Asphalt can be an attractive and economical choice for accessible pathways, but it's not without its challenges and limitations. These days, more scrutiny is placed on whether or not accessible routes have been constructed in accordance with regulatory requirements. If your proposed accessible routes are constrained to near maximum slopes, you should consider utilizing concrete instead, or plan on extensive measures before and during paving to increase the chances of success.
Unlike concrete, with asphalt paving there are no forms on which you can place a smart level to confirm slopes comply with standards. Measuring the base rock can be helpful, but doesn't tell the whole story either. On a constrained site, a slight variation in the initial thickness behind the paver or in additional pass with a roller is more than enough to cause compliance issues.
Concrete doesn’t have these issues, making it a more reliable material to achieve ADA compliant grades. But, if business reasons dictate the use of asphalt for accessible paths on your constrained site, what can you do?
- Hold a pre-paving conference to confirm the contractor understands the requirements and will have adequate manpower and calibrated levels to perform real-time checks.
- Check the base rock with a smart level to catch any obvious grading busts prior to the day of paving.
- Cold weather paving often leads to use of thicker asphalt lifts. Doing so increases the amount of compaction, which in turn increases the chances for roller-caused compliance problems. If possible, stick to two separate, thinner lifts. Not only is there less compaction but there is opportunity to see what corrections are needed on the final lift.
- Check finished asphalt mat immediately after the breakdown roll to find problem areas. Correct these areas with application of additional asphalt while the mat is still very hot. Keep in mind that on constrained sites, fixing one area by adding more asphalt may simply cause an adjacent area to fall out of compliance. This is one of the fundamental challenges with using asphalt on a constrained site. Also, if the mat cools too much, this additional mix will cause a ‘boney’ texture to the final product.
- Specify that the contractor provides an as-built survey of all accessible surfaces, to be reviewed for ADA compliance by the project engineer.
Hopefully these tips prevent having to correct problems with less than ideal solutions, such as overlays and/or cutting and replacing problem areas.