Detailed Investigations of the Sulphate Resistance of Fly Ash Concrete

Project Number 287

Over the last years, a thaumasite formation on a number of mortar samples was observed in laboratory tests regarding the sulphate resistance of concrete. The mortars were produced with different cements and mixtures of cement and additions. It is well known that lab tests do not directly represent the conditions in practise - particularly the concrete composition and density, the strength development at the beginning of the sulphate attack as well as the thickness of concrete structure. The test procedures expose the samples to a much harder attack than normally occurs in practice. In Germany, no damages were observed when the requirements of the valid regulations were kept.

The evaluation of the sulphate resistance of a cement or a cement fly ash combination is performed based on time-lapse examinations so far. However, these tests are controversial discussed regarding the evaluation of the received results because unfavourable binders according to lab tests showed a good sulphate resistance in practice. For this reason, the sulphate resistance in this project will be tested at a lower ambient air temperature (lower than 10 °C) and preferably with concrete samples instead of mortar prisms. The samples will be exposed to a long-term sulphate attack of 1,500 or 3,000 mg sulphate/l by storage in sulphate containing ground as well as by storage in sodium sulphate solution at 8 °C in laboratory tests.

The research project focus safeguarding of conclusions based on the lab results and the observations in practice. The project is organised by the German Committee for Reinforced Concrete (DAfStb S 006) and is partly supported by VGB Research. The examinations will be carried out by the F.A. Finger Institut für Baustoffkunde (FIB) in Weimar, by the Centrum Baustoffe und Materialprüfung (cbm) at Munich University and by the Forschungsinstitut der Zementindustrie (FIZ) Düsseldorf. The results of the project will be published in a report of the German Committee for Reinforced Concrete.