U.V. harms hotmix

Press, 4 March 1982, Page 6

U.V. harms hotmix

New Zealand's harsh ultraviolet light is causing problems with hotmix road surfaces that engineers thought would last much longer without deteriorating, Christchurch 'City councillors were told yesterday. The Streetworks Engineer (Mr H. ,E. Surtees) said he might have to seek about $200,000 more on estimates this coming financial year for a maintenance problem, the extent of which had not been recognised two years ago.

Street pavements would have to be “rejuvenated" in many areas much sooner than expected. New Zealand formerly had

used naturally-occurring bitumen from Lake Trinidad in the Caribbean for its road surfaces,; Mr Surtees said. Shipped in 40-gallon drums, some ofj those old surfaces were only now causing problems.

But bitumen from Middle East crude oil was not of the same quality, and its use in hotmix had not worked as well as engineers had expected.

Surfaces expected to last from 20' to 30 years seemed to have a life of only five to 10 years. The high concentration of ultraviolet light oxidised the bitumen, and caused it. to harden. It was

less sticky as a bonding agent. A “significant proportion” of city streets had hotmix surfaces, Mr Surtees told the works and traffic committees; Streets were rejuvenated- by-, applying, a product to “enliven” the bitumen’s surface. That treatment also had a limited life, making more frequent maintenance necessary. Mr Surtees said the council might have to consider using chip seal surfaces instead of bitumen. Chip seal provided a rougher and noisier street surface, but bitumen no longer had the expected advantage of lasting longer than chip seal.