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Sustainability - Recycled asphalt: efficient, effective, economical

By Robyn Grimsley

As focus shifts towards using more recycled material, the need for better recycling technologies becomes more pressing. So, too, does the need for more effective, efficient, and economical methods of processing secondary materials, as well as better ways of dealing with reclaimed asphalt pavement (RAP).

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The drive to increase the use of recycled materials in construction and road building, coupled with the requirement to decrease CO2 emissions, has led to increasing focus on recycled or reclaimed asphalt paving (RAP). 
Image credit: Pixabay

While new demands in the paving business are resulting in the evolution of asphalt plants, at the same time, companies and governments are on the lookout for ways to incorporate more recycled asphalt into road building and rehabilitation projects. This is not only to preserve natural resources, but also to optimise production costs thanks to the aggregate and bitumen savings resulting from the use of modern recycling techniques.

The availability of the aggregates and bitumen used in asphalt production is steadily decreasing as more is mined, and this results in higher costs for the quarrying of aggregates, as well as increased costs in bitumen production. Additionally, construction and demolition (C&D) waste is up to 22% by mass in landfills across South Africa. C&D waste recycling is a growing industry, particularly when landfill space is limited and the costs of virgin material can be high.

The drive to increase the amount of recycled materials used in construction and road building, coupled with the requirement to decrease CO2 emissions, has led to an increasing industry focus on recycled or reclaimed asphalt paving (RAP). Recycling is the most environmentally friendly method of dealing with C&D waste, ahead of landfill and incineration (Ortiz et al., 2010, in Ulubeyli et al., 2017). In addition to the environmental benefits of reusing materials, there are significant cost-saving implications, primarily due to the reduction of material costs, including asphalt binder, energy costs, and total job costs, including transportation.

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Asphalt pavement is 100% recyclable and reusable, and reclaiming asphalt material offers both financial and environmental benefits. 
Image credit: Pixabay

Making use of granulators — machines that gently separate reclaimed asphalt into its individual components without destroying the original grain structure — in combination with an asphalt mixing plant can create new roads comprising over 90% recycled materials.

Asphalt pavement is 100% recyclable and reusable. RAP is added to hot mix asphalt in varying quantities, depending on the project’s engineering design and the capability of the asphalt plant. Warm mix asphalt — a technology that has gained acceptance globally because of its environmental and other benefits — can make use of a significant percentage of recycled material. In May 2016, the Road Pavement Forum in South Africa approved a resolution to scope guidelines for the inclusion of secondary materials in roads.

ROAD PAVEMENTS FORUM

The South African Road Pavement Forum (RPF) was established in August 2000 to provide a forum for sharing and debating road-related matters relevant to the South African roads industry.

The RPF makes provision for wider representation and participation from the broader roads industry, particularly urban and provincial authorities, tertiary institutions, and contractors, and also allows for broader regional representation.

RPF objectives include:

  • Providing a perspective of overarching strategic issues as it affects pavement engineering;
  • Promoting best practice;
  • Co-ordination and linkage with other groupings;
  • Establishment of task groups with specific national objectives;
  • Provision of sufficient time for participation/discussion/advice and for social interactions;
  • Dissemination of new technologies;
  • Provision of a forum for acceptance of technological changes; and
  • Provision of a forum for interaction between theory and practice and for identification of technology development needs.

According to Mhlongo et al. (2014), RAP is one of the most recycled materials in the world. However, studies conducted in Europe and the US show that while 80% of the recycled material is reused in the construction of roads, strict regulation often allows for a maximum of 50% RAP in the production of new hot mix asphalt (HMA) mixtures.

There are several technologies that enable RAP reuse in the production of fresh mix, including counter-flow dryers (100% hot recycled material); parallel-flow dryers (up to 60% hot recycled material); middle ring dryers (up to 40% recycled material); and various cold addition systems (25–40% recycled material).

Kirsten Barnes is a waste economy analyst at GreenCape— a non-profit organisation established in 2010 by the Western Cape Government to support the development of the ‘green’ economy in the region. According to Barnes, nationally, other than the requirement to reduce waste to landfill, which is embedded within the National Environmental Management: Waste Act, 2008 (Act No. 59 of 2008), there’s no strict legislative bans or diversion targets related to C&D waste.

“However,” she adds, “we expect that to change, because both the City of Cape Town and the Provincial Department of Environmental Affairs in the Western Cape have C&D waste as one of their key focus areas.”

OR TAMBO INTERNATIONAL AIRPORT

A paper presented at the 33rd Southern African Transport Conference (Makgoka et al., 2014) examined the use of warmed asphalt with a recycled asphalt (RA) content of 55% using a foamed bitumen process during an Airports Company South Africa (Acsa) project. At that time, this was the highest amount of recycled asphalt ever produced in an asphalt plant in South Africa.

The project involved the rehabilitation of the cargo area at OR Tambo International Airport, and the use of this environmentally sustainable technology resulted in massive cost savings while allowing the contractor to work effectively in a highly congested area using conventional asphalt paving and milling equipment.

This approach was based on experience gained on previous Acsa projects where various environmentally sustainable asphalt products had been used effectively, including foamed treated asphalt with 35% RA, haul road with only RA with a surface emulsion treatment, and cold-mixed RA mixes with emulsion.

OR Tambo
Warmed asphalt with a recycled asphalt content of 55% was used during the rehabilitation of the cargo area at OR Tambo International Airport.


SOURCES

Makgoka, M., Grobler, J.E., Marais, H. & Bakker, D. 2014. Environmentally sustainable use of recycled asphalt at OR Tambo International Airport. Paper presented at the 33rd Annual Southern African Transport Conference 7–10 July 2014 “Leading Transport into the Future”. CSIR International Convention Centre, Pretoria, South Africa. 

Mhlongo, S.M., Abiola, O.S., Ndambuki, J.M., & Kupolati, W.K. 2014. Use of recycled asphalt materials for sustainable construction and rehabilitation of roads. Paper presented at the International Conference on Biological, Civil and Environmental Engineering (BCEE-2014), 17–18 March 2014. Dubai, UAE. 

Ulubeyli, S., Kazaz, A. & Arslan, V. 2017. Construction and demolition waste recycling plants revisited: Management issues. Procedia Engineering, 172:1190-1197.


 

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