Why does the road paving take so long
Test for comprehensive compaction control
But can this be used to demonstrate even, homogeneous compaction over the entire area? A roller test should answer this question. Four leading roller manufacturers wanted to know and sent their road construction equipment into the race. Caterpillar and its sales and service partner Zeppelin also faced a major roller test, accompanied by the University of Siegen, Faculty IV, Department of Civil Engineering, represented by the Institute for Roads.
5 km long test track
The initiative for this was provided by the Research Association for Roads and Transport (FGSV) and the working group 7.4.1. FDVK A, i.e. comprehensive compaction control asphalt, as well as the Federal Highway Research Institute (BASt). The State Office for Mobility (LBM) Rhineland-Palatinate provided the approximately five-kilometer test route on the B10 near Pirmasens. The tender for the measure was also specially tailored to the research project.
Three Cat CD 54B rollers on a one-kilometer section were intended to demonstrate how evenly homogeneous compaction can be achieved on the B10 near Pirmasens between the Waldfriedhof junction and the Münchweiler exit using electronic recording systems and how precisely the graphic evaluation of the area-wide compaction control is carried out .
The aim of the research project: to increase the quality of road construction and thus achieve a longer service life for the paved asphalt mix. So far, ruts or subsidence in the asphalt appear after a short time with uncompacted asphalt layers, although Germany has a high level of know-how in road construction. The nation of motorists themselves has correspondingly high demands on the construction of roadways, in particular on the surface layers, which should be even, low-wear, resistant to deformation, quiet and particularly easy to grip.
“For us, the test is a good opportunity to show what Cat road construction rollers can do and how they can deliver the compaction performance demanded by the market. What Cat machines do in earthmoving is known around the world. We don't shy away from comparisons with other providers and want to take a clear position in road construction, ”explains Staale Hansen, who heads product management for road construction equipment at Zeppelin.
Extensive test program
Each roller manufacturer had to take part in the scientifically supported test twice: First, the task was to compact an eight-centimeter thick asphalt binder layer over a length of one kilometer on the 7.5 m wide roadway. Then, in a second work step, a layer of stone mastic asphalt was paved with the paver and finally compacted to a thickness of four centimeters. The Juchem Group produced and delivered 1,500 t of asphalt for the binder course and 750 t of asphalt for the surface course every day in its asphalt mixing plant in Landau, directly on the B10, almost 30 kilometers from the installation site. The Juchem group of companies used up to 24 articulated trucks.
Adhere to the rolling scheme
A clear requirement was: Development and adherence to a rolling scheme. The paver set the pace: when paving the binder course it was 2.5 meters per minute - for the surface course it was 3.5 meters per minute. "What is important is a disciplined operator at the paver who ensures constant speed and makes sure that the paver does not stop or progress too quickly because he thinks the truck convoy with the hot asphalt is waiting too long," says Dr. Hermann Heppenheimer.
But not only the speed of the paver is decisive, but also that of the rollers. The drivers should adhere to the developed rolling pattern consisting of rolling speed, rolling track length as well as the sequence and number of passes. In order to obtain uniform reference values to which the other roller applications can be related, the company carried out the first kilometer of construction with its own road construction equipment.
The drivers were told to drive as they normally would. Before taking a seat in the Cat CD 54B roller, they received a briefing from Uli Schmelzeisen, Zeppelin product manager for road construction equipment, and Ronald Utterodt, specialist in the road construction segment at Caterpillar. Zeppelin and Caterpillar provided three CD 54B rollers and the required replacement device. The compaction measurement technology from Trimble and Völkel Microelektronik was installed. The drivers should also be able to see where they had to steer their roller in order to achieve uniform compaction over the entire area. Unfortunately, practice shows time and again that small areas are overlooked during compression, other areas are compressed too much and there is not always a complete, area-wide compression, as it should actually be the benchmark. The daily form and motivation of the roller operator can determine how consistently and well this succeeds.
