Procedure for modified proctor on reclaimed asphalt?

[jade69]

Need to find out the proper way to run a modified proctor on asphalt millings with a max. size of 2". The millings will be used under a concrete taxiway.

 

[Ron]

If you are using millings only, there is no convenient way to do a modified Proctor on the material. Keep in mind that a Proctor test is a moisture-density relationship. There will be no good moisture-density relationship for this material as the moisture content cannot be accurately determined, due to the asphalt.

 

[fattdad]

You'll need to use method C and there will still be an oversize correction.

Irrespective of what Ron says, the material will have a "moisture-density" relationship. Your job is to measure the moisture content so it's not affected by the asphalt content.

I'd do a sand cone in the field and contrast that to the nuke gauge.

f-d

¡papá gordo ain’t no madre flaca!

 

[Ron]

f-d.....I didn't say it wouldn't have a M-D relationship, just that it wouldn't have a good one. Just difficult to determine the moisture content. Can't use oven dry....melts the asphalt. Could use a Speedy, but repeatability might be difficult.

Your job is to measure the moisture content so it's not affected by the asphalt content.

...absolutely the issue and the difficulty.

Why not use the millings as a supplement to soil for stabilization? That works reasonably well.

Agree with Method C and replacement. Also agree with sand cone density.

 

[jade69]

But the nuke reads hydrogen which is also in the oil in asphalt right? so wouldnt that throw off your moisture reading?

Ran 4 points 2,4,6,8 percent moisture and the density has yet to break over. At 8% the water is running out the bottom of the mold.

The inspector on the job said it has to break over but i dont think it will since the water is not replacing the binder as it would in soil!

They want a proctor before they start putting down the millings!

Or am i completely confused?

 

[Drumchaser]

I am stunned that an airport taxiway calls for Reclaimed Asphalt Pavement as base matl.
Must be a cost savings/value engineering matter, however I do not see how the RAP will allow for proper thermal expansion of the concrete pavement.

 

[Ron]

jade69...it won't break over. You cannot develop a good moisture-density relationship here.

 

[jade69]

Thanks guys. Waiting to see what comes about this.

 

[Hoaokapohaku]

Try coating the bottom of the mold with vaseline before fitting into the base. I have the same problem finding the break point for certain granular base materials; the water leaks out of the mold before the break point. Vaseline does the trick with this material and I think it will for the RAP as well.

The problem with doing this is that the optimum moisture is very difficult to achieve in the field because a material that is free draining to the degree that the water wants to leak out of the mold when performing a proctor is often so free-draining that, in the field, the water drains out faster than it can be moistened and compacted.

 

[Ron]

Hoa...you are exactly right in your assessment of the Proctor...but don't subvert the results by artificially keeping the water in.

 

[Hoaokapohaku]

@Ron...How would this be subverting the results? Seems to me it is the only way to get a result. The free-draining material problem is most often caused by a gap graded material and D1557 (para 5.3.3) allows for modification of the method using engineering judgement in that case.

Actually, now that I think about it, I wonder if perhaps Jade's problem is actually caused by gap grading rather than the asphalt in the material? The maximum particle size of 2" makes me think this is likely unprocessed or minimally processed RAP and therefore gap grading would be likely since most of the fines from the original mix would be bound in clumps of pavement. Also, the problem with a material containing asphalt is usually that you can't get enough water into the material to compact because the asphalt containing fines repel the water. If the problem is that water does mix into the material but too much water is required to stay in the mold, that would point to an absence of fines, i.e., gap grading.

 

[Ron]

Hoa...you are right...gap grading is typically the issue; however, using vaseline to stop the bleeding does not give a true picture of the reaction of the material...after all, you can't use vaseline in the field to achieve the same conditions.

Bleeding in the test sample at or below the expected optimum tells you something....it tells you that the material is likely gap graded. It tells you that the material has insufficient fines to achieve appropriate stability.