Balfour Beatty Civil Engineering quality and environmental manager Martin Brock made the admission when quizzed by Environment Agency Wales waste policy advisor Karin Black.
She asked him at the recent Resource Efficiency and Waste Management conference whether the use of secondary aggregates really made a road sustainable if it had to be replaced and repaired regularly.
Brock responded by saying that there are huge pressures on companies such as Balfour Beatty and AMEC to deliver projects on time and without damaging the environment.
He also said that with clients invariably going for the most cost effective tender, they had to deliver the projects at a competitive price, meaning that the lowest cost design is more often than not used.
The contract is for the initial building of the road, not maintenance. We could complete a road and within two weeks, there may be cones up with workers sorting defects. But this is not down to the design, but the workforce, there is a big skill shortage.
However, unless cost is taken more into account, it is not always going to be the most efficient design which is used, Brock added.
But while the long term implications of using secondary resources have been questioned, the short term benefits are undeniable, which is illustrated in a recent Balfour Beatty project.
On the new junctions 12-15 for the M25 Motorway and spur for Heathrow Airport Terminal Five, the use of local markets and arisings from the project reduced the use of primary aggregates by 820,000 tonnes.
There was also a reduction in landfill disposal of 770,000 tonnes, a cut of 165,000 in construction and demolition waste going to landfill, while lorry miles were reduced by 1.6 million, leading to 55,000 fewer movements.