The Pavement Management Program is an Information Management System, which allows the City to track the history, surface condition and distresses of every street in Mesa. Pavement condition surveys are performed each year on over 1,200 miles of streets. Information from the annual surveys identifies specific areas where various types of preventive maintenance treatment, such as slurry seal, acrylic seal or other sealcoats, can be applied. The surveys also identify areas requiring more aggressive rehabilitation projects like a rubberized asphalt overlay or partial reconstruction.
Each year over 6,000,000 square yards of needed work is identified, prioritized and delegated. One goal is to establish a balanced treatment forecast plan for the street repair and preventive maintenance program that will help to maintain targeted pavement condition levels. These levels are based on a Pavement Condition Index (PCI) of 0 to 100, with 100 being excellent and 0 being failed. The PCI is calculated from data collected during the annual pavement condition survey. The City has been collecting pavement condition, inventory and maintenance history information on Mesa streets for over 18 years with details and quality of data improving with each year.
Pavement Maintenance Programs
A variety of programs are used to help keep our streets in the best possible condition and extend their service life. Below are definitions of commonly used pavement maintenance techniques.
Read an overview of how we maintain Mesa's streets with this brochure. [PDF]
When a small isolated section of roadway fails, we call it a "pothole." Typically water has seeped under the pavement surface, creating pockets of water that fracture the surface when traffic compresses the water underneath. These potholes are temporarily repaired with a cold-mix asphalt. If a section of roadway has numerous failures because the sub-base under the road surface is compromised, permanent repair may be delayed until a better solution can be funded and implemented.
When a roadway is generally in good condition but there are isolated sections that show signs of failure, asphalt patching is performed to improve the overall condition of the street. We currently utilize two practices for patching asphalt:
- Mill & Cap - Sections of the roadway that show signs of failure are milled down to the good pavement base. The milled down areas are then capped with new hot-mix asphalt.
- Remove & Replace - Sections of the roadway that show signs of failure are saw-cut and the asphalt is completely removed. The sub-base is compacted and the section is paved with new hot-mix asphalt.
Asphalt pavement is designed to be flexible. This allows it to adapt to the wide temperature swings we have in Arizona. The flexing causes cracks to develop in even relatively new pavement and this will continue throughout the usable life of the roadway surface. To limit deterioration, cracks are filled with a rubberized sealant we call a "Crack Seal" that will restrict water penetration and fill voids in the surface.
There are two main types of surface treatments applied to extend the life of the pavement: Fog Seal and Slurry Seal.
A fog seal is a thin layer of asphalt emulsion applied to the street surface to prevent oxidation, loss of fine aggregate and add asphalt material to the surface course. Depending on traffic speeds and street conditions there are three types of emulsions that may be applied as fog seal. Tire Rubber Modified Surface Seal and Plastic Seal both use additives to increase the life of the product and are used on residential and low-volume streets. Cationic Quick Set Emulsion has no additive and is used on arterial and high-volume streets.
A slurry seal is a 3/8" to 5/8" mat of asphalt emulsion, water and aggregate applied to the street to create a new wearing surface. This application is generally used to extend the life of the existing pavement on streets that show signs of surface deterioration.
When your street is scheduled to be treated, pre-warning signs will be placed at various entrances and streets into the neighborhood approximately two weeks in advance. Residents will receive a door hanger with instructions two to four days prior to their street being closed for seal coating.
Mill and Overlay
If large areas of a roadway are showing signs of structural failure, potholes or alligator cracking, the section can be milled down to the good pavement base. This is followed by a new hot-mix asphalt overlay, extending the life cycle of the original pavement.
When a roadway has reached the end of its life cycle and can no longer be rehabilitated, a new road must be constructed. All existing pavement will be removed and recycled for use as a new sub-base. The old sub-base will be re-graded and compacted and a new hot-mix asphalt surface applied.
The most common work seen on the road has nothing to do with pavement maintenance. These are areas where utility crews are cutting into the road surface and digging down below the surface to add or repair sewer, gas, or water lines. During the course of construction they will cover these areas overnight with metal plates or a cold-mix asphalt. When completed, the area will be re-compacted, a new sub-base installed and a hot-mix asphalt applied.