GENERAL
Criteria for determining the acceptability of test results is an integral part of the Quality Assurance Program. The comparison between two different operator’s results is used in the independent assurance program and sometimes in the validation process. The tolerances in this IM are for comparing individual test results except in the case of the profile index where averages are used. When criteria for comparing tests results is not established in this IM or any other IM, use of the AASHTO or ASTM test procedure precision criteria is appropriate for determining acceptability of test results.
When the tolerances are exceeded, an immediate investigation must be made to determine possible cause so that any necessary corrections can be made. Below are some steps that may be used to identify the possible cause:
1. Check all numbers and calculations.
2. Review past proficiency and validation data.
3. Review sampling and testing procedures.
4. Check equipment operation, calibrations and tolerances.
5. Perform tests on split samples or reference samples.
6. Involve the Central Materials Laboratory.
TOLERANCES
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TEST NAME |
TEST METHOD |
TOLERANCE |
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Slump of PC Concrete |
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1” or less on IA or Verification |
1/4 in. |
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More than 1” on IA or Verification |
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3/4 in. |
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Air Content of PC Concrete |
0.4% |
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Length of Concrete Cores |
0.10 in.)
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NDT Pavement Thickness (MIT) |
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<=0.15 in.
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Free Moisture in Aggregate, by Pycnometer |
0.2% |
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Specific Gravity of Aggregate, by Pycnometer |
0.02 |
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Moisture in Aggregate, by Hot Plate |
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0.3% |
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Moisture in Soil |
1.5% |
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Proctor Optimum Moisture Content |
2.0% |
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Proctor Maximum Dry Density |
5.0 lb./ft3 |
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In-Place Wet Density, Soils & Bases |
2.0 lb./ft³ |
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other approved |
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Gmm Maximum Specific Gravity |
0.010 |
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Gmb Density of HMA Concrete, by Displacement |
0.020 |
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G*/Sin Delta |
T315 |
10% of mean |
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% Binder, Ignition Oven |
0.3% |
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Gsa Apparent Specific Gravity |
0.010 |
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Gsb Bulk Specific Gravity |
0.028 |
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Percent Absorption |
0.37% |
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Fine Aggregate Angularity |
T304 |
2.0% |
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Sand Equivalency |
T176 |
10 % of mean |
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Pavement Profile Index (0.2” blanking band) |
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Verification Profile Index Test Result |
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Inches/mile |
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6.0 or less |
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1.0 in./mi. |
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6.1 to 20.0 |
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2.0 in./mi. |
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20.1 to 40.0 |
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3.0 in./mi. |
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More than 40.0 |
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5.0 in./mi. |
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Pavement Profile Index (0.0” blanking band) |
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Verification Profile Index Test Result |
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Inches/mile |
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25.0 or less |
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3.0 in./mi. |
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25.1 to 40.0 |
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4.0 in./mi. |
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More than 40.0 |
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5.0 in./mi. |
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Bridge Profile Index (0.2” blanking band) |
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Verification Profile Index Test Result |
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Inches/mile |
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6.0 or less |
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2.0 in./mi. |
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6.1 to 20.0 |
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3.0 in./mi. |
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20.1 to 40.0 |
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4.0 in./mi. |
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More than 40.0 |
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6.0 in./mi. |
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Pavement International Roughness Index (IRI) |
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Verification IRI Test Result |
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Inches/mile |
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50.0 or less |
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10.0% of mean |
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50.1 to 150.0 |
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8.0% of mean |
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More than 150.0 |
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7.0% of mean |
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TOLERANCES FOR AGGREGATE GRADATIONS
Determining the precision of an aggregate sieve analysis presents a special problem because the result obtained with a sieve is affected by the quantity of material retained on the sieve and by results obtained on sieves coarser than the sieve in question. Tolerances are, therefore, given for different ranges of percentage of aggregate passing one sieve and retained on the next finer sieve used.
Comparisons of test results are made on each fraction of the sample, expressed in percent that occurs between consecutive sieves.
NOTE: Unless otherwise noted, tolerances for aggregate gradations are only valid if the two tests were made on a split sample. Experience has shown that improper sample reduction, as well as differences in test procedures can contribute to results being out of tolerance. When a comparison exceeds the tolerance limits, a review of the test procedures and equipment will be performed. Where practical, additional comparisons will be done with similar equipment and methods.
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Table 1 Tolerances for All Aggregates Except HMA-Combined Aggregate |
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Size Fraction Between Consecutive Sieves, %* |
Tolerance, % |
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Coarse Portion: |
0.0 |
to |
3.0 |
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2 |
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#4 Sieve and larger |
3.1 |
to |
10.0 |
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3 |
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10.1 |
to |
20.0 |
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5 |
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20.1 |
to |
30.0 |
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6 |
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30.1 |
to |
40.0 |
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7 |
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40.1 |
to |
50.0 |
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9 |
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Fine portion: |
0.0 |
to |
3.0 |
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1 |
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#8 Sieve and smaller |
3.1 |
to |
10.0 |
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2 |
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10.1 |
to |
20.0 |
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3 |
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20.1 |
to |
30.0 |
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4 |
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30.1 |
to |
40.0 |
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4 |
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Table 2 Tolerances for All HMA-Combined Aggregate |
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Size Fraction Between Consecutive Sieves, %* |
Tolerances(1) |
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0.0 |
to |
3.0 |
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2 |
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3.1 |
to |
10.0 |
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3 |
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10.1 |
to |
20.0 |
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5 |
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20.1 |
to |
30.0 |
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6 |
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30.1 |
to |
40.0 |
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7 |
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40.1 |
to |
50.0 |
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9 |
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(1) Minimum tolerance of 5% is applied to all size fractions coarser than the #4 sieve when comparing cold feed to ignition oven as shown on page 3 of Appendix A. *The verification test analysis fraction is used to find the proper tolerance. |
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COMPARISON OF AGGREGATE GRADATIONS
Use of these tolerances is explained in the following examples. Computer spreadsheets to perform the analysis are available on the Iowa DOT Materials Office website. Use of the spreadsheets is preferred when possible. Appendix A contains a copy of the printouts from the spreadsheets.
