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Aggregate & Quarry Association

New basecourse requirement will drive up roading construction costs

New Zealand’s national aggregates organisation says it fears new requirements for roading aggregate from the NZ Transport Agency will end up reducing the number of sites making basecourse and increase the cost of road building.

New basecourse requirement will drive up roading construction costs

New Zealand’s national aggregates organisation says it fears new requirements for roading aggregate from the NZ Transport Agency will end up reducing the number of sites making
basecourse and increase the cost of road building.

Wayne Scott, Chief Executive of the Aggregate and Quarry Association, AQA, says several recent major roading failures appear to be behind NZTA’s drive to have all M/4 basecourse, used on motorways and many other roads, meet additional compliance tests.

However, he says the additional shape control requirements from NZTA for M/4 basecourse are seen by construction material technical experts as over the top and if put in place, would blow out the cost of road building.

“We support building durable roads but when roads fail, it’s not necessarily the aggregate that is at fault as the NZTA seems to be implying; there’s a series of decisions around procurement, design and construction processes.’

Across the country there are more than 200 quarries making M/4 and AQA members are worried that if the new NZTA requirement continues to creep into project specifications, the volume of compliant M/4 will plummet. Early analysis indicates that more than 24% of M/4 will be non-compliant, leading to additional testing costs, associated delays to roading projects and a reduction in sites producing M/4. One major quarry company with strong quality testing procedures in place for its many major roading projects had nearly a third of its M/4 fail to meet the new NZTA requirements.

Wayne Scott says NZTA is being inflexible in its demands. “NZTA is saying, here is the new standard for M/4; make everything to that standard or don’t produce it at all. That’s not a statistical envelope for us to work within – it’s an unrealistic line drawn in the sand.

“The AQA is supportive of finding a solution but at the moment our technical people are saying the new requirements are an unwelcome burden.

“We already have shape control provisions in M/4 – and if NZTA continues to insist on new requirements, it will cause a blow-out in the cost of road building where costs are already under pressure from rising demand for aggregate and increased cartage distances.”

The AQA Technical Committee supports basecourse test results being collated, similar to the accreditation scheme for asphalt, where an acceptable range within a statistical envelope is used to ensure good consistency and standards. Wayne Scott says he hopes with a new CEO being appointed to NZTA, there will be a fresh opportunity for the AQA to open discussions on the proposed M/4 aggregate specifications.

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