STANDARD TEST METHOD (ASTM C 131) FOR RESISTANCE TO DEGRADATION OF SMALL-SIZE COARSE AGGREGATE BY ABRASION AND IMPACT IN THE LOS ANGELES MACHINE

VII. STANDARD TEST METHOD (ASTM C 131) FOR

RESISTANCE TO DEGRADATION OF SMALL-SIZE

COARSE AGGREGATE BY ABRASION AND IMPACT

IN THE LOS ANGELES MACHINE

1. Scope, Significance, Use:

1.1 This test method covers a procedure for testing sizes of coarse aggregates smaller than 37.5mm

(1.5 in.) for resistance to degradation using the Los Angeles Abrasion Testing Machine.

1.2 The Los Angeles Abrasion Test is a measure of degradation of mineral aggregates of standard

grading resulting from a combination of actions including abrasion or attrition, impact, and grinding

in a rotating steel drum containing a special number of steel spheres, the number depending upon the grading of the test sample. As the drum rotates, a shelf plate picks up the sample and the steel

spheres, carrying them around until they are dropped to the opposite side of the drum, creating an

impact-crushing effect. The contents then roll within the drum with an abrading and grinding action

until the shelf plate impacts and the cycle is repeated. After the prescribed number of revolutions, the contents are removed from the drum and the aggregate portion is sieved to measure the degradation as percent loss.

1.3 The Los Angeles Abrasion Test has been widely used as an indicator of the relative quality or

competence of various sources of aggregates having similar mineral compositions. The results do not automatically permit valid comparisons to be made between sources distinctly different in origin,

composition, or structure. Specification limits based on this test should be assigned with extreme

care in consideration of available aggregate types and their performance history in specific end uses.

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2. Apparatus:

2.1 Los Angeles Abrasion Machine:

The Los Angeles Abrasion Testing Machine, Conforming in all its essential characteristics to

the design shown in Figure 3.5 shall be used. The machine shall consist of a hollow steel cylinder.

closed at both ends, having an inside diameter of 711+5mm (28+0.2 in.) and an inside length of

508+5mm (20+0.2 in.). The cylinder shall be mounted on stub shafts attached to the ends of the

cylinder but not entering it, and shall be mounted in such a manner that it may be rotated with the

axis in a horizontal position within a tolerance in the slope of 1 in 100. An opening in the cylinder shall be provided for the introduction of the test sample. A suitable, dust-tight cover shall be provided for the opening with means for bolting the cover in place. The cover shall be so designed as to maintain the cylindrical contour of the interior surface unless the self is so located that the charge will not fall on the cover, or come in contact with it during the test.

A removable steel shelf extending the full length of the cylinder and projecting inward 89+2mm (3.5+0.1 in.) shall be mounted on the interior cylindrical surface of the cylinder, in such a

way that a plane centered between the large faces coincides with an axial plane. The shelf shall be of such thickness and so mounted, by bolts or other suitable means, as to be firm and rigid. The

position of the shelf shall be such that the distance from the shelf to the opening, measured along the outside circumference of the cylinder in the direction of rotation, shall be not less than 1.27 m. (50

in.).

NOTE: The use of a shelf of wear-resistant steel, rectangular in cross-section and mounted independently of the cover, is preferred. However, a shelf consisting of a section of rolled angle, properly mounted on the inside of the cover plate, may be used provided the direction of rotation is such that the charge will be caught on the outside face of the angle. If the shelf becomes distorted from its original shape to such an extent that the requirements given in the Appendix-III are not met, the shelf shall either be repaired or replaced before additional tests are made. The machine shall be so driven and so counterbalanced as to maintain a substantially uniform peripheral speed (Note). If an angle is used as the shelf, the direction of rotation shall be such that the charge is caught on the outside surface of the angle.

NOTE: Back-lash or slip in the driving mechanism is very likely to furnish test results which are not duplicated by other Los Angeles Abrasion Testing Machines producing constant peripheral speed.

2.2 Sieves, conforming to Specification ASTM E11

2.3 Balance

A balance or scale accurate within 0.1% of test load over the range required for this test.

2.4 Charge

The charge shall consist of steel spheres averaging approximately 46.8 mm (1-21/32 in.) in diameter

and each weighing between 390 and 445 gm.

The charge, depending upon the grading of the test sample as described in Section 4, shall be as

follows:

NOTE: Steel ball bearings 46.0 mm (1-13/16 in.) and 47.6 mm (1-7/8 in.) in diameter, weighing approximately 400 and 440 gm each, respectively, are readily available. Steel spheres 46.8 mm (1-27/32 in.) in diameter weighing approximately 420 gm is also obtainable. The charge (or balls) may consist of a mixture of these sizes conforming to the weight tolerances of 2.4.

3. Sampling:

The field sample shall be obtained in accordance with Practice ASTM D 75 and reduced to test

portion size in accordance with Methods ASTM C 702.

4. Test Sample:

The test sample shall be washed and oven-dried 105 to 110° C to substantially constant weight

(Note), separated into individual size fractions, and recombined to the grading of Table-3.3. most

nearly corresponding to the range of sizes in the aggregates as furnished for the work. The weight of

the sample prior to test shall be recorded to the nearest 1 gm.

5. Procedure:

Place the test sample and the charge in the Los Angeles Testing Machine and rotate the machine at a

speed of 30 to 33 rpm for 500 revolutions. After the prescribed number of revolutions, discharge the

material from the machine and make a preliminary separation of the sample on a sieve coarser than

the 1.70mm (No. 12). Sieve the finer portion on a 1.70mm sieve in a manner conforming to the Method C 136 (sieve analysis). Wash the material coarser than the 1.70mm sieve (Note), oven-dry at 105 to 110° C to substantially constant weight, and weigh to the nearest 1 gm (Note).

NOTE: If the aggregate is essentially free of adherent coatings and dust, the requirement for washing before and after the test may be waived. Elimination of washing after the test will seldom reduce the measured loss by more than about 0.2% of the original sample weight.

NOTE: Valuable information concerning the uniformity of the sample under test may be obtained by determining the

loss after 100 revolutions. This loss should be determined without washing the material coarser than the 1.70

mm (No.12) sieve. The ratio of the loss after 100 revolutions to the loss after 500 revolutions should not

greatly exceed 0.20 for material of uniform hardness. When this determination is made, take care to avoid

Losing any part of the sample; return the entire sample, including the dust of fracture, to the testing machine

for the final 400 revolutions required to complete the test.

6. Calculation:

Express the loss (difference between the original weight and the final weight of the test sample) as a

percentage of the original weight oI the test sample. Report this value as the percent loss.

APPENDIX - III

MAINTENANCE OF SHELF

a. The shelf of the Los Angeles Machine is subject to severe surface wear and impact. With use, the

Working surface of the shelf is penned by the balls and tends to develop a ridge of metal parallel to

and about 32 mm (1-1/4 in.) from the junction of the shelf and the inner surface of the cylinder. If

the shelf is made from a section of rolled angle, not only may this ridge develop, but the shelf itself

may be bent longitudinally or transversely from its proper position.

b. The shelf should be inspected periodically to determine that it is not bent either lengthwise or

from its normal radial position with respect to the cylinder. If either condition is found, the shelf

should be repaired or replaced before further tests are made. The influence on the test result of the

ridge developed by peaking of the working face of the shelf is not known. However, for uniform test

conditions, it is recommended that the ridge be ground off if its height exceeds 2 mm (0.1 in.).