nuclear gauge

[bb29510]

stupid question but trying to settle an argument:

"how do you operate a nuclear density gauge on a limestone aggregate base material?"

note, any rock can be substite for limestone, not question the limestone but the rock aggregate. Dont leave out any steps, walk throught every movement. I'm looking for something. also need refrences of this.

 

[Rjeffery]

As a rule of thumb, my engineers do not like having us drive the pin in the aggregate base. The theory is that the pin will cause a change in the density, (good or bad?)

Therefore test it on "backscatter" to obtain the dry density and compare to laboratory proctor.

The best way to test something is to squeeze it, slowly, until it breaks!

 

[kumaran856]

I have done the testing on Cement Treated Aggregate in the field. Basically, the direct transmission method is the accurate result than Back Scatter as BS read only the radiation bounced of the top 2", while DT calculates through the depth of penetration of the rod.
Second, test the mateial immediately after placement and compaction.Treat it as a well graded aggregate. Mostly the results will be in 90%-95%. Check the area again in 30 miutes, you would have readings above 95% and if you test the area again next day, you will get more than 100% compaction. Ths is due to the curing of concrete/cementation.

The best thing to look for in this case is to check for well gradation, no seggregation, good moisture content while placement(on the higher side of optimum) and good number of passes with the roller after placement.

 

[DarthSoilsGuy]

make sure you're using the right equipment, there are Nukes that do the top 2" in Backscatter (BS) mode (these are called thin lift nukes and are for asphalt) and there are nukes that scan the top 6" in BS mode. it's true that the surface compaction affects this reading greater than the base, but it's all relevant and correlated.

spread out a little fine sand (sand-cone sand) to fill any surface voids and test on BS mode. the most important region in nuke test is the area directly behind the probe. i don't see how driving a pin in aggregate can be done in the name of accuracy. many stones in agg base are larger than the probed diameter.

test in conjunction with proofrolling.

perform a sand-cone test in at least one spot along with the nuke test to confirm testing accuracy.

take lots of backscatter tests. i can perform almost 10 backscatter tests in the time it takes to do 1 sand-cone. Sure, 1 sand-cone test is more accurate than 1 BS Nuke test but it's not more accurrate than 10 BS Nukes.

BTW: What's the argument? or, What are you looking for

 

[Ron]

Drive the pin into the base, 2 inches or so beyond the depth of testing, then test with direct transmission. You should occasionally do sand cone densities to correlate the nuke results. Follow ASTM, AASHTO or other written, accepted test procedures.

Have done thousands of tests in limerock base materials and have correlated numerous times with sand cone. Good correlation and consistent results. Backscatter method is not appropriate for this as it is sensitive to surface variations and has a minimal depth of penetration.

References are ASTM D2922 "Standard Test Methods for
Density of Soil and Soil-Aggregate in Place by Nuclear
Methods (Shallow Depth)" and the nuclear gage manufacturer's instructions.

 

[DarthSoilsGuy]

Ok...

i have to admit that i've only tried to drive a pin in compacted ABC a few times and all without success. so i am not qualified to criticize it. all i've ever tested is hard granite-based ABC stone. with the ABC stone i've worked on, you have a hard enough time making the "undisturbed" hole for the sand-cone because of the large aggregate and the need for a relatively smooth and cavityless sand fill zone... so i have trouble imagining a steel pin involved.

However, I am qualified to say that you can test with BS mode and get accurate results for stone bases 8" or less. it's also has a good application for scanning for low stone depth (nature trails are notorious for skimping on contract stone depth). the cocky SOB in me says ... i'll give you 3 backscatter tests for every 1 using a pin haha

 

[MALLAN]

Just a note to those that quote ASTM 2922, it no longer exists. Replaced by ASTM 6938.

 

[howardoark]

Thanks for responding. I had seen that thread, but there wasn't consensus. Ron, for example, said

Ron (Structural) 5 May 08 19:55
Drive the pin into the base, 2 inches or so beyond the depth of testing, then test with direct transmission. You should occasionally do sand cone densities to correlate the nuke results. Follow ASTM, AASHTO or other written, accepted test procedures.

Have done thousands of tests in limerock base materials and have correlated numerous times with sand cone. Good correlation and consistent results. Backscatter method is not appropriate for this as it is sensitive to surface variations and has a minimal depth of penetration.

References are ASTM D2922 "Standard Test Methods for
Density of Soil and Soil-Aggregate in Place by Nuclear
Methods (Shallow Depth)" and the nuclear gage manufacturer's instructions.

 

[genomty]

I would like to know what are you trying to establish here. Because if the question is that, Driving the pin in non-cohesive soils make readings are wrong? I would ask you, Do you think that making a hole of about 6 inches in non cohesive materials will not produce the same effect or disturbance. In defense of using nuclear gage, you drive a pin of about 5/8 or something like that, to the test depth and perform the reading in direct transmition, now, do you know the distance from the tip of the gage's rod to the Geiger-Müller detector in the back of the device, for instance if you drive your pin 8 inches, the distance from source to detector is about 12 or 13 inches,now I wonder how much disturbance can be introduced by the pin (remmember a little bit grater that 5/8" in diameter) driving in that length. That length is the thick of the mean that is being measured in density and it goes from source (rod's tip) to device's base.

Something that commonly happend with non-cohessive materials is that surface and top portion dry quite fast, and gage only measures moisture in top 3 or 4 inches at the most, so your readings of dry density could seem to be wrong or higher than real and obiously your compaction is also higher, well the first choice to blame always is the pin driving is affecting the readings. Remmember that it is highly recommendable to establish a correlation between nuke densities and sand cone densities even in cohesive soils when a job is starting to demonstrate that gage readings are right.

Gage is an excellent tool, but it is only that a tool, I remmeber a technician that was testing a material in a work where I was participating some years ago and he was concerned because gage readings indicate that compaction was about 75 or 79 percent in a layer, obviously every body at the job site do not even consider he's opinion, I taked him and his device to a material stockpile and asked him, do you have an idea of the compaction of this material, he answered In not sure may be 10 or 20 percent, no sir then I told him this material is about 70 or 75 percent of its maximum dry density, then we proposed a density and take some readings and surprise 76 percent, then he understand why nobody believe him, so nuke is like a calculator, give a child a calculator and then try that this child make some mental operations, probably he or she will not be able to make it, well it is the same thing with technicians, give them a nuke and Proctor results without learning how to perform a field density determination by other mean or without sure if he or she understand what are they doing and bam, you have created a nuclear monster, It's alive and hes in a job site ahhhhh!. Let's back to the basics before give a technician or even an engineer a nuke.