Arbejdsrapport fra Miljøstyrelsen 37/2006 – Udtørring af beton i byggefasen - Afrapportering af udtørringsforsøg

Udtørring af beton i byggefasen

Summary and conclusions

The Danish Technological Institute has carried out a test programme with the purpose of clarifying the mechanisms and parameters involved in drying of concrete used in Denmark for floor slabs and walls. The test specimens were supplied from the industrial partners of the project.

The test programme comprised:

Self-desiccation measured on 2 concretes and Densit matrix.
Desorption tests on 4 concretes and 2 lightweight aggregates concretes (LAC).
Drying of cast slabs under controlled climatic conditions.

The test programme is a part of a series of concrete projects financed by the Danish Environmental Protection Agency. The scope of the drying project was to focus on the excessive energy consumption taking place at building sites in order to dry-out concrete prior to other treatments (wooden floor, non-permeable floor coverings, etc.). The best way to act more environmentally friendly on the building site is to provide knowledge to engineers so that they are able to predict and plan the building process with respect to the drying needs of concrete. This test series is a vital part of this knowledge. Another part is a set of Guidelines for drying of concrete that are also to be published under this project.

It should be noted that there is a limited number of test results, a factor which must be taken into consideration when reviewing the conclusions reached.

The most interesting conclusions of the investigation are:

Using a low v/c ratio of about 0.40 makes it possible to utilise the self-desiccation (drying-out by means of hydration) of concrete to speed up the drying process. It was documented that this is a way to obtain a significant improvement in drying times compared with conventional concretes for floor slabs.
Desorption curves were established for Danish concretes and LAC. They were shown to be consistent with other published findings in this area.
The application of the Swedish software TorkaS was compared with results on Danish concretes and it turned out to yield very conservative results when it came to drying times of concrete for a floor slab. Therefore, it is recommended that more data should be collected so that the simulation software may be calibrated properly.