HMA Testing

[martin888888]

What is "normal" procedure for the compaction testing of an HMA surface? Do they core and send it to the lab?

 

[Ron]

"Normal" procedure is usually what is done by the State Department of Transportation in your state.

Commonly, this includes developing a "control strip" density standard using nuclear density readings correlated to cores. Once the control strip density is established, the production testing is usually done with a nuclear gage, with periodic verification using cores.

If you are dealing with a small parking lot or other similar small private project, then nuclear density gage readings correlated to cores is often done.

Check the procedures of your state's DOT. Some states have well establish procedures and are usually in the forefront of paving technology/research...these include:

California
Washington
Florida
Texas
Iowa
Ohio
and a few others

 

[martin888888]

Thanks. In Washington they dont core for their density testing but rather use a nuclear moisture density gauge.

 

[Ron]

Nuclear density testing without correlation to cores is a bad idea.

 

[martin888888]

what do you mean "without correlation to cores", and why is it a bad idea? In the state of washington they use a nuclear moisture density guage placed on the asphalt pavement to get density readings.

Thanks

 

[Ron]

The nuclear density gage should be check for its results against the physically accurate core density. The nuclear density gage is an indirect method of measuring the density of soil or asphalt. To check its accuracy, you must compare the nuclear density results to the physical results of core testing.

 

[BigH]

Martin888888 - what I think Ron is saying is that the nuclear density gauge must be calibrated and it is best to site calibrate to the materials you have on site. I found, when doing a lot of soil compaction testing years ago that the nuclear density gave strange results (especially with the water content) - so to have a direct calibration/correlation with actual cores is preferred.

 

[martin888888]

What do they normally do in this case? Do they take one core sample and test it in the lab and then calibrate the instrument to the one sample. Then use the gauge for the remainder of the testing?

 

[Ron]

One core for correlation or calibration is insufficient. I usually require at least 3 cores for each correlation or calibration.

Density testing is usually done on large pavement projects at a frequency of at least one test per 500 square yards of pavement. If you have a small project, you might want to test more frequently, since small projects often have more density problems than large projects, because of the difficulty of working in smaller, more confined areas. Further, the contractors doing the work are usually not as aware of asphalt technology as those who do larger pavement projects.

I would do a correlation/calibration of the density gage, using cores, for each day's production, assuming you have a multiple day paving job. This helps to pick up mix issues and pavement laydown procedure problems. For instance, the asphalt plant may have variations in the mix on a daily basis (due to variations in the plant settings, mix constituents, the stockpiles, and the consumption of asphalt cement).

The reason I use a 3-core minimum is that a single core might be anomalous, with either a high density or low density...you won't know which unless you take multiple cores to average them.

BigH...thanks for your more clear paraphrasing!

 

[martin888888]

Thanks for the information, very helpful.

 

[BigH]

I would use more than 3 cores to get a better handle on the standard deviation; you can do this on your test strip. Also, I would suggest that relative frequent confirmations be done as the work goes on.

 

[ACtrafficengr]

NYSDOT specs vary depending on the road. If I recall correctly:

Paving on interstates and similar roads get cored 4 times per day
Other state highways get 4 cores.
Local roads are tested with an NDM.
Inspection of other pavements (parking lots, patching, small areas, etc.)is based on compactive effort.

It makes sense to me. Inspection effort is proportional to the importance of the pavement.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928