GUIDELINES FOR DETERMINING THE ACCEPTABILITY OF TEST RESULTS


 

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 test 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

 

TEST NAME

TEST METHOD

TOLERANCE

 

 

 

Slump of PC Concrete

 

 

 

1” or less on IA or Verification

IM 317

1/4 in.

 

More than 1” on IA or Verification

 

3/4 in.

 

 

 

Air Content of PC Concrete

IM 318

0.4%

 

 

 

Length of Concrete Cores

IM 347

0.10 in.)

 

NDT Pavement Thickness (MIT)

 

<=0.15 in.

 

Free Moisture in Aggregate, by Pycnometer

IM 308

0.2%

 

 

 

Specific Gravity of Aggregate, by Pycnometer

IM 307

0.02

 

 

 

Moisture in Aggregate, by Hot Plate

 

0.3%

 

 

 

Moisture in Soil

IM 335, IM 334

1.5%

 

 

 

Proctor Optimum Moisture Content

IM 309

2.0%

 

 

 

Proctor Maximum Dry Density

IM 309

5.0 lb./ft3

 

 

 

In-Place Wet Density, Soils & Bases

IM 334, 326,

2.0 lb./ft³

 

other approved

 

 

 

 

Gmm Maximum Specific Gravity

IM 350

0.010

 

 

 

Gmb Density of HMA Concrete, by Displacement

IM 321

0.020

 

 

 

G*/Sin Delta

T315

17% of mean

 

 

 

% Binder, Ignition Oven

IM 338

0.33%

 

 

 

Gsa Apparent Specific Gravity

IM 380

0.010

 

 

 

Gsb Bulk Specific Gravity

IM 380

0.028

 

 

 

Percent Absorption

IM 380

0.37%

 

 

 

Fine Aggregate Angularity

T304

2.0%

 

 

 

Sand Equivalency

T176

10 % of mean

 

 

 

Pavement Profile Index (0.2” blanking band)

IM 341

 

 

Verification Profile Index Test Result

 

 

 

Inches/mile

 

 

 

6.0 or less

 

1.0 in./mi.

 

6.1 to 20.0

 

2.0 in./mi.

 

20.1 to 40.0 

 

3.0 in./mi.

 

More than 40.0

 

5.0 in./mi.

 

 

 

Pavement Profile Index (0.0” blanking band)

IM 341

 

 

Verification Profile Index Test Result

 

 

 

Inches/mile

 

 

 

25.0 or less

 

3.0 in./mi.

 

25.1 to 40.0

 

4.0 in./mi.

 

More than 40.0

 

5.0 in./mi.

 

 

 

Bridge Profile Index (0.2” blanking band)

IM 341

 

 

Verification Profile Index Test Result

 

 

 

Inches/mile

 

 

 

6.0 or less

 

2.0 in./mi.

 

6.1 to 20.0

 

3.0 in./mi.

 

20.1 to 40.0 

 

4.0 in./mi.

 

More than 40.0

 

6.0 in./mi.

 

 

 

Pavement International Roughness Index (IRI)

IM 341

 

 

Verification IRI Test Result

 

 

 

Inches/mile

 

 

 

50.0 or less

 

10.0% of mean

 

50.1 to 150.0

 

8.0% of mean

 

More than 150.0

 

7.0% of mean

 

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.

 

Table 1 Tolerances for All Aggregates Except HMA-Combined Aggregate

 

 

 

 

Size Fraction Between Consecutive Sieves, %*

Tolerance, %

 

 

 

Coarse Portion:

0.0

to

3.0

 

2

#4 Sieve and larger

3.1

to

10.0

 

3

 

10.1

to

20.0

 

5

 

20.1

to

30.0

 

6

 

30.1

to

40.0

 

7

 

40.1

to

50.0

 

9

 

 

 

 

 

 

Fine portion:

0.0

to

3.0

 

1

#8 Sieve and smaller

3.1

to

10.0

 

2

 

10.1

to

20.0

 

3

 

20.1

to

30.0

 

4

 

30.1

to

40.0

 

4

 

 

 

 

 

 

Table 2 Tolerances for All HMA-Combined Aggregate

 

 

 

 

Size Fraction Between Consecutive Sieves, %*

Tolerances(1)

 

0.0

to

3.0

 

2

 

3.1

to

10.0

 

3

 

10.1

to

20.0

 

5

 

20.1

to

30.0

 

6

 

30.1

to

40.0

 

7

 

40.1

to

50.0

 

9

 

(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.

 

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

 

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

1.5"

100.0

100.0

0.0

0.0

0.0

2

Yes

1"

97.1

99.1

2.9

0.9

2.0

2

Yes

3/4"

72.2

65.1

24.9

34.0

9.1

6

No

1/2"

38.1

34.9

34.1

30.2

3.9

7

Yes

3/8"

12.0

8.8

26.1

26.1

0.0

6

Yes

#4

0.6

0.2

11.4

8.6

2.8

5

Yes

#8

0.5

0.2

0.1

0.0

0.1

1

Yes

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.

 

NOTEThe applicable tolerance changes between #4 and #8 size fractions.


 

 

 

Example 2 - PC Concrete Fine Aggregate

 

 

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

Sieve

Size

 

3/8"

100.0

100.0

0.0

0.0

0.0

2

Yes

#4

95.0

95.0

5.0

5.0

0.0

3

Yes

#8

87.8

86.3

7.2

8.7

1.5

2

Yes

#16

72.0

71.5

15.8

14.8

1.0

3

Yes

#30

44.0

43.8

28.0

27.7

0.3

4

Yes

#50

12.2

13.0

31.8

30.8

1.0

4

Yes

#100

1.5

1.3

10.7

11.7

1.0

3

Yes

Minus #200

0.4

0.4

0.4

0.4

0.0

1

Yes

 

 

Example 3 - HMA Combined Aggregate


NOTEThe 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.