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The project was awarded in May 1990. The low bid was $10,783,486
which was $190,000 (17%) lower than the state estimate. The quantity
of asphalt rubber binder was 3.9Mkg (4,316 tons) the largest
amount ever bid by ADOT in a single contract at that time. The
unit cost of the asphalt rubber mix was $0.05/kg($45 per ton)
and the HMA was $0.025/kg ($23 per ton). Construction began in
June, 1990 with the installation of the edge drain and paving
of some of the ramps and crossroads with HMA. In late June the
crack and seat night operation began. Cracking of the pavement
was accomplished with a guillotine hammer. Several drop heights
from 0.6m (two feet ) to 1.2m (four feet) were tried. It originally
appeared from cores that 1m (40 inch) drop height was adequate
although ultimately a 1.2m (four feet) drop height was adopted
to be certain that the slab was cracked full depth. A 0.6m (two
feet) spacing was originally set and later reduced to 0.5m (18
inches). Seating was accomplished with a 45,359kg (50 ton) rubber
tired roller. Generally one to two roller passes was adequate
to seat the concrete. Paving of each nights crack and seat followed
the next day.
The 75mm (three inch) HMA overlay consisted of a dense graded
HMA with 4.6 percent asphalt by weight of mix of an AC-20 grade
(Table 1). No paving problems occurred,
although later after traffic was applied about a dozen small
areas failed. Each area was dug out and replaced with new HMA.
During removal it was noted that the concrete had been previously
in very poor condition. Apparently the crack and seat operation
totally destroyed the concrete pavements structural load carrying
capacity at these few spots.
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