Sammendrag
With natural (fluvial, glaciofluvial) sand/gravel resources being rapidly depleted in many countries, the last decade
has seen a significant trend towards using more alternative materials for construction purpose. In Norway the development
and implementation of crushed aggregate technology has been the most important way to get around
the problem with increased resource scarcity. Today Norway is one the European countries with the highest percentage
of crushed/manufactured aggregates. A crushed product will reveal a different particle size distribution, a
sharper, more angular particle shape, and not least – a significantly different mineral composition. The latter may
often be characterised by more polymineral composition, and it will also much more depend on the local bedrock.
When handled with care and knowledge, these differences can give the user a lot of new opportunities relating to
materials design.
Norwegian road construction practice has changed significantly during the last 40 years due to the replacement of
gravel by crushed rock materials in the granular layers of the pavements. The use of non-processed rock materials
from blasting was allowed in the subbase layer until 2012. This was a reason for a lot of problems with frost heaving
due to inhomogeneity of this material, and in practice it was difficult to control the size of large stones. Since
2012 there is a requirement that rock materials for use in the subbase layer shall be crushed (Handbook N200,
2014).
During the spring 2014 The Norwegian Public Roads Administration introduced a new handbook with requirements
for roads construction in Norway, including new specifications for the frost protection layer. When pavements
are constructed over moist and/or frost susceptible soils in cold and humid environments, the frost protection
layer also becomes a very important part of the road system. According to new specification; the size of large stones
for this layer should be maximum 0.5 m (longest edge) or 1
2 layer thickness. And minimum 30% of stones should
be less than 90 mm. Fines content (<0.063 mm) should be maximum 15% of the material less than 22.4 mm.
Analysing these new requirements, several questions are arising. First of all how this materials size will affect heat
exchange in the layer, secondly – if the allowable fines content will make the materials frost susceptible.
For calculations of frost protection layer thickness the knowledge of thermal conductivity of the aggregate layers
is required. Handbook for geotechnical investigations of the soils provides this data for natural gravel which is
limited by 0.7 – 1.3 W/mK. But when it comes to the crushed rocks, it can be significantly increased due to the
higher conductivity of minerals (especially if they contain high amount of quartz), as well as due to higher effective
conductivity. In rock-fill materials, i.e. materials with large particles and low degree of saturation, convection
and radiation are the predominant heat transfer mechanisms. Convection and radiation can increase the effective
conductivity by factor 2-10. Lebeau and Konrad (2007) showed that convection heat transfer could lead to the
formation of undesirable permafrost conditions in toe drains of embankment dams located in Northern Quebec,
i.e. in areas where there are no naturally occurring permafrost soils.
has seen a significant trend towards using more alternative materials for construction purpose. In Norway the development
and implementation of crushed aggregate technology has been the most important way to get around
the problem with increased resource scarcity. Today Norway is one the European countries with the highest percentage
of crushed/manufactured aggregates. A crushed product will reveal a different particle size distribution, a
sharper, more angular particle shape, and not least – a significantly different mineral composition. The latter may
often be characterised by more polymineral composition, and it will also much more depend on the local bedrock.
When handled with care and knowledge, these differences can give the user a lot of new opportunities relating to
materials design.
Norwegian road construction practice has changed significantly during the last 40 years due to the replacement of
gravel by crushed rock materials in the granular layers of the pavements. The use of non-processed rock materials
from blasting was allowed in the subbase layer until 2012. This was a reason for a lot of problems with frost heaving
due to inhomogeneity of this material, and in practice it was difficult to control the size of large stones. Since
2012 there is a requirement that rock materials for use in the subbase layer shall be crushed (Handbook N200,
2014).
During the spring 2014 The Norwegian Public Roads Administration introduced a new handbook with requirements
for roads construction in Norway, including new specifications for the frost protection layer. When pavements
are constructed over moist and/or frost susceptible soils in cold and humid environments, the frost protection
layer also becomes a very important part of the road system. According to new specification; the size of large stones
for this layer should be maximum 0.5 m (longest edge) or 1
2 layer thickness. And minimum 30% of stones should
be less than 90 mm. Fines content (<0.063 mm) should be maximum 15% of the material less than 22.4 mm.
Analysing these new requirements, several questions are arising. First of all how this materials size will affect heat
exchange in the layer, secondly – if the allowable fines content will make the materials frost susceptible.
For calculations of frost protection layer thickness the knowledge of thermal conductivity of the aggregate layers
is required. Handbook for geotechnical investigations of the soils provides this data for natural gravel which is
limited by 0.7 – 1.3 W/mK. But when it comes to the crushed rocks, it can be significantly increased due to the
higher conductivity of minerals (especially if they contain high amount of quartz), as well as due to higher effective
conductivity. In rock-fill materials, i.e. materials with large particles and low degree of saturation, convection
and radiation are the predominant heat transfer mechanisms. Convection and radiation can increase the effective
conductivity by factor 2-10. Lebeau and Konrad (2007) showed that convection heat transfer could lead to the
formation of undesirable permafrost conditions in toe drains of embankment dams located in Northern Quebec,
i.e. in areas where there are no naturally occurring permafrost soils.