Measuring the density of site materials
by Bill Swiacki on 10/12/05 at 13:32:47

I've been reading your archived forum messages about volume-weight conversions, especially as it relates to site-construction materials (various grades of gravel, earth fills, etc). I see from your responses that if the specific material happens to be listed in Reade then it is relatively easy to convert. But many of the questions you receive have to do with materials (or grades of materials) that are not listed in Reade. In these cases, what are the practical ways in which one can determine the specific gravity of commonly used but un-listed materials or grades? For example, dry gravel sized between 3"-4" (both compacted and uncompacted), or a mix of earth and gravel? Also, where can one find compaction rates for various types of site materials? Thanks.

Re: Measuring the density of site materials
by Robert Fogt on 10/12/05 at 18:42:15

The easy way is just to weigh a certain volume of it.

For example, weigh a 1 gallon jug of sand and you'll have the pounds/gallon density, which you can easily convert to a more traditional kilograms/liter density.

Though be sure to subtract the weight of the object you weigh it in.

Re: Measuring the density of site materials
by Wilfred on 10/12/05 at 18:52:25

One of the easiest ways to find the density of a material like aggregate, is to construct a box with a volume of exactly one cubic foot, and then weigh it on a scales.

The easiest way to construct a suitable box would probably be to use 3/4 inch thick plywood, or particle board. Be careful to construct the box with accurate internal measurements of 12 inches wide by 12 inches long by 12 inches high, so that you know you have a box of exactly one cubic foot volume.

Probably most of us have access to a set of bathroom scales, if we do not have anything more suitable. The next thing is to accurately weigh the empty box, and make sure that we always deduct this from the total weight when we weigh our sample material.

Make sure that the box is exactly level full, by using a straight edged piece of material, to ensure that you have exactly the right amount of your sample material.

If you just want the weight per cubic foot for your sample material, you will have it from the above method.

If you want the weight per cubic yard, then multiply the weight per cubic foot by 27.

If you want the specific gravity of your sample material, then you need to make use of the fact that one cubic foot of water weighs exactly 62.5 pounds.

So, for example, if you had a sample of crushed stone which weighs 136 pounds per cubic foot, the specific gravity would be 136 divided by 62.5, which equals 2.176. This just means that the sample is 2.176 times as heavy as water.