Pre-stressed concrete bridges defended

Press, 31 May 1985, Page 20

Pre-stressed concrete bridges defended

PA Wellington A claim that many prestressed concrete bridges are failing because of corrosion has been disputed by the secretary of the New Zealand Concrete Society, Mr R. J. Christie. “At the moment the problem is unknown to those involved in the design, construction and maintenance of pre-stressed concrete bridges in New Zealand,” he said. Mr Christie was commenting on an NZPA report from Sydney which quoted a senior executive of the New Zealand Timber Industry Federation, Mr John Kelly as saying timber bridges would last twice as long as concrete ones. “We are discovering ... that throughout New Zealand pre-stressed concrete bridges erected since the war are failing because the weather has got into the small cracks in the concrete caused by the stressing,

causing it to break away and then getting at the reinforcing steel," Mr Kelly was quoted as saying. “With timber bridges we are getting 80-year life compared with 40 years for socalled permanent concrete structures." Mr Christie said Mr Kelly had made an “unsubstantiated alarmist statement."

According to Mr Kelly's statement, two of the earliest pre-stressed concrete bridges built — the Melling bridge in Lower Hutt and the Waitaki bridge on State highway I north of Oamaru — must now be bordering on collapse, like dozens of others”. “In fact, both are in perfect condition,” Mr Christie said.