From Concrete Quarterly, Spring 2016
The University of Essex was built in the late 1960s, and, wandering its paths and pavements today, it is easy to feel the radical optimism of that time.
Architecturally, it is one of the best of the concrete campuses. Its bold buildings are unashamedly brutalist but tempered by the Utopian vision of its original designers, the Architects Cooperative Partnership. A placid lake graces the centre of the campus’ multi-level layout, and its towers and courtyards overlook each other a little like those of an Italian hillside town.
A cantilevered staircase in steel and oak contrasts with the exposed-concrete walls, floors and soffit
It is a legacy that has been enthusiastically embraced by architect Patel Taylor, designer of Essex’s new £26m Silberrad student centre. “The wonderful thing about the Essex campus is that it gives us the opportunity to use in-situ brutalist concrete as a sensitive contextual material,” says project architect Roger Meyer. “Back in the 60s, the university deliberately chose concrete to differentiate itself from the older, more traditional universities of stone and brick. We follow on from that, giving us the chance to express the forms of the building in a really pure way with structure and external expression as one.”
The three-storey Silberrad centre (named after a university benefactor) houses accommodation for a range of student services and also staff offices for the university council. It is situated next to the lake, which was extensively surveyed before work commenced. New sheet piling backfilled with earth now holds the lake some 10m back from its original edge. This allowed the plinth for the new building to be cast behind it on top of a series of continuous flight auger (CFA) concrete piles, topped with pile caps and ground beams.
The north elevation of the library extension is supported on a two-storey facted concrete column
From across the lake, students have a fine view of the new building, the dominant features of which are the three long concrete slabs that form the ceilings of the ground, first and second floors. All are cantilevered to some degree, projecting from the external walls of the building.
“The structure is read as a series of slabs with stone piers in between,” says Meyer. “The external wall is set in, and where the most prominent slab comes out at second floor level it is supported by slender concrete columns, forming a sort of external room and a new entrance to the university’s reception.”
Because the slabs are cantilevered – up to 3.9m at the second floor – care had to be taken to avoid “droop”, he adds. “The engineers did a great job precambering the cantilevers, so that as the concrete dried out and the building settled, the slab came down to that nice straight horizontal line.” For this to work, the cantilevered slab is cast pitched up, though the angle of the pitch has to be finely judged: “The concrete first depresses the formwork, then it might lift as formwork is taken off and then settle as it cures more fully,” says Meyer. “That’s where the art of the engineer comes in.”
In addition to the pre-cambering, the slabs were thickened for the cantilevered section. “Internally the slabs are typically 275mm thick, but externally this is increased to 350mm,” he says. Reinforcement was also dense in these areas, with bar at 100mm centres.
To prevent cold-bridging, the slabs are thermally broken at the building envelope, and they are edged with a 200mm upstand or parapet to give a more substantial feel. The top slab forming the roof of the Silberrad centre is planted with grass and shrubs, helping to make it attractive for those looking down from the higher levels of the campus.
Inside, the central columns are arranged on an 8m x 3m grid over 400mm-diameter circular concrete columns, with small perimeter wall columns at 3m centres.”It’s a simple layout which allows for flexibility in the future,” says Meyer, explaining that the whole-life performance of the building was very much in mind during the design process. “Even while we were designing, the requirements changed slightly. So the standardised grid makes it easy to use temporary partitions. The heating and ventilation system operates through a raised floor and is designed so that the ducts and vents can be moved relatively easily – for example, to accommodate different furniture layouts if the use of the spaces changes in the future.”
The two concrete cores are set at the third points of the building and feature a traditional boardmarked finish. Careful coordination has ensured that, though the pattern is random, the horizontal line of the boards remains matched and level, and that bolt holes are centrally located in each board.
“The result of using the boards is a rougher texture,” says Meyer. “The main design feature of the interior is a cantilevered steel and oak staircase which has a very smooth polished appearance – so the board-marked walls form a contrasting backdrop.”
They also contrast with the circular columns which, like the external columns supporting the entrance canopy, were formed using a disposable tube system to produce a seamless smooth finish.
More smooth concrete forms the exposed soffits, where the pattern of the 8ft x 4ft Wisaform boards is clearly visible. “Using concrete in this way, you have to draw and detail everything or the pattern won’t look good,” says Meyer. “We also wanted to avoid having services tracking on the outside of the concrete, so conduits – for the lighting, for example – were cast in. Again it means you have to go into a lot of detail in the services quite early in the project.”
The mix for the project was developed after discussions with The Concrete Centre and consultant David Bennett. “The concrete includes quite a bit of GGBS to achieve the pale shade of concrete we wanted,” says Meyer. “In addition, the contractor experimented quite a bit with the mix to ensure it would work with local supplies and perform during the colder months.”
Because the soffits are exposed, the thermal mass of the concrete slabs helps to minimise heating and cooling requirements. “The slabs absorb heat during the day and pay it back at night,” Meyer adds. “The slab helps in another way too, since the cantilevers outside the envelope provide shade and cut down on solar gain.” The structure has made a significant contribution to the environmental performance of the building which is currently rated BREEAM Very Good.
Essex is not the only campus where a bold approach to concrete architecture is being revisited. New developments at Lancaster and Loughborough, for example, have also embraced the confident mood of 1960s academia. But, if anything, today’s concrete designs are even more forward-looking that their groundbreaking predecessors. Energy-efficient, and with the flexibility to cope with changing future requirements, they are more subtle, more sustainable, and more user-friendly than those they now complement.
PROJECT TEAM
Architect: Patel Taylor
Structural engineer: Techniker
Contractor: Kier
Concrete contractor: MJ Gallagher
Concrete consultant: David Bennett
Landscape precast: Sterling Services
