The ‘royal league’ of compaction

BOMAG’s Hans-Josef Kloubert explains how modern, intelligent asphalt compaction techniques significantly improve quality.

Wherever roads are built across a continent, people's lives become connected to economies thereby supporting economic growth. The compaction of asphalt in particular has demands of very high quality applied to it. Asphalt roads, like highways or causeways, have to meet demands concerning evenness and durable grip. They must be able to cope with the expected transport loads as well as load burdens resulting from weather and temperature stress.

Asphalt layers of a road surface should be able to reliably carry the traffic loads. They must be able to discharge these loads to the substructure or sub-base, in order to prevent harmful deformation. Besides the mix composition and the paving, the compaction of the mix is of utmost importance with respect to the quality and the service life of the road. For asphalt compaction you need the right technique, knowledge and experience.

Compacting asphalt starts with the finisher. If you use a finisher with low pre-compaction you will probably need breakdown rolling as rollers that are too heavy or early compaction with vibration might affect the evenness of the layer or even cause undesired displacements and misplacements in the material.

However, if you use a finisher with high initial compaction you can start using vibratory rollers earlier. Final compaction can thus be achieved with just a few roller passes. This is because vibratory rollers are very powerful, versatile and require considerably less passes than static rollers. The vibration reduces the internal friction of the aggregates in the mix, so that the interaction between deadweight and dynamic load increases the density.

Besides the static linear load, other factors like vibrating mass, frequency and amplitude are also decisive for the compaction effect. But also the number of passes - too many might cause harmful loosening of material and disturbances in the structure of the asphalt layer. Therefore knowledge and experience is necessary.

Today a great part of this can be provided by systems using intelligent compaction - vibration systems that automatically control, optimise and document compaction - a technique in which BOMAG has led the way for many years. The core of these systems is based on directed vibration, offering an enormous range of compaction performance and depth effect from low-vibration surface compaction up to enhanced depth effect vibration.

To control, optimise and document compaction, BOMAG developed the ASPHALT MANAGER. A system that in automatic mode monitors compaction progress and adjusts compaction performance many times a second - no adjustments must be made by the driver. This eliminates drum bounce and operator error.

ASPHALT MANAGER requires no special user-training as the control panel is self-explanatory. During compaction the dynamic energy lead into the pavement is optimally and continuously adapted to the actual conditions. Grain damages and disturbances of the asphalt layer are effectively prevented. The system automatically limits compaction power where there is a risk of over-compaction.

At the same time asphalt mix stiffness and compaction progress, surface temperature, travel speed, exciter frequency and selected amplitude are continuously displayed to the roller operator and can be printed out on-site using the data recorder. Due to this adaptability and continuous control and optimisation, rollers with ASPHALT MANAGER are highly suitable for the complete spectrum of asphalt applications.

Drivers can also select a manual mode. This can be the case for the compaction of layers on bridges or pavements close to buildings, where low-vibration compaction might be recommended. But for up to 90 percent of all applications drivers are using the automatic mode.

Asphalt is the 'royal league' of compaction where quality depends on a huge variety of factors. Modern intelligent compaction vastly improves quality. 

Hans-Josef Kloubert, Civil Engineer (P.E.), IS Head of Application Technology at BOMAG. He has previously worked as a Geotechnical/Project Management engineer. For the past 20 years he has been BOMAG's application expert in soil and asphalt compaction and compaction measurement and is deeply involved in the development of new technologies.