Determining Particle Size Distribution in cemented, consolidated soils/rocks

[Szilard Titi]

Treatment of cemented or highly consolidated samples with hydrochloric acid results in unusually high silt particle percent (Determination with sieve and sedimentation methods) and sometimes the cemented pieces don't dissolve after treatment.
Is there a more effective method for determining particle size distribution in samples that are stiff/cemented? What is best to use?
The hydrochloric acid that is recommended in the standards is 0.2 M/L

 

[emmgjld]

My first response would be, How do you know the measured silt content is unusually high?
Next would be, what is the mineralogy of the samples? Is more being broken down, in excess of the cementing agent?

 

[Szilard Titi]

We had a couple of samples, where the carbonate content was above 40% and we treated the sample with acid, but we wanted to do a test on the samples with some material that we did not treat with the same process. The clay particle content in percent was way higher in the untreated samples. We noticed a big dip at the 4minute - 8 minute - 15 minute readings in the case of the treated samples, which leads to a lower clay percent (10-15% lower on average)and higher silt percent in the end.

We did not determine the mineralogy of the samples, but almost every sample that we treat with acid has 40-60% silt. We are working with samples that should have predominantly clay particles, according to macroscopic laboratory sample description.

 

[GeoEnvGuy]

If your not happy with the hydrometer look for a lab with a laser particle size analyzer.

 

[emmgjld]

Without knowing what the assumed depositional environment of your samples is:
It is very possible the carbonate cementation actually contains a lot of silt.
The clays may be a later product of the chemical weathering of portions of the mineralogy, after the cementation process.
The particles which are cemented may include carbonaceous material, which contains a lot of silt.

 

[Szilard Titi]

It is possible that the cemented parts contained a lot of silt.
How do you prepare your sample for the test if it doesn't break down in acid? Our lab had numerous occasions where even after treatment the cemented parts didn't dissolve.
We're having problem with determining the particle size distribution in highly cemented samples.