Pavement Elevation Tolerances

[SirAl]

For a large, broad, paved (ACP) commercial lot (a parking lot for example) I would appreciate your comments as to a reasonable construction tolerance in elevation from design to as-constructed grades.

 

[BigH]

SirAl - as you are undoubtedly aware, the biggest problem in such a lot is the local ponding of water so you should be pretty tight on the tolerances. You should see the crap in our office parking lot here. Big problem is the "small" working areas (corners, short runs, and the like).

I don't have any specs for such a large parking area - in our highway project we use plus/minus 6mm for asphalt work and plus/minus 10mm for base course (both laid with a paver). Our surface irregularity is a "few" greater than 7mm and "more" greater than 4mm. The ability of realizing the tolerances, of course, is more in line with contractor's experienced personnels' attention to detail and good workmanship.

 

[MPENN]

Our DOT tolerance for deviation in the surface course is 1/4 plus/minus when using a ten foot straightedge. If the max deviation is taken at the midpoint of the straightedge, the resulting grade is 0.42% which will neither effect the ridability of the road nor present a problem with drainage.

However, when parking lot designers use a minimal grade of 1% there is greater potential for a ponding or spread problem. When there is little room for error in the finished grade, the triming and fine grading of the subbase is critical. Any paver adjustments while moving to accomodate pavement thickess can translate into high or low points. Good luck with the finished surface.

 

[BigH]

Sorry - to clarify - surface regularity is measured by 3m straight-edge at centrepoint - like MPENN's.

 

[cvg]

generally with parking lot design, better to specify steeper slopes, such as 2% minimum. Even with poor tolerances on the paving, it will still drain (no birdbaths)

 

[jheidt2543]

In general, I prefer MINIMUM pavement slopes of 1.0% for concrete and 2.0% for asphalt. As far as tolorances go, MPENN's comment of 1/4" +/-, boils down to 1/4" maximum under a 10' straight edge. Compare that to the "normal" floor slab tolorance of 1/8" +/-. It is actually a pretty tight tolorance. The FF System developed by the Face Corporation has been adopted by ACI and, while it takes some getting used to, it provides a way of measuring pavement flatness and level.

Two good sources of information on tolorances for paving and floor slabs would be the Portland Cement Association (PCA) and the American Concrete Insititute (ACI). They both have specific publications and specifications that address the topic.

 

[SlideRuleEra]

I agree with many of the comments that your are receiving - the slope (1% minimum, 2% desired) is probably the most important design feature. As jheidt2543 mentioned the F Number system is a very nice, objective way to define surface flatness. Many engineers think of it a tool for the construction of "super-flat, super-level" floors. However the F number can easily be selected to acheive "everyday" tolerances.
At the expansion of an industrial plant in the early 1990's we had the flatness F number measured for many existing slabs that we knew from experience had good drainage characteristics. From this data base, we selected F numbers to specify for new construction. This approach to specification enforcement worked well.

 

[SirAl]

Thanks for your input. I value your comments.