Secondary Emissions from Concrete Floors with Bonded Flooring Materials - Effects of Alkaline Hydrolysis and Stored Decomposition Products

Sammanfattning: It has been demonstrated before that the presence of VOC lowers the quality of indoor air. There are also several indications that certain organic compounds in indoor air (OCIA) can give rise to sick building syndrome (SBS). This thesis investigates and describes one of the most important sources of elevated concentrations of VOC in indoor air in the Nordic building stock. This source, foundation and floor constructions damaged by moisture, has often been identified in conjunction with SBS investigations and has been given remedial treatment with good results.

By studying ca 100 test specimens in different experiments and evaluating measurements which included monitoring relative humidity (RH) in the construction, as well as almost 300 samples of emissions, chemical decomposition of flooring adhesive has been established as the source of secondary emission products. In this thesis, the causative relationship is summarised in a model which is based on an understanding of the physical transport processes and reactions, as well as material properties which can be measured by non-accelerated methods.

By evaluating the results of measurements and through parametric studies in the model, the critical parameters for decomposition of the adhesive and secondary emission to indoor air have been identified and quantified. The moisture content of concrete, its pH value and the method of bonding are some of the factors that govern decomposition of the adhesive. The rate of secondary emission to indoor air is governed, inter alia, by the rate of decomposition, the resistance of the flooring to the flow of decomposition products, and the storage capacity of the concrete for decomposition products.

The storage capacity of concrete for decomposition products is a critical factor for future emissions from the floor, since up to one half of the decomposition products can be transported downwards and stored in the concrete. The organic compounds stored in the concrete (OCIC) can, if conditions change, be emitted to the indoor air over a long period. It is therefore important, for instance during a renovation project, to make a careful note of the total quantity and penetration depth of OCIC in concrete.