100% of ASTM 1557D Proctor????

[SamCPC]

I have been tasked with role of quality manager for repaving of aircraft taxiway. My company is the GC.

My background: CSM Degree OSU 2012, 5 years ACI field geotech, lab rat.

Spec book indicates the following:

3.14.3.3 Subgrade for Airfield Pavements
Compact top 24 inches below finished pavement or top 12 inches of subgrades, whichever is greater, to 100 percent of ASTM D1557; compact fill and backfill material to 100 percent of ASTM D1557. Core of Engineers spec is actually 95-100%.

Plan book calls for 95% on foundations however road base is usually not considered foundations but rather a portion of the roadway.

Material is State Spec Road Base. T-180: 139.0@6.3, ASTM D1557C Modified 138.2@6.9 and rock corrected 142.9@5.7%.

Subgrade is a poorly graded sand. Very little to no clay. I estimate around 125lbs at 10% or greater optimum moisture. Good stuff as long as it has moisture in it. Holds up fully loaded dump truck with marginal rutting.

I have another 1557 proctor in process with another lab.

We are getting 96-98% and within 1-2% moisture using nuclear density tesing in the field on a 12" layer of road base using 142.9. I have always operated under the notion anything at 100% or greater is usually due to a change in material density beyond what was ran for the proctor, an error in the gauge, or a combination of both. Proof roll gives virtually no rutting or pumping.

I do not want to present "failing" density tests (<100%) to the design engineer however I believe getting EVERY density test to read 100% is not only un-obtainable, but also hard to believe even if we do achieve it. You can turn a density gauge 90* and get different readings...

So which is right? My spec book, the plan design criteria? Is the excerpt in the spec book out of context? DO i have a case to argue or at least get a more clear requirement for compaction?

Thanks!

 

[oldestguy]

Double posting is not needed. Most of us look at many rooms.

On your problem,I'd try to verify that the nuc is accurate. Use some other method to check. Even cutting out a square foot and examine its density if necessary.

That nuc looks at more than just one layer.

 

[SamCPC]

I guess we could use a sand cone method to check density but this test is not very common and finding a tech well versed in the technique may serve as a challenge in my experience. The spec book does not cite this ASTM as a field test method.

The nuke was only set to depth of 6" so it was well within the road base layer. I believe the nuke gauge results to be accurate.

The material is very well graded from a reputable pit here in Utah.

Thanks for the input!

PS. IF one of the MODS wants to move this to a more relevant sub-forum I would be OK with it. Cheers!

 

[oldestguy]

There is a lot of different atoms in a pavement than in the usual "standards" for calibrating. The best you can do is calibrate it on the job and cutting a square of asphalt paving would be a lot more useful and it is relatively easy to do. Knowing how the nuk works, I wouldn't trust any so called depth of test setting. As for sand cone, that can be goofed up if the tech isn't fussy. That sand is affected by moisture in storage facilities.

 

[Ron]

100% of modified Proctor is challenging but nothing wrong with it as a specification, particularly for a pavement.

If you get 100% of your Proctor value it doesn't mean your Proctor value is wrong. When you start getting consistent 103-105% values it is time to check the Proctor.

I would suggest using a drive sleeve method in your sands to check against the nuclear gauge. For graded aggregate base, use a sand cone.

How do you know the nuclear gauge is accurate if you don't correlate it?

 

[fattdad]

You can get it! You likely need to verify the oversize and make test-specific corrections to the field density test. You see, if the oversize at the specific test location does not jive with the oversize of the lab proctor, you need to make adjustments.

It would be better if the spec was 98 percent!

f-d

ípapß gordo ainÆt no madre flaca!

 

[cvg]

airfield jobs which are generally done to FAA requirements are nearly always 100% of modified proctor. In fact, the modified test was developed during World War II by the Corps to better represent the compaction required to support heavy aircraft. Make sure you check your nukes with sand cones before starting and during placement.

12 inch might be too thick of a lift for the available equipment

 

[Okiryu]

I think that 100% compaction can be applied for base and subbase but for the subgrade I think that it is excessive, especially when subgrades can also be composed of fine grained soils.

If your project is for the US DoD, you can refer to the UFC for airfield pavement design. You will see there a table with different grade of compactions depending on the depth of compaction.

 

[cvg]

it is very unlikely that the GC will be allowed to change the designers spec so referring to the UFC would not be a viable option. You had better have a darn good reason why you cant roll it a couple more times and get the specified density