Problems and Tips

Today almost all asphalt plants are computer controlled. It is worthwhile mentioning the necessity for caution during SMA production. This also applies to these modern asphalt plants. Usually such machines give personnel a feeling of confidence and a sense of complete control over the production process. However, many instances have proved that an excess of trust leads to problems (some of which are described in Chapter 11).

Particular attention should be paid to checking weight batchers, thermometers, and proportioning meters. All data produced by the computer system should be peri­odically checked. A good example of the type of problems that may occur is the clog­ging of batching devices for granulated stabilizers between the balance and the chute

Stabilizer

FIGURE 9.11 The SMA asphalt mixture with the stabilizer after extraction and before aggregate screening. (Photo courtesy of Krzysztof BlaZejowski.)

gate. The actual amount of stabilizer weighed out by the machine can be checked by disconnecting the chute pipe and measuring the amount of material batched during a production cycle (Figure 9.10). Another typical method is performing an extrac­tion and checking for the presence of the stabilizer in the mixture (Figure 9.11). Unfortunately this method does not allow for the determination of the exact amounts of fibers added to each batch.

Finally, a brief note about extraction. While performing an extraction of an SMA mixture, the rules for the correct preparation of the sample should be observed (hav­ing the stabilizer in mind as the mixture’s constituent—see Figure 9.11). The stabi­lizer fibers should be removed prior to starting the aggregate screening.