The Burj Khalifa officially opened on 4 January 2010. The centrepiece for a new world capital, it has lived up to the hype: it now stands over 800 meters tall, the tallest building in the world. It has also set new architectural benchmarks and pushed the boundaries of engineering and science to new limits. Making the structure possible were the contractors, engineers and materials suppliers. Among them, BASF Construction Chemicals.
Says Dick Purchase, Director BASF Construction Chemicals, Middle East, Africa and Central Asia: “To reach world records the structure of the Burj Khalifa had to comply with strict design and durability criteria. One unique challenge was ensuring the concrete mix design for the structural core of the tower was capable of being pumped to formidable heights. Another was reducing corrosion of the steel rebar supporting the predominantly concrete structure to achieve the 100-year design life of the building. BASF Construction Chemicals was able to assist in both instances.”
Reaching formidable heights
The structural core of the tower required nearly 170 000m3 of concrete designed for 80N/mm2 compressive strength. A series of concrete trials preceded initiation of the project and BASF’s Glenium SKY 504 won hands down. It was the only concrete admixture that could offer the required early strengths and workability retention at ambient temperatures of above 45o C in a mix to be pumped to a height of at least 660 meters - using a single pump at ground level.
Getting the mix right – consistently – was critical. Explains Purchase: “Concrete pumps employed a pair of pistons to push the mix through a pipeline to the point of delivery. There is enormous pressure on the concrete in the pipeline from the pistons at these record breaking heights. In addition, there is the weight of the concrete itself to factor in. Any deficiency in the mix design would create a blockage in the pipeline. Glenium SKY enabled exacting mixes to be supplied consistently, on an industrial scale, and pumped to the required heights.”
Unimix, the main contactor on the project, was impressed with the solution. Noted a spokesperson from the company: “Normally, you can get either workability or high early strength; rarely do you get both. BASF’s Glenium SKY hyperplasticiser enabled us to achieve 100Mpa working on a water cement ratio of 0.24 (i.e., a high cementitious content).”
Says BASF’s Purchase: “Seen as a reliable industry partner whose guidance and support was valued from the very start of the project, BASF has subsequently supplied over twenty other products from its Construction Systems range to waterproof the foundations and pile-caps, and solve various finishing, bonding and bedding issues typically encountered on large construction sites.”
Built to last
To ensure the structure could meet the 100-year design life requirement, designers wanted a single source waterproofing solution from a company with a local presence and track record. A Cathodic Protection system was specified which meant traditional waterproofing solutions could not be used. The system also had to lend itself to a trouble free connection with the support structures and buildings around the Burj, which were being designed and constructed by various other consultants and contractors.
Says Purchase: “BASF Construction Chemicals’ met the required criteria with its three decades of service to the region and its capability to engineer a suitable solution from its Watertight Systems ranges.”
BASF’s 2mm Masterpren BG geomembrane was selected to provide the required long life performance. The membrane also had high mechanical characteristics that enabled it to withstand abuse during the construction and over the design life of the structure. Geotextiles (SNW 40 & 50) and W4 Waterstops completed the system, along with Masterflex 900 re-injectable hoses and Masterflex 610S re-wellable gaskets that were installed in the construction joints to provide a maintenance solution for the future.
Masterflow 410 Plus epoxy grouts were used to encompass the pile heads and sandwich the waterproofing membrane. This allowed high compression loading of the piles as the super structure was constructed. The epoxy/membrane interface also allowed for shear loading of the piles which causes them to move when the structure is subject to wind loading.
Says Purchase: “Engineered solutions often have to be developed at short notice as construction progresses and problems are encountered. As construction of the Burj was fast tracked, the local support provided by BASF personnel proved invaluable. It was truly a case of global experience and local expertise combining to deliver service and solution excellence. We are proud to have been able to play so pivotal a role in the creation of the masterpiece that is the Burj Khalifa.”