Asphalt Thin Surfacings
One of the advantages of asphalt thin surfacings is the cost factor, which is moderately less than that of conventional asphalt surfacing.
The thin surfacings are often called Ultra Thin Surfacing (UTA), and the original techniques used in them were developed in Europe, with the aim of generating thin economical treatments that would restore the normal surface characteristics of otherwise useful pavements.
The definition of Ultra thin asphalt (UTA) surfacings is different from country to country, and many country do not have definition for the standard.
For Australia, UTA surfacings are typically placed with a minimum thickness of around 12-15 mm, or about half the thickness of similar sized conventional local asphalt wearing course mixes.
The main characteristics of UTA surfacings are the use ofa heavy tack coat or sprayed seal to form an integral bondwith the underlying surface, and the use of coarsegap-graded mixes to provide good surface texture.
The achievement of a strong bond distinguishes UTA fromconventional asphalt surfacings that has a high level ofindependent integrity in each layer.
The tack coat, or seal, used to bond the surfacing in place also assists in waterproofing the pavement where permeable surfacingmaterials are used.
In UTA, the coarse gap-graded mixes can even achieve an open texture that is similar in appearance to the open-graded asphalt, thus offering good noise, skid resistance, and water spraycharacteristics.
However, it is good to realize that achieving a uniform thin layer of paver- laid asphalt can only be achieved where the underlying surface is typically in good shape.
Where necessary, shape correction to achieve this result should be carried out before placing UTA.
The AustRoads Pavement Research Group lists the advantages and disadvantages of UTA surfacings as:
AdvantagesEconomical cost – moderately less than that ofconventional asphalt surfacing.High standard of surface texture giving good skidresistance and reduced water spray.Reduced noise levels compared to dense-gradedasphalt and sprayed seals.Good ride qualities.Flexible and tolerant to surface deflections.Assists waterproofing of underlying surface.Thin layer reduces need for cold planing, etc. tomatch adjoining surfaces. No loose aggregate such as in a spray seal.
DisadvantagesHigher cost than sprayed seal.Effective treatment may require preliminaryregulation and SAMI treatments.Low shear resistance may make it unsuitable in areasof high shear forces.
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