Wireless Control Guarantees Maximum Precision

Wirtgen GmbH

The Airbus A380 will land at Amsterdam's International Airport Schiphol on a regular basis very soon. Dutch contractor Reef Infra B.V. built the new, suitably large and stable parking and traffic for the big airplane, using a Wirtgen slipform paver SP 1600.

Reef Infra B.V. did not use stringlines for levelling, but relied instead on the numerous benefits offered by wireless control.

Altogether, the SP 1600 placed a total of 31 500 m3 of B 55 grade concrete for the new parking areas. During the second construction phase in spring 2007, a total surface of 27 000 m2 was built in just 5 days: 6 sections of 450 m length, 10 m width and 42 cm thickness each, corresponding to a paving volume of some 2000 m3 per day. The Wirtgen slipform paver worked non-stop.

The XXL-size aircraft has a maximum takeoff weight of 560 t, which is higher than that of any other civil aircraft. To account for these high loads, the SP 1600 was equipped with a dowel bar inserter which reinforced the concrete by inserting dowel bars with a diameter of 45 mm at 5 m intervals. The paver's central tie bar inserter inserted longitudinal tie bars to reinforce the concrete across the paving direction. The slipform paver was additionally equipped with a heavy-duty oscillating beam and super smoother to ensure good surface evenness. A well-rehearsed team followed behind the slipform paver, applying a special manual broom finish and spraying a dispersion to prevent the concrete from drying out.

Reliable technology requires less personnel
The well-organized crew from Reef Infra B.V. needed a surprisingly small number of personnel for the many different jobs to be carried out. In addition to the site manager and truck drivers responsible for transporting the concrete, no more than 2 machine operators, 6 concrete workers and 2 crew members taking care of the wireless control system worked in the immediate vicinity of the Wirtgen slipform paver. Product manager Willem Verstraaten relies on the high performance capability of the Wirtgen machines, "Their high degree of automation and reliable engineering allow us to reduce the number of personnel to a minimum." At the same time, the client had set the bar high, allowing a maximum tolerance of 5 mm over a length of 3 m in both longitudinal and transverse direction.

Excellent machine engineering combined with a highly mature machine control system that furnishes all signals for steering and height adjustment enable the slipform paver to achieve such a high degree of precision. In this project, the specifications for cross-section, line and level of the concrete pavement were not fed into the machine's control system by scanning a stringline, however, but via the computer of the wireless 3D levelling system. This 3D controller made by Leica Geosystems uses a special interface to communicate with the SP 1600's standard levelling and steering controller.

An increasing number of Wirtgen customers have meanwhile discovered the benefits of this system. Road and railway construction companies have praise, in particular, for the drastic reduction of error sources, decrease in set-up times, improved safety and integrated documentation.

Two prisms are installed on the slipform paver, each of which has direct visual contact to a total station. The total station establishes the position of the prism at a frequency of 10 Hz. The measured results are then transmitted by radio to the system's computer on the paver. Two multi-axial slope sensors integrated in the machine additionally determine the paver's longitudinal and cross slope. The system computer uses these data to calculate the machine's actual position and direction of travel. The position data are compared with the design data previously stored in the system's computer as a digital model. Any deviation is forwarded by the system computer to the SPS of the slipform paver within the fraction of a second. The SPS then initiates the required corrections in level, inclination and steering angle of the crawler tracks. The resulting concrete cross-sections meet the specified requirements with pinpoint accuracy. Processing the data in the system computer also enables a complete documentation to be generated of the paving operation.

Fast, safe and accurate
Concrete paving without using stringlines saves on installation and removing time. Drivers of transport trucks and mixer trucks do not need not pay attention to tensioned stringlines and can drive up to the paver straight away. The system also provides increased safety for the crew working on site, as the wireless system eliminates the hazard of stumbling over the stringlines.

Touching the stringlines may alter their surveyed position, resulting in an incorrect position of the paved concrete layer. This is particularly critical, because damages to the stringlines or an alteration of their position are not necessarily visible to the naked eye. This cause of sometimes serious mistakes is eliminated completely when using the wireless control system.

Civil engineer Willem Verstraaten is highly satisfied with the SP 1600 and its wireless control system. "Here at Schiphol, we would have had to install the stringlines in the very hard subgrade. That would have involved an extremely high effort. The wireless control system allowed us to save both the time and the costs. And the result meets all our expectations: It's perfect."

Schiphol is situated at an average altitude of some 3 m below sea level, making it the lowest-level airport in Europe. In earlier years, the polder in which the airport lies was a large lake, and countless ships went down in its waters. The airport's name refers to the history of its location, as "Schiphol" means as much as "ships' hell". With 46 million passengers and 1,5 million t of airfreight in 2006, Amsterdam's Schiphol Airport is Number 4 in Europe.

Source: Wirtgen Group