Innovative. The word is often used in everyday life – most often too quickly. Truly innovative is only whoever drives technical, social and economic change; who does pioneering work. In connection with Implenia Schweiz AG, the term is used rightly so- especially in the context of their work with the new ultra high performance concrete (UHPC). Simplified, the material UHPC can to be understood as an advancement of conventional concrete, but in comparison it has a four to five times higher compressive strength (approx. 150N / mm²) and a tenfold bending strength (approx. 45N / mm²), which leads to a considerably longer life of all civil works. Time savings resulting from a quick installation are another big benefit. These claims are not based on theoretical tests in the laboratory, but have proven to be true in the implementation of real construction projects. The Implenia Schweiz AG has developed its own version of UHPC over eight months and has already installed 2,400 m³ or 30,000 m² with a GOMACO concrete slipform paver. Together with the BODO Int. GmbH & Co. KG they did pioneering work by developing a special mold solely for the purpose of installing UHPC. UHPC is particularly promising for bridge repairs, such as the Küssnacht - Brunnen project presented later on. This project can prove that the use of UHPC is practical, efficient and promising.
The work with the GOMACO – concrete paver is teamwork: everything has to be well coordinated.
Conventional concrete already has advantages in direct comparison to asphalt paving, such as a significantly greater longevity and durability of the roads. Areas of application include logistic centers, heavily used traffic areas, water gutters and various prefabricated components. But due to a high, constantly increasing strain, e.g. due to heavy-duty traffic, repairs to traditional concrete or asphalt structures arise faster and more frequent than in the past. This is where the advantages of UHPC come into play, because according to Daniel Hardegger, the head of special projects at Implenia Schweiz AG, UHPC significantly extends the lifespan of buildings while life cycle costs are minimized. The reason why UHPC is particularly suitable for highly stressed components is due to its composition. There is no gravel in it, but three times as much cement as conventionally, plus fine sand, steel fibers and micro-silicates. This means that the consistency of UHPC is firmer than concrete, can be installed thinner, dries faster and is therefore more weather-independent during installation. After 48-72 hours, the strength that conventional concrete exhibits after 28 days is reached. The effort and, above all, the economic restrictions that a construction site brings with it are enormously reduced with UHPC, as clients save six to eight weeks of construction time!
Other advantages of UHPC are particularly evident in structures such as bridges that are exposed to strong environmental influences. Bridges weak points are known: the concrete becomes cracked, water penetrates and moistens the concrete. As a result, stress corrosion occurs. In the past, such porous bridges were usually torn down and rebuilt, because repairing concrete bridges is very time-consuming. After the old layer has been removed, work must be carried out in several layers. On average 7-8 layers are required, e.g. primer, mortar, surface seal, waterproofing, where the latter in particular is being discussed in relation to environmental issues. UHPC has the power to change this as its properties eliminate the need for a lot of these costly work steps. The building material is acid, sulfate and frost resistant as well as vapor tight and therefore corrosion-inhibiting. UHPC has a sealing function against salt water and serves as a protective layer for a concrete structure. This means that only the old layer of a porous bridge has to be removed and a new thin layer is applied, which takes over all static and sealing functions with low weight. This leads to enormous time savings and makes the previously sensitive process independent of the weather. Apart from roughening the surface, no post-processing is necessary. The times when most bridges have to be demolished and rebuilt are over with UHPC.
And one company in Europe recognized this and set itself the goal of making UHPC the standard. Implenia Schweiz AG is the leading construction company in Switzerland, works across Germany, Austria and many other countries and employs more than 10,000 people across Europe. The construction company with 150 years of building tradition is always breaking new ground and driving innovation, as is currently the case in road construction. Implenia traditionally has a large number of road construction projects that are manufactured in concrete. However, in order to be able to successfully carry out bridge projects with UHPC, Implenia needed a testing phase that lasted several months with three critical pillars: First, of course, the building material was developed (its exact composition remains a secret). Then a special concrete mixing plant was built and at the same time, a new mold was developed for paving with the GOMACO GP 2400 slipform paver. For this step, Implenia collaborated with GOMACO and the DACH service team BODO Int. GmbH & Co. KG. GOMACO concrete slipform pavers have been an integral part of the Implenia fleet since 1985 - currently they own the GP 2400. The GP 2400 can manufacture concrete slabs up to 7.32 m. According to Hardegger, the deciding factor for the purchase last year was the this: “The GP 2400 is a compact machine with options for various mold inserts and the installation of a rear mold, which we use especially in tunnels for concrete carriageways and track slabs. Weight and compatibility also match our requirements. The machine is flexible and very suitable for our projects in Switzerland.”
