High-tech road building: new technology wins cost and energy savings

By BOMAG

Specifications for high-tech road building are becoming increasingly sophisticated – especially in the field of automatic compaction, compaction control, measurement and total documentation. Faced with the challenges of lower government spending, higher energy costs and tougher environmental protection, contractors need to be sure about the efficiency of their plant and the quality of their output. The avoidance of premature road failure due to insufficient compaction and the implementation of lower-cost compaction process are twin goals where intelligent technology is becoming indispensable.

For years, measuring technology has been synonymous with efficiency and quality control in compaction and has proven itself on innumerable construction sites and large-scale projects. BOMAG’s measuring and documentation system not only optimises the compaction process and documents results, number of passes, amplitude, frequency and working speed, but even detects and stores material stiffness values.

Documentation is handled via the well-proven BOMAG BCM 05 Compaction Management System. The E VIB value is the only measured value based on MN/m 2 which offers reliable compaction control as a physical value for all soil-based and most asphalt-based applications. This produces a significant advantage for the contractor as he can monitor the compaction of all layers from subbase to asphalt, using the same measurement value – comprehensive and consistent documentation for the entire project.

State-of-the-art BOMAG rollers can be equipped with an automatic compaction control system – ASPHALT MANAGER, single drum rollers can be equipped with VARIOCONTROL. These systems allow drivers to see key compaction data on a display screen – thus dispensing with guesswork. Unnecessary passes are avoided, saving time, money and protecting the environment. With each pass, the driver sees a surface picture of the site and the level of compaction achieved. The E VIB value in MN/m² is continuously calculated and indicates the achieved level of stiffness. Both ASPHALT MANAGER and VARIOCONTROL regulate the compaction force to the load bearing capacity of the sub-base. Drivers use automatic mode for approximately 90% of all applications, but a manual setting for jobs in a sensitive environment, e.g. close to buildings or on bridges, is always available

Job report: Bridge deck surfacing – sensitive work
Something of a masterpiece in road surfacing has been created 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 3,000m² of stone mastic asphalt road surfacing was laid along a bridge deck measuring 293m between the end bearing supports and with a width of 29.5m measured between the side railings. The contractor for the work, Arlt GmbH from Frankenhain, used three BOMAG BW 174s on this job, each one equipped with ASPHALT MANAGER and BS 180 precision chip spreaders. After four hours the work, carried out using the “hot on hot” method, was completed. Nothing extraordinary on normal road surfacing, maybe, but there are special working constraints on bridge-work because of the flexible bearing supports. If the contactor uses a smooth drum roller and conventional vibration technology the flexible bridge deck absorbs the vibration and specified compaction cannot be achieved. In any case, dynamic compaction is more efficient than static compaction of the mix. The ASPHALT MANAGER system was set to deliver minimum vibration loads. Test results showed that the required quality had consistently been achieved.

Arlt, the company contracted for this work, is not just a specialist 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 the maintenance of bridges. "We decided on BOMAG machines right from the start. Altogether, we have eight BOMAG units amongst our plant fleet. This includes tandem rollers with ASPHALT MANAGER, single drum rollers with smooth drums, polygonal and padfoot drums and VARIOCONTROL – plus one milling machine", says Kerstin Arlt, who together with her husband is Associate Managing Director of Arlt GmbH.

Job report: monitoring temperature for improved compaction – compacting porous asphalt with ASPHALT MANAGER
Compaction control and effective measuring technology, even if automatic vibration is not used, is particularly important to meet specifications like the laying of porous asphalt for noise protection. Here, the progress of work, the temperature of the asphalt and the status of the compaction needs constant checking.

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 to within the specified time, Max Bögl Bauunternehmung GmbH & Co. KG used tandem vibratory rollers exclusively from BOMAG. As was the case 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 specified compaction on 100,000m² of porous asphalt for the A 9 / D 366 R section from the Lauf/Hersbruck junction to the Nürnberg motorway intersection – a length of 6.71km.

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 was made to the "Merkblatt für den Bau offenporiger Asphaltdeckschichten" (Guidance Notes 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. Accordingly, the porous asphalt was to be laid hot on hot across the full mat width – the pavers not being permitted to stop after laying commenced. Compaction was only to be carried out with heavy smooth drum rollers with no vibration. The relatively low laying temperature and the rapid cooling of the layer required a large number of rollers and frequent temperature checks. If laid too hot, the structure of the asphalt changes and the density produced becomes too high. The material then looses its efficiency as the open structure is lost and both the drainage and noise absorbing effects are nullified.

The contract specification required that: "Rollers with temperature measuring sensors are to be used to communicate the road surface temperature to the roller driver. The number of roller passes is to be determined on a test area. The optimum rolling pattern is to 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 achieving this. Based on the pre-compaction tests, compaction level, 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 at 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 BOMAG BW 174 AD cab the driver can watch the surface temperature and react during rolling. He can decide the best reversing point to return back to the paver; and close up 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, gives efficient static compaction – and the large drum diameter is also of benefit – 1,220mm on the BW 174 AD and 1,400mm on the BW 184 AD. Also the driver benefits from the comfort and ease with which the roller can be operated. For new operators these models can be used effectively after a short introduction to the control systems. And drivers appreciate the uniform results: "The BOMAG BW 174 AD with ASPHALT MANAGER is the perfect roller for us. We can evaluate results and the compaction changes after each pass, and react straight away." The option of automatic compaction is not used on the current BAB A9 job because compaction is carried out in static mode due to the material type, but continuous measurement of temperature is essential. The site management was particularly impressed with the reliability of the rollers and the low fuel consumption. "We have to be able to rely totally on our rollers, having such a tight time schedule and cost framework," says foreman Willi Bogner and Site Manager Ludwig Dotzer from contractor Max Bögl Bauunternehmung. The completion of this contract in just five days shows once again that they were right.

Reliable measuring technology, highly accurate documentation and flexible use – that’s measuring technology and GPS combined
Compaction control using 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 has 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 stations. Positioning precision depends on the GPS system chosen by the contractor. The raw data supplied by the system is then transformed into on-site coordinates using the BCM 05 positioning software and are documented along with the BCM 05 results.

Key variables for compaction are recorded and can be displayed individually or combined on the BCM 05 display as a multi-coloured map to support the roller driver. The system is fully automated: manual, track-bound entry of positioning data is no longer necessary. However, if the GPS reference satellites 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 install and works with a satellite supported reference service with an accuracy down to at least 20cm. 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 including systems with reference stations. BOMAG offers the most comprehensive, accurate, flexible and reliable system for GPS supported compaction control and documentation on the market, capable of handling increasingly demanding specifications for high-tech and long-life road construction projects.