CRACKS were found in the concrete supporting Edinburgh's tram lines shortly after last week's test run.

Experts say the cracks could become an ongoing maintenance headache for the controversial and delayed £776 million transport project.

Engineers spotted the cracks in concrete under an elevated section of the track near the Edinburgh Park tram stop. Trams made their maiden voyages along the lines last week, and the project is due to open to the public next year. Professor Lewis Lesley, technical director of light rail company Trampower, warned that expansion joints had not been added to the concrete.

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He said: "What will happen is the reinforcement wires will rust and then the concrete will break apart.

"It's clearly going to be a maintenance problem.

"They would need to check for any further cracks and fill them with an epoxy cement grout, but it indicates that this is a bit of a rushed job and they didn't quite get it right."

An Edinburgh-based chartered structural engineer firm, which did not want to be named, said the cracking was "most likely associated with shrinkage after casting the concrete".

A written assessment of the damage said: "I would imagine the contractor should be asked to confirm the cause and provide a solution for remedial work."

A council spokesman said: "Cracking within concrete is common and the majority of cracks, such as this one, have no structural influence on performance. The contractor and the council have a monitoring process in place."