FAA and Nuclear Density Gauges

Does anyone know where I may find information or articles about the use of nuclear gauges for density testing on airports (United States FAA only). It seems there may have been some discussions (debating?) at one point between the FAA and various parties on whether or not the gauges are appropriate for use with *subbase* during airport construction.

Thanks in advance.

 

[RandDMan]

If by subbase you mean asphalt (as opposed to various crushed stone possibilities), then why would you use a nuke gauge? Use a non-nuclear gauge instead...it's safer, it's easier, quicker and lighter, and at least equally reliable... there is no worry about any type of problems/accidents with a nuclear source which may cause the airport to shut down and cost the contractor on the order of $1,000/hour until the airport is able to open again!

 

[Ron]

At present, the only allowed methods for in-place density determination are rubber balloon and sand cone methods as noted in FAA Advisory Circular AC150/5370-10.

 

[jheidt2543]

Ron:

Is this a result of 9/11/01 or is there some other reason? I have seen nuclear testing used on many private and state/local government jobs.

 

[Ron]

Regarding the FAA, they have never been allowed in the general specifications (to my knowledge). This is just a long-standing requirement of FAA. Has nothing to do with 9/11/01.

Many states and other federal agencies allow their use.

As for control of these devices as a result of increased threats of "dirty bombs", I have not seen memos or other correspondence from the regulatory agencies. The controls on the devices are already reasonably stringent, though there have been lost ones and thefts over the years. Fortunately, their radioisotope sources are rather weak and probably wouldn't be much good for anything other than their present use!

 

Randman:

I was talking about crushed stone subbase, ITEM P-154: SUBBASE COURSE. The FAA does, as far as I know, allow the gauges to be used within the airport. I didn't know that the gauges would pose that much threat or inconvienence as you make them out to be. I'm sure the FAA is in its own world though.


Ron:

I may be missing something, but I think you are wrong in saying that the gauges have never been allowed on FAA projects. You did say that they have never been allowed under the "general specifications" (versus special provisions), which may be true--in that case you would be correct.

If you were saying that the gauges are NEVER allowed (only the ballon or sand cone), then I think you are mistaken. I'm not totally familar with the FAA specifications, so it got confusing for me really fast while reading through your referenced article. I couldn't find the original specifications that these modifications are supposed to be applied to. I also couldn't find any where they state that only the ballon/sand cone are acceptable methods. In fact, I found the opposite after reading some "notes to the engineer" which give additional stipulations if the guages are used. If you follow the link below, you will see some modifications regarding crushed subbase (P154). Scroll down to 3.8 in this link.

http://www.faa.gov/arp/ace/aipguide/ce1370_p154.htm

I may have misunderstood you, but it sounded like you were claiming the guages are not allowed, period. Correct me if I'm wrong.

Thanks.

 

[Ron]

J.L.V....I was referring to general specifications, for which the rubber balloon and sand cone are the only referenced methods. Special provisions are possible on many projects and often times, test methods can be approved on a project specific basis.

I have run into similar issues with US Army Corps of Engineers projects. When correlation studies are presented, sometimes you can get other methods approved for use.

In the most current version of P-154, only the rubber balloon and sand cone are specified.

 

[dirtsqueezer]

I used a nuclear densiometer to test crushed surfacing base course for taxiways on the Skagit Regional Airport, three miles west of Burlington, WA. Test standards were at minimum 100% of modified proctor ASTM D1557, set by the FAA. The contractor was able to achieve after over a week of steady compactive effort. I have also personally used and heard of it's use on crushed surfacing and structural fill on other airport runways, one of them being the Naval Air Station on Whidbey Island.

 

dirtsqueezer,

You say it took over a week of compaction. What was the contractors method? It sounds like they continously rolled the material for a week? I would think that the subase would dry out (and drain) much of the moisture after a week, thus adding to their difficulty. Did they continue to apply water. Was the subase brought to the site at the correct moisture content, or was water only blended upon spreading and the start of the compaction?

Excessive rolling/vibrating can cause water to migrate upwards within subgrade. Was their any subgrade problems? *I would think* that excessive rolling/vibrating of dry material would also cause the material to start breaking up on the surface. Did this happen at all?