried out to confirm and complete the insights won so far. Aim of the examinations is to draw up differentiated evaluation criteria for concretes with fly ash.

The project is the continuation of the project 300 and technically assigned to the VGB Research Programme "Waste Management of Coal-fired Power Plants and Combustion Plants" (ERKOM). It is carried out by the Institute for Building Materials and Construction at the Technical University of Munich directed by Prof. Detlef Heinz and is technically supervised by the VGB Technical Committee "Power Plant by-products".