Fine Aggregate Clay Lumps & Friable Particles

[AKSherpa]

Anyone have experience with ASTM C142 Clay Lumps & Friable Particles test on fine aggregates?

The procedure requires aggregate particles of size passing #4 and retained on #16 to be individually "squeezed and rolled between thumb and forefinger to attempt to break the particle into smaller sizes. Do not use the fingernails to break up the particles or press particles against a hard surface or each other."

I am finding it essentially impossible to perform the test due to the fact many of the particles that pass a #8 and are retained on a #16 are too small to practically handle individually as required by the ASTM procedure. If the procedure is modified and multiple particles are handled simultaneously they subsequently roll against each other resulting in greater loss and potentially failing results.

Of note, the project we are currently evaluating the material source for requires a loss of less than 0.3% for ASTM C142. To me this is too strict of a specification for this test procedure that lists the acceptable range as 1.7% for tests run on the same material by different laboratories but this is what we are dealing with so I am curious if anyone has experience with this procedure and is able to provide comments.

Thanks

 

[TigerGuy]

If memory serves me correctly, your sample size should be small enough that it doesn't take long. C142 includes a table specifying the size of sample to be tested for fine aggregate. I think it's about 25 grams, could be more.

 

[AKSherpa]

You are corect, 25 g is the minimum sample size. See attached picture of 60 g sample for reference on particle size.

I have found the smaller particles are not pratically able to be individually picked up and rolled between the fingers. The videos I have found of people running this test shows them grabbing the material by the handful and rubbing to check for clay lumps and friable particles. Not surprisingly, when I do the test grabbing multiple particles simultaneously and rubing them together as shown in the videos I come up with much higher loss than if manipulating particles individually.

One issue I have noted with using the minimum sample size of around 25 g is our scale weighs to 0.1 g and for a 25 g sample if the weight pre and post differs by 0.1 g the % diff is 0.4%. The spec we are dealing with is 0.3% max loss so this is one problem we have with the test.

The main thing I am hoping to get some input from someone with experience performing this test is if they have noticed the same thing I am seeing which is the manner in how the fine particles are manipiulated greatly impacts the outcome. Also interested in what someone with experience performing this test has to say about a specification of 0.3% for this test. After performing this test on several materials this 0.3% max loss seems to me to be ridiculously low.

 

[TigerGuy]

Most of the samples I ever tested were a processed concrete sand. The particles are quite rounded in shape and very durable. The test is tedious at best. I just sit down and start picking up individual particles from the pan, rolling them, and placing them in the second container. I set up to be able to pick up particles with both hands and just keep the rhythm going.