AASHTO R 76-2016 Standard Practice for Reducing Samples of Aggregate to Testing Size.pdf

1、Standard Practice for Reducing Samples of Aggregate to Testing Size AASHTO Designation: R 76-161,2Release: Group 3 (August 2016) ASTM Designation: C702/C702M-11 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1c R

2、76-1 AASHTO Standard Practice for Reducing Samples of Aggregate to Testing Size AASHTO Designation: R 76-161,2Release: Group 3 (August 2016) ASTM Designation: C702/C702M-11 1. SCOPE 1.1. These methods cover the reduction of large samples of aggregate to the appropriate size for testing, employing te

3、chniques that are intended to minimize variations in measured characteristics between the test samples so selected and the large sample. 1.2. The values stated in SI units are to be regarded as the standard. 1.3. This standard does not purport to address all of the safety concerns associated with it

4、s use. It is the responsibility of the user of this procedure to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to its use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: T 2, Sampling of Aggregates T 84, Specific Gravity and Abso

5、rption of Fine Aggregate 2.2. ASTM Standard: C125, Standard Terminology Relating to Concrete and Concrete Aggregates 3. TERMINOLOGY 3.1. Definitionsthe terms used in this standard are defined in ASTM C125. 4. SIGNIFICANCE AND USE 4.1. Specifications for aggregates require sampling portions of the ma

6、terial for testing. Other factors being equal, larger samples will tend to be more representative of the total supply. The methods described in this standard provide for reducing the large sample obtained in the field or produced in the laboratory to a convenient size for conducting a number of test

7、s to describe the material and measure its quality. These methods are conducted in such a manner that the smaller test sample portion will be representative of the larger sample and, thus, of the total supply. The individual test methods provide for minimum masses of material to be tested. 4.2. Unde

8、r certain circumstances, reduction in size of the large sample prior to testing is not recommended. Substantial differences between the selected test samples sometimes cannot be 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a viol

9、ation of applicable law.TS-1c R 76-2 AASHTO avoided, as, for example, in the case of an aggregate having relatively few large-sized particles in the sample. The laws of chance dictate that these few particles may be unequally distributed among the reduced-size test samples. Similarly, if the test sa

10、mple is being examined for certain contaminants occurring as a few discrete fragments in only small percentages, caution should be used in interpreting results from the reduced-size test sample. Chance inclusion or exclusion of only one or two particles in the selected test sample may importantly in

11、fluence interpretation of the characteristics of the original sample. In these cases, the entire original sample should be tested. 4.3. Failure to carefully follow the procedures in these methods could result in providing a nonrepresentative sample to be used in subsequent testing. 5. SELECTION OF M

12、ETHOD 5.1. Fine AggregateSamples of fine aggregate that are drier than the saturated surface-dry condition (Note 1) shall be reduced in size by a mechanical splitter according to Method A. Samples having free moisture on the particle surfaces may be reduced in size by quartering according to Method

13、B, or by treating as a miniature stockpile as described in Method C. 5.1.1. If the use of Method B or Method C is desired, and the 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 perfo

14、rmed. Note 1The method of determining the saturated surface-dry condition is described in T 84. As a quick approximation, if the fine aggregate will retain its shape when molded in the hand, it may be considered to be wetter than saturated surface-dry. 5.1.2. If use of Method A is desired and the sa

15、mple has free moisture on the particle surfaces, the entire 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 sample is very large, a

16、 preliminary split may be made using a mechanical splitter having wide chute openings 38 mm (11/2in.) 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. 5.2. Coarse AggregatesReduce the sample us

17、ing 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. 5.3. Combined Coarse and Fine AggregateSamples that are in a dry c

18、ondition may be reduced in size by either Method A or Method B. Samples having free moisture on the particle surfaces may be reduced in size by quartering according to Method B. When Method A is desired and the sample is damp or shows free water, dry the sample until it appears dry or until clumps c

19、an be easily broken by hand (Note 2). Dry the entire sample to this condition, using temperatures that do not exceed those specified for any of the tests contemplated, and then reduce the sample. The miniature stockpile Method C is not permitted for combined aggregates. Note 2The dryness of the samp

20、le can be tested by tightly squeezing a small portion of the sample in the palm of the hand. If the cast crumbles readily, the correct moisture range has been obtained. 6. SAMPLING 6.1. The samples of aggregate obtained in the field shall be taken in accordance with T 2, or as required by individual

21、 test methods. When tests for sieve analysis only are contemplated, the size 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-1c R 76-3 AASHTO of field sample listed in T 2 is usually adequate. When a

22、dditional tests are to be conducted, the user shall determine that the initial size of the field sample is adequate to accomplish all intended tests. Similar procedures shall be used for aggregate produced in the laboratory. METHOD AMECHANICAL SPLITTER 7. APPARATUS 7.1. Sample SplitterSample splitte

23、rs 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 alternatively to each side of the splitter. For coarse aggregate and mixed aggregate, the minimum width of the individual chutes shall be approxi

