Back on Stream after 58 Days - Wacker Chemie AG

Back on Stream after 58 Days

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.