This guide is a short summary of what asphalt pavement is, how long it should last, some methods for approaching its maintenance and categories of its maintenance.

INTRODUCTION

If you own or manage asphalt pavement you are responsible for an increasingly expensive asset.  Asphalt was initially developed as an inexpensive surface for the many newly required roadways in the early twentieth century.  This was made necessary by the introduction of the automobile and its need to have a hard, smooth and regular surface over which it could traverse and park.

In the intervening years the price of oil and aggregate has risen along with environmental regulations regarding asphalts use resulting in the increase of the price of asphalt pavement.  The cost of asphalt pavement is now to the point that in its own right it is considered to be an important and expensive asset of any industrial, transport, commercial, retail or educational institution that owns it.  This consideration has replaced the traditional attitude that asphalt is something we do not notice until it is broken.

Managers of public asphalt pavement (roads) employ professional civil engineers whose full time work is evaluating the condition and performance of the public pavement and optimizing the methods and treatments in its required maintenance.

Unfortunately the owners of private asphalt pavement do not have the time or resources to employ such professionals. However, in most of the private (non government owned) cases of asphalt ownership the employment of professionals to assess its condition and to manage its maintenance is unwarranted and the optimization techniques they use are too pavement specific to benefit small amounts of different pavement.  In addition parking lot pavement ages more as a result of weathering rather than of loading.  Many of the professional techniques used to assess pavement performance use anticipated loadings as a significant precursor to pavement performance.

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 each other in supporting 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 generally decreases with age and use.  While asphalt pavement is flexible Portland Cement Concrete (PCC) pavement is usually referred to as a rigid pavement.

Traditionally asphalt has been cheaper to install but is more expensive to maintain than concrete and does not last as long (particularly under heavy, repeated loadings) as concrete.  Conversely, concrete pavement is usually more expensive to install but lasts longer and requires less maintenance than does asphalt.  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.

For information regarding how to assess asphalt pavement condition and how to give it a rating, please see our companion eBook How to Identify Asphalt Pavement Problems.  More information can be found at ebay store Pavementmanagement

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.  This length of time is called the pavement’s design life.

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

The life of asphalt pavement can be reduced by any or all of the following five factors.  Each of these factors however may be prevented or managed.

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

MAINTENANCE, REHABILITATION OR RECONSTRUCTION

Maintenance

Maintenance is the treatment of an asphalt surface with an application of surface or crack seal (and sometimes patches) such that it extends the life of the pavement and is preventive in nature.  It is applied to the surface when it is not absolutely required to be.  It is an investment in the longevity of the paved asset and is a proactive approach in managing paved assets. 

Maintenance does not generally need the design or assistance of a professional civil engineer to responsibly acquire and install.

Rehabilitation

Asphalt pavement rehabilitation is the redressing of significant problems that are already part of the pavement section.  Rehabilitation is inherently reactive in nature and is more expensive than pavement maintenance.  Examples of asphalt pavement rehabilitation are asphalt overlays, mill and overlays, and extensive full depth patches. 

Pavement rehabilitation may or may not require the services of a professional engineer.  Many times a simple overlay or overlay and geotextile fabric may be installed without a pavement design.  Sometimes, however, there are many options to choose from, the areas and amounts of money are great enough and the necessity that the pavement function is high enough that the services of an engineer are warranted and cost effective.

Reconstruction

The reconstruction of an asphalt pavement is the total replacement of the asphalt pavement structural section because it has performed to its maximum service life and no longer offers any utility as a paved surface.  Reconstruction is an extreme form of reactive pavement rehabilitation and is very expensive.  It is more expensive than a simple pavement installation as the existing remnants of the pavement section usually have to be removed and disposed of off site or rejuvenated on site (in-situ recycling) before a new paved surface can be installed.  Complicating factors include many local and regional government’s strict laws and prohibitions regarding the storage, handling and waste of old asphalt pavement.

The services of a professional civil engineer in the design and installation of a reconstructed pavement are essential.  Not only will the engineer provide a design for the adequate structural thickness of the pavement for the intended use but will provide for adequate drainage and drainage collections systems.  Engineers will also provide bid documents that you the owner may use to solicit apples to apples bids from many qualified contractors.  Bidding from professional bid documents in and of itself pays in the short run in lower responsible competitive bids and in the long run in reduced maintenance and rehabilitation costs.

