Concrete manufacturers doubt quality of recycled aggregates

Concrete firms are slow to take up recycled aggregates, despite their wide use in low-grade applications, recyclers and materials testers have claimed.

Mike Watson, head of aggregates at recycling body Wrap, said around 5% of recycled aggregate is used in concrete, compared with around 90% in low-value applications such as sub-base. He said: “It would be true to say recycled aggregates in general wouldn’t meet the requirements, but they are used quite a lot in low strength applications like precast. We’re currently looking at pushing higher grades. What we would like to see though is a little recycled material used in a lot of applications.”

However, Bureau Veritas laboratory manager Roger Rattue said he sees few problems with the standard of recycled aggregates, and that many firms are being over-cautious.

He said: “The tests we carried out didn’t show much difference, but I think it’s still an unknown at the moment. I don’t think there’s been enough work done on it, but when it hits the market it’s going to hit in a big way.”

Rattue added: “No one’s been brave enough to put it into buildings yet. I can’t see the problems with it.”

He said the cost of using high- quality recycled aggregate may play a part in the lack of interest.

“Someone should bite the bullet, because it’s going to be more expensive.”

Aggregate Industries group environmental manager Miles Watkins said recycled aggregates can have a detrimental environmental impact on concrete.

He said increasing the recycled content can require more water, which then requires more cement in the mix.

He added that recycled aggregates can suffer poor structural performance. “Not all material is suitable to go into a high-strength or decorative product. The will to make this work is very strong, but the technical issues do have to be appreciated.”

Watkins blamed poor routine on demolition sites for the quality of the aggregates. He said: “The classic recycled aggregate is a poorly sorted material. If there was a better job done in sorting at the outset, we would end up with a better product.”