HMA Pavement Section Thickness 6

[cohoman1]

We have a project that is widening an existing roadway. The question was raised as to whether the thickness of the asphalt in the widened area should match the existing thickness of asphalt in the existing pavment area.

What I am wondering is if there is some type of industry design standard that would say you shouldn't create a situation where there is a sudden change in asphalt thickness.

 

[Ron]

The pavement structural design depends on multiple layers. There is no need to match one thickness of asphalt with another, even adjacent to it provided you have adequate structural capacity and you accommodate the joint so that it does not open up and allow water intrusion to the base. The one exception to this is that I would not put a full-depth asphalt pavement adjacent to a granular base pavement as these tend to perform slightly differently and more deformation could be expected in the full-depth asphalt.

Make sure all surfaces are primed and tacked (including the vertical transition face. Secondly, make sure the new pavement section is cross-rolled into the old section to provide a good bond.

 

[VAD]

Hello cohoman1

I am not sure what approach you will use in determining an adequate structural capacity for the widening portion as Ron has alluded to. From your question I presume that those advocating the equivalent asphalt thickness are experienced and understand that ntheory does not really apply to this type of design rather the performance of the existing roadway would be of importance. From my personal experience unless you can determine the stiffness characteristics of the existing roadway using FWD for example, then the wise approach would be to match the pavement of the existing road. It would be unwise to have a pavement structural section that is variable in stiffness characteristics as the new section will suffer rutting problems. Remember that the stiffness characteristics of asphalt concrete and granular base are quite different.

With respect to the use of full depth asphalt adjoining a conventional pavement section, another reason for not pursuing that idea is the likelihood of blocking pavement transverse drainage. One needs to maintain drainability of the structural section in any widening endeavour. This is often forgotten. A thicker asphalt pavement would be more appropriate with drainage ensured.

While my comments may be in some contradiction to what Ron has stated one has to remember that there are a multitude of factors that come into pavement design, one of which is local experience. In the end, this should be looked at before a final decision is made.

Regards

 

[SirAl]

A few good points brought forward. The drainage issue that VAD suggested is an important one. Older roads may have multiple overlays - matching ACP thickness to the existing structure may not be economical. I agree with Ron regarding the structural capacity. Also, you will probably realize a longitudinal crack along the seam at some time over the service period.

 

[wolfhnd]

If the original base was designed to drain then the new adjacant pavement base should drain.

 

[consman]

I work in an overseas highway construction project and I need AASHTO Guide for Design of Pavement Structures 1993, layer coefficients' nomograms for flexible pavements, for all kinds of layers (subbase, crushed stone base, cement treated base, asphalt base and asphalt). No matter how hard I tried I could not find it anywhere. I'd be extremely happy if somebody could tell me the web site where I can find them.
Thank you. very much.

 

[wolfhnd]

http://www.aashtoware.org/?siteid=28&pageid=76

http://www.tfhrc.gov/pavement/ltpp/rigid.htm

http://www.asphaltalliance.com/upload/Pavement Type Selection Processes.pdf