Published: July 28, 2008 11:41 pm            

Cutting edge, cutting costs?

A new paving technique could make Oklahoma roads more durable and save the state money in the long run.

Crews from the University of Oklahoma’s College of Engineering and the Oklahoma Department of Transportation worked on a stretch of Timberdell Road last week to test the pavement in an effort with the Oklahoma Aggregates Association.

“These new aggregate base designs are expected to lead to longer lasting pavements in future road and street construction, with the potential to save millions of dollars in future repairs,” Naji Khoury, a research associate and instructor with the OU College of Engineering, said in an e-mail.

The project began Oct.1, 2006. Crews Tuesday and Wednesday conducted one of the quarterly tests on three different paving techniques to determine the one that drains the best.

Water can get trapped in the road bed and cause the road to break up prematurely, especially in the eastern part of the state where groundwater moves up into the strata in addition to flowing down, said Jim Rodriguez, executive director of OKAA.

ODOT currently has one type of drainable paving, but it is difficult to mix and maintain the proper blend of gravel, he said

“It’s a very difficult material to handle and place properly,” Rodriguez said.

So the OKAA, ODOT and the College of Engineering got together and decided to try to make a better pavement.

“What we’re trying to do is find an aggregate gradation that gives us good permeability, good drainage characteristics, … something that’s easy for the aggregate producers to make,” said Jeff Dean, ODOT pavement engineer.

ODOT and OKAA both came up with one possible mix for the subgrade, or road base. ODOT installed both in a 250-foot test section of Timberdell Road, between Asp and Jenkins Avenues, along with a portion of the normal impermeable road base, Rodriguez said.

“The project focuses on testing alternative aggregate base designs that would optimize drainability without sacrificing too much on strength and stability,” Khoury said. These designs for the base are made up of crushed stones of different sizes, he said, and are more porous than the typical road design.

“And, they are expected to drain out water more quickly from underneath a pavement structure compared to the common design practice,” Khoury said.

Most roads are built with only a thin base layer of gravel or none at all, Rodriguez said.

These roads are cheaper to build initially, but when water doesn’t drain properly out of the roadway, freezes can cause the road to break, he said. This costs taxpayers more money in the long run for maintenance and replacement.

The road in the test section of Timberdell Road is made up of four layers. In addition to the subgrade, or base, that is unique to these designs, engineers also added a water-proof fabric between the subgrade and the base material of the road to keep water out of the subgrade, Rodriguez said.

Tuesday and Wednesday ODOT personnel from the Materials Division and the OU research team tested a section of Timberdell road for stability and permeability.

“The purpose of these tests is to determine the strength and drainability of a specific aggregate base layer and the overall performance of the pavement,” Khoury said.

ODOT conducted falling weight deflectometer tests to determine stability. In this test, ODOT workers dropped weights onto the pavement from specific heights and measured the results.

OU researchers Khoury and Musharraf Zaman, associate engineering dean for research and graduate education, conducted the field permeability test, which used a field permeameter designed to measure the flow rate of water through the street’s underlying layer of base material.

The road will be tested every quarter until Sept. 30, 2009. At that point, ODOT will evaluate the results and possibly use the type that was created for this study, Dean said.

“We hope to use that data to hopefully increase the life of our pavement and save the taxpayers money, ’cause that’s what it’s all about.”

        

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