STANDARD PRACTICE (ASTM C 702) FOR REDUCING FIELD SAMPLES OF AGGREGATE TO TESTING SIZE

III. STANDARD PRACTICE (ASTM C 702) FOR REDUCING

FIELD SAMPLES OF AGGREGATE TO TESTING SIZE

1. Scope and Significance:

1.1 This practice describes methods for the reduction of field samples of aggregate to the appropriate size for testing, employing techniques that are intended to minimise variations in measured characteristics between the test samples so selected and the field sample.

1.2 Larger samples will tend to be more representative of the total supply. This practice provides

procedures for reducing the large sample obtained in the field to a convenient size for conducting a

number of tests to describe the material and measure its quality in a manner that the smaller portion

is most likely to be a representation of the field sample, and thus of the total supply. Failure to

carefully follow the procedures in this practice could result in providing a non-representative sample

to be used in subsequent testing. The individual test methods provide for minimum amount of

material to be tested.

1.3 Under certain circumstances, reduction in size of the field sample prior to testing is not

recommended. Substantial differences between the selected test samples sometimes cannot be

avoided, as for example, in the case of an aggregate having relatively few large size particles in the

field sample. The laws of chance dictate that these few particles may be unequally distributed among

the reduced size test samples. Similarly, if the test sample is being examined for certain

contaminants occurring as a few discrete fragments in only small percentages, caution should be

1sed in interpreting results from the reduced size test sample. Chance inclusion or exclusion of only

one or two particles in the selected sample may importantly influence interpretation of the

characteristics of the field sampie. In these cases, the entire field sample should be tested.

2. Selection of Method:

2.1 fine Aggregate: Field samples of fine aggregate that are drier than the saturated-surface-dry

condition (see note) shall be reduced in size by a mechanical splitter according to Method A. Field

samples having free moisture on the particle surfaces may be reduced in size by quartering according to Method B, or by treating as a miniature stockpile as described in Method C.

If the use of Method B or Method C is desired, and the field sample does not have free moisture on

the particle surfaces, the sample may be moistened to achieve this condition, thoroughly mixed, and

then the sample reduction performed.

If use of Method A is desired and the field sample has free moisture on the particle surfaces, the

entire field sample may be dried to at least the surface-dry condition, using temperatures that do not exceed those specified for any of the tests contemplated, and then the sample reduction performed. Alternatively, if the moist field sample is very large, a preliminary split may be made using a mechanical splitter having wide chute openings 38 mm (1.5 in.) or more to reduce the sample to not less than 5000 g. The portion so obtained is then dried, and reduction to test sample size is completed using Method A.

NOTE: As a quick approximation, if the fine aggregate will retain its shape when moulded in the hand, it may be considered to be wetter than saturated-surface-dry.

Standard practice for reducing samples of aggregate to testing size,Reducing Samples of Aggregate to Testing Size

2.2 Coase Aggregates and Mixtures of Coarse and Fine Aggregates: Reduce the sample using a

mechanical splitter in accordance with Method A (preferred method) or by quartering in accordance

With Method B. The miniature stockpile Method C is not permitted for coarse aggregates or mixtures of coarse and fine aggregates.

3. Sampling:

The field sample of aggregate shall be taken in accordance with Practice D 75, or as required by

individual test methods. When tests for sieve analysis only are contemplated, the size of field sample

listed in Practice D 75 is usually adequate. When additional tests are to be conducted, the user shall

satisfy himself that the initial size of the field sample is adequate to accomplish all intended tests.

METHOD-A, MECHANICAL SPLITTER

4. Apparatus:

Sample Splitter: Sample splitters shall have an even number of equal width chutes, but not less than

a total of eight for coarse aggregate, or twelve for fine aggregate, which discharge alternately to each side of the splitter. For coarse aggregate and mixed aggregate, the minimum width of the individual chutes shall be approximately 50% larger than the largest particles in the sample to be split. For dry fine aggregate in which the entire sample will pass the 9.5 mm (3/8 in.) sieve, a splitter having chutes 12.5 to 20 mm (1/2 to 3/4 in.) wide, shall be used. The splitter shall be equipped with two receptacles to hold the two halves of the sample following splitting. It shall also be equipped with a hopper or straight-edged pan which has a width equal to or slightly less than the overall 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.

5. Procedure:

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 specified for the intended test. the intended into test the. The portion of the material collected in the other receptacle may be reserved for reduction in size for other tests.

METHOD-B, QUARTERING

6. Apparatus:

Apparatus shall consist of a straight-edged scoop, shovel, or trowel; a broom or brush; and a canvas

blanket approximately 2m by 2.5 m (6 ft. by 8 ft.).

7. Procedure:

Use either the procedure described in 7.1 or 7.2 or a combination of both.

7.1 Place the field sample on a hard, clean, level surface where there will be neither loss of material

the accidental addition of foreign material. Mix the material thoroughly by turning the entire

sample over three times. With the last turning, Shovel the entire sample into a conical pile by

depositing each shovelful on top or the preceding one. Carefully flatten the conical pile to a uniform

thickness and diameter by pressing down the apex With a shovel so that each quarter sector of the

resulting pile will contain the material originally in it. The diameter should be approximately four to

eight times the thickness. Divide the flattened m mass into four equal quarters with a shovel or trowel and remove two diagonally opposite quarters, including all fine materials, and brush the cleared space clean. Successively mix and quarter the remaining material until the sample is reduced to the desired size.

7.2 AS an alternative to the procedure described in 7.1 when the floor surface is uneven, the field

Sample may be placed on a canvas blanket and mixed with a shovel as described earlier, or by

alternately lifting each corner of the canvas and pulling it over the sample toward the diagonally

opposite corner, causing the material to be rolled. Flatten the pile as described earlier. Divide the

sample as described in 7.1, or if the surface beneath the blanket is uneven, insert a stick or Pipe

beneath the blanket and under the centre of the pile, then lift both ends of the stick, dividing the

Sample into two equal parts. Remove the stick leaving a fold of the blanket between the divided

portions. Insert the stick under the centre of the pile at right angles to the first division and again lift

both ends of the stick, dividing the sample into four equal parts. Remove tíwo diagonally opposite

quarters, being careful to clean the fines from the blanket. Successively mix and quarter the

remaining material until the sample is reduced to the desired size.

METHOD-C: MINIATURE STOCKPILE SAMPLING (Damp Fine Aggregate Only)

8. Apparatus:

Apparatus shall consist of a straight-edged scoop, shovel, or trowel for mixing the aggregate, and

either a small scoop or spoon for sampling.

9. Procedure:

Place the field sample of damp fine aggregate on a hard, clean, level surface where there will be

neither loss of material nor the accidental addition of foreign material. Mix the material thoroughly

by turning the entire sample over three times. With the last turning, shovel the entire sample into a

conical pile by depositing each shovelful on top of the preceding one. If desired, the conical pile may

be flattened to a uniform thickness and diameter by pressing down the apex with a shovel so that

each quarter sector of the resulting pile will contain the material originally in it. Obtain a sample for

each test by selecting at least five increments of material at random locations from the miniature

stockpile, using any of the sampling devices described earlier.