Asphalt testing 2

[Okiryu]

Hi, what could be the best tests to verify the quality of the asphalt? New asphalt was placed 5 months ago but not open to real traffic yet. Client is concerned about tire marks are left on the asphalt. These marks are from steering the wheels without movement. Asphalt is PG 60/80 with aggregate size 20 mm. I am located in Japan and it is summer now. Temperature in a hot day goes up to 32 C (90 F) easily. We told the client that once real traffic starts and asphalt ages, this issue will be minimized/disappear. However, he is not convinced and we need to proof that the placed asphalt is OK. Sorry for if these questions are too amateur. I am not an asphalt guy so any input will be appreciated. Attached is a photo of one of the tire marks left on the asphalt recently. Thanks !

 

[dik]

I'd be a bit concerned... how hot was the asphalt when this occurred? and how long had the vehicle been parked? Asphalt temperature could easily be 80C or 90C in the open calm hot sun. On a hot day, I've often had my motorcycle support sink into asphalt and carried a 12x12 plywood pad.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Okiryu]

Not sure about the asphalt surface temperature but the outside temperature was 30 C plus for several days. Looking at the asphalt material properties, the softening point is 46 C. I would expect that the asphalt surface was close to the softening point temperature when this occurred.

 

[dik]

Exposed to direct sunlight on a hot day, with little wind, asphalt can get much hotter on the surface than 46C. Do you have a local geotekkie that works with asphalt?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dhengr]

Okiryu:
They do typically warn against excessive steering, sharp radius turns, and manipulating the steering wheel while standing still, until the asphalt has aged/cured a bit and hardened. That later situation shows up exactly as your photo shows. You can literally dig a depression in the asphalt surface by cranking the steering wheel back and forth a number of times, and the black, still soft (or soft from the sun) asphalt comes to the surface, just as your photo shows. Or, the very top aged surface is abraded way, exposing the softer under layer. Ask the asphalt contractor for the asphalt mix design, compaction procedures, compaction and density testing results, etc., and put him on notice that this has happened. Have him tell you what to do first, after all, he is the one who has to guarantee his work, and make is customer happy.

 

[Okiryu]

Hi dhengr, we are working with the asphalt contractor but they are not sure about what type of tests can be done to check against this issue. We were thinking on density tests, penetration tests and softening point temperature verification tests but I was looking if anyone has other recommendations. Thanks for the input.

 

[Ron]

This condition is known as "tenderness" in the asphalt. It usually occurs in finer mixes but can occur in any hot mix. It is caused by a high asphalt cement (asphalt binder) coupled with a low air voids content.

The tests you should consider are extraction and gradation of the asphalt, stability testing of cores taken from the asphalt, density, and determine the voids in the mineral aggregate (VMA). Extraction and gradation are often replaced now with incineration in an NCAT oven.

Also, this condition will decrease with time as the asphalt cement hardens. Usually it takes going through a cool/cold weather cycle.

 

[Okiryu]

Thanks Ron !

 

[Okiryu]

We got our lab test results back. Void ratio are high and therefore the densities are slightly lower than the specified. The stability value is about 50% of the specified value which means that the strength of the asphalt is very low (bearing capacity problems??).

Do you have any recommendations for economical repairs? Traffic is low and composed by passenger cars and small maintenance pickup trucks.

 

[Ron]

The best solution would be to mill and overlay the section. With low density as much as noted, premature failure is likely, even under light loading.

 

[Okiryu]

Thanks Ron. So basically, the contractor just need to redo the damaged areas...

 

[Breyti]

Hi Okiryu

has this issue been resolved. What was the remedial action?