Each sample is subjected to extraction testing, resulting in a gradation of the aggregate mix and a content of soluble binder. The sieving operation should be conducted using a set of sieves as in Table 14.2. The standard stipulates testing the aggregate gradation through five sieves (plus possibly a sieve for oversize particles 1.4D). The small number of test sieves speeds up the control analysis but at the same time increases the responsibility of the mix producer to achieve other final SMA properties determined by a recipe. It appears that the proper selection of optional sieves for the coarse aggregates that control the skeleton is of great significance.
14.8.3.3 selection of a method for Estimation of Extraction Results
Prior to the comparison of extraction results with admissible deviations, the method for assessment of extraction results should be selected. The choice should be made between the following two methods:
• Single result method—test results of individual samples are treated independently and assessed in comparison with admissible deviations from a target in accordance with Table A.1 of the standard; the sets of the previous 32 results form the basis for the OCL assessment (classified as conforming or nonconforming).
• Mean of four results method—test results of individual samples are treated in groups of four analyses of the same mixture, and the mean result of each group is compared with admissible deviations from a target (classified as conforming or nonconforming); after a comparison of results of the eight mean results (e. g., eight groups, each with four results for a total of 32), they are classified as conforming or nonconforming and form the basis for the OCL assessment.
Thus in the single result method, we assess 32 individual results; in the mean of four results method, we assess eight results (means) calculated for groups of four single results.
Comments on Requirements for Permitted Deviations from the Target for Mixtures Produced Using EN 13108-21, for Small Aggregate Mixtures with D <16mm—the Single Result Method
Small Aggregate Mixes (D <16 mm)
|
Percentage Passing |
(Single Result Method for |
(Control of Production |
|
|
(% m/m) |
OCL Calculation) |
Variability) |
Comment |
|
1.4 D |
— |
— |
The sieve 1.4D—additional sieve on which requirements for passing 98-100% have been established |
|
D |
-8/+5 |
±4 |
The sieve determining maximum particle size in a mix (without oversize particles), (e. g., the record SMA 11 means D = 11.2 mm [at the same time the boundary sieve for oversize particles]) |
|
D/2 or characteristic coarse sieve |
±7 |
±4 |
The sieve indicated in an NAD for the standard EN 13108-5 for each SMA mixture |
|
2.0 mm |
±6 |
±3 |
— |
|
Characteristic fine sieve |
±4 |
±2 |
The characteristic sieve has not been determined in EN 13108-21; it should be established in an NAD for EN 13108-5 for each SMA mixture; the choice has been limited to one of the sieves: 0.125, 0.25, 0.5, or 1.0 mm |
|
0.063 mm |
±2 |
±1 |
Sieve of filler fraction |
|
Soluble binder content |
±0.5 |
±0.3 |
Soluble binder content with extraction after EN 12697-1 |
|
Individual Samples Tolerance about Target Permitted Mean Deviation Composition from Target |
Source: Modified from EN 13108-21. Bituminous Mixtures—Material specifications—Part 21: Factory Production Control. Note: NAD = National application document; SMA = stone matrix asphalt.
These two methods may not be applied in parallel. In other words, only one method can be used at the same time in the same asphalt plant.
Analyses of deviations using only the single result method will be discussed later.
