LABORATORY TESTING SECTION. Method of Test for CALIBRATION OF MECHANICAL SIEVE SHAKER

Transcription

1 Commonwealth of Pennsylvania PA Test Method No. 608 Department of Transportation 7 Pages 1. SCOPE LABORATORY TESTING SECTION Method of Test for CALIBRATION OF MECHANICAL SIEVE SHAKER 1.1 This method of calibration describes a procedure to be used in determining the shaking efficiency of a mechanical sieve shaker. 2. APPARATUS 2.1 Balance- The balance or scale shall conform to the following criteria: Readability and Class Sensitivity Accuracy a G2 0.1 g 0.2 g or 0.1% G5 1 2 g or 0.1% G20 5 g 5 g or 0.1% G g 20 g or 0.1% a Accuracy equal to the mass stated or 0.1% of the test load, whichever is greater, throughout the range of use. NOTE 1- The balance shall have sufficient capacity to handle the greatest weighing made in conducting the test. 2.2 Sieves- The sieves shall be mounted on substantial frames constructed in a manner that will prevent loss of material during sieving. The sieves shall conform to the requirements of AASHTO M Mechanical Sieve Shaker- A mechanical sieve shaker shall impart a vertical, or lateral and vertical motion to the sieve, causing the particles to bounce and turn so as to present different orientations to the sieving surface. 2.4 Timers- Electric or mechanical timers shall be accurate and variable in 1 minute increments. The timers shall have a capacity of at least 15 minutes. 2.5 Oven- The oven shall be capable of maintaining a uniform temperature of 110 ± 5ºC (230 ± 9 ºF).

2 NOTE 2- Hot plates may be used when test results must be obtained quickly. Confirmation samples shall be tested using ovens as described above. 3. SAMPLES PTM No. 608 Page A representative sample sufficient to yield not less than the appropriate mass of dry material, as shown below, shall be selected in accordance with AASHTO T-248. The selection of samples of an exact pre-determined mass shall not be attempted. 3.2 After drying, sample fractions of fine aggregate shall have an approximate mass as follows: Material with a minimum of 95 percent passing the 2.36 mm (No. 8) sieve g Material with a minimum of 85 percent passing the 4.75 mm (No. 4) sieve, and more than 5 percent retained on a 2.36 (No. 8) sieve 500 g NOTE 3- In no case, however, shall the fraction retained on any sieve at the completion of the sieving operation weigh more than 200 g for the usual mm (8") diameter sieve. The amount of material retained on the critical sieve may be regulated by the introduction of a larger sieve immediately above the critical sieve or by the selection of a sample of a proper size. 3.3 After drying, samples of coarse aggregate shall have a minimum mass as follows: AASHTO Minimum Mass of Sample Number kg lb. #3 20 (44) #5 10 (22) #57 10 (22) #67 10 (22) #7 10 (22) #8 5 (11) PA No. 2A 15 (33) NOTE 4- Samples failing to meet the mass requirements of Sections 3.2 and 3.3 shall be deemed to be insufficient to produce reliable results and shall not be tested. However, the intent of this method will be satisfied for samples of aggregate larger than 50 mm (2") nominal maximum size if a smaller mass of a sample is used, provided the criterion for acceptance or rejection of the material is based on the average of the results of at least three samples. The sample size used times the number of samples averaged shall equal the minimum mass of the

3 Page 3 sample shown in Section 3.3. The differences in individual sample sizes shall not vary by mass by more than 20 percent from each other. 4. PROCEDURE 4.1 Coarse Aggregate This procedure is to be used for each aggregate size produced. After obtaining a representative sample, shake the particular material at least one minute less than the time currently being used on the mechanical sieve shaker for a given aggregate size Weigh and record the amount retained on each individual sieve. Return the amount retained onto each one of the individual sieves where there is a significant amount of material retained. Typically, these are the middle sieves of the gradation Place the first sieve that has a significant amount of material retained on the sieve mesh into the shaking device. Shake for an additional minute. Weigh and record the amount retained on this sieve after one minute of additional mechanical shaking. Follow the same procedure for the remaining individual sieves that have been determined to have a significant amount of material retained Calculation to Determine Shaking Efficiency: P = W o - W a x 100 W t Where: P = Percentage difference of weight retained on the individual sieve W o = Original weight retained on the individual sieve W a = Weight retained on the individual sieve after additional sieving W t = Total sample weight, dry