“The rolling work is very tiring. At some point, the concentration drops. That's why electronic systems should support the driver, ”says Uli Schmelzeisen. Sensors were installed in the drums and GPS receivers on the cabin, which recorded the compaction values and the position of the roller and transmitted them to the cabin. In order to make work easier for the drivers, the travel paths of the roller, including the sections that have already been compacted and the areas that have not yet been processed, were displayed in color on the Trimble and Völkel monitors. “This means that the drivers have an aid at hand and know how many transitions they have already made. Even professional roller drivers who have a good feel for which areas they have compacted can now see exactly where they still have to do compaction work with the roller. You thus have a control over the work you have done. The display is easy to use and clear.
Ultimately, the system should optimize machine use and help to work with fewer devices and with less fuel, ”says Norbert Mattivi from Trimble, describing the advantages of the system. The data determined are documented, can be called up on the PC at any time and are therefore not only available to the drivers, but also to the clients as evidence and for evaluation at any time. The surface temperature, which was also displayed graphically on the monitors, was also measured. The driver can adjust his rolling work accordingly. He knows where he is in the compression-favorable area and the minimum temperature allowed for vibration has not yet fallen below. Due to the binder used here, dynamic compaction is possible in a temperature range between 110 and 140 degrees Celsius. Below these temperatures, only static compaction is permitted in order to avoid binder breakage and grain fragmentation.
"You get used to the electronic system for comprehensive compaction control very quickly," says Andreas Fellenzer, the driver of the first Cat roller. However, it was good that we got a briefing every day. Because we had to adjust to a different roller and a different system every time. Even experienced people work up a sweat. All in all, it can be said: The Cat roller offers a good overview, plenty of space, precise control and is quiet, ”said Fellenzer about his first impression of the use of the Cat CD 54B roller. This is not least due to the fact that the control unit can be rotated 360 degrees and can also slide out sideways by up to ten centimeters over the cabin edge in order to have a good view of the drum edge and the edge pressure device.
“The question is always how much information does the driver need in order to achieve even compaction over an area? The roller test should also provide an answer to this ”, says Micha Tobias Buch, graduate civil engineer and research assistant from the University of Siegen. However, this always depends heavily on the roller operator - one demands more, the other less information.
The final evaluation will provide more precise information. For this purpose, six drill cores were drawn and mix samples were taken at two different points on each section of the route. The results achieved by the Cat rollers were checked using the radiometric compaction measurement - a so-called Troxler thin-film probe was used for this purpose.
Gamma emitters are often used to determine the density of the paved asphalt. The probe is placed on the material to be examined. The radiation source emits radiation that is weakened and scattered by the material. With the help of the integrated counter tube, these differences can be determined and conclusions can be drawn about the density of the material. The evaluation runs fully automatically in the device.
“Ultimately, the efficiency of the rolling work - even when using modern information systems - depends directly on the work preparation of the entire construction site. The best system fails when the installation is uneven. And it is precisely here that the contracting company Juchem has impressively demonstrated that paving can be carried out almost without interruption and with very even mix temperatures, ”says Ronald Utterodt. Particular emphasis was placed on the uniformity of the material flows, which was achieved by using a feeder in combination with a large-volume paver setting bucket. In addition, there was a good coordination of the material flow from the slatted frame to the side delimitation plates of the screed as well as low and rotating material levels between the metering plates and the front walls of the screed extension parts. The screw conveyors also turned slowly and evenly, so that overall installation was carried out like something out of the textbook. In this way, the construction company created the prerequisites for the roller compaction to be built on good starting conditions and for the research project to be successful. The University of Siegen, Faculty IV, Department of Civil Engineering, represented by the Institute for Roads, will present a first interim report to the Federal Roads Institute at the end of October. A final evaluation of all results should be ready by August 2014.
The basic prerequisite for obtaining comparable and objective measurement results are uniform test conditions. This research project, which the scientists at the University of Siegen under the direction of Professor Ulf Zander from the Institute for Road Construction Technology, is carrying out and evaluating on behalf of the BASt, also has this claim. “The installation conditions were favorable. We are paving a standard mix here - as it is usually used in practice and we deliberately do not have any special features with regard to binding agents or the paving thickness, ”says Dr. Hermann Heppenheimer, responsible for asphalt production and quality management of the Juchem group of companies. "After all, it was a matter of working out the differences in the rolling work."
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