24、mately 50 percent larger than the largest particles in the sample to be split (Note 3). For dry fine aggregate in which the entire sample will pass the 9.5-mm (3/8-in.) sieve, the minimum width of the individual chutes shall be at least 50 percent larger than the largest particles in the sample and

25、the maximum width shall be 19 mm (3/4in.). 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 straightedged pan, which has a width equal to or slightly less than the overall width of the assembly of

26、 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 (see Figure 1). Note: (a) may be constructed as either closed or open type. Closed type is

27、preferred. Figure 1Sample Splitters (Riffles) Note 3Mechanical splitters are commonly available in sizes adequate for coarse aggregate having the largest particle not over 37.5 mm (11/2in.). Feed ChuteAt Least EightOpeningsRiffle Sample Splitter(a) Large Sample Splitter for Coarse AggregateRolled Ed

28、ges(b) Small Sample Splitters for Fine AggregateAt Least TwelveOpenings 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.TS-1c R 76-4 AASHTO 8. PROCEDURE 8.1. Place the original sample in the hopper or p

29、an 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. 8.2. Reintroduce

30、 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 portion of the material collected in the other receptacle may be reserved for reduction in size for other tests. METHOD BQUARTERING

31、9. APPARATUS 9.1. Apparatus shall consist of a straightedge; straightedged scoop, shovel or trowel; a broom or brush; and a canvas blanket or tear-resistant tarp approximately 2 by 2.5 m (6 by 8 ft). 10. PROCEDURE 10.1. Use either the procedure described in Section 10.1.1 or 10.1.2, or a combination

32、 of both. 10.1.1. Place the original sample on a hard, clean, level surface where there will be neither loss of material nor the accidental addition of foreign material. Mix the material by turning the entire sample over at least three times until the material is thoroughly mixed. With the last turn

33、ing, form the entire sample into a conical pile by depositing individual lifts on top of the preceding lift. Carefully flatten the conical pile to a uniform thickness and diameter by pressing down the apex with a shovel or trowel so that each quarter sector of the resulting pile will contain the mat

34、erial originally in it. The diameter should be approximately four to eight times the thickness. Divide the flattened mass into four equal quarters with a shovel or trowel and remove two diagonally opposite quarters, including all fine material, and brush the cleared spaces clean. The two unused quar

35、ters may be set aside for later use or testing, if desired. Successively mix and quarter the remaining material until the sample is reduced to the desired size (see Figure 2). 10.1.2. As an alternative to the procedure in Section 10.1.1 or when the floor surface is uneven, the field sample may be pl

36、aced on a canvas blanket or tear-resistant tarp and mixed with a shovel or trowel as described in Section 10.1.1, leaving the sample in a conical pile. As an alternative to mixing with the shovel or trowel, lift each corner of the blanket or tarp and pull it over the sample toward the diagonally opp

37、osite corner, causing the material to be rolled. After the material has been rolled a sufficient number of times (a minimum of four times), so that it is thoroughly mixed, pull each corner of the blanket or tarp toward the center of the pile so the material will be left in a conical pile. Flatten th

38、e pile as described in Section 10.1.1. Divide the sample as described in Section 10.1.1, or insert a stick or pipe beneath the blanket or tarp and under the center 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

39、 between the divided portions. Insert the stick under the center 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 two diagonally opposite quarters, being careful to clean the fines from the blanket or tarp. The

40、 two unused quarters may be set aside for later use or testing, if desired. Successively mix and quarter the remaining material until the sample is reduced to the desired size (see Figure 3). 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplica

41、tion is a violation of applicable law.TS-1c R 76-5 AASHTO Figure 2Quartering on a Hard, Clean, Level Surface Figure 3Quartering on a Canvas Blanket or Tear-Resistant Tarp Cone Sample on Hard,Clean SurfaceMix by FormingNew ConeQuarter after Flattening ConeSample Divided into Quarters Retain Opposite

42、QuartersReject the Other Two QuartersMix by Rolling on Blanket Form Cone after Mixing Quarter after Flattening ConeSample Divided into Quarters Retain Opposite QuartersReject the Other Two Quarters 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. D

43、uplication is a violation of applicable law.TS-1c R 76-6 AASHTO METHOD CMINIATURE STOCKPILE SAMPLING (DAMP FINE AGGREGATE ONLY) 11. APPARATUS 11.1. Apparatus shall consist of a straightedge; straightedged scoop, shovel, or trowel for mixing the aggregate; and either a small sampling thief, small sco

44、op, or spoon for sampling. 12. PROCEDURE 12.1. Place the original 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 by turning the entire sample over at least three times until

45、the material is thoroughly mixed. With the last turning, form the entire sample into a conical pile by depositing individual lifts on top of the preceding lift. If desired, the conical pile may be flattened to a uniform thickness and diameter by pressing the apex with a shovel or trowel so that each

46、 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 in Section 11.1. 13. KEYWORDS 13.1. Aggregat

47、e; aggregate sample; mechanical splitter; quartering. 1 Technically equivalent but not identical to ASTM C702/C702M-11. 2Formerly T 248. First published as a practice in 2016. 2016 by the American Association of State Highway and Transportation Officials. All rights reserved. Duplication is a violation of applicable law.