Asphalt Review - Volume 29 Number 2 (June / July 2010)

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ASPHALT REVIEW research and quality control testing has been carried out in association with this work, with considerable successes being obtained. 4. Benefits of Half-Warm Mixes The two main benefits of Half-Warm asphalt mixes are: 1. Reduction in greenhouse gas emissions; and 2. Improvement in field crew health and safety. A closer examination of the technology reveals additional benefits for both producers and purchasers of Half-Warm asphalt mixes. 4.1 For the producer Producing mix at a lower temperature means that the differential between ambient and mix temperature is reduced. This means that the Half-Warm asphalt mix will cool more slowly compared with hot mix asphalts. A slower rate of cooling allows longer cartage distances, extended workability time in the field and the ability to place and compact in cooler conditions. Because the Half-Warm asphalt cools more slowly, the formation of a chilled ‘crust” on the surface of payloads does not form to the same degree. Another benefit of the Half-Warm asphalt technology is cleaner truck decks and hand tools. 4.2 For the Client Conventional hot-mix asphalts are produced at around 165° C so that the viscosity of the bitumen binder is lowered enough to permit adequate workability of the mix. A negative effect of this high production temperature is the aging of the bitumen due to reaction with atmospheric oxygen. This is a well known phenomenon and is controlled by including aging tests in bitumen specifications The chemical additives in the Half- Warm process contain active adhesion promoters. Thus the risk of water damage in the asphalt pavement is reduced or eliminated. This use of adhesion promoters is contrasted with some Warm Mix systems that depend on the use of water, potentially trapping water in the mix and degrading longterm performance. The Half-Warm process provides for long-term adhesion of bitumen to the aggregate by including active chemistry in the additive chemicals. The reduction in temperature differential between the half-Warm asphalt and ambient temperatures, the extended workability and the minimisation of “crust” formation means that compaction is more readily achieved in the field minimising the risk of rutting, permeability and binder oxidation. The Half-Warm asphalt process is a means for the production of asphalt paving mixes. The same material is being manufactured and placed; it’s only the manufacturing process that has changed. 5. New Zealand Experience with Half-Warm Mixes In 2005, Fulton Hogan began assessing warm mix and half-warm mix technologies available around the world, and selected the low emissions asphalt (LEA) process to implement in the company’s New Zealand asphalt plants. Following laboratory development and early pilot trials constructed on a haul road within one of Fulton Hogan’s quarries in Christchurch, some high profile/high-demand sites were paved: 1. Buckley’s Road, Christchurch, December 2007 2. Montreal Street, Christchurch, March/April 2008; 3. Christchurch International Airport taxiway, February 2008. To date the performance of all the trials has been exemplary. Cores were taken of the trial sections in August 2008 (4 months after they were laid), and tested in Fulton Hogan’s laboratory wheeltracking device. The AC14 initially had a higher rate of rut development compared with the CoolPave, but after 10,000 passes they had similar rut depths. Our experience to date is that the Half-Warm process allows asphalt pavements to be placed at a quality equal to, or better than, conventional hot mix asphalt pavements. Fulton Hogan has produced Coolpave in 5 of its 14 fixed plants, all of which are continuous drum plants. Fulton Hogan has produced approximately 6000 tonnes of Coolpave, mostly a standard 14 mm dense mix. Small runs of 7mm and 10 mm mix have been produced for hand work trials which worked successfully. Mixes have been laid to date on minor city streets, multi-lane city arterials, airport taxiways and factory yards/ carparks. Compaction results in the field show that Coolpave compacts similar to hot mix, and the workable time and time to compact increases using Coolpave. Minimal laboratory-based performance testing has been conducted, although one wheel tracking test showed that after 10,000 passes the AC14 Coolpave had almost exactly the same degree of rutting as hot mix AC14. The Coolpave product reported total rutting equal to 96% of the hot mix value after 10,000 passes. 6. Clients’ Perspectives 6.1 Christchurch City Christchurch City Council leads and strongly supports local environmental initiatives in transportation and other fields – particularly where these initiatives may have benefits for the wider regional and national community. The production of standard asphalt has a high energy requirement due to the need for materials to be heated during production and the need for high temperatures to be maintained through to final placement. The high temperatures required to manufacture asphalt also result in high emissions to atmosphere as well as temperaturerelated safety issues for site staff and the public during the laying-down process. This initiative by Fulton Hogan meets council’s expectations for practical solutions to both environmental and safety issues. The material met initial trial requirements and meets all council asphalt test needs. The full scale trials at the two sites have to date demonstrated that material design, manufacture, cartage and laying methodologies are similar to standard asphalt; resulting in burner fuel savings during manufacture due to lower energy requirements, reduced emissions, easier achievement of density requirements when laying in cooler air temperatures and greater safety during placement. Council tendering and contract methodologies encourage innovation and Fulton Hogan’s proposal was developed within this framework. Council works with the local contracting industry to explore new initiatives. The local industry has demonstrated a willingness to work with council to meet both community and industry needs and has shown great passion in their endeavours. 6.2 Christchurch International Airport Christchurch International Airport Limited (CIAL) has worked with Fulton Hogan for the last 18 years on Airfield Pavement Maintenance Works (APMW). In 2006, CIAL encouraged Fulton Hogan to undertake a process of innovation to reduce the total cost of ownership and reduce the carbon footprint in the delivery of the APMW programme. CIAL is a CarbonZero Airport, the first in the 26 ROADS JUNE <strong>2010</strong>/JULY <strong>2010</strong>
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Page 3 and 4: Chairman’s report ASPHALT REVIEW
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Page 8 and 9: ASPHALT REVIEW AAPA/Austroads Warm
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Page 19 and 20: The Road to Innovation Ever increas
Page 21 and 22: Fulton Hogan and PRS Join Together
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Page 25 and 26: Boral Asphalt Boral’s LoCarb asph
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Asphalt Review - Volume 29 Number 2 (June / July 2010)

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