CONTRACTING: HOT MIX OVERLAY AND PATCHING
 
What is Hot Mix Overlay and Patching?
Pavements fail by several mechanisms. Go to technical library for a full discussion and email for a CD-Rom of power point presentations.
Hot mix asphalt is the premium product for pavement rehabilitation. Hot mixed asphalt is a mixture of graded aggregates and asphalt. It is made in a purpose built plant and hauled to site.

The material is applied hot and compacted using rollers. The material, depending on its design and the thickness laid can form a structural layer. This makes it ideal for patching. It also can be compacted to a smooth and almost impermeable surface making it quiet, high skid resistance and attractive and pleasant to drive on.
What is it used for?
Hot mix can be used to replace existing failed areas- full depth patching, filling potholes, full overlays to restore level or structural integrity or over petromat ( fabric, geotextile) as a crack and surfacing treatment.
Are there different types?
Hot mixes vary in stone size from (25mm) 1 inch or so top size to 7mm (3/8 inch) to sand mixes. The grading may be dense, open or gap graded with different levels of fine fillers such as lime and fly ash. The binder may be asphalt of various penetrations from 40 to 200 and this may be modified with crumb rubber, polymers or other additives such as fibers.

For patching and standard overlay work a 60-90 pen binder and sense gradation is usually used.
How is Patching done?
  1. The hole or area to be replaced is assessed
  2. The hole is squared by jack hammering or sawed- snap lining
  3. Damaged asphalt is removed to a depth of about 75mm (2.5 inches) along with 35-75mm of existing rock. Some base rock may be added. This will then be compacted using a vibratory roller. The inside edge is cleaned and the area sprayed with tack oil.
  4. The asphalt is laid in one or two passes. Usually the first 75mm is usually 20mm (3/4 inch) top size material that is compacted with a roller or wacker plate. The surface is finished with 25 mm of 12mm top size (0.5 inch) for a smooth finish.
  5. If the depth is greater the same procedure is used and the levels adjusted.
  6. The surface is finished with a light spray of the tack coat to seal the surface. A light sand coat may be applied if the patch is to be trafficked immediately.
How is Overlay done?
The procedure for overlay is similar.
  1. The surface is prepared by sweeping and levels checked. Drainage is important and grinding may be required.
  2. The surface is sprayed with a light coat of tack emulsion.
  3. The thickness to be laid is predetermined by the design and intent.
  4. The hot mix is laid through a paver with a screed to a set level.
  5. This is compacted by a steel roller for breakdown and rubber tired for finish.
  6. The type of mix selected depends on the job. At least a 1 inch overlay is recommended to ensure compaction adhesion and to give required life.
  7. Fog Sealing is recommended.
Fabric- Petromat Overlays.
Where extensive cracking has occurred a fabric overlay might be considered.
  1. Clean and apply a hot tack system ( AR4000)
  2. The petromat is laid fuzzy side down. This should be laid no closer than 3 feet from concrete curbs.
  3. A min imum of 35mm (1.5 inches) of 14mm (0.5 inch top size) Hot mix is laid and compacted.
  4. The new material is sanded along the joints to prevent pick up and sealed with fog seal.
What does it do?
Hot mix is the premium product and may be used for a range of applications. It is a surfacing, a structural layer and a patching material.
What does it cost?
A VSS estimator will be pleased to estimate your job.
Specifications
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