This guide is a short summary of what asphalt pavement is, how long it should last, some methods for determining its condition and general categories of asphalt distress.

WHAT IS ASPHALT PAVEMENT
Asphalt is the term used to describe a mixture of bitumen (oil) with aggregate (rock).  Asphalt may also contain other additives such as emulsifiers, cut back agents, polymers, etc.  Asphalt pavement is this mixture placed and compacted over a base course or sub base course or both.  This pavement is also referred to as a pavement structure in that each course (surface, base, sub-base) will act structurally and each provides support to the given loading.

The design of an asphalt pavement can vary significantly but usually always includes a surface course (asphalt) and a base course.  This base course is usually made up of various gradations (sizes) of angular rock or gravel designed to interlock under compaction and provide support to the asphalt wearing or surface course.

Asphalt pavement has been the cheap and plentiful option to provide dependable surfacing for foot and wheeled traffic around the world.  It is commonly referred to as a “flexible” pavement in that it has a limited ability to move and distort under load.  This ability increases with temperature but decreases with age and use.  While asphalt pavement is flexible Portland Cement Concrete Pavement is usually referred to as a “rigid” pavement. 

Traditionally asphalt has been cheaper to install but is more expensive to maintain in that it does not last as long (particularly under heavy, repeated, point loadings) as concrete.  Conversely, concrete pavement is usually more expensive to install but lasts longer and requires less maintenance.  Usually the planned use of the pavement, the owner’s budget and a reasonable life cycle cost analysis are used to determine which pavement gets installed for any given application.

EXPECTED LIFE OF ASPHALT PAVEMENT
An asphalt pavement structure (surface and base courses) is designed to support a given number of repetitions of a given load every day.  A typical asphalt pavement is expected to last between 15 and 20 years without maintenance, with proper drainage and without being subjected to heavier than design loadings.

Concrete pavement by way of comparison is typically design for a service life of 30 to 40 years depending on the particular use, concrete type and mix and environment.

The life of asphalt pavement is usually reduced by the following five factors.  The negative affect on asphalt of all of the factors may either be prevented or managed.

• Poor Drainage
• Excessive Loading
• Weathering
• Poor Design or Construction
• Fuel spills

METHODS OF ASSESSING ASPHALT PAVEMENT CONDITION

There are many ways of assessing the condition of asphalt pavement.  Roadway departments may utilize ground penetrating radar or sophisticated cameras with software and storage systems or profilometers mounted on trucks to quickly inventory the condition of miles of roadway pavement.  They may also utilize mechanical methods of assessing a pavements structural integrity such as falling or heavy weight deflectometer testing.

All of these methods have their place.  However they all share the fact that they are expensive and have been designed for high volume evaluation of roadway pavement or the evaluation of a specific pavement for an unusual load.  Some of these methods may be successfully applied to large sections of industrial asphalt pavement but they were designed for highway application.

The facility or property manager will almost exclusively rely on assessing his pavements condition using visual methods.  These methods are usually very effective for the problems encountered and are easily completed.

TYPES OF DEFECTS

There are four types of common asphalt pavement distress.

• Surface Defects
• Surface Deformation
• Cracks
• Potholes, Patches and Utility Cuts
  

SUMMARY

It is important to evaluate your pavement condition as part of a formal inspection and inventory on a regular basis (such as once a year).  Yearly reviews help in comparing segments of different pavement, establishing and tracking performance, and identifying and anticipating the types and amounts of actual maintenance you will need in order to budget.

It is important to understand that when doing a pavement inventory that you write down and photograph pavement condition information for future reference as memories are difficult to depend on.

It is also important that a single pair of eyes complete the evaluations within a relatively short period of time so that inconsistencies related to time and perception are minimized.

If there is a great deal of pavement that needs to be evaluated and it is geographically separated then it may be worthwhile to train the individual evaluators on this system so that the system manager may have apples to apples information for comparison and use in budgeting and establishing priorities.

If you would like more information on pavement management or assistance with training or you would like to host a training seminar on asphalt condition ratings or asphalt maintenance please contact us through our Pavementmanagement.store

For information on a useful numerical ratings system for asphalt condition please see our eBook How to Identify Asphalt Pavement Problems and for appropriate asphalt maintenance strategies associated with each of the pavement condition ratings please see our eBook  Asphalt Pavement Maintenance Options.