What If?

Fall 2016

Modeling life-cycle costs of interlocking concrete pavements for municipal street systems

by David R. Smith

By

What If?

Many cities maintain a database describing the condition of their road pavements. The database includes the pavement structure, condition information listed as various ‘distresses,’ as well as their extent and severity. The database is used to calculate a pavement condition index (PCI) based on these combined factors. A PCI can rate a single pavement or a network from 1 to 100 with 100 being a brand new, perfect pavement while 1 suggests a surface like the Ho Chi Minh Trail after a B-52 bombing raid.

Two ASTM standards describe the index calculation process. For asphalt and concrete pavements, there is ASTM D6433 Standard Practice for Roads and Parking Lots Pavement Condition Index Surveys. For segmental concrete pavement, there is ASTM E2840 Standard Practice for Pavement Condition Index Surveys for Interlocking Concrete Roads and Parking Lots. (Both standards can be purchased at www.astm.org.)

Pavement condition surveys for asphalt and concrete streets have been in existence for decades. Municipal and state road agencies refine their models characterizing wear over time to accurately predict required maintenance, types, costs and budgets. For interlocking concrete pavements, such surveys exist in The Netherlands due to extensive segmental pavement use there. For the U.S. and Canada, there are millions of square feet of municipal interlocking concrete pavements. However, most are installed as specialty applications to highlight downtown or neighborhood business district improvements. There are only a handful covering an entire neighborhood, larger residential or commercial districts, or entire city centers.

Most municipalities struggle financially to maintain existing asphalt and concrete pavements. These pavements are institutionalized over the past 100 years through design, construction and maintenance requirements, plus equipment and crew investments. Considering wider use of interlocking concrete pavements by municipal road agencies is simply out of the question unless the industry presents compelling evidence for substantial reductions in material, equipment and personnel costs.

Such reductions from interlocking concrete pavement beg exploring in the context of a road network in a neighborhood or district. Experience has demonstrated that when properly designed and installed, interlocking concrete pavements last 30 to 40 years. The absence of damage and reduced pavement life from utility cuts, almost all-season repairs, no resurfacing, possible lane and parking space striping with colored pavers, lower capital expenses from using less and simpler maintenance equipment, and paver re-use all appear to present lower life-cycle costs for a municipal street system. ASTM E2840 provides tools to calculate PCIs from databases as a prerequisite to measuring costs and benefits.

ICPI would like to take this to the next level. Here’s the pitch: The industry seeks a willing municipal road agency (and possible supporting pavement consultant) with a pavement management system who would like to model the what-if life-cycle costs of interlocking concrete pavements to better understand and reduce agency costs, plus operational and institutional changes that would yield taxpayer benefits. Together, we might be surprised after examining the what-ifs that the next question turns out to be why not?

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