Road Recycling Gains Attention Again
The rush of engineers using crushed glass and old rubber types in pavement materials is to be congratulated. Although it appears new to the media, the NSW Government of Australia has used crushed glass and crumbed rubber in asphalt for the last 20 years. In fact, road recycling practices in NSW date back to the 1950s when engineers referred to the practice as “good engineering judgement”. In 1995, the Roads and Maritime Services of Australia (RTA) ran the workshop on pavement recycling Newcastle—probably the first! The RTA also captured the historical story of road recycling with one of their oral history segments.
For young engineers, the key lessons learned that George Vorobieff, General Manager-Head to Head International and ISCP Director, shares with young engineers trialling waste and industrial by-products into pavements are:
• Does the material lend itself to being mixed uniformly?
• Is there a regular source of the waste product and if not, what is Plan B?
• Is the waste product safe for use during construction and safe for the community if it becomes a ‘dust’?
• Is it cost-effective to transport the material to a site 200 km or more away?
• What happens to the material at the end of its design life and can you recycle it again?
Vrorbieff’s recommendation to young engineers:
Please understand the origins of the design process
and its limitations when using the software
“I don’t want to discourage engineers from conducting new research and trials, but let’s maintain high research standards and acknowledge the past achievements by others,” Vrorbieff stated.
For the LinkedIn Post and comments, please go to: www.linkedin.com/feed/update/urn:li:activity:6607062914283249664/
George Vrorbieff on LinkedIn: https://www.linkedin.com/in/george-vorobieff-aa6231120/
Links:
RMS Oral History Program with 25 audio files/bytes:
Click on image above, or go to the Dec. 2019 ISCP article titled “Australia: 25 Pavement Recycling & Stabilization Audio Sound Files/Bytes (3+ min. ea.)”: https://www.concretepavements.org/2019/12/29/australia-25-pavement-recycling-stabilization-audio-sound-files-bytes-3-min-ea/
RMS Oral History Program Website (RMS Oral History Program with 25 audio files/bytes): https://www.rms.nsw.gov.au/about/environment/protecting-heritage/oral-history-program/pavement-recycling-and-stabilisation.html
What is Homogeneity of a Pavement Material?
One can find many definitions of homogeneity on the Internet and the definition George Vrorbieff prefers is “Homogeneous just means the same throughout”. Contractors that find it difficult to comply with the homogeneity requirements in road-making specifications will typically argue that you cannot prove the material is not the same as the equipment to measure the properties, have large degrees of uncertainty, or the test procedure is sensitive to the operator conducting the test. In some cases, a surveillance officer does not have to conduct any testing as a short crack appears in the pavement, or the material shows color changes, or as the photograph below shows the balls of material at the skirt of the stockpile makes this material visually not homogeneous.
One of the challenges with road agencies developing a test method or guideline on the assessment of homogeneity of pavement materials is that it will vary according to the pavement material type and the stage at which the material is in production, placement or compaction. For a pavement material in its compacted state, statistically, one can conduct numerous tests and define homogeneity as the ‘same’ provided the nominated properties is within a specified tolerance.
Vrorbieff commented: “For young engineers and surveillance officers, my tip is to understand which are the key material properties that make the term ‘same’ count. Even with all the test results submitted, the Lot must be visually homogenous.”
Nick Jones, Management Consultant-Partners in Performance commented, “For a less technical perspective: What’s been impressive over the last 25 years across the world has been the pricing power of aggregates in urban areas, as scarcity value has been understood, and as budgets have become dedicated to surface transportation. Unlike base metals, prosaic sand, gravel, granite, and crushed limestone are anything but commodities. [There have been] annual price increases of 4% in lean multi-year periods of declining volumes. Look at the 25-year chart of Martin Marietta Materials share price. Anything but prosaic.”
For the LinkedIn post, please go to: https://www.linkedin.com/in/george-vorobieff-aa6231120/detail/recent-activity/
Concrete Overlays in Australia 20 Years Ago
It is not to correct to assume that none of the road agencies has trialled concrete overlays on asphalt. The first two trials occurred in Adelaide in 1998. In 1995, George Vrorbieff had the opportunity to inspect numerous concrete overlay sites in Iowa with James (Jim) Grove, Iowa DoT. Jim then kindly came to Australia to talk on concrete overlay design and construction and fast track paving, and Jim published & presented a paper titled “The Fast Track revolution” at the ROADS96 conference in New Zealand. At the time RTA did not wish to trial the technique. The road agency in South Australia—then, Transport SA—conducted two trials of the technique at high volume traffic intersections in Adelaide where the existing flexible pavement had severe
rutting in the wheel paths. The concrete overlay technique consisted of milling the existing pavement to a depth of 150mm and then place 75mm of AC14 (Dense graded asphalt), and 75mm of Grade 32 concrete with polypropylene fiberss. There was no mesh in the concrete and the joints were at 1.2m spacing. Iowa practices include very thin concrete overlays to 50mm in thickness.
Vrorbieff stated: “For young engineers, the lessons learned from the trials were:
• There are many things that can go wrong with the adoption of a new technique.
• Although you can’t ‘dial up the best weather’ for concrete placement so if the weather is unfavorable, think about a Plan B.
• The trial relied on the use of significant sawcutting and this must be done ASAP if the climatic conditions are hot.
• Early entry saws would have reduced the number of early cracks, so plan the location of joints around utility covers.
• Consider sealing the joints with a (highway grade) silicone sealant.
• As the overlay was limited to the intersection, the transition between the concrete and existing flexible pavement showed signs of excessive cracking.
• Don’t expect the adoption of overseas technology to be easy—it may require several attempts to refine the technique.”
Vrorbieff stated: “I took the photographs in September 2019
and the pavement is over 20 years old!
A remarkable achievement for a trial.”
Nick Jones Management Consultant-Partners in Performance commented: “One aspect that I immediately contemplate (and how it was controlled for) is design for road pavements in Iowa (with massive freeze thaw range during a typical year – and even in fall/winter itself – and with the accompanying salting during a typical mid west winter) – will be different for Australian conditions. Moreover, being a significant agricultural economy – one does not have to travel far from Des Moines, nor the “Quad Cities” cluster in Iowa, to typically find 6-7 tons of combine harvesters to be motoring about on the roads. And today, loading will allow for the growing wind farm industry build. I find a significant amount of value in you lining out the lessons learned from your trials and leanings; and being generous to post them for young design engineers; and your ongoing mentor-ship of the next generation(s).”
Vrorbieff replied, “It is interesting that the concrete overlays … near Des Moines, [Iowa] were on agricultural roads where the existing asphalt pavement were typically +150mm in thickness. There was no need to match existing K&G or other road furniture items. In terms of freeze-thaw, I agree the roads in Iowa are subject to these conditions, [but] we are lucky in Australia to not be subject to these formation design issues.”