Attendees of a recent Local Roads Seminar were told that due to the high price of oil that has resulted in higher prices for asphalt, concrete has become much more competitive.
"Concrete is now a lot more competitive on initial cost," Steve Waalkes, P.E., West Michigan director of engineering for the Michigan Concrete Paving Association, said.
Waalkes also pointed out that higher oil costs impact construction in general, because construction is very fuel intensive.
Waalkes said that maintenance on concrete roads that need minor attention includes filling voids underneath the flats, full and partial-depth patching, grinding, and sealing all of the joints.
"Typically, the voids come from the subgrade material pumping around underneath heavy traffic loads. If you have a clay type of subgrade, it's very susceptible to pumping. That's why we try to place a sand subbase and an aggregate base underneath the pavement. Voids can also come from consolidation. If you have an aggregate base material that is open-graded and has voids in it, under very heavy truck loads, aggregate particles can crush down against each other, and the voids between the aggregates fill up and then you are left with a void underneath your slab or the entire slab will drop. That can occur if you don't have a very stable base material, or subgrade bearing failure from water saturation," Waalkes said.
"So, we're drilling multiple holes in slabs. You can't just drill one hole and expect it to fill the entire void. There were problems on projects in the 1970s and 1980s when this technique was used a lot more using grout material. They would form cones where the grout material would penetrate around the holes where they pumped it, so the slabs were sitting on all of these point loads. The slabs cracked because of the cone-shaped grout material underneath the holes.
"The objective is to avoid detection and accurately drill the holes in the right spots and determine whether or not this is a feasible technique."
Waalkes pointed out that grout required applying a great deal of pressure on the drill hole, whereas polyurethane foam, which is currently being used to fill voids, does not require as much pressure on the hole when the polyurethane expands.
The 2007 Local Roads Seminars were sponsored by Michigan's Local Technical Assistance Program.