Example 1 - PC Concrete Coarse Aggregate
Sieve Size
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DOT Coarse Aggr Percent Passing |
Prod./CPI Coarse Aggr Percent Passing |
DOT Coarse Aggr Percent Retained |
Prod./CPI Coarse Aggr Percent Retained |
Fraction Difference |
Applicable Tolerance |
Complies |
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1.5" |
100.0 |
100.0 |
0.0 |
0.0 |
0.0 |
2 |
Yes |
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1" |
97.1 |
99.1 |
2.9 |
0.9 |
2.0 |
2 |
Yes |
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3/4" |
72.2 |
65.1 |
24.9 |
34.0 |
9.1 |
6 |
No |
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1/2" |
38.1 |
34.9 |
34.1 |
30.2 |
3.9 |
7 |
Yes |
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3/8" |
12.0 |
8.8 |
26.1 |
26.1 |
0.0 |
6 |
Yes |
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#4 |
0.6 |
0.2 |
11.4 |
8.6 |
2.8 |
5 |
Yes |
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#8 |
0.5 |
0.2 |
0.1 |
0.0 |
0.1 |
1 |
Yes |
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Minus #200 |
0.3 |
0.2 |
0.3 |
0.2 |
0.1 |
1 |
Yes |
The size fraction between consecutive sieves is found by calculating the difference between the percent passing reported for the two sieves. For example, the fraction between the 1.5 in. and 1 in. sieves for the above verification test is 100.0 - 97.1 = 2.9%. Between the 1/2 in. and 3/8 in. sieves it is 38.1 – 12.0 = 26.1%. Since nothing passes the pan, the size fraction between the #200 sieve and the pan is equal to the percent passing the #200.
The example shows the fraction between each pair of consecutive sieve sizes for both tests and the difference between these fractions for both tests. The difference is compared with the applicable tolerance to determine a disposition. In this example, a suspect result is found in the fraction between the 1 in. and 3/4 in. sieves. Since the suspect difference is due primarily to the percent passing results on the 3/4 in. sieves, it is these results that should at least be investigated first. Only further investigation can determine which 3/4 in. sieve, if any is faulty.
NOTE: The applicable tolerance changes between #4 and #8 size fractions.
Example 2 - PC Concrete Fine Aggregate
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DOT Fine Aggregate Percent Passing |
Prod./CPI Fine Aggregate Percent Passing |
DOT Fine Aggregate Percent Retained |
Prod./CPI Fine Aggregate Percent Retained |
Fraction Difference |
Applicable Tolerance |
Complies |
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Sieve |
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Size |
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3/8" |
100.0 |
100.0 |
0.0 |
0.0 |
0.0 |
2 |
Yes |
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#4 |
95.0 |
95.0 |
5.0 |
5.0 |
0.0 |
3 |
Yes |
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#8 |
87.8 |
86.3 |
7.2 |
8.7 |
1.5 |
2 |
Yes |
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#16 |
72.0 |
71.5 |
15.8 |
14.8 |
1.0 |
3 |
Yes |
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#30 |
44.0 |
43.8 |
28.0 |
27.7 |
0.3 |
4 |
Yes |
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#50 |
12.2 |
13.0 |
31.8 |
30.8 |
1.0 |
4 |
Yes |
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#100 |
1.5 |
1.3 |
10.7 |
11.7 |
1.0 |
3 |
Yes |
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Minus #200 |
0.4 |
0.4 |
0.4 |
0.4 |
0.0 |
1 |
Yes |
Example 3 - HMA Combined Aggregate
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NOTE: The applicable tolerance for this combined aggregate sample is from Table 2. In this example, the suspect fractions would indicate a possible problem for two pairs of consecutive sieve sizes involving the #4 sieves. This evidence and the difference in the test values found for the #4 sieves, strongly point to an error in one of the #4 sieve results.
When RAP mixes are used, the comparison data is of the composite gradation results and not of the cold feed.
Example 4 HMA Cold-Feed to Ignition Oven Comparison
When comparing an ignition oven extracted gradation to a cold-feed gradation a correction factor must be applied to the ignition oven extracted gradation before comparing it to the cold-feed gradation. The correction factor is determined by calculating the difference between a cold-feed gradation and an ignition oven gradation on the first day of HMA production according to IM 501. The correction factor is then applied to all subsequent comparisons. In the example above, the correction factor was determined on a previous sample. The District Materials Engineer may establish new or average correction factors when needed.