Determination of Compliance of a Tested Sample with a Recipe

After extraction, the result of each sample is compared with admissible deviations on test sieves and soluble binder content. A mix may be regarded as compatible with a recipe when all its components are within admissible tolerances.

Table 14.2 depicts an excerpt of Table A.1 of Annex A of the standard demon­strating admissible deviations from a target appropriate for producing SMA mixes with D less than 16mm (e. g., the group of small aggregate mixtures using the single result method). Using admissible deviations, the accuracy of measuring methods has already been taken into account.

14.8.3.4 reaching the ocL Assessment

After assessing the mixture extraction results (the set of 32 results), one can deter­mine the OCL level. According to the standard, there are three OCL level—A, B, and C. They can be roughly interpreted as follows:

• OCL A proves a high rate of compliance with the target for manufactured mixtures.

• OCL B is an intermediate assessment and is still good.

• OCL C is a warning assessment for asphalt plant personnel (and their customers) that the composition of produced mixtures fluctuates considerably.

The OCL assessment is established after 32 consecutive analyses, but it should be kept in mind that they do not have to be samples of only one mixture type; the standard stipulates taking into consideration 32 consecutive results of any produced mixture. The selection of an appropriate OCL then follows, considering the total number of samples that do not conform with requirements

In the event that more than 8 of the latest 32 results are nonconforming, the plant’s equipment and procedures should be subject to an immediate and thorough review.

The OCL assessment is a dynamic process because the latest 32 results are always used for calculations. After startup at the beginning of the construction sea­son, the test frequency at the starting level should correspond to the lowest OCL-C of a designated level of requirements (X, Y, or Z). Sampling frequency is subject to change weekly based on the lowest OCL achieved during the previous calendar week.

Minimum frequencies of testing samples in relation to the achieved OCL from the previous week are valid for the next calendar week. The following are OCL sample testing frequencies for the single result method:

OCL-A Level X: 600 tons Level Y: 1000 tons Level Z: 2000 tons

OCL-B Level X: 300 tons Level Y: 500 tons Level Z: 1000 tons

OCL-C Level X: 150 tons Level Y: 250 tons Level Z: 500 tons

Interestingly, the better the OCL, the lower the test frequency. These data also show that for each category (X, Y, or Z), when the OCL advances by one level, the test frequency decreases by half (or twice as much material can be produced between tests).

The startup of a new plant means an operational startup with the OCL-C assessment. A shutdown of longer than 3 months during the season or a major repair of the asphalt plant results in the OCL being reduced by one level from where it was before the stoppage. The OCL level cannot be changed until 32 results have been obtained and the first new OCL assessment is available. In the case of an asphalt plant with a low rate of production, the standard stipulates testing the composition of a mix at least every 5 operating days. Mobile coating plants, after relocation, are treated like plants shut down for 3 months or restarted after a major repair.