Ancient and modern: while the physical and spatial fluidity of concrete is no new thing, computer modelling techniques and advances in chemical science are allowing the humble concrete mould to produce exciting new forms of expression.

While the work of Zaha Hadid may rarely be associated with classical antiquity, believe it or not there is a link between Hadrian's Pantheon in Rome and Hadid's latest project currently on site in central Germany. Despite being separated by almost 2000 years, both buildings present significant shifts in the formal and spatial expression of their time, and both have achieved this through the progressive and innovative use of in-situ cast concrete.

In much the same way that the work of Hadid is described today, the Pantheon was presented by Banister Fletcher as a polemic building. Despite its Classical gravitas, the Pantheon was, he observed, a building 'which has dissolved the distinction between wall and roof. In comparison with the more conventional Parthenon, the vast dome which is widely accepted as the oldest and finest example of in-situ relief concrete, had produced 'an interior of a new kind, no longer bounded by four walls and a roof. Similarly today, when considering Hadid's latest work, Fletcher's words can easily be reapplied. The Phaeno Science Centre in Wolfsburg--which will be open to the public in 2005--will soon have its own 'interior of a new kind'. An interior where the boundaries between the wall, floor and ceiling are increasingly blurred, and where the fluidity of concrete is once more exploited in complex geometric relief.

By creating a series of spaces that optimize not only the material efficiency of cast concrete, but also its spatial efficiency, Hadid's studio continues to develop an architectural expression that seeks to minimize the distinction between the spatial organism and the structural organism. As described by project architect Christos Passas, the building was conceived as a series of horizontal and vertical surfaces that have been deformed and shaped by the influences of spatial and programmatic requirements. By notionally inflating a concrete skin to produce a monumental form, the monolith will have a powerful internal and external presence and will comprise three principal spaces: a 15 000sq m subterranean car park, a new contoured public space (maintaining views between the historic centre and the city's famous VW factory), and a 12 000 sq m exhibition space held 8m above the ground by 10 conical inhabited pilotis that taper and rise through the space from the basement below.

In collaboration with engineers Adams Kara Taylor, these three spaces have been shaped as one element, conceived as a single mass that simultaneously creates space, void, and structure. In a manner reminiscent of Gaudi, the team has followed the pursuit of authenticity and structural efficiency, whereby concrete as a plastic material has been moulded to reach its optimum form and thinness.

With spans of up to 50m between the 10 irregularly distributed cones and with significant cantilevers reaching out to the building's trapezoidal perimeter, the project represented a unique structural challenge; not only with the raised exhibition space twisting in plan within a distorted 150m X 90m grid, but also with the tapering and leaning cones adding eccentric loads into an already complex equation.

As described by project engineer Paul Scott, a collection of complex elements would traditionally have been broken down and engineered as separate structural systems, which when combined would produce a significantly over-designed entity. However here, to satisfy the design team's rigorous pursuit of efficiency, the use of computer-aided complex element analysis was essential. So, with AKT's finite element analysis software, a modelling process was developed that enabled the complex forces within a single element to be resolved, thereby reducing the volume of concrete to its absolute minimum. Five years ago this would have been virtually impossible, and as Scott admits, without advances in computer modelling, this building would have been engineered with walls that were twice as thick. Furthermore, by considering the elements as one, Hadid was afforded the freedom to cut, puncture, and distort the supporting cones beyond the limits of their individual stability due to their calculable continuity with the adjacent folded floor plates.

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When resolving these forms, specific attention was given to the points of articulation, such as the radii of the junctions and folds in the slab, where high stresses were imposed; a process of refinement that demanded close collaboration between architect and engineer. By working across an all digital platform, which continually fed Hadid's spatial refinements into AKT's model, information was exchanged by e-mail, translated into the model and analyzed. This proved to be an effective, innovative and collaborative design process that worked well, which enabled the two disciplines to converge to instantaneously see what the space looked like and test its structure.

In parallel with the design process, thoughts naturally turned to the proposed method of how physically to cast the highly sculptural forms that had been created. Not only were the walls incredibly thin, and geometrically complex, but in many instances also needed to be fair-faced on both sides. So, to achieve visual continuity in the most extreme areas, 8m deep sections would need to be cast in one hit, in moulds that were only 200mm wide. With no room for mechanical vibration, the potential for grout loss and the honeycombing in the contorted corners of the formwork was a genuine concern, and the only practical solution was to redesign the concrete itself.

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The final solution was proposed by German concrete contractor Heitkamp, and lay in a new concrete additive that significantly increases the workability of the concrete without any resultant loss in strength. By comparing slump test results, where an inverted bucket of concrete is used to demonstrate the viscosity of the mix, the fluidity of the self-compacting mix is immediately apparent. While standard concrete will deflect by approximately 50 per cent maintaining its sandcastle form, the self-compacting mix disperses coarse and fine aggregate evenly across the test plate, clearly demonstrating its capacity to reach the most awkward corners of the formwork.

Today on site, as the formwork is slowly being struck, the white concrete revealed demonstrates that the technology has been extremely successful. While the finished surfaces have an appropriate muscular rawness, results have been virtually faultless, with complex arrays of timber shuttering skilfully cast. Hadid and her team have therefore mixed ancient and modern to full effect, exploiting the dynamic fluidity of cast concrete with masterful virtuosity.

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