Construction
Smooth finish
The TarmacDry surface course is designed to give the required ride quality by providing a smooth finish with no trip hazards and to impart skid resistance as required. This layer can also serve to provide an aesthetic finish.
Filtering and treatment of surface water
Another important function
of the TarmacDry porous asphalt surface course is
to filter and treat surface water through the removal of
contaminants such as silts/organics/ heavy metals. Because most of
the silt is contained within the surface course it is easier to
maintain the hydraulic conductivity by cleaning as necessary.
The Binder and/or Base layer(s) provide the main structural support
and allow water to easily pass through to the unbound granular
reservoir layer below. Base materials may not be required in
certain applications (subject to individual design
requirements).
The open granular subbase layer serves as the reservoir for water
storage within the pavement system. The thickness of this layer
depends upon the structural and hydraulic requirements of the
project.
Geotextile for Infiltration purposes
For infiltration applications a Geotextile is
incorporated on top of the prepared sub-grade to provide additional
filtration prior to discharge into the underlying layers. The
geotextile also stops very fine material present in the sub-grade
being pumped upwards into the granular sub base layer, which could
result in partial blocking and reduced storage capacity.
Attenuation systems will require a Geo-Membrane to prevent egress
of water to the sub-grade.
The sub-grade permeability will vary on a project specific basis and needs to be known and taken into account when the system is designed.
