Arbejdsrapport fra Miljøstyrelsen 18/2006 – Afdampning fra beton

Afdampning fra beton

Summary and conclusions

The purpose with this project is to describe the impact of concrete on the indoor climate. Focus has been on the potential evaporation of chemical substances to the indoor air.

A number of concrete manufacturers have been asked, which kind of concrete they produce. Based on an assessment of the kind of concrete exposed to the indoor air, four types of concrete have been collected for further testing.

A hollow core slab
A wall element of ordinary concrete
A wall element of light-weight aggregate concrete
A ready-mixed floor concrete

Samples of a hollow core slab and a wall element of light-weight aggregate concrete were crushed and the head space over the crushed material was analysed for volatile organic compounds (VOC). VOC in the head space was monitored in concentrations to justify further testing in chambers.

Measurements of the emissions of VOC, alcohols, aldehydes and volatile organic amines from the concrete samples were carried out in the chambers. On two selected concrete samples additional sensory evaluations (odour tests) were performed.

In the laboratory, two samples of concrete with almost the same composition as the wall element of ordinary concrete previous mentioned were cast. The only difference between the two samples was that one sample contained cement and fly ash while the second sample only contained cement. The fly ash contained 63 ppm ammonium/ammonia

The two samples were tested in champers and the evaporation of ammonia was quantified.

Based on measurements and literature review, the following conclusions were drawn:

Concrete casts using mineral-oil-based form-oil emits volatile organic hydrocarbons. However the problem is rather limited and will probably not give any indoor climate problems unless excessive amounts of form-oils are used.
Concrete which contains fly ash from coal-fired power plants emits ammonia to the atmosphere. When using the fly ash tested in this project, the rate of evaporation however is rather low and will not give any indoor climate problems.
Concrete made without any fly ash but purely on the basis of cement also emits ammonia. When using cement testing in this project, the rate of evaporation was low and did not give any indoor climate problems.
The evaporation of ammonia can be modelled using Fick's second law. The rate of evaporation is proportional to one divided by the square root of time
Concrete releases neither amines, nor alcohols and aldehydes to the indoor climate in significant amounts.
The release of odour from concrete is moderate to weak and the odour declines over time.
All the tested concrete samples could be approved in the indoor climate test.
Hydrocarbon emissions from concrete are eliminated completely if vegetable-based form-oils are used instead of mineral-oil-based form-oil.