September 30, 2008

Asphalt recycling breaks new ground, expert says

DAN O’REILLY

correspondent

From experiments exploring the possibility of using asphalt shingles for highway construction to full-depth asphalt reclamation, the construction industry and its academic and consulting engineering partners are breaking ground in the recycling of old materials for new projects.

That at least was the message that emerged during a seminar on recycled materials and processes for sustainable infrastructure at the recent Transportation Association of Canada conference in Toronto.

Who Thought Recycled Asphalt Shingles Needed to be Landfilled: Why not Build a Road? was the title of presentation delivered by University of Waterloo civil and environmental engineering professor Susan Tighe.

A well-known asphalt specialist, she provided an overview of the preliminary results of a research project the university is conducting with several partners, including Miller Paving Limited, into the feasibility of using recycled asphalt shingles in road construction.

“Asphalt shingle roofs typically last from 12 to 20 years and each repaired roof produces between eight and 10 tons of waste,” said Tighe, explaining the rationale for the project is to divert used shingles away from landfill sites and incorporate them into asphalt mixes.

Some of the objectives of the research including determining what percentage of recycled asphalt shingles (RAS) would be optimal in the mixes and how they would in work in combination with recycled asphalt pavement (RAP).

In order to measure the performance of mixes with RAS, the university conducted a laboratory study of five different types of mixes with different loading cycles. Overall the results were very encouraging, she said.

“Where is this (research) leading us? We think it is possible to have triple solutions — economic, environmental and technical,” said Tighe, adding the study is evolving from the laboratory into fieldwork.

A case study of how using local materials and a reevaluation of the site conditions generated huge material and project savings on a Nova Scotia bridge project was presented by a second speaker.

In the summer of 2007 the provincial transportation department issued a tender for the replacement of a corrugated steel tunnel crossing Highway 10 near the city of Windsor. The new concrete arch structure was stipulated as “design build” allowing the contractor to use innovative construction techniques, said Paul Proctor, manager of Reinforced Earth Company Ltd., an Antigonish-based consulting engineer.

Some of the measures used by the contractor in the construction included a reduction in the original proposed excavated area after test pit results and other studies proved this was feasible.

As a result there was a 3,700-square-metre material reduction in the excavation with an estimated $10,000 savings and an equal 3,700-square-metre savings in backfill material with an estimated savings of $100,000, said Proctor.

“The excavated materials around the existing structured were reused for a $20,000 savings and the existing steel arch was sold for recycled scrap metal to a demolition contractor who hauled it away.”

Another featured guest was Ontario Ministry of Transportation soils and aggregates engineer Stephen Senior. During the period 2000 to 2004, the ministry recycled 9.8 million tons of material through full depth asphalt reclamation, he said.

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