DOI: 10.5593/SGEM2014/B62/S26.015


P. Kucera, M. Lidmila
Wednesday 1 October 2014 by Libadmin2014

References: 14th International Multidisciplinary Scientific GeoConference SGEM 2014, www.sgem.org, SGEM2014 Conference Proceedings, ISBN 978-619-7105-21-6 / ISSN 1314-2704, June 19-25, 2014, Book 6, Vol. 2, 113-120 pp

The main purpose of subballast layers in railway track bed is to guarantee a sufficient bearing capacity and to protect subgrade from negative effects of rain water and frost. Since 1960’s several railway administrations have utilized hot-mix asphalt instead of conventional granular subballast in selected tracks with special requirements, such as high-speed or heavy traffic tracks. The experiences gained during the last decades have shown that the hot-mix asphalt layers provide a good support for ballast bed, distributing the load equally to the subgrade. Moreover, their impermeability prevents the rain water from penetrating to the subgrade. Also, significant savings of granular materials can be achieved while introducing the bituminous subballast instead of the allgranular solution. Incorporation of a high percentage of recycled asphalt pavement and a decrease in production temperatures is a way to make the use of bituminous subballast cheaper and greener than it currently is. However, both these alternations may negatively affect durability, performance and resistance of the bituminous mixtures to water and frost. The aim of this study was to assess the effects of water and frost on selected mechanical and physical parameters of 100% recycled half-warm asphalt mixtures. The standard water-sensitivity and freeze-thaw resistance tests were carried out. The effect of water content on thermal conductivity, which is an important parameter in terms of frost protection of the subgrade, was also observed. During soaking, the height of the specimens was measured to proof whether any swell was occurring. The results showed a significant influence of water and frost on the mechanical performance of the 100% recycled asphalt mixtures, particularly for compacting temperature of 80°C. Higher water content after soaking was probably a cause of increased thermal conductivity. Some swell of the specimens immersed in water was observed, but only at a negligible rate.

Keywords: recycled, asphalt mixture, subballast, water resistance, frost