Implenia also approves of the paver’s high mobility and maneuverability on site and throughout the paving process - guaranteed by its slewdrives, a technology that has been used at GOMACO for over 10 years. Its mentioned flexibility has been proven various times. Implenia covers a large number of possible projects with just three different molds. With the specially developed zero- clearance rear mold for instance, Implenia has successfully completed a large tunnel project. The globally unique combination of rear mold and paver made it possible for Implenia to manufacture 3.55 m wide without requiring additional space on the edge. Here, GOMACO and Implenia have already done pioneering work together.
The GOMACO GP 2400 is extremely variable. Here you can see a zero clearance-rear mold that makes it possible to pave in tunnels with extremely limited space.
With the GOMACO paver and the UHPC mold, a total of 2,400 m³ UHPC have already been installed in open fileds, in casettes and banquets, as well as in various prefabricated components. The slab heights were between 4 -12cm. For the first time on a large scale, the new fiber construction material was installed on behalf of the Swiss Federal Roads Authority (ASTRA) on a 20 km section of the A4 as part of Switzerland's important north-south axis, the section between Küssnacht and Brunnen. After 40 years, the section was in urgent need of renovation. The total area of the construction activity was 20,000 m². The work was carried out in four construction phases from 2018 to 2019 so that the flow of traffic for the approximately 27,000 vehicles was affected as little as possible every day. A total of 1350 m³ UHPC were paved with the GOMACO GP 2400 with a thickness of 4.5 to 10 cm and an paving width of 4.55 m. The daily production rate per nine hour shift was 65-80 m³ or 750-1,200 m², where the GOMACO GP 2400 could have worked faster, according to Implenia. The complicated production and delivery of the building material hindered the paving speed. The building material came from the specially designed concrete mixing plant that was set up 0-3 km away from the paving site. It had a capacity of 14-18 m³ / h. Two to three trucks delivered the mix with a loading volume of 2 m³. The concrete was then fed into the paver using an excavator and concrete bucket. It was installed with 3D control. Implenia has been using this technology for 20 years. According to Hardegger, the alternative, using string line, has long been history. The smooth interaction between the material, the GOMACO slipform paver and the good coordination of the overall process by the experts led to the fact that the requirements for flatness and dimensional accuracy of 4 mm could be easily met or undercut. Responsible for this outcome are the paver’s vibrators. Each GOMACO customer has the option to choose between electric or hydraulic vibrators, Implenia picked the latter for its GP 2400. Another parameter was almost perfect, the edge dimensions were in the millimeter range. The fiber building material was strengthened with bar reinforcement in accordance with the SIA MB 2052 standard and all structural requirements. UHPC is without joints. Post-processing or structuring is also not necessary, since the concrete already has a good friction coefficient due to the special material structure. The process is complex, all steps must be precisely coordinated and carried out by experienced installation specialists. But it has been shown that the installation of UHPC not only makes sense on paper, but that its advantages have stood the test of time throughout practical testing. The project was extremely successful, was completed without any major problems and ASTRA was able to update the status report of these renewed bridges from critical to perfect.
An impressive view from high above the construction site.
Because of the successful completion of the first construction projects, Implenia expects that the demand for UHPC on the market will increase significantly. Bridge repairs will definitely remain a big topic, but there are also other application examples where UHPC will show its strengths in the future: prefabrication, tunnel construction, track slabs, road surfaces, static reinforcements, nuclear repositories / boxes, heavy-duty components. And Implenia's research and development department doesn't stop there, but is currently working on a concept development for reinforcing asphalt surfaces with UHPC. The company is confident about the future, although Hardegger explains: “Implenia also has to continue to research, although the know-how is already huge. Especially in the area of application. The challenge is always to coordinate all processes with one another. ”Here is the GOMACO DACH dealer, the BODO Int. GmbH & Co. KG, at the side of the company to further adapt the paver and the UHPC mold to the changing requirements. UHPC is the future, this is no question for Implenia Schweiz AG and GOMACO Corporation.
