Methods of Repair
Surface dressing is the application of hot
bitumen and chippings to the road
surface. It is one of the most cost effective methods of highways
maintenance available and is very widely used, but is not usually
suitable for high stress sites e.g. roundabouts.
Surface dressing seals the road to prevent the ingress of water
and the bitumen forms a protective barrier against rain and frost
to protect the road foundations, significantly extending the life
of the road. Surface dressing also restores skid resistance leading
to increased safety as well as enhancing the appearance of the
Once the bitumen and chippings have been laid, a heavy roller
provides an initial degree of embedment but the real work of
consolidation is provided by the traffic. Shortly after application
and rolling, the road is swept and markings applied, usually within
2 to 4 working days.
Surface dressing, has a limited life of between seven to fifteen
years depending on traffic and environmental factors.
If the foundations of a road have collapsed, surface dressing
cannot provide additional strength. In such circumstances it will
be necessary to Resurface or Reconstruct.
Micro Asphalt Surfacing
Slurry seal is a relatively cheap material consisting of a
bitumen emulsion and aggregate slurry, which is laid cold by a
paving machine following the existing shape of the road or footway
surface. It seals the surface and improves skid resistance and has
very good stress absorbing characteristics. It will normally last
between 5 and 10 years.
Micro-asphalt Surfacing is a multi layer version of Slurry Seal
and can restore a desirable profile, improving ride quality. It is
typically undertaken on busy urban thoroughfares, housing estates,
roundabouts and motorway hard shoulders. The finished surface has
low noise characteristics, and good riding qualities. It is an
efficient process that allows us to reduce time spent on site and
High Friction Surfacing
When the road surface is wet, skidding resistance is lowered and
accident potential increases. While traffic levels have risen over
recent decades, the use of high friction surfacing at crossings,
road junctions and other potential danger points has contributed to
an overall reduction in the number of pedestrian accidents.
The term high friction surfacing covers a range of material
types with differing costs, effectiveness and durability.
Resurfacing is designed to restore the surface profile of a
road, usually for rideability and drainage purposes and to provide
improved texture and skid resistance. The resurfacing usually
takes the form of Inlay or Overlay.
Inlay is where the old surface is planed off and replaced by a
new one. This can also involve the base layers to give
additional strength. This is normally done where the existing
surface has failed badly and could not support a new surface or
where restraints such as kerb levels, accesses etc prevent the road
level being raised. Inlay is most common in urban situations.
Overlay consists of adding material on top of the existing road
to improve the profile and add strength and is more common in rural
situations. As well as overlaying the surface localised
reconstruction may be required before the road is overlaid. The
most common material currently used is stone mastic asphalt (SMA)
along with bitumen macadam and hot rolled asphalt. The laid
thickness is normally between 25-50 mm.
Re-tread (Carriage way reconstruction)
Where the carriageway pavement or footway is beyond repair then
conventional or retread reconstruction is necessary.
'Retread' is an in-situ recycling process and is more
'environmentally friendly' than some other treatments. It involves
treating the top 75mm of the existing road, milling down the
existing surface and adding bitumen and aggregate (if necessary).
The surface material is then regraded and rolled to form a
re-vitalised pavement. The surface is finally sealed with a surface
treatment as part of the process.
Pavement failure may be attributed to any one or a combination
of the following:-
- Sub-grade softening due to poor drainage.
- Sub-grade softening due to ingress of moisture through cracked
and pervious pavement layers as a result of progressive
- Sub-grade failure due to insufficient pavement thickness.
- Frost Heave
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This page was last reviewed 3 October 2011 at 16:54.
The page is next due for review 31 March 2013.