Air dry vs oven dry soil sample for hydrometer test

[Jameschen6]

I like to continue the discuss starting with the thread "Grain Size Distribution by Hydrometer".

According to the Ontario standard. The soil will be oven dry at begining. after having the total weight, the sample will be grinded with a pestle. Sieve it over 2mm sieve. The portion retained will be washed and sived again. The percentage of the soil passing can be calculated then. The sub-sample will be taken from the portion passing the 2mm sieve for the hydrometer analysis.

My question is that the sample for the hydrometer has already been oven dried. For the soil thich has both coarse and fine portion is necessary for these strps. For instance, the maxnominal size of the particle is 10mm and there is significant amount of silt/clay portion.

I can't recall the difference between Ontario standard and ASTM on this aspect.

Any coments? Thank

 

[Ron]

Do you have a question? What is it you want to discuss?

 

[Jameschen6]

The procedure in the standard would not allow to oven dry the sample for the hydrometer. To obtain the dry weight, the standard introduce "hygroscopic moisture correction factor" for the air dried sample.

My question is that the sample has already been oven dried for the 2 mm sieve seperation. why not be allowed to be oven dry again?

 

[BigH]

One could argue "who cares" (I'm being facetious a bit). Hydrometers have so many other inherent problems (i.e., plate-like particles instead of the theory's round particles) and the like. The trouble with standards, like many specifications - they are whims of the panelists on some of the finer points - my view.

 

[BigH]

BTW, my previous post was with respect to your question on oven drying vs air drying . . . I do hydrometers - want infomration for activity - and it is better than not having the data.

 

[Jameschen6]

Thank BigH. One way I can think will make the test more complicated.

1. Saperate the air dried sample with 2mm sieve.

2. Weigh the air dried weight of the passing

3. Take a sub-sample from passing for the hydrometer, and take another sub-sample from passing for Hydroscopic Factor. This way we can get dry weight of the passing (A).

4. oven dry the material retained on 2mm. this way we can get total dry weight of the retained (B). wet sieve it and get true dry weight of retained (C)

5. True percentage of passing is (A+B-C)/(A+B)