Measuring technology and accurate documentation – the key factor for success in future road building

Tomorrow’s tasks for future high-tech road building become more and more demanding – especially in the field of automatic compaction, compaction control, measurement and complete documentation. BOMAG, the world market leader in compaction technology, is the only manufacturer with the capability of presenting results using the EVIB format based on a physical value which records material stiffness in MN/sq m , allowing the contractor to monitor the compaction of all layers from subsoil to asphalt, based on the same reference value. More than 30 percent of all worldwide sold BOMAG heavy tandem rollers for example are today equipped with ASPHALT MANAGER, a system for automatic optimisation of compaction performance. Like no other system in the industry, ASPHALT MANAGER is able to optimise the whole compaction process in terms of performance and quality. Since 2007 BOMAG has launched a combination of BOMAG measuring technology and GPS for compaction control on earthworks and asphalt materials. Documentation is possible with GPS using a reference service or a reference station and is also available if GPS cannot be used, e.g. according to a defined rolling pattern.

For years now, measuring technology is synonymous with efficiency and quality control in compaction and has proven itself on innumerable construction sites and large-scale projects. Compaction control, exact measuring of compaction progress, and a complete, reliable documentation are today indispensable for state of the art road building. The BOMAG measuring and documentation system detects and logs not only the stiffness; it also controls the compaction process and documents compaction progress, the number of passes, the amplitude, the frequency and the working speed, as well as asphalt compaction and asphalt temperature. Documentation is via the proven BOMAG Compaction Management System BCM 05. The EVIB value is the only measured value based on MN/sq m which offers reliable compaction control as a physical value for all soil-based and asphalt-based applications. This provides a huge advantage to the contractor as he can monitor the compaction of all layers from subsoil to asphalt, based on the same reference value – comprehensive and consistent documentation for the entire project.

State-of-the-art rollers from BOMAG are equipped with an automatic compaction control system – ASPHALT MANAGER, single drum rollers are equipped with VARIOCONTROL. This means that the drivers can see key compaction data on a display screen and no longer have to rely on guesswork. Unnecessary passes are avoided, saving money. With each pass, the driver sees a surface picture of the site and the level of compaction achieved. The Evib value in MN/sq m is continuously calculated and indicates the achieved level of stiffness. Both, ASPHALT MANAGER and VARIOCONTROL regulate the compaction force automatically suited to the bearing capacity of the subbase. Drivers use the automatic mode for approximately 90% of all applications, but a manual set for sensitive jobs is at every time possible.

Case study: bridge building – a sensitive task
A masterpiece in road surfacing has been achieved on the A 38 near Leipzig. This is where a bridge for the new motorway crosses the "Weiße Elster" River and a rail track. About 3,000 sq m of road surface made from stone mastic asphalt had to be laid along a length of bridge measuring 293 m between the end bearing supports and with a width of 29.5 m measured between the railings. The company contracted to carry out the construction work, Arlt GmbH from Frankenhain, used three BOMAG BW 174s for this job. They were equipped with ASPHALT MANAGER and the precision spreader BS 180. After four hours, the work which was carried out using a “hot on hot” procedure was finished. That would not have been extraordinary on a normal road surface, but there are special working conditions on a bridge because it rests on flexible bearing supports. If you work with a smooth drum and conventional vibration technology, this causes the flexibly supported bridge to absorb the vibration and the specified compaction cannot be achieved. In any case, dynamic compaction is more efficient than static working of the mix. The ASPHALT MANAGER system was set with minimum vibration load. The test results showed that the required level of quality was definitely been achieved.

The employees from Arlt, the company contracted for this work, are not just specialists in road surfacing. The company was founded in 1991 and now has 130 employees. Arlt is active in bridge building and foundation work. It also carries out earthworks – especially for bridges. Since the beginning of 2002, the company has specialized in maintenance of bridges. Of course, bridge structures also use other designs. "We decided on machines from BOMAG right from the start. Altogether, we have eight BOMAG machines amongst our fleet of equipment. This includes tandem rollers with ASPHALT MANAGER, single drum rollers with smooth drums, polygonal and padfoot drums and VARIOCONTROL as well as one milling machine", says Kerstin Arlt, who together with her husband is associate and managing director of Arlt GmbH.

Case Study: monitoring temperature for improved compaction
Compaction of porous asphalt with the ASPHALT MANAGER
Compaction control and effective measuring technology, even if automatic vibration is not used, gets particularly important when meeting special demands like the laying of porous asphalt for noise protection as the progress of work, the temperature of the asphalt and the status of the compaction needs constant evaluation.

Porous asphalt was laid for noise protection on the six-lane widening of the major BAB A9 road between the Schnaittach junction and the Nürnberg intersection. To ensure this sensitive surface was laid within the specified time, Max Bögl Bauunternehmung GmbH & Co. KG used tandem vibratory rollers exclusively from BOMAG. As in the previous year between Schnaittach and Lauf, four pivot steered BW 174 AD rollers with ASPHALT MANAGER, a pivot steered BW 184 AD and a BW 164 AD produced the necessary compaction levels when recently laying 100,000 m² of porous asphalt for the A 9 / D 366 R lot from the Lauf/Hersbruck junction to the Nürnberg motorway intersection over a length of 6.71 km.

