By David Smith, ICPI Technical Director
State departments of transportation (DOTs) rely on millions of tax dollars for road construction and maintenance. They also look after thousands of structures including bridges. For decades, DOTs are immersed—and one might say entrenched--in design, maintenance and improvement of asphalt and concrete pavements. These are mostly highway pavements.
Most DOTs look after local roads as well, especially if they are national or state routes passing through a city or town. About one fourth of all roads are urban, so some portion of this percentage is under state DOT care. While the percentage of their total road inventory likely varies from state-to-state and province-to-province, urban roads represent an opportunity for interlocking concrete pavements (ICP).
Here is a story from the New York State DOT (NYSDOT) who made a new path for ICP. In 2004, the U.S. Federal Highway Administration contacted the NYSDOT requiring removal of ICP from pavement use due to crosswalk failures. This was likely a federally funded road project. In the fall of 2005, at the request of the industry, a task force was created to implement new specifications and subbase requirements to allow ICP.
In 2006, provisional ICP specifications were written with drafts of typical sections for ICP crosswalks in high use areas. The drafts included a 12-inch thick crushed stone subbase, 8 inches of concrete, ¾ inch sand-bitumen setting bed and adhesive under 3 1/8-inch thick (80 mm) thick pavers in a herringbone pattern. Interestingly, the paver thickness was increased from 2 3/8 (60 mm) to 3 1/8 inch as recommended by ICPI. The NYSDOT found a trial location, where a crosswalk(s) in a street could be built. The street had about 8,000 average annual daily traffic (AADT) and provided a pilot project to monitor the success of the draft specifications.
In 2007, the State Historic Preservation Society decided that ICP must be used to replace the pavement on Main Street in East Aurora, NY. AADT was over 20,000 with 10% to 12% truck traffic. This equates to roughly 10 million equivalent single axle loads (ESALs) over 20 years assuming 1% annual traffic growth. This becomes NYSDOTs pilot project. It was built in 2009 with five lanes, curb to curb ICP for about 4 blocks or about 1000 feet. The project involves over 250,000 pavers or over 55,000 sf.
|Above: Four blocks of interlocking concrete pavement are paved
on Main Street in East Aurora, New York in 2009.
After three years of monitoring, the pilot project was deemed acceptable in 2012. NYSDOT issued a new Standard Specification 601 for Architectural Pavements (see their 2016 Standard Specifications Section 601), as well as standard drawings (sheet M601-01 in the 2015 collection of New York State Standard Sheets). In 2017, the East Aurora ICP continues to perform well with the additional blessing of no utility cuts in the pavement.
|Above: Main Street in 2014.|
The diligence of an NYSDOT advocate, Jim Patnaude, Associate Engineering Materials Analyst, Materials Bureau in Albany, was a prerequisite to the industry becoming involved. While the state specification is only for concrete bases, it is a start. The next step might be writing design guidance and specs for lower traffic areas that include less expensive, dense-graded aggregate bases and those stabilized with asphalt or cement. While design guidance for these areas is available in a national design standard (see ASCE 58-16 Structural Design of Interlocking Concrete Pavement for Municipal Streets and Roadways), DOTs would embrace ICP more readily if the industry committed to full-scale load testing. This type of validation is done daily by several DOTs and universities across the U.S. and Canada for asphalt and concrete pavements. Since DOTs have great influence on municipal road specifications, this investment could make DOT and industry missionary work on local road applications turn into a Reformation.