Uni among 70 dud-concrete sites

A section of ramp 4 on the Great North Road Interchange, Waterview will have to be repaired after a delivery of faulty concrete was used. Photo / Dean Purcell

Discovery shows NZ fortunate to have robust quality assurance standards, says cement association head .

Weak, substandard concrete has been delivered to 70 sites from an Auckland plant, says Firth owner Fletcher Building.

Fletcher said on Tuesday that 35 customers were affected, but yesterday revealed the number of sites involved was twice as big. These are now known to include the $1.4 billion Waterview Connection, $200 million University of Auckland science faculty building and $42 million VXV3 office block in the Wynyard Quarter.

"All 70 affected construction sites were visited by a Firth representative to test the concrete and discuss any remedial options required," the Fletcher spokeswoman said.

She said Firth had front-footed the issue and had been active since problems were discovered last month.

"Firth was proactive in notifying all the affected customers. It was not a customer who came to Firth," she said.

Firth had a stringent quality control testing programme to ensure customers received high-quality concrete products. The substandard concrete was detected as part of this daily testing.

Affected customers ranged in size from individuals having a garden path installed to the Waterview project.

"Tests showed that in half of the affected sites no remedial action is required and the concrete can safely remain in place.

"Firth is continuing to work with customers on the remaining 35 construction sites to provide appropriate remedial action as quickly and effectively as possible," the spokeswoman said.

Cement and Concrete Association chief executive Rob Gaimster said the discovery of the problem showed that New Zealand was fortunate to have robust quality assurance standards for ready-mix concrete.

"There was a malfunction at the Firth plant and that was picked up as part of the supplier's rigorous quality assurance procedures and they alerted their customers," he said.

"This was a weigh scale issue," he said, referring to a possible malfunction in cement measurement.

Tests were carried out to ensure concrete was up to the standard required. Concrete samples were tested at a laboratory at seven-day then 28-day intervals to be sure the concrete was performing in line with the production standards, Mr Gaimster said.

Concrete information

• Concrete is made of cement, aggregates (coarse and fine) and water.

• Water combines chemically with the cement to bind the aggregates together.

• The ingredients used in any mix depend on the application.

• Regular concrete withstands pressure from about 10 mega pascals (MPa) to 40 MPa.

• High-strength concrete can withstand pressure greater than 40 MPa.