Question

You have a 20 ton pile of aggregate you'll be using to design a concrete mixture and you need to determine the particle size gradation of the aggregate. What steps can you take to try to ensure that the sample of aggregate you're measuring particle size analysis of is representative of the entire pile?

Answer 1

Hi friend,

To obtain a representative sample of the material from the original sample by either a sample splitter or the quartering method.(Reference AASHTO T 27)

1. Sample Splitter-

Sample splitters shall have even number of equal width chutes, but not less than a total of eight for coarse aggregates, or twelve for fine aggregates, which discharge alternately to each side of the splitter.

The splitter shall be equipped with two receptacles to hold the two halves of the sample following splitting. It shall be equipped with a hopper or straight edge pan which has a width of the assembly of chutes, by which the sample may be fed at a controlled rate to the chutes.

The splitter and accessory equipment shall be so designed that the sample will flow smoothly without restriction or loss of material. Place the field sample in the hopper or pan and uniformly distribute it from edge to edge, so that when it is introduced into the chutes, approximately equal amounts will flow through each chute.

The rate at which the sample is introduced shall be such as to allow free flowing through the chutes into the receptacles below. Reintroduce the portion of the sample in one of the receptacles into the splitter as many times as necessary to reduce the sample to the size specialised for the intended test.

Quartering Method :

1. Distribute a shovel full of the aggregate as uniformly as possible over a wide, flat area on a tight weave canvas or other smooth surface. Continue to distribute shovels full of material in layers until all the sample is used to make a wide, flat pile that is reasonably uniform in thickness and diameter. Do not permit coning of the aggregate.

2. Divide the pile cleanly into equal quarters with a square-ended shovel or straight piece of sheet metal. When a canvas is used, the division may be conveniently made by inserting a thin stick (or rod) under the canvas and raising it to divide the sample equally, first into halves, then into quarters.

3. Remove two opposite quarters, including all fine materials, and set aside.

4. Repeat the foregoing procedure with the remaining portion of the aggregate until a test sample of desired size is obtained.

5. If desired, store the portion that has been set aside for possible check testing.