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Functional, imposing, even quirky - buildings can be many things in the eye of the beholder. But in truth very few contemporary buildings aspire to the ultimate accolade - that of being beautiful. Foster + Partners鈥� recently completed project in Jordan is certainly one of that select group, and it is, of all things, an airport.

Emerging from the desert 35km south of the capital Amman, Queen Alia airport is an Arabian Nights fantasy of arches, domes and pillars stretching in tessellated patterns across the palatial expanses of its floorspace. Outside, palms sway in the desert breeze and beneath them families gather to greet or bid farewell to travellers. Aesthetically, this is as far from the identikit tubular steel terminals plonked outside many a UK provincial city as it is possible to get.

That the airport is built almost entirely from concrete is hardly a surprise. In this part of the world, where temperatures soar by day and plummet at night, stone and concrete have been the building materials of choice for hundreds of years. Concrete鈥檚 thermal mass is essential to even out the diurnal extremes of temperature, absorbing the desert鈥檚 heat in the day and releasing it slowly throughout the freezing night.

But even if passive temperature control were not the priority that it is in the Middle East, it is hard to imagine that any other material could achieve what has been accomplished here - because this is a building with curves.

The central terminal building is roofed with more than 50 shallow domes, each supported by four gently curving x-beams. These sprout like palm fronds from enormous column heads which top the gently tapering supporting pillars.

The curves do much to explain why Queen Alia airport is so easy on the eye, and also why concrete, with its ability to be moulded into almost any shape, had to be the material of choice. But there were other reasons too, as Foster project architect, Jonathan Parr, explains: 鈥淚n the Middle East there is no real tradition of steelwork. But because concrete works so well with the climate, the resources to build with it - the materials and the skill sets in the local workforce - are all in place and well developed. And using a local material works environmentally on a number of levels and also helps the building to fit into its surroundings.鈥�

Indeed, it is the use of local aggregates, says Parr, that gives the concrete at Queen Alia airport its distinctive colour: 鈥淚t is a light beige - a warmer shade than the greys we are used to in northern Europe.鈥� This also gives the building the feel of having been sculpted from the local terrain - an effect the builders of ancient Petra, 200km to the south, might have appreciated.

Unlike Petra, however, Queen Alia has been constructed using an intriguing mix of in-situ and precast concrete technology. 鈥淭he structure is supported by substantial columns made from reinforced concrete,鈥� says Parr. 鈥淭he airport comprises two, or in places three, storeys and in the lower ones these columns have parallel sides. But in the upper storey they taper gently outwards so the top, which supports the column heads, is wider. Structurally they work rather like the tapered legs of a dining table.鈥�

Circular in section, these columns were cast in situ, using self-compacting concrete to give a naturally smooth finish. To ensure a regular shape, steel formwork was chosen to minimise deformation caused by the weight of concrete.

Because the roof was constructed from a selection of precast elements, the column heads had to be very precisely located and levelled if all the elements were to fit together properly. This was achieved by means of a self-levelling mortar, and steel plates. The column heads were fixed to the columns by welding a steel ring, fixed to the bottom part of the column head, onto the steel plate on top of the column.

Nearly 4m wide, more than 7m high, and weighing up to 20 tonnes, these precast column heads were central to the whole construction process. 鈥淭hey had to be large to take the substantial stresses placed on them by the weight of the roof, and have sufficient height to allow them to blend into the curving x-beams,鈥� says Parr. 鈥淚n fact, the column heads were cast hollow, and had relatively thin walls. This made them much lighter than if they were solid, and allowed them to be lifted and manoeuvred into position more safely and easily.鈥�

Once welded in place on top of the column, more reinforcement was placed inside each column head. An in-situ pour was then used to cover exposed reinforcement sticking out of the column top, in-fill the column head, and bond it to the column.

Using a local material works environmentally on a number of levels and also helps the building to fit into its surroundings

鈥淓ach column head is a four-pointed shape providing corbels to rest the x-beams on,鈥� says Parr, explaining that the beams were, like the column heads, hollow to reduce weight.

鈥淭hey are precast, with each beam split into a Y or wishbone shape, and the split ends engaging into two of eight 鈥榝emale鈥� pockets on the column head. The beams were supported on scaffolding - the non-split end meeting its counterpart coming the other way from an adjacent column.鈥�

These beams were some 11m long in order for two, along with the column heads themselves, to span the 25m between columns. Once in place, reinforcement was dropped inside the beams and more in-situ concrete was used to in-fill and glue the beams to the column heads.

This process left each column with four beams 鈥渟prouting鈥� from its head. Where the beams split as they near the column, they have left a series of tear-shaped gaps, which have been glazed to provide an elegant natural light.

By this stage, the beams, forming rough squares on plan, were ready to accept the precast dome segments. Each dome comprised eight segments which, after being lifted into position, were supported on scaffolding. 鈥淭hese rested on an invisible ledge coming off the beams,鈥� explains Parr.

He adds that while the appearance of the concrete was vital to the overall architectural effect, it could not be considered independently from the construction and structural requirements: 鈥淔or example, we spent a lot of time testing various concrete mixes to ensure a smooth interior finish with no stress lines, but the top surface of the segments was left deliberately rough and with steel hoops sticking out.鈥� This provided a key for a topping of in-situ concrete, which was poured like icing over the dome segments to increase their thickness and strength, and to create a joint-free roof surface. 鈥淎 dryish mix was used, and this, together with the rough top surface, prevented the in-situ from slumping off the domes.鈥�

Each dome is protected from the desert sun by a layer of insulation and an aluminium shade sitting on upstands: 鈥淏ecause there is a gap of free-flowing air between the concrete and the aluminium, it helps keep the building cool,鈥� says Parr.

Apart from an anti-dust coating on the columns, all of the concrete at Queen Alia has been left with a natural bare finish. 鈥淭o us, concrete is a lovely material, and it should be left as such,鈥� says Parr. 鈥淲e were adamant it should stay untreated - especially because of the colour of the concrete. Such making good as was necessary we tried to keep to just cleaning and sanding smooth.鈥�

The result is undeniably impressive, as the pattern of beams and domes repeats and repeats, calling to mind the many-pillared audience halls of bygone Eastern rulers. Jordan hopes its $960m (拢624m) airport redevelopment will result in Queen Alia becoming something of a regional hub, handling up to 12 million passengers per year. They will, one feels, have much to admire.