On the still quiet tourist island of Lombok, work on the Mandalika International Street Circuit is in full swing. After completion, the circuit will be one of the most exciting tracks in the motorsport world. The first street circuit in motorbike racing since 1977 is set to host the Indonesian grand prix next year. As many as 150,000 visitors are expected on any given racing weekend. The new track was designed by Bahraini company MR1 Consulting – not as a permanent race track but as a road course that will only be closed to public traffic on racing weekends. The track surface has to meet the highest standards, as it is crucial for the motorbikes' grip and tyre wear.
The loads exerted on the asphalt during a race are tremendous. In the premium motorbike class today, top speeds of over 360 km/h are reached. At such high speeds, overpressure is generated in front of the tyre and underpressure behind it. The heated tyres develop an adhesive effect that pulls the material upwards. Hermann Tilke, a German civil engineer and well known for developing many race tracks, once explained in a Motorsport-Total article: “For the asphalt, it's like hitting it with a hammer at the front while using a vacuum cleaner at the back.”
The contractor opted for BOMAG machines for the paving and compaction of the asphalt for the entire track, the verges, run-off zones and service roads. The greatest challenge: the track must continue to meet all future demands, so the asphalt must be geared to durability. Even if the track is used by everyday traffic 350 days a year, it still has to subsequently withstand the extremely high speeds of racing motorbikes.
Even the slightest unevenness results in less grip, potentially increasing the risk of accidents. To fulfil all the specifications, the optimum paver settings for evenness, degree of compaction and surface texture were first determined on a test section. In Mandalika, for example, a surface evenness of +/- 5 mm was required for the bearing and binder course (measured over a distance of 4 metres). The tolerance for the wearing course was even lower at +/- 3 mm. The local paving team was supported throughout the project by BOMAG Singapore's service team and experts from PT United Tractors Tbk provides support. Based in the capital Jakarta, the company has a reputation as one of the leading heavy machinery dealers in Indonesia. It offers a wide range of services, including spare parts sales and technical support.
Two BOMAG BF 800 C pavers were used to install the bearing course. With their combination of high productivity and flexibility, these all-rounders are the perfect choice for both high-quality and efficient road construction. Equipped with innovative BOMAG assistance systems and options, they greatly simplify the job for the operator and the entire paving team – for example, with all-weather protection that protects the machine operator not only in the rain, but also in intense sunshine, or by the use of technologies such as BOMAG ECOMODE, an intelligent control system that keeps the engines in the optimum range at all times, thus reducing fuel consumption and noise levels.
Although the system was not part of the specification requirements, the pavers used in Mandalika were equipped with components for 3D levelling. This system eliminates the need for stringline tensioning, which is costly and time-consuming to set up. Instead, the machine's three-dimensional position is measured with a total station. One side of the screed is then controlled in 3D in position and height; the height of the other side of the screed is determined by the cross slope, which is also specified in the project data. The use of 3D control systems offers great advantages, especially when paving banked curves. They allow the designs of the track layout to be implemented with exceptional precision. The highly accurate paving makes the surface especially even and optimises – i.e. reduces – material consumption. And where there is no stringline tensioning, it cannot cause any interference or inaccuracy. Yet another factor that increases the paving quality and operational safety while speeding up completion. 3D measuring and levelling systems are flexible in their use and compatible with all BOMAG high-performance screeds.
To reduce the number of longitudinal joints, the client decided to use only two pavers side by side during paving instead of the usual three. To achieve this, two screed extensions of 750 mm each were used per paver, giving each a maximum working width of 9 m. Extending the screed was a cinch with BOMAG's QUICK COUPLING system as it enables short and safe set-up times without time-consuming bolting. Furthermore, BOMAG pavers are equipped with heavy-duty screeds and extra-long screed plates. Features that also ensured excellent pre-compaction and particularly even paving.
Analogue to phase 1, a 2-paver configuration was used in this phase. A third paver was deployed to pave the wide curves as well as to establish the connection to the pit lane. One of the biggest challenges, however, were two sharp bends in the track layout. This section required detailed planning to ensure continuous asphalt paving without interruption. Here, too, paving was no problem for the two BF 800 C pavers as they offer an optimal view of the machine’s edge, hopper, auger and screed. The control panel and seat form an adjustable unit. All switches are arranged logically and ergonomically. This allows the operator to concentrate on what really counts: continuous, smooth asphalt paving.
The surface course consists of stone mastic asphalt (SMA mix) with polymer-modified bitumen. It was paved in five segments to minimize the amount of the transverse joints. The sections were also defined precisely in order to meet the aesthetic requirements of the track. A 3-paver configuration was used for this phase. It took five days to complete the whole surface course. Thanks to the "hot-on-hot" paving method and the use of three pavers, the longitudinal joints are invisible.
High temperatures are the secret to success in the paving process. BOMAG pavers are equipped with BOMAG MAGMALIFE technology. All the heating rods are cast in an aluminium block. Aluminium's outstanding thermal conductivity enables significantly shorter heat-up times and thus faster operational readiness of the pavers and their crews. Another advantage of MAGMALIFE is the extremely even heat distribution.
In phase one and two, the asphalt was compacted with BOMAG BW 161 AD-4 articulated tandem rollers and BW 24 RH pneumatic tyred rollers. During the first two passes, the tandem rollers were used directly behind the pavers for static compaction. Next came two low-amplitude passes. Then it was the turn of the pneumatic tyred rollers.
For the compaction of the surface course tandem rollers were used only. This was due to the mix and to achieve the surface as required. These rollers ensured an optimum surface quality and the required degree of compaction of at least 98%.
Thanks to the rollers' BOMAG ECONOMIZER technology, there were no unnecessary passes. The system shows the degree of compaction on a display, enabling the operator to achieve the best compaction results. The test lab measured values of 98.9% (left-hand side of the track), 99.2% (centre of the track) and 99.1% (right-hand side of the track) for the degree of compaction of the binder course. An impressive result.
The Mandalika International Street Circuit is now ready for its first races in front of a great audience.