Putzmeister at the Vienna DC Tower 1 – Austria's highest building

The VIENNA DC district of Vienna has developed into an internationally acclaimed, architecturally sophisticated urban centre within just a few years, boasting an array of residential buildings, office buildings and research centres. At 220 metres, the DC Tower 1 is the highest building in Austria and defines the Vienna skyline with a "crystal facade" made from glass. The construction of its smaller brother, DC Tower 2, should begin in two to three years' time.

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The 17.4 hectare site located along the north bank of the Danube is owned by Vienna's Danubeside Development Agency AG (WED), which is mainly composed of Austrian banks and insurance companies. Vienna DC was designed for a diverse range of uses. International companies have set up shop alongside cultural institutions, leisure facilities and luxury residential property.

Around 100,000m3 of concrete with demanding logistical requirements had to be pumped to the concrete placement site from the start of construction halfway through June 2010 to completion of the 60-storey DC Tower 1.

The floor slab required a solid design in order to account for the extremely small floor space to height ratio of 1:11 and the conditions of the subsoil. In only 5 days, a combination of one stationary Putzmeister concrete pump (BSA 2110 HP D) and two truck-mounted concrete pumps poured 13,000 m3 of concrete into the mesh formwork consisting of 3,000 tons of reinforced steel.

The company that was subsequently awarded the contract to carry out the structural work for DC Tower 1 (Max Bögl) first contacted the engineers from Putzmeister Concrete Project Division (CPD) as early as 2008 during the  calculation stage of the tendering process in the build-up to the project. A stationary concrete delivery concept based on the underlying plan for the building site equipment formed the basis of the calculation and was substantiated in the summer of 2010 by the engineers of CPD in the form of a CAD design ready for implementation.

Experience gained from cooperation with construction companies, formwork erectors and concrete chemical suppliers during numerous projects allowed Putzmeister and its CPD department to supply machinery suitable for the project as well as expertly plan processes. Putzmeister was responsible for a range of operations designed to ensure that construction progressed smoothly in spite of the large volumes of concrete involved. These included the delivery of concrete from the site mixer, adaptation of the delivery route in line with the construction site, concrete placement and operational processes ranging from “priming“ to cleaning the concrete conveying system.

In coordination with the site management, Putzmeister engineers drew up the technical part of the site facilities plan based on the concrete pump equipment and the delivery line installation. The maximum horizontal and vertical line lengths were 130 m and 235 m respectively. Type ZX 125 HD delivery lines with a wall thickness of 8.8 mm and a maximum concrete pressure resistance of 200 bar were used. Implementing this know-how will contribute to reducing the risk of blockages in the delivery line, decreasing wear on all concreting components and minimising downtimes and operating costs. Two type BSA 2110 stationary concrete pumps were used to carry out the job delegated to Putzmeister. Two MX distributor booms with a reach of 36 metres were incorporated into the meticulously planned piping system together with professional pipeline attachments and essential gate valves. The two distributor booms in the RS 850 tubular column system climbed through the ceiling slabs using automated Putzmeister self-climbing technology.

Concrete logistics requirements were taken into consideration when the concrete delivery concept was planned. Putzmeister also supplied a mobile buffer storage unit on rails located under the mixing plant to collect the delivery batches of approx. 2.5 m3 from the site mixing plant and convey them to the 600l concrete filler hopper reserved for alternate loading of the stationary pumps and delivery of concrete to the truck mixer. The delivery lines were routed horizontally from the concrete pumps 130 m across the site equipment area into the ground floors and vertically through the stairwell to the relevant floors with a connection to the placing booms.

The cycle plan for the DC Tower included a central monolithic core advancing three floors upwards followed by a support / ceiling structure on the rising floors. The two MX 36-4 distributor booms were installed outside the core with a diagonal offset. The supply of concrete was guaranteed for the core rising up to three storeys and the entire ground plan.

Plans for the "upward cleaning" variant were finalised in order to optimise cleaning of residual concrete at the end of concreting cycles. This approach is economically favourable and from an ecological standpoint, beneficial in inner city areas. If the end of concreting is near and the quantity of fresh concrete in the delivery line is sufficient to complete the work, a gate valve in the vicinity of the stationary concrete pump is closed. A medium separation plug is manufactured using sponge balls and cement bags and introduced into the pipeline. As a result, the residual concrete is separated reliably from the water column and forced upwards into the formwork. After the concreting work was complete, the minimal amounts of residual concrete were pressurised via the cleaning end piece attached to the end hose on the distributor boom and could be discharged directly into the recycling unit on the construction site.

Service engineers from the Munich branch of Putzmeister were on call at all times throughout the entire construction phase to provide technical and service assistance to local construction and project managers.

Extremely high static requirements combined with a high reinforcement density make it necessary to use high-strength concrete with good flow properties. The large number of concrete additives and greater complexity of concrete recipes mean that the friction values and subsequent pumpability of concrete are becoming increasingly important factors for success in large projects.

The extremely high pumping resistance and disproportionately high wear of pipelines and machine technology that occurred during concreting of the 13,000 m3 floor slab prompted Putzmeister to analyse the flow properties of the concrete and develop potential optimisation measures in the laboratory in collaboration with the company Mapei Wien using concreting technology from Max Bögl.

With the sliding pipe rheometer developed and patented by Putzmeister, it is possible to analyse the tendencies of small batches of concrete in the concreting laboratory to determine static and dynamic friction coefficients and subsequently work out potential for optimisation. The inspection revealed that the high pumping resistance of the concrete recipes and severe wear during work on the DC Tower could be ascribed to the increased abrasiveness of the additives and negative influences of the cement powder. The different conditions in the sand and cement storage depots of alternative suppliers improved the pumpability of the concrete recipes and significantly reduced wear, whereby the structural properties of the concrete remained untouched and therefore continued to meet the high strength requirements for the DC Tower. From this point in time, concreting proceeded without incident and a 4-day cycle was achieved for every 3.50 m section of concrete and the three floors were completed within two weeks.

Skilled planning that covered all aspects of the concrete delivery process, professional assistance during installation, instruction from Putzmeister and knowledge of the pumping behaviour of different concretes made a pivotal contribution to the success of the concreting work in Vienna.