Comparison of melting processes of dry uncompressed and compressed snow on heated pavements

• The melting processes of dry uncompressed and compressed snow are studied.
• More time and energy was needed to melt compressed snow than uncompressed snow.
• Compression results in higher capillary forces and stronger snow.
• Air gaps were formed between the asphalt plate and the snow layer.
• Air gaps would decrease the conductivity in a thin bottom-layer of the snow.

Heated pavements are used as an alternative to salting and snow ploughing to keep roads and pedestrian areas free of ice and snow. The snow layer changes during the melting process due to heating, weather and traffic loading, but the snow layer itself also largely affects the energy balance at the pavement surface. This paper describes a snow melting experiment done in the cold laboratories of the NTNU to gain a better understanding of the snow melting processes of dry uncompressed and compressed snow on heated pavements and the change of the properties of the snow layer during the melting process. Compression largely affects the snow melting process due to changes in the snow structure and snow properties; it increases the density and thereby also the thermal conductivity. This should give a more efficient heat transfer and a shorter melting time but this was not found to be the case. The compression and increased density has two other vital consequences; a) Higher density gives a lower permeability and higher capillary forces and b) Stronger snow. The higher capillary forces give the snow better capability to absorb melt-water so that air gaps can form between the asphalt surface and the snow layer. Air gaps on the asphalt plate would decrease the conductivity significantly in a thin bottom-layer of the snow and reduce the heat transfer coefficient between the asphalt plate and the snow. The stronger snow would contribute to maintaining such air pockets or layers as stronger snow can support a larger span under gravity actions.