Dowel Retrofit Case Study, Minnesota, USA

The Minnesota Transportation Department (MnDOT) reported in their National Road Research Alliance (NRRA) newsletter about Scott Holmes, Transportation Supervisor for Olmstead County Public Works-Minnesota, USA. He was concerned about County Highway 22 (Also known as 37th Street NW, between the intersections of Trunk Highway 63/52 and N. Broadway Ave/County Highway 33) upon which his 2011 concrete overlay was already showing signs of joint faulting, and was not performing as predicted. He suspected that the heavy traffic from a new industrial site nearby was doing the damage—heavy trucks were wearing out his road much sooner than he expected.

 

History
Highway 22 was already a busy road. Originally a full-depth 14-inch bituminous roadway to be repaved due to rutting, the county decided repave with a concrete overlay. They milled 6.5 inches off the top and put down a portland cement concrete (PCC) overlay without dowel bars at the joints. With the solid bituminous base, there didn’t seem to be any need for more support.

Due to faulting, the ride deteriorated and the public began to complain about the poor ride quality. Holmes said the only explanation was the very heavy loads being hauled to and from the industrial site. In 2015, he contacted MnROAD to have the researchers perform some in-depth analysis. Tom Burnham, Materials and Road Research Lab-MnDOT, examined the road using both ground penetrating radar and the new high-speed digital correlation system. In the report, he wrote, “Good load transfer would be depicted as having fairly equal deflections on both sides of the joint.” Instead he found very little load transfer (see figure below):

The Solution
Holmes considered smoothing the ride by only diamond grinding the surface, but decided that would only last a couple of years. Needing something that had more long-term potential, he went with the dowel bar retrofit technique—one that he had a good experience with in the past. After further consulting with MnROAD staff, he decided to put dowels across the transverse joint in the panels, three in each wheel path.

Further consultation with the Concrete Paving Association of Minnesota (CPAM) led him to choose smaller one-inch dowels across the joints. Afterward, the entire surface of the pavement was diamond ground to restore ride quality, thus extending the service life of this road for many years.

Costs
Conventional wisdom would say that performing the dowel retrofit on this road would be more expensive than installing them in the original PCC overlay rehab, but Holmes said it might have been slightly cheaper. In this retrofit he isn’t using dowels or baskets throughout the whole slab. Instead he is using fewer dowels to maximize their effectiveness.

To read the case study in the NRRA Newsletter, please go to: http://www.dot.state.mn.us/mnroad/nrra/newsletter/currentissue.html?utm_content=&utm_medium=email&utm_name=&utm_source=govdelivery&utm_term=#dowel

For the PDF of the International Grooving and Grinding (IGGA) Resource titled “Dowel Bar Retrofit for Thin Concrete Pavements”, please click on image to the right, or go to: http://7e846f23de4e383b6c49-2fba395bb8418a9dd2da8ca9d66e382f.r19.cf1.rackcdn.com/uploads/resource/423/CSJune2017_MN_dowel_bar_retrofit.pdf

For the Public Works online article titled “Retrofit Dowel Bars Restore Thin-Section Pavement—Smaller-diameter dowels are a cost-effective way to restore load transfer in low-volume concrete roads”, please go to: http://www.pwmag.com/roadways/retrofit-dowel-bars-restore-thin-section-pavement_o