Applications & Innovations
Better Roads Staff
To avoid these, crews should not lower the isolated low spots (holidays) that are less than 2.7 square feet, according to the ACPA. If the operation causes an unacceptable amount of holidays, they should lower the grinding head and make another pass.
The probability of a diamond-ground surface lasting eight years before needing another rehabilitation is 98 percent, according to the study The Longevity and Performance of Diamond-Ground Pavements by Sreenath Rao, Thomas Yu and Michael I. Darter in the Portland Cement Association Research and Development Bulletin RD 118.
What caused the cracks?
The problem: Road crews pour concrete pavement on a warm day in October. The temperature drops substantially in the afternoon, and the concrete is not covered. The next day, they see a 600-foot section of roadway has transverse cracks every 12 feet. The cracks occur about every second or third joint. There were no changes in materials, saw timing, the base or subgrade with this section.
What happened: Concrete expands as the temperature rises and contracts as it falls, which can cause early-age cracking when the top of the slab is considerably colder than the bottom of the slab. In this case, there was a sharp drop in the temperature when the concrete was at its warmest. The pavement was expanding during the concrete hydration and heat of the day. After the cold front moved in during the night, the top of the newly poured section was cooling following the final setting. The differential temperature in the concrete from the top to bottom caused movement. This resulted in stress building up in the new section that was greater than its strength, causing the cracks.
The solution: They should have kept the pavement covered for the first night to prevent substantial temperature change throughout the depth of the new pavement. It is also important to saw the joints as soon as possible with an early-entry saw to relieve the stress. When tying lanes, road contractors may also need to start paving later in the day when it is not as hot.
Source: Iowa Department of Transportation, Dale Harrington
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