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Boston Big Dig investigators warn of 'concrete cancer'


INVESTIGATORS IN the US have advised the Boston Big Dig project owner to carry out tests on concrete used throughout the scheme fearing that it could be susceptible to alkali silica reaction (ASR), or concrete cancer.

The revelation is made in an engineering review of the entire Boston Central Artery project, ordered by governor of Massachusetts Mitt Romney.

The report reveals an alarming catalogue of defects on the project. It calls for cracked and spalling concrete, found in all of the project's seven tunnels, to be further investigated by owners Massachusetts Turnpike Authority and the state government. Its authors fear that traf c fumes and water ingress could trigger ASR.

ASR occurs when silicates in concrete aggregate react with alkalis, for example, salts in sea water. The reaction creates an expanding gel that can cause rapid deterioration.

The report was ordered after the fatal collapse of reinforced concrete ceiling panels in the Big Dig Interstate 90 Connector Tunnel on 10 July. It was carried out by engineering rms Wiss, Janney, Elstner Associates, Schirmer Engineering and Environmental Systems Design.

Concrete core samples should be extracted from all of the tunnels, as well as bridges, and petrographic tests carried out in the near future, the authors urge.

Its publication coincides with the announcement last week that Massachusetts attorney general Tom Riley is suing I90 Connector Tunnels project managers Bechtel and Parsons Brinckerhoff, contractor Modern Continental, designer Gannett Fleming and other suppliers to the project.

Extensive problems were found with epoxy grouted anchors used to suspend ceiling panels from the tunnel roof in the I90 Connector Tunnel and in three other Big Dig tunnels.

Other defects uncovered by the report include the pulling out of anchors used to suspend lighting and signage, poor quality construction materials, bad workmanship and signs of advanced fatigue in structures such as lighting and signage poles.

It states that safety concerns had been raised earlier about the bolts securing the I90 Connector Tunnel ceiling panels.

'Assessment of design documents, as-built conditions and construction and post-construction documentation revealed significant safety concerns relative to the suspended ceiling system in the I90 Connector tunnels.

Additional mechanical anchors have now been installed in the I90 tunnel to provide redundancy and the report advises a six-monthly check on all anchorages and phased replacement of epoxy fixings with mechanical alternatives.

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