For 40 years, runway 14/32 has been the landing and departure point for millions of passengers at the Zurich Airport. The foundation of the runway was built in the 1970s, only parts of the surface have been refurbished regularly over the years.
After many years of reliable service the runway will now be rehabilitated so that it can continue sending passengers into the air or bringing them back to the ground safely. The refurbishment work on the runway will also be used to modernize the electrical system of the runway lighting which has ensured best views over the last 40 years. A project that challenges planning and time management but also the concrete additives provided by Sika.
Busy while it’s dark
The refurbishment of the heavily used runway is a project that takes several years and needs detailed planning. The daily air traffic on runway 14/32 puts strict requisites on the construction work. It can only be conducted during the night between 11.30 p.m. and 5.30 a.m. Till 5.30 a.m. the runway has to be completely cleared, cleaned and must be ready for departures and landings immediately. Overstepping the time would have huge impacts on the air traffic.
Floodlights are helping the construction workers to keep an overview. Outside the lighted area there is almost complete darkness, only the lights of the airport buildings far away are visible. Light reflective clothing, helmets and hearing protection are essential parts of everyone’s equipment and even in summer warm clothing is needed as it can get very cold especially during windy nights. The work at night is physically and socially challenging for construction workers, the project owner and Sika consultants and requires understanding and support from their families and friends.
Preparation is key
Already in 2012/2013 the refurbishment work has begun. In regular intervals chambers have been built along the runway to accommodate the electronics for the runway lighting system. Now, further preparation work for the refurbishment of the medial strip is under way. The runway is 60 meters wide and is currently made of concrete. Starting 2014, a 22.5 meter wide medial strip will be refurbished with asphalt. The 18.75 meters on each side of the runway made of concrete will remain.
Trenches are cut out from the concrete in intervals of 20-25 meters. Each trench provides space for one to five pipes in which the cables for the new runway lights will be placed. The lower 20-30 centimeters are filled with lean concrete covering the pipes.
The construction workers can estimate surprisingly well how much material they need to fill the trench to the specified height and in no time they distribute and level the concrete. On top of the lean concrete they lay a plastic foil which allows some flexibility between the concrete layers. Above the plastic foil the reinforcing is installed and then filled with rapid-hardening concrete based on SikaCem®-501S.
The right recipe
The concrete is delivered by a nearby Holcim concrete plant. It consists of cement, sand, gravel, water and additives. The latter influences properties such as fluidity, curing time or water content. Depending on the intended use, climate, temperature and other criteria the concrete mix is adapted with the appropriate additives.
For the runway refurbishment at Zurich Airport the curing time of the concrete is very crucial. The concrete has to stay fluid long enough in order not to harden between concrete plant and construction site. If it stays fluid too long however, the concrete will not be cured in time for the runway to be ready in the morning. Therefore, SikaCem®-501S, a cement-based binder, is used for this project.
In the control room of the concrete plant a Holcim employee configures the concrete mix. Accordingly, the ingredients are added to the concrete mixer: Cement, sand and gravel are added through flaps, the binder SikaCem®-501S is added from the cement silo and mixed to concrete. The thoroughfare for trucks is situated underneath the concrete mixer, making it easy to load the truck and ensuring that it will reach the construction site as quick as possible.
Concrete logistics – time is running
The drive between the concrete plant and the Zurich Airport only takes about 15 minutes; nevertheless, a transport time of approximately 30 minutes has to be calculated for the concrete mix due to the security check. It applies for passengers as well as for construction workers and every vehicle that enters the airport ground. As soon as the concrete truck and its driver pass the security check it only takes a couple of minutes on the unenlightened, 3.4 km long runway to the place of action.
There is only little time for the construction workers to process the concrete. Thanks to their excellent teamwork including ten people the concrete is filled into the trench, leveled and roughened in record time. To ensure the best quality the concrete is then sprayed with the protective lining Antisol® E-20 which prevents water to volatilize from the concrete too quickly.
Before the concrete is completely processed the truck is already returning to the concrete plant for the next load. There, the truck is cleaned and any remains of the previous load are removed. Within a few minutes the next load is filled and ready for the drive to the airport.
Bright outlook for travelers
Each night, four trenches on the runway are cut open, excavated, pipes places and filled up. Multiple teams are working simultaneously on these trenches in different stages of progress. A total of 240 trenches are done laying the foundation for the refurbishment of the medial stripe. The last construction work will be done in 2014 including the cabling of the runway lighting system though the pipes.
Detailed planning, excellent teamwork, reliable raw material suppliers and the right concrete mix are the basis for a successful realization of such a project. Travelers can look forward to the runway presenting itself in the new light, sending passengers around the world or welcoming them safely on the ground.