As with any slab, there are several ways to construct concrete parking lots. The simplest but least precise method is simply to wet screed the concrete to the desired thickness. Setting side forms and using hand screeds, truss screeds, or other vibrating screeds is another option—probably the most common. Slip forming is fast and produces very high quality pavement, although the equipment is expensive and positioning the equipment is difficult except for very large lots. The latest option is to use a Laser Screed with a 3-D attachment that can place concrete very precisely and rapidly.
|The 3-D Laser Screed can profile concrete pavement to precise slope requirements.
Here are some tips for parking lot construction:
- Be sure to compact the subbase to get a smooth surface and uniform density. The subgrade should be within plus ¼, minus ½ inch of specified grade. Since parking lot pavements tend to be thin, high spots can lead to thin sections that can fail. Thick sections can cause problems with cracking.
- Compact the backfill for any excavations under the parking lot in 6-inch lifts. Controlled low strength material (flowable fill) is a good option for this.
- Dampen the subgrade prior to concrete placement in hot and/or windy conditions.
- Finishing of parking lot slabs is typically just screeding, bullfloating, and brooming to get a slip-resistant surface. Find more info on slip-resistance. Troweling air-entrained concrete often leads to delamination of the surface layer and surfaces that would be dangerously slippery when wet.
- Curing is essential to get a good strong surface. Cure the slab with a spray-on curing compound. You could fog-cure, but that's probably more effort than it's worth for most parking lots. Find more info on curing concrete.
- A good idea for a successful project is to hold a pre-placement conference with the designer, the owner, the concrete producer, the general contractor, and the concrete contractor. Florida Concrete & Products Association has published an excellent checklist for this conference that is available at www.concreteparkinglots.com under the "downloads" tab. You have to get an access password to retrieve the checklist but it only takes a couple of minutes and is well worth the effort.
- The 3-D Laser Screed is a great way to place concrete parking lots if you have a screed and want to get the most use out of it. Using a robotic Geodimeter, the screed can adjust the slope of the surface to any profile desired. The only problem with this approach is that it is so fast it is difficult for the crew to keep up.
- Joints should be sawed as soon as possible without raveling the concrete—from 4 to 12 hours with conventional saws and 1 to 4 hours with early entry saws. If there are any re-entrant corners, start your saw cuts near the corners first to prevent diagonal cracks. Find more info on preventing cracks.
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