4 Page When the difference between the weights retained on each individual sieve after additional mechanical sieving and the original sieving is 0.5 %, or less, of the total oven dry sample weight, FOR ALL SIEVE SIZES, the shaking time used in Section is sufficient. If any of the differences calculated are greater than 0.5 % of the total oven dry sample weight, repeat this process outlined above with a new representative sample. Increase the mechanical shaking time by one minute. Repeat the process as many times as necessary, but do not exceed 12 minutes of shaking time for any aggregate on any shaking device. If the shaking device cannot meet this requirement, replace or repair the shaking device Example of a Shaking Efficiency Determination: No. 57 Coarse Aggregate Total Dry Sample Weight = lbs 7 Minutes of Mechanical 1 Minute of Additional Shaking, lbs. Mechanical Shaking, lbs. Sieve. 5/8 in /2 in /8 in Calculation to Determine Shaking Efficiency 5/8 in lbs 6.10 lbs = 0.10 lbs lbs x 100 = 0.3 % difference 1/2 in lbs lbs = 0.10 lbs lbs x 100 = 0.3 % difference 3/8 in lbs 4.00 lbs = 0.10 lbs lbs x 100 = 0.3 % difference The results of this calculation to determine shaking efficiency for each of the three sieves indicate that all three sieves meet the 0.5% requirement stated in Section In this example, therefore, a mechanical shaking time of 7 minutes is sufficient for this #57 coarse aggregate material on this shaking device.

5 Page Fine Aggregate This procedure is to be used for each aggregate size produced. Retain the fine aggregate after the wash test and mechanically shake for at least 1 minute less than the time currently being used on the mechanical sieve shaker for a given aggregate size. NOTE 5- Washing the sample before performing the shaking efficiency determination is not necessary for bituminous sands and Type 1, 1A, 2, 3, 3A, and 4 anti-skids Weigh and record the amount retained on each individual sieve. Return the amount retained onto each one of the individual sieves where there is a significant amount of material retained. Typically, these are the middle sieves of the gradation Hand sieve each individual sieve size in accordance with AASHTO T-27, Section 8.4 stated as follows: Hold the individual sieve, provided with a snug-fitting pan and cover, in a slightly inclined position in one hand. Strike the side of the sieve sharply and with an upward motion against the heel of the other hand at a rate of about 150 times per minute, turning the sieve about one-sixth of a revolution at intervals of about 25 strokes. Weigh and record the amount retained on each individual sieve after one minute of additional hand shaking Calculation to Determine Shaking Efficiency: P = W o - W a x 100 W t Where: P = Percentage difference of weight retained on the individual sieve W o = Original weight retained on the individual sieve W a = Weight retained on the individual sieve after additional sieving W t = Total sample weight, dry

6 Page When the difference between the weight retained on each individual sieve after additional hand sieving and the original sieving is 0.5 %, or less, of the total oven dry sample weight, FOR ALL SIEVE SIZES, the shaking time used in Section is sufficient. If any of the sieves have differences calculated that are greater than 0.5 % of the total oven dry sample weight, repeat this process outlined above with a new representative sample. Increase the mechanical shaking time by one minute. Repeat the process as many times as necessary, but do not exceed 12 minutes of shaking time for any aggregate on any shaking device. If the shaking device cannot meet this requirement, replace or repair the shaking device Example of a Shaking Efficiency Determination: Type A Concrete Sand Total dry sample weight = grams Sieve 7 Minutes of Mechanical 1 Minute of Additional Shaking, lbs. Mechanical Shaking, lbs. No No No Calculation to Determine Shaking Efficiency No. 8 No. 16 No g g = 5.0 g 490 g x 100 = 1.0 % difference g g = 2.0 g 490 g x 100 = 0.4 % difference g 98.0 g = 2.0 g 490 g x 100 = 0.4 % difference Although the No. 16 and the No. 30 sieves met the requirement of 0.5 % for this material, the No. 8 sieve did not. Therefore, increase the shaking time for this material to 8 minutes and repeat the process with another new representative sample. 5. REFERENCES PTM 616 AASHTO T- 27

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