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Engineers clash over Northampton tower concrete cancer claims


STRUCTURAL ENGINEERS this week clashed over claims that the Grade II listed Northampton Express Lift Tower has 'concrete cancer' and needs to be demolished.

Tower owner Wilcon Homes has claimed it has evidence that the 127m tower is suffering from cracking caused by alkalisilica reaction (ASR) and says it should be taken down.

But Northampton Borough Council and English Heritage told NCE this week that the ASR claims are unproven, and they will not allow demolition to go ahead.

ASR, sometimes known as 'concrete cancer', occurs when alkali in the cement reacts with silica in the aggregate in the presence of moisture.

The reaction produces an alkali-silica gel that absorbs water and expands, causing cracking in the concrete. Over time, the cracks can become larger and can threaten the structure's integrity.

The tower was built in 1982 for the Express Lift Company, to test lifts and train personnel. It was given Grade II listed status in 1997.

Developer Wilcon Homes bought the tower site from the lift company in 1999 for redevelopment as homes. Wilcon originally agreed to maintain the listed structure as part of the purchase deal.

But initial studies by Wilcon Homes' engineering consultant Rolton Group revealed the structure had evidence of ASR.

Concrete specialist GBG was then subcontracted to carry out a more detailed study.

As a result, Rolton concluded that the tower was a safety hazard because of the risk that concrete chunks dislodged by the ASR could fall on to people below.

But English Heritage's consultant Structural Studies & Design claimed there was no evidence of cracking on the outside of the structure.

Northampton Borough Council principal planning officer Harvey Steers also said that Rolton's research was not detailed enough to justify a decision to demolish.

'According to the Institution of Structural Engineers, there are three tests that prove the scope of ASR. None of these have been done, ' he said.

Only if the reinforcement structure is weak, and there is substantial reaction and cracking, does demolition become necessary, said Steers.

'Is it (ASR) creeping along the structure or is it galloping? The ball is in their court to provide additional data, ' he added.

GBG defended its conclusions. 'I do consider that there is sufficient evidence of ASR in the structure to warrant risk of failure in the surface, ' said GBG principal George Ballard.

He added that investigations had been limited by cost, but that he had studied a 3m wide strip of the structure from the base to the top.

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