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Makeup of a Street
Streets are composed of two main layers: the base and the surface. The primary weight-bearing portion of a street is the base. The surface layer is made up of asphalt or concrete and protects the base.
The majority of a roadway’s cost lies below its surface. When properly maintained, asphalt and concrete streets have an average life span of 25 or 50 years, respectively.
Types of construction
When considering what type of street to construct, it’s important to consider the initial capital cost, the life span and the long-term maintenance needs.
Mill and overlay
During this process, a street’s top layer of existing asphalt is ground down, removed and overlaid with new asphalt. High-volume roadways showing signs of major distress need to be milled and overlaid every 15 years. Mill and overlay is the most common type of street maintenance done by the City.
Full-depth reclamation
During the FDR process, the existing roadway’s gravel and asphalt layers are grinded together before cement and liquid asphalt are mixed and rolled out to make the new base. In a short time, the base is drivable. An asphalt layer is then added on top, finalizing the new roadway.
FDR is a great solution for roads that don’t require curb replacements or roads that don't have bases in shape for the common mill and overlay process.
Complete reconstruction
Complete reconstruction of a roadway is required when damage is beyond repair, typically at the end of its service life. During reconstruction projects, the road will be completely rebuilt with new material from the base up. Some roadways are reconstructed using asphalt, which lasts about 25 years, while other streets may use concrete, which has a 50-year lifespan but can be up to 10x costlier than asphalt due to the steel bar material that supports the concrete. New curb, gutter and sidewalks are also part of the reconstruction.
Complete reconstruction is the most expensive method of street construction.
Major maintenance costs for one mile of a 40-foot-wide street over a 75-year period can cost around $8 million.
Preventative maintenance
Sealcoating
Sealcoating is not to be confused with resurfacing a roadway. Sealcoating involves applying a thin layer of asphalt and rock to a street’s surface. This method of maintenance prevents moisture from seeping into the asphalt and damaging the roadway’s base. The process assists in preventing new or additional cracking that can eventually lead to pothole formation.
In 2015, the City began an 8-year project to sealcoat every City-maintained roadway in San Angelo.
Sealcoat master plan 2016-2023
High density mineral bond (HA5)
HA5 is a surface treatment that limits oxidative damage on asphalt from moisture and ultraviolet (UV) radiation.
It serves two primary functions when applied to a roadway:
- It seals the roadway to prevent moisture from penetrating into the street’s base.
- The product acts like a sunscreen and protects the street from oxidation from the sun’s UV radiation.
This treatment is ideal for roads with minimal wear and cracking. Utilizing this method is part of an effort to change the City’s focus from a reactive/repair-focused operation to a proactive/preservation operation.
Once HA5 is applied, it cannot be driven on for 24 hours. Although inconvenient, the benefits HA5 can provide are considerable. Streets treated with HA5 versus sealcoat are cleaner, quieter, smoother and maintain their aesthetic black color for up to 8 years on average.