Project Number 310

Production of Air-entrained Fly Ash Concrete with Plasticising Concrete Admixtures

In practice, problems concerning the stability of air voids have increasingly occurred at air-entrained concretes recently, which hint at incompatibilities among the applied concrete admixtures or at incompatibilities between concrete admixture and binder. To some extent there are problems with air entrainment in concrete and the lacking stability of air voids especially when using superplasticisers (SP) of the newer generation based on polycarboxylate ether (PCE). When superplasticisers and air-entraining agents (AEA) are used simultaneously, the effectivity of the AEA may be impaired by the defoamer contained in the SP. In this case, the characteristic values of the air voids are not kept at the hardened concrete.

The principal effectivenesses of AEA and SP are examined and durable AEA/SP combinations are developed in a parallel research project handled by the Verein Deutscher Zementwerke e. V. (German Cement Works Association). The effects of SP on the air void formation and stability in the fresh concrete as well as the air void structure in the hardened concrete are determined in this research project at the Institute for Building Materials Research (ibac) of the RWTH Aachen University. A simple test method shall be developed to systematically assess the interactions of different concrete admixtures regarding the air void formation and the AEA demand regarding changing basic materials at low material and equipment costs. The so-called Foam Index Test (FIT), which will be modified accordingly in this project, serves as a basis.

The characteristic values of the air voids and the freeze-thaw and de-icing salt resistance are examined on test specimens. With it, a correlation between the fresh concrete properties, the characteristic values of the air voids and the possibly different performance of the concretes at the freeze-thaw and de-icing salt test can be determined. Based on the findings of the research project, handling instructions will be developed, which shall enable a targeted production of air-entrained concrete even at varying basic material properties by adjusting the AEA dosage. Subsequently, the findings of the laboratory tests are verified by practical tests in a ready-mix concrete plant. The handling instructions can be verified or, if necessary, adjusted by means of these practical tests.

The project is assigned to the VGB research programme “Waste management of coal-fired power plants and combustion plants” (ERKOM). Starting in March 2008 and finishing in February 2010, the project is carried out by the Institute for Building Materials Research (ibac) of the RWTH Aachen University directed by Prof. Brameshuber and is technically supervised by the VGB Technical Committee Power Plant By-products . The project is funded by the Federal Ministry of Economics and Technology via the German Federation of Industrial Research Associations "Otto von Guericke" (AiF Project No. 15546 N).