Making it happen at 432 Park Ave
Thanks to EB’s Green Sense Concrete technology, the concrete for Manhattan’s new landmark skyscraper 432 Park Avenue meets an unprecedented bundle of requirements. And its visually dazzling white surface is the result of the cooperation of BASF's Construction Chemicals & Kaolin Minerals businesses.
432 Park Avenue is not only a prestigious address in downtown Manhattan but also the name of a spectacular new building currently under construction there. Standing at 426 meters, it will be one of the tallest skyscrapers in the world – with a footprint of just 28 by 28 meters. The designers decided against a steel?girder construction and opted for concrete as the structural material. The structural engineers on the project, however, required the material to meet extremely rigid specifications.
The concrete requirements for this landmark project were a step into new territory in many respects. The material had to exhibit a compressive strength of 110 N/mm2 and a modulus of elasticity of 53,000 N/mm2 – the latter a first, as such a high modulus of elasticity had never before been specified for a residential building. The specifications also required a self?compacting concrete with a slump, or flow, of at least 76cm that was not to exceed a temperature limit of 71 degrees Celsius during hydration, and was to retain its performance properties during construction at all conceivable temperatures.
In addition, the concrete was to show high early strength development. Surfaces had to be walkable only five hours after placement of the material. Further requirements included the pumpability of the concrete across the entire height of the structure, even after transport times of up to two hours. This requirement, however, was in direct opposition to another: the white color of the concrete. Normally, this goes along with trade?offs in workability, but the color here was mandatory – as was a smooth, fine?pored, perfect fairfaced?concrete quality without any discoloration or visible cracks. Probably the biggest challenge was in obtaining all these characteristics at the lowest?possible cement content.
Clearly a case for the experts of the North American Admixture Systems team and their Green Sense Concrete technology, which has successfully, and impressively, proven its efficiency on the One World Trade Center, among other projects. “But a bundle of requirements such as this one was new even for us”, says Andreas Tselebidis, Director Sustainable Concrete Technology and Solutions in North America. An important piece of the puzzle was provided by the colleagues from the Performance Chemicals Division: MetaMax, a highly reactive metakaolin and an EPN product that ensures the consistent white color of concrete and improves its compressive strength as well.
However, harmonizing all requirements and meeting them completely required all the expertise of EB’s concrete admixtures experts. “Ultimately, there is no simple solution to a complex challenge of this kind”, Tselebidis clarifies. “Here, physics and chemistry have to come together; rheology and mineralogy play important parts, as do hydraulics, hydromechanics and pore?water composition.” After a series of tests, both in the laboratory and on?site in Manhattan, the concrete finally yielded the desired performance properties – even though a considerable part of the Portland cement had been replaced with alternative binders. A few trials later, the team had also adjusted the mix design in terms of pumpability and consistency retention. An additional plus for the environment: The mix design only requires locally available raw materials.
Upon completion, the building will receive LEED certification – this has already been ascertained. Sustainability, incidentally, is also a topic journalist Joe Nasvik addresses in his cover story on 432 Park Avenue for trade magazine Concrete Contractor. He cites sustainability as an important measure and goes on to say that the building could have a service life of hundreds of years with low maintenance and low energy costs: “That’s what makes concrete such a great material!” And indeed, the eco?efficiency analysis carried out by the EB team has arrived at very encouraging results – owing to the Green Sense Concrete technology. This combination of highest performance and sustainability, of product quality and dedicated customer service makes the EB proposition so unique – as unique, in fact, as the buildings created with its help. “Without our solutions and our expertise, the construction of 432 Park Avenue would not have been possible at this point in time in quite this way”, Tselebidis says. “And yes, we do take pride in that.”