Construction industry finds better ways to dispose of aggregates

Increased environmental stewardship is driving demand for aggregate recycling alternatives. Landfill is no longer an acceptable disposal solution for demolished roads, parking lots and buildings.

Since aggregates are a non-renewable resource, and its extraction, production and transportation generate harmful greenhouse gas emissions, it makes sense that Canada’s construction industry is looking for alternate recycling options.

Several factors are motivating the construction industry to find better ways to dispose of aggregates. One key deterrent is the ability to expand or develop new sources of aggregate supply. The process is no longer simply an application and subsequent allowance for an extension, but has become an intensive and arduous process that needs community support and respect for all environmental aspects of the site. Aggregate production facilities and pits, originally separated from urban areas of cities, have become part of municipal boundaries over time. As a result, these facilities must engage more of the community in accepting their case for expansion or new development. This translates into costs that pressure the industry into more viable alternatives. Recycling is one option that provides a cost-effective solution.

Another factor impacting the drive for new solutions is the need for a higher diversion of any material from landfills. This has been a problem that many municipalities face as landfills and populations grow in their respective areas. Many municipalities have programs in place to divert materials such as blue, green and black box programs for the common citizen, but the need for industry recycling has been slow to catch on.

Ontario consumes approximately 167 million tons of primary or virgin aggregate annually. Ontario’s municipalities are the largest consumer of the material, with between 60 and 70 million tones consumed. The marketplace uses about 13 million tones of aggregate. Currently aggregate producers are stockpiling recycled aggregate, but without a greater demand from the market, the yards will become full. Although industry responds to needs of the marketplace, a combined effort from regulators and industry initiatives will be necessary to have effective recycling programs in action.

Ontario Provincial Specifications (OPSS) allow for both recycled asphalt and concrete aggregate, but due to the ongoing infrastructure replacement of pavements, the recycled aggregates are not fully used in a year, creating a surplus of product. Aggregate Recycling Ontario (ARO) addresses the challenges and advocate for the reuse of aggregates provincially. The objectives of the group are as follows:

1. Advance best practices to industry province-wide
2. Identify gaps, benchmarks, availability, constraints and opportunities
3. Promote use of recycled aggregate in infrastructure projects, sustainability plans and/or green procurement policies
4. Educate and inform municipalities and consulting engineers
5. Look at a certification process for all recyclers to ensure best practices and adherence to quality standards and dependability

For more information  visit www.aggregaterecyclingontario.ca.

Another organization leading the charge in sustainable aggregate extraction is the Cornerstone Standards Council. It established a voluntary, market-driven certification process for the responsible extraction of aggregates that links back to the environmental stewardship of these resources. www.cornerstonestandards.ca.

Recycling is not as simple as just crushing the material and reusing it, there are technical challenges and specifications that have to be met for both the material and its end use. The standard for recycled aggregate material is the same as virgin material. The end product is not intended to be downgraded. Material must be free of contamination and must pass OPSS & CSA quality tests for aggregate. The recycled aggregate must be free of chemical reactants and the origin of the material must be known. Suppliers are responsible for managing their piles properly and ensuring material meets the appropriate standards.

Municipal and Ministry of Transport specifications allow for recycled aggregates under certain limitations. For example, the OPSS specification for a granular A material is as follows: 10.05.02 Granular A, Granular M, and Granular SGranular A, Granular M and Granular S may be produced by crushing one or more of the following:

• Quarried bedrock
• Naturally formed deposits of sand, gravel and cobbles
• RAP (reclaimed asphalt pavement) up to 30 per cent by mass
• RCM (reclaimed concrete material)
• Air-cooled blast-furnace slag or nickel slag
• Glass or ceramic materials up to 15 per cent by mass combined

Granular A and M may contain up to 100 per cent RCM, but shall not contain more than 30 per cent by mass of asphalt coated particles and not more than a combined total of 15 per cent by mass of glass and ceramic material. The combined amount of deleterious material shall not exceed a total of one per cent by mass.

For granular B under OPSS the following are the limitations:

1010.05.03.01 General

Granular B may be either Type I or Type II as described below.

1010.05.03.02 Granular B Type I

Granular B Type I may be produced from naturally formed deposits of sand, gravel and cobbles or by crushing one or more of the following:

• Quarried bedrock
• Air-cooled blast-furnace slag or nickel slag
• RCM (reclaimed concrete material)
• RAP (reclaimed asphalt pavement) up to 30 per cent by mass
• Glass or ceramic materials up to 15 per cent by mass combined

Granular B Type I may contain up to 100 per cent RCM, but shall not contain more than 30 per cent by mass of asphalt coated particles.

Granular B Type I may not contain more than a combined total of 15 per cent by mass of glass and ceramic material. The combined amount of deleterious material shall not exceed one per cent by mass.

The advantage of using concrete is that it’s 100 per cent recyclable whereas RAP is more restricted. The other issue with RAP is that substantially more is generated annually due to its use in paving. Surplus of RAP is also a concern.

Resource conservation is good for the environment and is now a mainstream objective. The industry reacts to the economic conditions that control its industry. It has embraced the ability to recycle aggregates as the requirements for environmental sustainability increase. Challenges still remain for specifications to be able to address and ensure a sufficient supply and consistent quality product to the job when needed. Governments will be challenged to develop and enforce specifications that allow for this expanded resource to be used in all types of construction, and pave the way for a cradle-to-cradle process for construction materials.