Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

Laboratory test results - HPC under acid attack

The hpc mixtures from the ConLife project were tested in their behaviour against acid attack. After the immersion testing of hpc specimens in diluted sulphuric acid a relative ranking of the mixtures in their behaviour under acid attack was established. In general it can be said that all high performance concrete mixtures showed a better resistance against acid attack than the reference ordinary type concrete that was tested in comparison.

The main trends seen in the acid attack results include:
- Using fly ash in combination with micro silica fume resulted in an improved acid resistance. The reason for the performance was a denser packing of the cement paste and aggregates due to the fly ash. The micro silica fume reacts pozzolanically and transforms the calcium hydroxide chemically and by that decreases its content in the binder matrix. This also increases the acid resistance. Without fly ash, the micro silica fume alone can result in micro cracks, which will increase the path for acid intrusion. The fly ash releases alumina ions and above a certain level of ion content the shrinkage is lower and therefore less cracks will occur. This was confirmed by the observation that using micro silica alone resulted in a lower acid resistance.

- Using air entrainment resulted in an increased acid resistance because the entrained micro air voids improved the workability and the ability of the concrete to be packed denser. In other words, the concrete is more homogenous. Furthermore, the air voids block micro capillaries and prevent the acid from invading the concrete through these canals.

- Using extra fine blast furnace slag did not provide any improvement to the acid resistance. It can be assumed that the combination of fly ash and silica fume is more effective than the use of extra fine blast furnace slag alone. The reason for this is probably that the slag does not change the amount of calcium hydroxide in the concrete.

- To produce a dense concrete like in high performance concrete is favourable for the durability under acid attack. The dense matrix slows down the speed of the acid penetration and the dissolution of the matrix itself. The damage development is delayed.

With that information it should be possible to select a good concrete test mixture which means to give recommendations or to make predictions to improve the mix design of hpc to resist acid attack prior to laboratory testing which has to be done before a special concrete mix design is used. From that scientific result a commercial result may off spring in the following manner.

The acquired know how may be used to give advice to potential users that are trying to make acid resistant concrete. If this is possible a better acid resistant hpc will be available for general use. The main commercial value is additional knowledge about acid resistant high performance concrete combined with the existing information from former investigations documented in the literature.

This knowledge can be used to give advice to potential users. A key innovative feature can be that an inherently acid resistant concrete can be produced that doesn't need any protective surfaces, which are quite often used. By that maintenance costs can be reduced. An acid resistant concrete may have a longer service life than a protective surface. This information or knowledge transfer to users in practice can be done by the project partners.

Reported by

MC-Bauchemie GmbH & Co.
Am Kruppwald 2-8
46238 Bottrop
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