According to Matt Laipple, PE, civil engineer with the public works department in Overland Park, Kan., his young community is lucky. City officials and staff have always understood that pavement preservation is necessary to keep road quality high and life-cycle costs low, and have been using pavement preservation techniques for the past 50 years.
“Many communities use mill-and-overlay — removing the top 2 inches of asphalt — on a 10- to 15-year cycle to provide a new wearing surface on asphalt pavement,” he says. “We can preserve nearly five times more lane-miles of pavement with micro surfacing or chip seal for the same cost. Other maintenance treatments may extend that figure further.”
Laipple says the goal of using pavement preservation techniques rather than wholesale mill and overlay (or mill-and-fill) is to keep the pavement's life-cycle cost low while maintaining serviceability and user satisfaction. Without some form of preventive maintenance program, it's not uncommon for an asphalt pavement to need complete reconstruction after 20 to 30 years.
While a regular mill-and-fill program will extend pavement life just as well as a preventive maintenance program, the life-cycle cost between the two approaches is dramatically different. Using recent local pricing and discounting future activity costs to present value with a 4% discount rate, the difference is $400,000 to $500,000 per mile of two-lane street over a 50-year period. That may not seem like a lot over 50 years, but multiply it by the number of miles in an agency's street network, and it adds up to serious dollars,” Laipple adds.
Formula for success
“The key to implementing preventive maintenance techniques and maintaining a pavement management program is developing and maintaining an inventory of pavement condition and quantity,” says Laipple. In Overland Park, streets are broken into sections and student interns survey the same locations on a biennial basis, counting cracks and deficiencies as identified in the Federal Highway Administration's Pavement Distress Identification Manual. “We compare scores of the current assessment to those of prior assessments and monitor the rate of deterioration,” he explains.
The Pavement Condition Index, developed by the Army Corps of Engineers, is generally accepted as the industry standard for scoring pavement condition (see chart below). It provides a rational basis, calculating deterioration rate and deterioration modeling. The data can be used in conjunction with a pavement management program to develop a plan for pavement preservation, proactive maintenance, and rehabilitation.
Most of Overland Park's pavements receive some form of preventive maintenance every seven years, but in the future, Laipple may prioritize maintenance based on pavement condition and construction type rather than elapsed time between treatments.
Overland Park generally uses the following schedule for residential streets. Major maintenance at year 28 and reconstruction at year 50 may be shifted as budget allows, however preventive maintenance occurs consistently:
- Year 0: New pavement
- Year 3:Crack treatment
- Years 7, 14, and 21: Crack treatment and micro surfacing/chip seal
- Year 28: 2-inch mill-and-fill
- Year 31: Crack treatment
- Years 35 and 42: Crack treatment and micro surfacing/chip seal
- Year 50: Rehabilitation or reconstruction
Budgeting for longevity
Most agencies know pavement preservation techniques such as slurry and micro surfacing, chip sealing, and crack treatment can extend their budgets. Now residents are beginning to understand the benefits of pavement preservation. “A mill and overlay is similar to the idea of removing the siding from your home every 25 years and replacing it with new siding. It's cheaper and more efficient to paint the siding and preserve it over time,” says Laipple.
However, pavement preservation measures don't work as reactive maintenance. If roads that are in fair-to-good condition are ignored and budget dollars are devoted only to rehabilitation of the worst roads, then overall road conditions will get poorer and agencies will always be playing catchup, even when budgets grow as the recession declines.
— Contributed by the International Slurry Surfacing Association.
|PAVEMENT PRESERVATION TREATMENTS AT-A-GLANCE|
Micro surfacing — A mixture of aggregate, asphalt emulsion, water, and additives applied in a smooth layer over existing pavement. When applied early in the pavement's life cycle, it can cost-effectively extend surface life by seven or more years.
Slurry seal — Applied to existing pavement by a spreader box linked to the surface slurry-mixing unit. Used over newly laid pavements, slurry seal will prevent surface distresses such as the effects of weathering. Existing distresses in older pavements — surface cracking, raveling, loss of matrix, increased water and air permeability, and slipperiness due to flushing and aggregate polishing — can be corrected with a slurry application.
Chip sealing — A bituminous binder covered with clean graded aggregate, applied to an existing asphalt surface.
Crack treatments — Specialized materials are placed into prepared cracks to prevent water and incompressible intrusion into the cracks and underlying pavement layers and to reinforce the adjacent pavement. Used for pavements that primarily have working cracks (greater than 1/8-inch annual movement).