Back on Stream after 58 Days - Wacker Chemie AG


Back on Stream after 58 Days

As a source of cooling water and hydroelectric power, the Alz Canal is the lifeline of WACKER’s Burghausen site. The canal has now undergone its first full renovation in 100 years, and the canal bed now incorporates a WACKER innovation: self-filling concrete.

“It was like open-heart surgery,” recalls Michael Stauber, one of the engineers responsible for maintaining infrastructure at the WACKER site in Burghausen. He was describing the late-2016 renovation of the roughly 17-kilometer Alz Canal – the lifeline of the largest WACKER plant in the world. “We use the water for cooling our chemical plants, for example, which allows us to cover 70% of our cooling needs,” the engineer explains. The canal also delivers 10% of the electrical energy consumed at the Burghausen plant: before plunging into the Salzach river some 60 meters below, the canal water passes through the Alzwerke hydroelectric power plant. The difference in height between the Alz and the Salzach – and thus the ability to generate hydroelectric power – was actually the reason why WACKER decided to build its chemical production facility in out-of-the-way Burghausen in 1916. The average annual output of the Alzwerke remains impressive to this day: this on-site hydroelectric power plant generates 266 million kilowatt hours of electricity each year – enough to power about 90,000 households, or a medium-sized city. If needed, the Alz Canal also provides the plant fire department with water for firefighting. The site’s hydrants are supplied with water from the canal as well.

In 2016, the Alz Canal was completely drained for the first time since it came into operation in 1922, and was closed down for 58 days.

“After nearly 100 years in operation, however, the canal bed, the tunnels and the buildings were all showing extensive signs of age,” Stauber explains. Algae had colonized the concrete walls over the decades, reducing the flow rate and hence the performance of the canal, but that was not the only issue: the building fabric had also suffered a great deal from the elements. “The structural components are nearly 100 years old, but repairs in recent decades have largely just been local,” notes the WACKER engineer. “The asphalt lining applied in 1984 only covered four kilometers of the channel. Large areas of spalling, defective coatings and rotten bits of old formwork made comprehensive renovation an absolute necessity.”

The 2016 Alz Canal renovation was a mammoth project, both for the maintenance team and for the WACKER Group as a whole – one that presented many challenges. During the construction phase, the canal would have to be drained and completely shut down, but industrial operations needed to continue unaffected. And, at just 10 weeks, the construction time frame was extremely tight, especially given that the canal was filled throughout the entire nearly four-year planning phase.

New Technology Employed

The Alz Canal is an important lifeline in the region – not just as a source of energy and cooling water. For its shutdown, 3.8 metric tons of fish were fished out and relocated to the Alz river.

Whereas Stauber and his team had to keep their eyes on the big picture, WACKER applications engineer Klaus Bonin and his colleagues focused on a relatively small area to be renovated. “Last year’s comprehensive restoration of the Alz Canal gave us an opportunity to use a brand-new technology that we’d developed, and test it under real-life conditions,” Bonin recalls. As the chemical engineer explains, “We renovated an area of roughly two square meters with what is known as a self-filling concrete compound, or SFCC.” SFCCs can only be formulated with the aid of dispersible polymer powders – the field in which Bonin and his laboratory assistants, Peter Rauchberger and Christine Köster, specialize.

“We had estimated 70 days for the renovations, but we brought the canal back on stream on October 26, 2016 – after just 58 days.”

Michael Stauber Infrastructure repair engineer at WACKER

“The idea of developing a self-filling concrete compound came from Indonesia. Researchers there were looking for a simple, quick-drying technology for making relatively small road repairs,” the engineer recalls. “The time frame for blocking off roads and restoring the road surface is usually small.” Customized dry-mix mortars modified with dispersible polymer powders meet those constraints. Unlike traditional concrete, which is transported as a prepared, ready-to-pump mixture of cement, additives and aggregate stone, this product is handled somewhat differently: the desired filler aggregate (pebbles or crushed rock) is separate from the cementitious binder – in this case the dry-mix mortar. At the construction site, the stone is first spread out on the prepared section of roadway, after which the dry-mix mortar is then combined with water as directed and poured over the layer of gravel. “The compound then fills in all the gaps between the rocks and binds them into a solid layer of concrete. Depending on the formulation, the system sets very quickly – sometimes in even less than an hour if requested. We can adjust that to the customers’ precise specifications,” Köster explains. “Since the pieces of crushed stone are packed close together, you end up with a strong bond after just a short period of time.”

Facts

  • When the canal is completely filled, 7.5 million cubic meters of water flow through it each day, a figure corresponding to roughly three times the volume of the Pyramid of Cheops.
  • Built between 1916 and 1922, the Alz Canal began operations in December 1922.
  • At peak times 400 people were working on the canal around the clock.
  • The Alz Canal had to be completely shut down for 58 days for the renovation work, although 70 days had been planned for the project.
  • Planning for the restoration project began in June 2012.
  • 80 people worked for 22 full hours to relocate a total of 3.8 metric tons of fish to the Alz River.
  • €45 million were budgeted for the restoration. The repairs actually cost only €41 million.
  • The work of draining the Alz Canal began on August 27, 2016, and lasted for two days.
  • To renovate the two tunnels, workers drilled 6,000 holes and pressure-injected 1.6 million liters of a cement-bentonite suspension.

