[b]Tests for lightweight agg in Normal Wt Agg[/b] 1

[BigH]

Colleagues:
We have a situation where boulders are being used to produce coarse aggregate. There are occasional pumice-type boulders in the area and unless the crushing operator is "on the ball" some of them get into the mix. What test can I run on the aggregate to determine the percentage of aggregate that has a specific gravity of, say, less than 2?

 

[concretemasonry]

Pumice can be a very good aggregate for special needs if used as specified. Pumice can also be a very beneficial and costly item if used as specified.

Apparently, you feel your situation should not have an excessive amount of pmice. Fine pumice can act as a pozzolan in concrete.

Do you have an idea of what percentage of pumice would be detrimental for your needs? Are there other options for the boulders to be crushed?

Light aggregates like pumice usually crush easily and can further be degraded into fines by either poor or excessive handling. - In other words, it is a dynamic problem and the sizes may change after the point of sampling (even into the mixing process).

Because of this, you should look for decreases in the average specific gravity of the smaller fractions of the finished aggregate at a consistant location in the process. You will have to separate the sample by gradation, looking at the smaller non-dust particles and determine the specific gravity. Do not expect a high degree of accuracy because some fractured pumice may absorb water very quickly, complicating the tesing and skewing the particle density.

It is not an easy or cheap task because of the variability of the properties of pumice. - I had a number of #4 sized Greek pumice particles floating in my aquarium for over 4 years, so it does not necessarily absorb water quickly in some cases.

This is one of those concrete engineering problems you wish you could spend more time on.

Dick

 

[BigH]

Dick - one of the reasons for not wanting the pumice - the aggregate will be used for RCC; and we need the "weight" with respect to hydrostatic uplift. Also, the specifications say no more than 2% of the aggregate can have a Gs less than 2. One reason I would like to know if there is a standard test to run. Pumice from tropical Asian sites. But, many thanks for the information on the effects of pumice as pozzolan and the like. You get a for that!! Cheers

 

[JedClampett]

We require ASTM C123 "Standard Test Method for Lightweight Particles in Aggregate." I've never seen it done, but they apparently use liquids with high specific gravities and check for floaters.

 

[BigH]

Will look into the ASTM spec if I can find it. It is what I thought might be used. Thanks JedClampett!!

 

[JedClampett]

In case you haven't found out for yourself, ASTM documents are not only impossible to find on line, but stinking expensive to purchase. We have a complete library, but they're from 1996.
Maybe whoever's providing or testing your aggregate has got a copy they could lend you. It's only three or four pages.

 

[concretemasonry]

Just join ASTM!!! It is one of the greatest values in the professional/technical world!

A personal membership is now less than $100 and entitles you to a book of standards that costs substantially more than the dues. You also get on-line downloads for items in that 200-400 page books of similar subjects. You also get a member discount on other standards that any firm would be glad to reimburse you for.

Join a committee on a subject and you may be able to get great opinions from people in that area. It took me 15 or 20 years to get to be a voting member on the committes that I was interested in, but I learned a great deal while being involved.

They have comprehensive standards on everything from baloons and party hats to construction materials and electronics. - I first got involved when working on the Saturn program and I respect the professionalism and international credibility.

Dick

 

[iandig]

BigH
I have done the 'lightweight particles in aggreagte' test, and it is typically used to find/identify lignite [brown coal] in sand and gravel deposits [typically of glacial otigin]. In order to find material with a density of less than 2.0 Mg/m³, you would need a 'liquid' with a density of at least 2.0 Mg/m³.
The test itself is very simple, you make up the liquid of the appropriate density, pour in the aggregate, aggitate, then remove any material which floats, dry and determine the percentage of the original sample. Over-simplified for the response, but you get the idea.
As this is likley to be very difficault [nigh on impossible!], have you considered determining the relative density of the parent material with varying percentages of pumice. This will have a number of advantages
1. You don't have to manufacture a liquid with a very high density [likley to be paractically impossible and still get the liquid to be thin enough to work]
2. It should be possible to graph the results, then by measuring a set dry mass of the aggregate, placing this in liquid and determining the volume of water displacment you can rapidly asses the percentage of pumice. Nice and repeatable on site using pre-marked measuring cylinders after a little bit of calculation/experimentation.

 

[cvg]

I assume your finished stockpile will be relatively well graded once the crushing is done and the lightweight will be distributed throughout. why can't you just take a number of samples of agg from the stockpile and check the weight and volume, determine the unit weight and determine if this will compromise the statics analysis for uplift? If you only have an occasional boulder, than the stockpile should not be affected if the aggregate from the light weight boulders is mixed in. If your spec only allows 2% (2 out of every 100 boulders) and your operator only misses the occasional one, it sounds like you would be OK. If your source has more than 2% pumice and your operator just can't catch enough, then you need to disallow the source, or change your spec...