MC know-how integrated in Bulgaria’s highest skyscraper

The Sky Fort Business Center is an office high-rise currently under construction in Sofia. Measuring 202 m, it is destined to be the highest building in Bulgaria. Due for completion in 2021, it will boast 49 storeys and a floor space of around 80,000 m². Both the planning engineers and the constructors involved in the project have put their reliance in MC’s expertise.

The Sky Fort is located in the heart of the Bulgarian capital and will provide modern offices with a panoramic restaurant offering an incredible view of the city and the surrounding area. The building also has three underground floors providing parking for around 850 vehicles. The skyscraper was designed by AAA Architects for the investor Fort Noks (both of Sofia). The company Structo was commissioned with the planning work and is collaborating closely with the construction company Bulcarp.

 

Creep deformation test successfully passed

Back in the planning phase in 2015/6, the parties involved consulted various companies to find the right partner for the required concretes, with strength class C 35/45 needed for the foundation and C 50/60 required for the building core, columns and ceilings. Due to seismic and structural challenges, tests were required to determine the creep deformation of the concretes. Ultimately it was the MC formulations which won through against all the competition. MC was the only supplier able to develop the right recipes, the properties of which were confirmed by an independent materials testing institute. “Having achieved the necessary test results, we were duly selected as a supplier for this project,” says lead engineer Nikolay Monev, the man taking care of the technical aspects of the work on behalf of MC Bulgaria.

High-specification concrete

Despite the large volume of the foundation totalling 20,000 m3 with a depth of more than 3.5 m, the temperature in the core had to be kept to below 60 °C.  MC therefore developed a concrete formulation that combines a special cement with the concrete admixtures MC-PowerFlow 2695 and Centrament Retard 370 to ensure a low hydration temperature. With this peaking at 51 °C, the specified value was never in danger. MC-PowerFlow 2695 is the primary admixture incorporated in the concrete used for the skyscraper. The high-performance superplasticiser based on the latest MC polymer technology takes effect after a short mixing time, delivering good, sustained liquefaction as well as high early strength. MC-PowerFlow 2695 can be used to produce concretes exhibiting low tack combined with very good workability and pumpability as well as high-quality surfaces. Centrament Retard 370 setting retardant was used to counter the hot temperatures of the Bulgarian summer, enabling solidification of the concrete to be delayed so as to extend its workability and ensure sustained pumpability. The superplasticiser Muraplast FK 19 and MC-Top B, the surface-hardening dry mortar for industrial floors, were used to lay the floor of the underground car park, covering a total area of 30,000 m². This resulted in good homogeneity and a decrease in the internal frictional forces in the concrete, as well as a reduction of the effort involved in placing, spreading and compacting the mix. Still on the up, this ambitious structure has yet to reach its final height. The opening of what will then be the highest building in Bulgaria is scheduled for June 2021.