Open-texture asphalt surface layers have an air-void-content of between 20% and 28 % which gives them a noise absorbing capability of at least 5 dB(A) over many years. This asphalt also prevents aquaplaning and road spray due to its ability to drain off water. After around ten years the asphalt on the BAB A9 between Schnaittach and Nürnberg had reached the end of its design life.

In the tender for the Motorway to Northern Bavaria, reference is made to the "Merkblatt für den Bau offenporiger Asphaltdeckschichten" (bulletin of practice for porous asphalt surface layers), 1998 edition published by the Forschungsgesellschaft für Straßen- und Verkehrswesen (Road and Transportation Research Association) and the Guidance Notes Asphalt – StB 01. This means that the porous asphalt has to be laid hot on hot across the full mat width and the pavers are not permitted to stop after laying commences. Compaction may only be carried out with heavy smooth drum rollers without vibration. The relatively low laying temperature and the rapid cooling of the layer requires a large number of rollers and ongoing checking of temperature. If laid too hot, the structure of the asphalt changes and density achieved will be too high. The material then looses its efficiency as the open structure is destroyed and both the drainage and noise absorbing effects are lost.
The contract specification required that: "Rollers with temperature measuring sensors must be used to communicate the road surface temperature to the roller driver. The number of roller passes must be determined on a test area.  The optimum rolling pattern must be submitted to the client before compaction of the surface material." For the roller driver this means operating strictly in accordance with the temperature measurements and keeping an exact distance between compaction equipment and paver. The temperature display in the BOMAG BW 174 AD with ASPHALT MANAGER is extremely important in this respect. Based on the tests carried out before compaction, as laid down in the specification, the optimum rolling temperature and the number of passes were determined and this method was applied on site. The temperature window for compacting this asphalt with a thickness of 4.5 cm is between 130 and 160 degrees Celsius depending on the viscosity of the binder. Using the temperature display in the cab of the BOMAG BW 174 AD tandem vibratory roller, the driver can observe the surface temperature of the asphalt layer and react during rolling. He can determine the best reversing point to return towards the paver; and near to the paver he can see if the start temperature for compaction is right.

The relatively high operating weight of the heavy BOMAG tandem vibratory rollers, weighing in at around 10 and 13 tonnes, ensures efficient static compaction of the layer, where the large drum diameter is also of benefit – 1,220 mm on the BW 174 AD and 1,400 mm on the BW 184 AD. Also, the driver benefits from the comfort and ease with which the roller is operated. These models can be used effectively after a short introduction to the control systems. And they appreciate the uniform results: "The BOMAG BW 174 AD with ASPHALT MANAGER is the perfect roller for us. We can evaluate the progress of work and the compaction changes after each pass, and react straight away." The option of automatic compaction is not being used on the current BAB A9 job because compaction is static, i.e. without vibration due to the material, but the continuous measurement of temperature is essential. The site management was particularly pleased with the reliability of the rollers and the economic fuel consumption. "We have to be able to rely totally on the rollers with such a tight time schedule and cost framework," says foreman Willi Bogner and Site Manager Ludwig Dotzer from the contractor Max Bögl Bauunternehmung; and the completion of this contract in just five days shows once again that they were right.

Reliable measuring technology, most accurate documentation and flexible usage – the combination of measuring technology and GPS
Compaction control with ASPHALT MANAGER or VARIOCONTROL and documentation via the BCM 05 measuring system is only one of the examples for modern high-tech compaction and road building. Since 2007, BOMAG made the BCM 05 positioning software module available for comprehensive GPS supported documentation on all tandem rollers with ASPHALT MANAGER, on single drum rollers with VARIOCONTROL and on all 4th generation single drum rollers. The BOMAG software interfaces with all conventional DGPS systems with and without reference station. Positioning precision depends on the GPS system chosen by the contractor. The raw data supplied by the system can then be transformed into on-site coordinates using the BCM 05 positioning software and are documented along with the BCM 05 measured data.

All decisive variables for compaction are thereby recorded and can be displayed individually or combined on the BCM 05 display as a multi-coloured map to aid the roller driver. The system works fully automatically; manual, track-bound entry of positioning data is no longer necessary. However, if the reference satellites required for the GPS are not available, compaction control and documentation of track-bound work can continue and position data can be entered manually.

As a DGPS solution, BOMAG uses the compact and fast Starfire iTC system which is simple to assemble and works with a satellite supported reference service with accuracy down to at least 20 cm. A reference station is not required with this system. However, the BCM 05 positioning software can also be combined with all other conventional DGPS systems and with systems with reference station. Thus,  BOMAG is offering the most comprehensive, accurate, flexible and reliable system for GPS supported compaction control and documentation on the market, apt to solve also tomorrows more and more demanding tasks for high-tech and reliable road building.

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The advantage with the BOMAG BW 174 AD with ASPHALT MANAGER: the roller driver can operate by following the temperature measurement displayed in the cab and can maintain a precise distance between the roller and the paver when compacting porous asphalt. Download

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Size is everything with these BOMAG tandem rollers: drum diameters of 1,400 mm and 1,200 mm, plus heavy operating weight. Reliable performance on sensitive surfaces e.g. rolling porous asphalt on the BAB A9 between Lauf und Nürnberg. Download

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The BOMAG BW 174 AD with ASPHALT MANAGER gives optimum compaction on porous asphalt with temperature measurement on-the-run. Download