STRATEGIES

As a pavement owner or maintenance manager there are several key strategies that can be employed in managing the necessary repairs to your pavement.  Some of the following strategies only apply to large pavement owners and managers but all should be considered when deciding how to allocate monies for pavement maintenance, rehabilitation and reconstruction.  The following are the strategies in dealing with the prioritization and costs of asphalt pavement maintenance:

• Worst First
• Bang for the Buck
• Appearance
• Operational
• Political

MAINTENANCE

Asphalt maintenance can be broken down into the following four categories:

Seal Coats or Surface Treatments
Crack Seal
Patches
Heating/infrared

REHABILITATION

Overlays

Asphalt overlays are thin coverings of hot asphalt mix applied and compacted over existing paved surfaces (asphalt or Portland cement concrete).  They are typically 1” to 3” in thickness and are often combined with a crack inhibiting geotextile fabric.  The existing paved surface is cleaned and sprayed with a tack coat, the fabric is placed according to the manufacturers recommendations (for overlap, etc.), and the asphalt overlay is then placed and compacted.

Asphalt overlays are good solutions for pavements which are aging, but which have not experienced severe or generalized structural failure.  A pavement with a few locations of alligator or block cracking or pot holes may still be a good candidate for an overlay if the structural problems are taken care of first with a full depth patch.  Pavements with general alligator or block cracking, depressions, rutting, shoving or corrugations should not be candidates for overlays.

Overlays may be placed over block cracked areas and over areas with temperature and shrinkage cracking.  However, it is a good idea to seal these cracks before placing the tack coat and fabric particularly if you are not using a crack inhibiting fabric.

In situations of high loadings and where an overlay must function (such as in an industrial yard) we recommend the assistance of a licensed civil engineer with experience in asphalt.  This type of overlay is called a structural overlay and is 2” or greater in thickness.  The engineer can help you specify thickness, types of fabric and types of asphalt concrete that will be most appropriate for your application.  In addition, the engineer can help you in preparing technical bid documents for this work which will include specifications that can be used in turn to insure quality and provide a standard for construction testing.

It is important when installing any pavement that the type of asphalt (mix design) including type of oil, gradation of aggregate and any filler is known to the owner.  This is important because pavement varies and certain pavements are much better at handling certain types of loads under certain temperature ranges than others.  With plans and specifications you as the owner can hire a testing company to ensure that the asphalt you specify and pay for is the asphalt that you in fact receive. 

Some asphalt contractors will exploit the fact that you do not use specifications or bid documents and they will use asphalt pavement that has been rejected on state or municipal roadway projects or asphalt that has cooled or is left over from another job.  They do this because private asphalt owners are usually only concerned with cost and are unaware that inadequate asphalt mix and inadequate installation can cut years off the longevity of your expensive asset.

RECONSTRUCTION

Pavement reconstruction is the entire replacement of your asphalt pavement with a new or recycled pavement.  It is the permanent fix for Design and Installation flaws and for a pavement which has completely failed or which has failed to the extent that continued full depth asphalt patching is not cost-effective. 

The primary difference between pavement reconstruction and a new asphalt pavement is the question of removal and/or re-use of the old asphalt, base material and sub base materials.  Many regulations exist regarding the disposal of old asphalt and many localities do not have sources of hard, angular and durable rock aggregate available for new asphalt pavement.  In these cases it is desirable to look at recycling the asphalt in place or at the site.  There are many options.  The best approach is to contact a licensed geotechnical engineer and have him conduct tests on the existing pavement and sub grade and give you options for recycling and for a new, virgin pavement along with a cost estimate.   Civil engineers can assist you with grading and drainage design as well as parking layout/traffic flow striping and bid documents.

Pavement reconstruction is usually expensive.  In order to save money it is tempting for property owners to forgo the services of a geotechnical and civil engineer in the design of a pavement reconstruction.  They will typically solicit bids from several contractors and select the low bid.  The contractor is under no obligation to install a paved surface that will provide the longevity associated with a quality design and installed asphalt pavement.  Contractor’s warranties usually expire after one year.  The best asphalt paving contractors do not offer warranties over two years.

Considerations of sub grade conditions (which may have contributed to the failure in the first place) grading, drainage, and the proper design thickness of asphalt and road base are usually ignored or skirted by the contractor in an effort to get you the best price and get your business.  This can end up in a nightmare for you, the property or facility manager, who may now be faced with paying for additional extensive overlays, repeated full depth patching or even another pavement reconstruction in as little as 3 to 5 years.

The 8% to 10% fee (of the estimated cost of construction) the civil engineer or geotechnical engineer charge combined with a 3% to a 5% fee for a testing service is well worth the cost in the assurance to the owner that they are getting a paved surface that is fundamentally sound and that will continue to serve them for a long time to come.  Proper designs and quality construction pay for themselves many times over in reduced maintenance costs and headaches.

After you have reviewed these items and decided which specific maintenance, rehabilitation or replacement strategy is correct for your pavement it is time to find a contractor who can responsibly meet your requirements.  Please see our eBook How to Select a Contractor for Pavement and Pavement Maintenance.

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.