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The main objective of transporting a mixture from the asphalt plant to the laydown site is to deliver the mix without changing its properties and in a state that allows for appropriate placement and compaction. Minimizing heat loss and preventing seg­regation of the mixture constituents are two of the most important issues regarding transportation. Requirements for transporting the mixture to the work site are often defined in technical specifications. Typical requirements are shown, as examples, in the following:

• Specified maximum distance between the asphalt plant and laydown site (e. g., 40 km)

• Maximum travel time from the asphalt plant to the work site (e. g., 2 hours)

Specifying the distance between the asphalt plant and the construction site can be quite a misleading operati...

Once the SMA has been produced at a hot mix plant, it must be transported to the job site where it will be placed and compacted. This chapter describes issues that need to be considered during this stage of the construction process.

10.1 TRANSPORT OF THE MIXTURE TO A LAYDOWN SITE

While it may seem that hauling SMA to the job site is straightforward, there are things that can go wrong that can affect the rest of the construction process and ultimately the performance of the pavement. This section will describe potential problems and how to prevent them.

10.1.1 Loading a Truck

The hot SMA mixture, at first stored in a silo, must be transported to the work site. The way the mixture is loaded into the bed of the truck affects its subsequent quality...

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

Issues concerning procedures for production of bituminous mixtures under EN 13108-21 and specified tolerances are discussed in Chapter 14.

9.5.2 Other Examples of Production Control

Some brief examples from around the world include

• In some countries, the accuracy of stabilizer dosage is ±10% of its mass as determined in a laboratory formula.

• If binder viscosity is the basis for establishing the mixing temperature of a binder and aggregate, some specifications may quote a permissible devia­tion from that temperature (e. g., ±10°C).

• In most countries, the permissible deviation of a mixture gradation and the content of binder depends on the number of tested samples.

• Some regulations provide clauses permitting a situation in which the grada­tion curve of a produced mix, consi...