One of the mostly widely used and visible components that the City of Beatrice provides to the public is its 115 miles of roadways. The roadway system is predominately comprised by 3 types of surfaces: concrete, asphalt, and aggregate.
Our asphalt streets account for 34 miles, or approximately 30 percent, of the City’s roads.
Like many local road agencies, the City of Beatrice has a limited budget to maintain our roadway. The City tries to address these limited dollars by preserving the existing asphalt system with an annual surface treatment program.
Asphalt Surface Treatment (often referred to as armor coating, chip sealing, tar and gravel, BST-Bituminous Surface Treatment) is a widely used and very cost effective way to maintain roadways, parking lots, driveways, and more. The City of Beatrice commonly refers to this treatment as Armor Coating.
Armor Coating provides a waterproof layer to protect the underlying pavement, it increases skid resistance, is a filler for existing cracks or raveled surfaces, and it can aid as an anti-glare surface during wet weather.
Armor Coating is created using two main materials; an asphalt emulsion and a cover aggregate. The existing asphalt pavement is sprayed with the asphalt, then immediately covered with aggregate and then rolled.
Emulsified asphalts (or binder) consists of an oil suspended in water. A surfactant is added in order to make the oil and water mix and provide a more uniform mixture throughout. Having the asphalt suspended in water allows the placing temperature of mixture to be significantly lower and more manageable.
Aggregates typically used include natural gavel or crushed stone. Due to availability and costs, the City often uses a 3/8 inch natural gravel that meets a specific graduation requirement which is obtain from Beatrice Concrete. Aggregate gradation and size are important to the success of the Armor Coating process.
The design of an armor coat system must take into consideration the amount of binder and cover aggregate to apply. In order to prevent excessive aggregate loss, about 70 percent of the aggregate must be embedded in the residual asphalt. In order to accomplish this the City of Beatrice specifies that the rate of application for the asphalt shall be 0.30 gallons per square yard.
The real question is how or why does armor coating the asphalt roadways makes sense?
If an asphalt roadway is in need of complete replacement, the City of Beatrice is currently seeing costs of $21,000 per block. The anticipate life of a newly reconstructed roadways in Beatrice without any surface treatments is estimated to be 15-20 years. However, a surface treatment like armor coating has a cost of only $1,000.00 per block and yet can extend the life of the existing pavement another 5 years.
So based on this information, lets evaluate a one block section of roadway over a 40 year span. The complete replacement option with no maintenance would have a total cost of $42,000 ($21,000 at year one and another $21,000 at year 20). However, the armor coating option would have a total cost of only $25,000 ($21,000 at year one, and then 3 - $1,000 treatment).
This equates to a costs saving of $17,000. So while armor coating may cause some inconvenience, it can lead to significant costs savings.