Self-Desiccation of Self-Levelling Flooring Products and Investigations of Different Moisture Measurement Methods
Abstract: Self-levelling flooring compounds (SLCs) are mainly used on concrete floors. Their purpose is to smooth the floors and make them horizontal. The fact that they are self-levelling means that they spread out like water over the floor before hardening to a horizontal layer. Some of them are also advertised as being self-desiccating. A quote from a big manufacturer on the Swedish market regarding their self-desiccating SLCs is: “In a self-desiccating product the chemical reactions and the physical processes represents the majority of the dehydration. These products are used when early surface coating is needed. RH in the product is during the time of the early surface coating still high, but decrease as the inner processes continues. Moisture measurement for these products before surface coating is therefore not relevant”. As the products are applied late in the building process it is often of interest that they hydrate quickly and contain less water and more binder. Self-desiccation means that free water is removed by chemical reactions in the hydration process, to such a high degree that the relative humidity (RH) of the system decreases. In concrete products self-desiccation can be of importance as such products can dry without external drying and it is of interest to investigate whether this is of the same importance for SLCs as well, or if the SLCs always mainly dry by surface evaporation. When e.g. a carpet or parquet shall be placed on floor it is important that the floor does not give away too much moisture that can cause chemical degradation, health problems and other issues in the indoor environment. The purpose of this master thesis was to evaluate two types of SLCs and different methods for measuring self-desiccation. There are a number of methods that can be used, for example, relative humidity based methods mostly used in Sweden and moisture content based methods used in many other European countries. Two self-levelling flooring products were cast and their moisture states were followed at 20 °C. Some samples were sealed during the hydration process, so there was no drying to the ambient air. Any decrease in relative humidity in such samples would be a validation of self-desiccation. Other samples were allowed to dry to the ambient to see the impact of surface evaporation. With different extracting and storing methods differences in moisture levels due to such aspects could be evaluated. These following methods were used: • Isothermal calorimetry with built in RH sensors. • RH-sensors in large glass jars. • RH-sensors in test tubes. • Drying samples at 65°C at different times. • Drying samples at 105°C at different times. • Measurement of moisture content by a carbide meter at different times. • Measurement with the calcium chloride method at different times. None of the products tested showed self-desiccation in the meaning of a decrease in RH through binding water chemically when sample was sealed from drying to the ambient air. RH and moisture content describes different aspects of the moisture state of a material and therefore it is our opinion that a combination of the two is to be preferred when evaluating moisture conditions.
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