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Concrete proves its worth in the age of aquaria

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Construction by Galliford of what will be the uk's largest aquarium benefited from both partnership and innovative use of concrete. Janet Awe reports

Due to open this summer, the Blue Planet Aquarium at Deep Sea World promises to become a major tourist attraction of the North-west of England, and is expected to attract up to one million visitors in its first year. Located in Ellesmere Port, Cheshire, the £12 million project builds upon the success of Deep Sea Leisure's first uk aquarium in North Queensferry, Scotland, and was designed by Manchester-based architect Buttress Fuller Alsop. The aquarium will host exhibits featuring the 'Waters of the World', ranging from highland streams and rivers to African lakes, from sub-tropical mangrove swamps to temperate seas. A special feature will be the Caribbean underwater safari, where visitors will be treated to a spectacular 'diver's- eye view' of a stunning tropical reef with sharks and fish by means of an 85m transparent acrylic tunnel with a moving walkway.

Construction of the aquarium is by Galliford uk's northern division, which won the £5 million contract following a competitive partnership tender involving Higgs & Hill, Tarmac and Amey. Galliford completed the enabling works and infrastructure for the project, including building an access road and a tree-lined car park. Deep Sea Leisure was impressed by the company's pact (Project Achievement through Co-operation and Teamwork) partnering initiative, which sets out to establish mutual co-operation through partnership of the many different parties involved in such large- scale projects. This includes regular discussion to resolve everyday project- management problems and decisions, and is, the company believes, the only feasible way that the project could have been completed with so many players involved.

Galliford was given 50 weeks to construct the 8000m2 aquarium. Local concrete supplier, rmc, supplied 5000m3 of concrete, designed to water- retaining codes of practice, with 1500m3 used for the rock-work alone. At any one time there were up to 70 men on site placing up to 100m3 of concrete per day.

The building's reinforced-concrete frame, which alone took 16 weeks to build, consists of 6m column grids. The construction included heavily reinforced concrete floor structures capable of accommodating the combined weight of the main aquarium tank and 25 smaller tank exhibits. Throughout, reinforced-concrete columns, cast in traditional timber formwork, support the weight of the structure.

The basement area, 60m x 60m and 4.2m below ground level, consists of a 400mm-thick concrete slab to accommodate the weight of the 36m x 24m main aquarium tank which will hold some 4 million litres of water. Both the main and the smaller tanks are built to a water-retaining specification with bentonite water stops at construction joints.

Galliford used a blend of Portland cement and slag on the tanks to prevent dehydration and cracking, and Vandex Super was liberally applied to overcome any possibility of concrete contaminates leaking into the water and poisoning the fish.

Two tunnels run through the main tank. Concrete-based, with walls 1.2m high, they will be fitted with an arched acrylic top. The acrylic tunnel was designed by Marinescape, a specialist subcontractor based in New Zealand and owned by marine civil engineer Ian Mellsop, a director and shareholder of Deep Sea Leisure. The remoteness of Cheshire from New Zealand meant that specific tolerances had to be adhered to when constructing both the concrete base of the tunnel and the acrylic roof to ensure that the two fitted perfectly together. Portholes run the length of the main tank, with 45degrees chamfers and 1.2m diameters, to enable visitors to view the fish from the restaurant.

Marinescape also produced a 225mm-thick acrylic window, 4.5m x 3.5m, for insertion in the tank wall, next to the lecture theatre. Weighing four tonnes, this window was delivered early during construction and was placed in its final position before the roof was dropped into position. The lecture theatre will provide a unique place of learning for local schoolchildren who will be able to see tropical marine life first hand.

Both the ground and first floors of the Blue Planet Aquarium consist of waffle floor slabs about 200mm thick. Peri forms were used to support the structure while the concrete floor was constructed.

Galliford also created the rock formations in the exhibitions, which involved manipulating the concrete into unusual, irregular shapes. For this Galliford developed the innovative approach of using sawdust bags to fill unusual spaces and form the required shapes, then filling the area with concrete. Once the shape was formed, the bags were removed.

The last three months of construction will be completed with live fish in the building. Marinescape has designed sophisticated life-support and filtration systems for the aquarium and artificial seascaping for the exhibits and will install them under Galliford's supervision.

The aquarium's architecture, as well as its interior, is based on a water theme. The roof consists of several curved rafters varying in radii from 4m to 250m to give a wave-like appearance. On top of the rafters sits a structural aluminium liner tray, over which is a Kal-Zip outer sheet. These elements were installed in two sections, first the tightly curved section and then the 50m-long section.

The objective of the Blue Planet Aquarium is to enlighten, increase knowledge and raise interest in the marine environment using an interactive, entertaining and sustainable approach. As such the aquarium will become a major tourist attraction. Nearly nine million people live within a 80km radius, and it is estimated that one million of them will visit the aquarium in its first year of opening.

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