Architectural concrete is the choice

Concrete, Apr 2007 by Maddalena, Stephen

Although drawings and specifications give a good idea of finished results, there is no substitute for seeing what concrete can do 'in the flesh', so to speak. Exploiting the almost limitless choice of shapes, sizes, colours and textures that bespoke precast concrete offers, the members of the Architectural Cladding Association are able to provide examples of its diverse application in the construction of new buildings in residential, commercial, retail and educational sectors.

Residential

For the St George Wharf and Battersea Reach developments between Vauxhall Bridge and Wandsworth Bridge in London, The Marble Mosaic Company continues to provide the reconstructed stone-finished precast concrete wall cladding panels and structural balcony units. The wall cladding panels that span between the floor slabs are installed without the need for an external scaffold. The design of the cantilever balcony units has also been developed to become as complete a component as can be practicably produced off-site. Each balcony unit is cast with projecting reinforcement bars, stainless steel spigots for attaching balustrades and hoppers for collecting rainwater. The top face is subsequently waterproofed and tiled before dispatch to site on a just-in-time basis for the frame contractor to incorporate into the structure as work progressed.

Close to Birmingham's new Bullring retail development is a McLean site that will include a number of predominantly residential medium- and high-rise buildings with varying façade treatments, the common denominator being quality of finishes. The first phase is a 15-storey apartment building for which Techrete was appointed to supply the precast cladding that, apart from fenestration, forms the entire façade.

Elevational treatment includes stepped balconies with a bold double-sweeping curve. Instructing Techrete at an early stage enabled McLean's chief architect to consider suitable finishes for the cladding and the panelisation of the elevations. A bright white, reconstructed stone was produced for the basic panel, the standard finish being acid-etched. For areas of heavy colour contrast, Techrete developed a polished black basalt mix, while final panel configuration necessitated the use of two-colour casting.

In Ireland, Techrete has developed a range of sandwich panels that offer a fully integrated load-bearing structure and skin system. The panels can form the structural walls of a building, supporting intermediate floors and roof, and incorporating an insulated cavity. Like conventional precast cladding panels, they provide a weather-resistant external finish in a range of options.

Several major Dublin residential developments feature such components. The Hanover Quay apartments use a composite structure that includes Techrete's load-bearing precast concrete sandwich panels and load-bearing precast concrete single-leaf panels. On the other side of the River Liffey is Spencer Dock, a development that includes 12 apartment blocks with a precast concrete structure that is similarly constructed with a load-bearing outer skin of precast concrete sandwich panels.

Commercial

Decomo's project at One Coleman Street, in the heart of London's financial centre, is both unusual and striking in appearance, with deeply ground and polished precast architectural concrete columns and spandrels giving a prominent aggregate exposure. Due to the building's shape, none of the 425 units was repeated more than six times. Hardly surprising then that Decomo had to innovatively design and develop adjustable steel moulds that could be adapted for each element. Once cast, the units were ground and polished by automated polishing machines. Installation was carried out by PCE Ltd, using an EDM Total Station working to computergenerated coordinates, with connections grouted and sealed. This prestigious building illustrates what can be achieved with the use of precast architectural concrete when there is early design development with a specialist subcontractor.

Decomo was also the supplier for seven-storey offices just off Waterloo Bridge, on the corner of Savoy Street and the Strand. External walls are prefabricated load-bearing facing units, designed to carry the floor structure. As the 3.6m-high × 1.5m-wide precast perimeter panels act as the floor-to-ceiling structure, walls were erected and the concrete floor cast before moving on to the next floor on a fortnightly cycle. Principal façades are made from structural panels at 6m centres with infill panels of window or nonload-bearing insulated panels. Main structural panels have SOmm-thick facings of natural Portland stone, cast onto a 70mm concrete 'backing' panel, on 40mm rigid extruded Polyurethane foam with alu-polythene foil, on 225mm structural concrete.

Retail

As part of the current expansion programme at the eight year old Trafford Centre, Manchester, the original colonnade is being enclosed and integrated within the main shopping centre, and a new main entrance portico is being created.