The key issue is for the SFCC to have the right flow characteristics – the right rheology, in other words. Using VINNAPAS® 7016 F dispersible polymer powder from WACKER meets that requirement: “It gives us a really unique rheological profile – one you can’t get with conventional flow improvers,” Bonin explains. “After all, you don’t want the liquid mixture to flow too slowly or too quickly through the pebble structure. If the formulation is not intrinsically stable, if it solidifies too early or forms air bubbles, then it won’t work the way it’s actually supposed to – and that will jeopardize the stability of the entire concrete structure.”

Recycling with Concrete

One advantage of the new WACKER development is that stones that have broken loose or other solid recyclable materials can be crushed and then mixed with the SFCC, allowing old construction materials to be immediately reincorporated into a project. “Since our modified dry-mix mortar can be mixed with water on site, using SFCC allows us to recycle materials right on the construction site. That reduces the amount of new construction materials that we have to transport,” says Köster.

Lab model made of functionally graded concrete. The dots on the test specimen describe the density of the particular element. SFCC allows a part with low (left) and high density (right) to be produced in one step.

The VINNAPAS® product line includes a large number of different polymer dispersions and spray-dried powders. As co-binders in cementitious dry-mix mortars, these products improve adhesion, flexibility and workability – and, in the case of SFCC, deliver outstanding flow properties. “That means we can even apply concrete around a corner, which we hadn’t been able to do before now,” says Bonin, pointing to a V-shaped Plexiglas tube. The hard, vinyl-acetate-based VINNAPAS® 7016F dispersible polymer powder used here offers ideal technical properties for this application due to its specific rheological profile. The WACKER experts have cleverly modified the SFCC formulation in order to keep friction between the cement particles very low, increasing their mobility and making the mixture extremely flowable.

Self-filling concrete technology has the big advantage of being a low-cost solution for filling large areas.

Laboratory studies back that up: when SFCC is introduced into one end of a V-shaped tube filled with aggregate, the fine concrete particles slowly flow down one end of the tube to the bend and then rise up to the other end. As a result, the entire V-shaped element quickly fills with the self-filling concrete compound and then sets. What this means is that adding water causes the cement to harden, forming long, filamentous crystals, that interlock to form a stable network – a hardened cement that is no longer water soluble. This in turn binds all of the components, up to and including the largest pebbles, into a solid object.

“Last year’s comprehensive restoration of the Alz Canal gave us an opportunity to use a brand-new technology that we’d developed, and test it under real-life conditions.”

Klaus Bonin WACKER POLYMERS technical manager

The dispersible polymer powder also plays an important role in the curing process. “The cement first reacts with the protective colloid and deactivates it,” Köster explains. “Only then can the polymer particles form a waterproof film. The result is what are known as resin domains, which act as an additional binder reinforcing the cement,” says the WACKER expert. SFCC also offers another major advantage over traditional concrete: it is virtually shrinkage-free – the volume, in other words, does not change and the workpiece does not contract. “Concrete generally shrinks by roughly one to two percent. The longer the component, the greater the effect,” Bonin explains. “With this new system, the granulate stones are right up against each other. So in our sample application, the filled spaces in between are at most a centimeter long – and shrinkage is correspondingly low. It hardly enters into the equation at all.” This also prevents stress or cracks from arising in the component.

Tests on New Applications

The SFCC technology was developed and tested in the WACKER lab.

WACKER experts Bonin and Köster already have a number of ideas for their SFCC, one of which is in their lab: a home-made gabion. A gabion is a rock-filled cage used as reinforcement, visual screens and noise abatement in landscape architecture and in the construction of roads, paths and waterways. “Our application allows us to dispense with the wire cage without sacrificing the structure of the gravel. All we need is a mold, which we can just remove when we’re done,” says Bonin. SFCC is also useful in the urban mining process, in which construction waste in densely populated cities is reused for building projects. Here SFCC is suitable for what is known as functionally graded concrete, in which lightweight elements such as expanded clay are integrated into the concrete to produce different densities and to allow for more sustainable construction practices. The two experts agree: “You could say SFCC is a diamond in the rough that we can use in many more innovative construction applications.”

The water from the Alz Canal has since begun flowing over the SFCC and putting its stability to the test. The mammoth Alz Canal restoration project is now finished – and much earlier than planned. “We had estimated 70 days for the renovations, but on October 26, 2016 – after just 58 days – we were able to bring the water back,” Stauber points out. “The internal and external employees on our team all did a great job of working together. We made the most of every minute and everyone involved was really committed.” The Alz Canal was filled with water within a day and the WACKER lifeline was fully restored – at least until the next renovation project somewhere in the distant future.