Pavements provide a safe, all-weather, smooth traveling surface for all users (commuters, commercial motor carriers, other deliveries, service providers, local travel, and leisure travelers). Smoother roads reduce vehicle wear and tear which helps lower operating costs.
There are two primary types of pavements in use today – flexible and rigid. Typical flexible pavements are built with high-quality bituminous asphalt surface courses over a series of granular unbound layers.
Strength
Pavements are subjected to a wide range of stresses from wheel loads, freeze-thaw cycles, temperature changes, and solar radiation. Over time, they experience fatigue and deteriorate to the point that they no longer serve their function and must be reconstructed or abandoned.
Modern pavement construction makes use of a variety of materials to improve the strength and durability of pavements. These include fibers that hold cracks together, steel in the form of dowel bars or reinforcement to distribute loads and limit crack widths, and soil stabilizing additives such as fly ash, silica fume, and recycled quarry byproducts.
Rigid pavements are typically cement concrete slabs constructed directly on the subgrade or a layer of granular material placed below the concrete. The slab is designed based on its stiffness and the stiffness of the subgrade soil. Cement concrete requires careful curing to develop its full strength. It also has closely spaced contraction joints. These need to be properly maintained to prevent water infiltration and reduce stress on the slab.
The surfacing course is the top layer that comes into contact with traffic. It must be thick enough to resist rutting but thin enough that surface friction is maintained for safety. It may contain an asphalt binder or other similar materials. A capping layer of aggregate is often used to prevent the ingress of water into the base layers. A geotextile separator or soil stabilization geogrid is also incorporated to prevent the migration of fines from the subgrade upward into the pavement layers.
Durability
The durability of pavements is a critical factor in both construction and maintenance. Pavement structures must be able to withstand traffic loading and environment for years while providing an adequate level of ride quality. Pavement design aims to control this deterioration to ensure that the structure remains functional over the life of the roadway.
The most common paving material is asphalt concrete (AC), which can be made in two broad types: flexible pavements whose surface course consists of an aggregate skeleton bound by AC, and rigid pavements whose whole surface is constructed from Portland cement concrete. Rigid pavements do not bend appreciably under traffic loads and disperse the load over a larger area of the subgrade.
In both flexible and rigid pavements, under the surface course are one to three additional layers of weaker materials – usually crushed rock or soil mixed with a stabilizing agent. These layers – called the base and subbase – redistribute the load from the surface course, enhance bearing capacity, and provide a stable foundation for the pavement.
Steel is a key material for both flexible and rigid pavements to increase their load-carrying capability and enhance structural integrity. Reinforced with either concrete or steel mesh, these elements transfer load between slabs and limit crack growth. Both the base and subbase layer and the surface course may be further strengthened by incorporating a geogrid at the subgrade level.
Maintenance
Pavements play a vital role in transportation. They provide a surface that can bear the weight of vehicles and other traffic while providing safety, comfort, and efficient movement. The quality of pavements depends on their construction and maintenance. They are a complex system of different materials and layers, all of which have their own functions. Each layer must be designed to perform the required task. This requires a thorough understanding of the engineering principles of pavement design.
A good pavement design balances risk and cost, ensuring that the roadway will meet traffic requirements over its service life. This can be done by incorporating appropriate design procedures into the project planning process or by conducting a preliminary pavement design concept conference with district pavement engineers and construction staff.
Every pavement, no matter how well designed/constructed, will deteriorate over time due to both traffic loading and environmental conditions. Maintenance and rehabilitation can slow this deterioration and reset the deterioration curve, thus prolonging the service life of the pavement.
The choice of maintenance actions is determined by identifying and addressing specific pavement deficiencies that contribute to the overall deterioration of the pavement. These maintenance activities are typically categorized as preventive or corrective. Preventive maintenance is most effective when applied at the right time on the deterioration curve, as it can delay or eliminate more costly treatment applications later in the pavement’s life. Corrective maintenance, on the other hand, is performed in response to the onset of a deficiency that negatively impacts the safe and efficient operation of the roadway. Examples of corrective maintenance include the repairing of ruts and resurfacing of the roadway.