For the other two bases – the permeable treated base on the crushed stone, or the 4 inches of crushed stone – the material must be imported. So that material is included in the paving contract.
“So because the paving contractor is placing the base and the pavement, we set the subgrade elevation for the thinner pavement,” says Donahue. “If it goes concrete, then that contractor just places the base on the finished subgrade, then paves it. But if an asphalt contractor gets the project, he has to blade off the subgrade, which is doable, because it’s a fine-graded material. Then the asphalt contractor cuts the subgrade down by whatever the difference in the pavement thicknesses is and places his base on top of that.”
Naturally, if grading and paving are both included in one contract, the winning contractor will control the subgrade elevation because he is committed to one pavement type or the other. v
How They Do It In LA
For several years now, Louisiana has done an alternate design-alternate bid (ADAB) process on projects where the difference in life-cycle costs between concrete and asphalt is less than 25 percent. “If the difference is greater than 25 percent, then we only bid it in the less-expensive material,” says Jeff Lambert, pavement design engineer with the Louisiana Department of Transportation and Development.
The state’s ADAB model adds a factor “C” that represents costs for future rehabilitations and user delays associated with a contractor’s base bid, called “A”. The “B” component is time-based bidding that may also include an incentive for early completion. The state transportation department calculates the “C” component and awards the contract to the company with the low sum of A + B + C.
For asphalt, the “C” component includes two mill-and-fill rehabs over 40 years. Similarly for concrete, two rehabs are calculated into the life cycle cost over 40 years. At 20 years, joints are cleaned and resealed, and some patching and shot blasting is included. Additional patching and surface retexturing is figured in at year 30, says Lambert.
“We’re sure that both industries accept the fundamental principles of it,” says Lambert. “They appear to be happy with it; they’re still bidding on our projects. It has increased the number of bidders.” He says Louisiana uses the ADAB model on most larger new construction and reconstruction projects.
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