PT-1: Long-Life Pavement

Post by SteveM Aug 27th, 2010
at 4:38 pm

For BG:
I agree that NPS roads are not likely to experience high ESAL levels, which is what several of your comments address. On the PT-1 SECTION 2 comment, if the CBR is >= 10 the minimum section becomes 5 inches of HMA over 6 inches of aggregate base. The cost argument you present is compelling but in many cases the added up-front expense can be more than compensated for over the life of the roadway. Often the payback period for a long-life pavement is on the order of 20 years but the research here is sparse. The thicknesses in Figure PT-1.1 see to be born out by the evidence - for low traffic levels you need to be about 5-6 inches thick to drive the distress to the surface of the pavement and create what this credit (and others) call a long-life pavement, which is what this credit is after. As an aside, I did an investigation of Washington State DOT low-volume (< 1 million ESALs in 40 years) pavements a few years ago (2004)and found many that met this criteria.

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-1
SECTION 5
As per the chart shown in this Section: An ESAL = 18,000 pounds. As an example, a 20 million ESAL load is equivalent to 1375 semi-trucks per day, every day for 20 years. The lower inflection point on the graph is for 500,000 ESALs, which equates to 34 trucks per day, every day for 20 years. How many NPS roads receive that kind of loading?
NPS-BG

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-1
General comments on this Section: NPS roads would never get the huge 5-point score for this category because , in combination: a) the lower ESAL limit is too high for NPS roads, b) 6-inches of HMA is a minimum, cost and resource impacts preclude serious consideration in most instances.
NPS-BG

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-1 3 and 4
The examples given for both HMA and PCC pavements are interstates or other higher volume roads that experience ESAL loading beyond the vast majority of NPS roads
NPS-BG

Post by JanB Aug 11th, 2010
at 3:29 pm

PT-1
SECTION 2
As per the chart shown in this Section: An ESAL = 18,000 pounds. As an example, a 20 million ESAL load is equivalent to 1375 semi-trucks per day, every day for 20 years. The lower inflection point on the graph is for 500,000 ESALs, which equates to 34 trucks per day, every day for 20 years. How many NPS roads receive that kind of loading?


As per the chart, the minimum thickness that a pavement section can have is 12 inches (6” base and 6” HMA), regardless of the ESAL load.
Two Park Service issues preclude thicker sections: resource impacts and program dollars. If 4:1 side slopes are used, a 12 –inch section can be as much as 8 feet wider than the section it is replacing. By doubling the HMA thickness from say, 3 to 6-inches, a cost of about $325,000 per mile is added to the project, based on $130/ton for HMA.

PCC pavements are even more expensive.

NPS-BG