Maintenance Techniques for Pavement

Different types of maintenance techniques are used according to the nature of defect, level of deterioration and budgetary constraints. These techniques are explained briefly in the following.?

Crack Sealing:?This is simply a narrow band of bituminous sealing material which is painted onto the surface of a road as a temporary measure to prevent water from penetrating a crack in the pavement and causing further damage.

Patching:?A more extensive cracked or rutted area, but still of limited extent, would be patched. This again is a rarely permanent repair through it may last several years if it is carried out well and depending on the type of failure which has occurred.

Haunching:?Haunch repairs are carried out where the edge of the road has collapsed under the action of traffic often combined with the effects of poor drainage. This tends to happen on narrow roads which take a certain amount of heavy goods traffic. The solution is not simply to repair the damage area but to strengthen it in order to ensure that the problem does not recur. This may also necessitate the introduction of a drain where previously there was none.

Bush Hammering: The bush hammering process involves a number of independent fully controlled treatment tips which mechanically restore skid resistance to any existing surface. The technique is applicable to all road surface types including surface dressings, asphalts, e.g., hot rolled asphalt, thin surfacing, and concrete. This treatment improves and restores micro texture by re-profiling aggregate to recreate the original sharp angularity of the aggregate and removing polished particles and fines. Macrotexture will also be improved depending on the surface.

Shot Blasting: Abrasive blasting is effective in removing surface polish, giving an improvement in micro and macro texturing.

Longitudinal Scrabbling: Uses hardened tips set into steel washers, loosely mounted side by side hydraulically loaded and drawn/rotated (on several axles around a central axle) along the road surface. The arisings are swept up separately.

Micro texture is improved by cutting through the surface aggregate and exposing new aggregate faces, creating a corduroy effect

Longitudinal Grooving/Grinding: Grinding with longitudinal grooving (following surface profile) involves the creation of longitudinal grooves using diamond tipped saw blades. This closely spaced saw blades cut grooves at a predetermined width and depth and this process follows the profile of the surface. The surface levels of the treatment area remain the same as the surrounding surface and the treatment is repeatable.

This technique improves micro texture and macrotexture and has the potential to reduce tyre/road noise. The treatment causes no damage to joints/repairs and road markings, road studs, ironwork and traffic loops do not have to be removed prior to treatment.

Transverse Grooving/Grinding: Uses diamond tipped blades and pressure washing to remove slurry. It can be used to provide discreet grooving patterns and can aid surface water drainage (has little effect on skid resistance) and can lead to increased tyre/road noise levels.

Fine Milling: Fine milling (following surface profile) involves the creation of longitudinal grooves using tungsten tipped cutting tools set at 6mm spacing. The machine has accurate level control and removes the top 2-6 mm of the road to achieve a new running surface. This can also be used to provide a key for an overlay treatment. The cutting drum can adjust the number of revolutions per minute to alter the texture depth in different surface materials. In reducing the overall level of the surface, all cat eyes and street furniture need to be removed or reset. The technique is fast and improves micro texture and macrotexture, thereby improving skid resistance and increasing texture depth. It can be used under all weather conditions.

Water Jetting: The process involves the controlled jetting of water through a series of nozzles at high pressure onto the road surface. It does not restore skidding resistance lost through the polishing action of the traffic. It thoroughly cleans the surface and removes surface contaminants and rubber deposits to expose and improve the existing macrotexture.

Resealing:?There are two options for resealing:

• Fog spray
• Slurry seal

A fog spray is a very light film of binder that is sprayed onto a ‘dray’ or hungry road surface to bind together and hold in place stone particles that otherwise would be picked off by traffic. The binder normally used is a bitumen emulsion and, where ‘pick-up’ of the binder by tyres is likely to occur, the surface may be blinded with a light sprinkling of find sand or crushed dust.

The slurry seal process uses a fine, graded, aggregate that is mixed at ambient temperature with water, dope (an additive) and bitumen emulsion that has a relatively high bitumen content. Some cement is also usually added. The mixture is applied to the road surface as a free-flowing slurry in a layer of 5-10 mm thickness. The mixture penetrates and seals surface as a free-flowing slurry in a layer of 5-10 mm thickness. The mixture penetrates and seals surface voids and cracks very effectively; hence the process is particularly well suited to the maintenance of old bituminous surfaces. Note that the skid resistance of slurry seals may be low, so they are sometimes used as a second treatment on top of a single surface dressing. With this method the tops of the chippings will penetrates through the slurry and provide the skid resistance. The slurry holds the chippings very securely and provides a durable, impervious and non-skid surface. Slurry seals may not resist reflection cracking in asphalt concrete surfacing.

Surface Dressing:?Surface dressing is normally a periodic maintenance activity that uses mechanised methods, and can be used for dealing with a large surface area where:

• The surface is extensively worn
• The surface has become permeable or cracked, allowing water to penetrate the base and cause deterioration
• There is inadequate surface texture so that skid resistance is reduced

Micro-Surfacing: This category comprises layers of bituminous material between 15 and 25 mm in thickness, only slightly greater than a surface dressing. In recent years there has been considerable interest in these materials, and they are being actively considered as alternatives to the standard Hot Rolled Asphalt wearing course.

Essentially these materials comprise fairly single sized aggregate held together by a bitumen and fine aggregate mortar which still leaves room for a fairly high void content. The void content introduces what is known as ‘negative texture’, an alternative to traditional macro-texture but which still gives good wet skidding resistance. It has the additional benefit of low noise when compared to most other forms of pavement surfacing. The binder used can either be pure bitumen or an emulsion.

Although not much thicker than a surfacing dressing, a micro-surfacing is a machine laid course of material and can be used to correct minor undulations or ruts in a surface. This is in addition to providing a restored skid resistance and a sealed surface. However, the structural contribution from such a layer remains small.

Graded seal:?One layer of bituminous binder followed by either:

• Two layers of chippings of different sizes, the second layer serving to fill the gaps between the larger first stones and completely covering the road surface
• One layer of graded aggregate or gravel with stone graded over a wide range

Sandwich seal:?One layer of chippings, followed by a layer of bituminous binder, covered by a second layer of chippings

Surface dressing is generally applied over the complete width of the pavement and over lengths of road ranging from a few hundred metres to several kilometres. With good planning and organisation, this work can achieve high outputs. It should be applied only in dry weather. It will usually be necessary to carry out some patching work before proceeding with the operation, particularly where there is base damage, subsidence, potholes, etc. Surface dressing will not correct depressions, deformation of road pavement or severe cracking.

Overlays:?Overlays are a periodic maintenance activity and are applied over a large area.

Thin Overlays:?Fill small surface deformation that are uncomfortable and dangerous to traffic. They improve surface texture where this is inadequate and dangerous to traffic. They also seal permeable surfaces that allow water to penetrate the road base and cause deterioration

Thick Overlays:?The overlays are more durable than surface dressings, so tend to be applied to more important roads with heavy traffic and high speeds. Thick overlays for strengthening purposes are normally more than about 50mm thick and require detailed investigation and design. When deformation is severe, the overlay work must be preceded by the levelling of depressions and ruts, and the repair of potholes. This work may also be accompanied by the restoration of shoulders and ditches. Overlays must be applied during dry weather.

In case of high level of deterioration, the option of pavement reconstruction may be considered instead of overlay.