Coat it to float it

One topic on everyone's minds in Dubai is the traffic. Currently, crossing the Creek has been limited to three bridges and a tunnel, and these have been stretched beyond capacity as the emirate's population growth and car-use have skyrocketed. But the floating bridge, which is due to open at the end of June, will add a fifth crossing, allowing the Dubai-Sharjah traffic to make a smoother transition from Al Ittihad Road into Bur Dubai.

Waagner Biro Gulf won the US $42 million (AED155 million) main contract last October. The Roads and Transport Authority (RTA) is the client, Parsons is the consultant and Clement is the project manager. A joint venture of Nukote Coating Systems Middle East and Horizon Metal Products Coating Company won the coating contract earlier this year - a total of 25,000m² of Nukote CG coating and Polyprime primer will be used to form an impermeable layer on each of the 92 ‘pontoons', which will form the base of the structure. A three-lane road (in each direction) will then be laid on top. So far, much of the construction has taken place on land, as each of the pontoons is cast, coated and prepared for launch.

According to Amir Adib, managing director, Horizon Metal Products Coating, the techniques involved in coating each pontoon are similar to those used for floating marinas.

"We've done other pontoons for floating docks but not floating bridges," he says.

"There are very few firms that offer this coating and even fewer that have the experience that we have. We specialise only in this type of coating - nothing else.

"Also, we are associated with Nukote, the manufacturer, for building projects, so we tendered for the project as a conglomerate - we had one other competitor that had a similar product."

The coating used is a Polyurea - a 100%-solid elastomer coating - which is spray-applied using plural component equipment.

"Once the two components touch each other then you have about five or 10 seconds before they actually gel, and within 30 seconds to a minute, it can be touched tack-free. Because of this, we are able to launch it into the water immediately," says Adib.

The pontoons are 20m-long and 6m-wide hollow concrete blocks cast around a polystyrene centre. After the formwork is in place, the rebar framework is put in, followed by the pieces of polystyrene. After casting, there is a 12cm wall of concrete on the outside and a 15cm wall on the two ends.

"The pontoon is cast, and then it has to stay inside the mould for three days," adds Adib. "Once that is done it can be popped off the mould. It has to cure for a few more days, and then we can start our surface preparation. So we are looking at a period of seven days before we can touch one."