Non-destructive methods to measure pavement structure?

[Arizona3106]

Our City is looking into creating a catalog of all significant roads to develop a measuring system for rehab/rehabilitation. One important factor in categorizing the roads is existing pavement structure.

We will use borings for some roads, but are looking for possible non-destructive techniques that may be more cost effective that might even be able to be correlated with borings somewhat.

Refractive hammer testing has been brought up. How does this work? Does anybody have any recommendations for trying to quantify pavement structure using methods that would be more cost effective than borings?

Thank you,

 

[Arizona3106]

So it appears that the Falling Weight Deflectometer (FWD) and Ground Penetrating Radar (GPR) are probably the most applicable methods. Any comments?

 

[Ron]

The most accurate way to nondestructively test a pavement structure is by Falling Weight Deflectometer. This method is quick, has been correlated to numerous materials and pavement types, has been extensively used by state and federal governments and has been around for over 30 years.

For some relevant information, go to the following websites:

http://www.dynatest.com

http://www.ara.com/transportation

http://www.pavementconsultants.com/

Dynatest manufactures FWD equipment and provides some consulting as well. ARA/ERES Consultants is a consulting engineering firm doing pavement consulting and nondestructive testing. Pavement Consultants is located in Phoenix and Seattle, so judging from your handle, might be close to you. Dynatest is headquartered in California.

Almost all pavement consultants work anywhere in the country, though some are more specialized than others. My firm does pavement consulting, but we generally stay in the Southeast US.

Good luck. Establishing a quality pavement management system is a smart move.

 

[SirAl]

Can be a big undertaking to establish and maintain a database. Ground penetrating radar might be the best NDT approach to obtain pavement structure thicknesses although nothing can replace borings or cores where actual road structure thicknesses and subgrade can be measured and categorized.

 

[oldestguy]

What does your state DOT use as standards for determining pavement adequacy, rating, etc. when it comes to determining how much money to send you for your share of those state gasoline taxes?

In our state they have a rating system that depends on several factors, but generally a ranking as to when the pavement may be due for replacement, etc. It goes from a low number of 1 to best at 10. It does not require any borings or testing, just experienced observations and it works well.

I suspect you already do have that in your system somewhere that perhaps some person filed that away and others do not know about it.

I'd check with DOT first.

 

[Ron]

Arizona...GPR is ok for thickness measurements, but it works better for rigid pavements in that respect than for flexible pavements. Depending on the material, it is difficult to discern transition layers of similar material.

The FWD is for determining pavement structural response. GPR does not do that.

Regardless of the nondestructive method used and its purpose, destructive observation (coring, classification, field testing, lab testing) should be done to correlate. Keep in mind that nondestructive testing only serves to reduce the amount of destructive testing that is necessary.

There are several rating schemes available for condition rating of the pavement as oldestguy noted. The two most common are the Pavement Condition Rating (PCR) that was developed by AASHTO a long time ago and rates the pavement on a scale of 5. The more common and more accurate rating is called the Pavement Condition Index (PCI) which was also developed by AASHTO and others. It is also an accepted ASTM method [highlight](ASTM D6433-Standard Practice for Roads and Parking Lots Pavement Condition Index Surveys)[/highlight]. This method is based on a scale of 100, is all visual, and is very repeatable between several different trained observers. It uses a series of defined distress manifestations (cracks, potholes, repairs, depressions, rutting, etc), each of which is counted within a sample area.

Using the PCI in conjunction with FWD and a pavement management database will put you way ahead of the curve for predicting pavement performance and long term costs.

There are also firms that do high speed condition rating using a specially equipped vehicle with video and other equipment to determine the condition of the pavement at normal driving speeds.

As OG says, check with your DOT.

 

[Arizona3106]

Is it correct that FWD can estimate the number of load repetitions the pavement can accommodate until a level of serviceability is reached?

I'm trying to understand exactly how this accomplished, since pavement subgrade and structure will provide different deflection data for each roadway segment. Or, do you need a reasonable estimate of AC and base thicknesses to backcalculate moduli from deflection data and therefore pavement lifespan?

 

[Ron]

Arizona3106...yes, load repetitions can be estimated from the data.

You do need reasonably accurate thickness data to help with the backcalculation. We usually core the pavement at reasonable intervals, say 500 to 1000 feet (farther apart if consistent, closer if not)

 

[apsix]

When I was younger I spent some time walking behind a Benkleman Beam, a device for measuring the pavement deflection under a loaded truck.

Are they still in use?

 

[Ron]

apsix...yes, Benkelman beams are still used...not much for large pavement networks, but for isolated evaluation, yes.