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The following sections outline some considerations regarding the operation of rollers once the roller combination for a specific job has been determined. 10.4.2.1 General Rules In standard conditions, rollers should follow as closely as possible behind the paver. If it is not possible for the rollers to keep up with the paver, the speed of […]

The number of rollers, their types, and number of passes should be selected with regard to the SMA gradation, layer thickness, weather conditions, and the planned paving speed. Obviously the rollers should be in good working order, able to work at low and constant speeds. The Minimum number of rollers to compact one layer one […]

Vibratory rollers should be carefully or, more precisely, consciously used. An addi­tional condition for using vibration is maintaining the appropriate temperature behind the paver to enable the movement of particles during rolling. Applying vibra­tion to a cool SMA mixture is a mistake that leads to the crushing of particles. Vibration is not an option when […]

The following types of rollers can be used for compacting SMA mixtures: • Static—used as basic equipment for SMA compaction. The heavy (fin­isher) and medium ones operate chiefly in the set. When compacting is executed on thin layers or layers on a stiff underlying, heavy rollers are excluded. • Vibratory— used for compacting SMA, but […]

In general, most regulations and guidelines do not permit manually placing SMA mixtures; however, there are places where there is no other option but to place the mixture manually (e. g., small and irregular pieces of a roadway) (Figure 10.10). In such cases one should remember not to scatter the mixture with shovels but to […]

It is worth remembering the following when mechanically spreading a layer of SMA mixture: • Manually scattering mixture over the mechanically placed mixture is not permitted. • Allowing any vehicles other than rollers on the hot mixture, before it is finally compacted and its temperature drops below the expected level, is not permitted. • The […]

The appropriate passage of material through the paver plays a key role in the proper spreading of a mixture. After starting in the hopper, the mixture is moved by slat con­veyors (with flow gates in older equipment) to augers and then under a screed. During each of these stages the following significant parameters affect the […]

Nowadays, mechanical placement is the only reliable method of executing an SMA layer. Requirements for pavers can very rarely be found in the specifications. Basically, selection, setting, and operation of a paver are the responsibilities of the paving contractor. Most road-engineering companies, after gaining experience with SMA pavements, work out their own procedures for spreading, […]

Almost all publications on SMA underline the necessity of carefully observing the temperature of the mixture during placement and rolling. The expected range of mixture temperature is determined in different ways; it chiefly depends on the kind of binder, but such factors as the layer thickness and weather conditions are impor­tant, too. However, the most […]

Corrections to mixture problems occurring during delivery of a mixture may be pos­sible up until the moment of placing the SMA. The moment the SMA layer appears behind the screed plate of a paver, the chances of improving the quality diminish to a minimum. After that time only compaction is possible; errors made during the […]