Developing Christchurch’s state highways to keep high volumes of traffic moving on ground that is subject to extremes of heat and cold is a real challenge for conventional roading materials. Foamed bitumen is proving its worth on this project.
Since 2004 Hiway Stabilizers has pioneered this specialised process in New Zealand. Allen Browne Hiway Stabilizers Technical Manager says, “The magic all happens when the recycler hoes the basecourse and a small amount of cold water is squirted into the hot bitumen before it mixes with the basecourse. The bitumen is so hot that the water instantly vaporises causing the bitumen to foam aggressively expanding up to 15 times its original volume. The foam is then mixed with the basecourse as it passes through the recyclers rotor chamber.
Downer Group and McConnell Dowell New Zealand are four-laning the two lane SH1 Russley Road from Yaldhurst Road to Avonhead Road. This is one section of their joint venture work on the SH1 project, part of the New Zealand Transport Agency’s Christchurch Motorways project, one of the seven Roads of National Significance.
Steve Ricketts, Contract Manager from Downer says that designers, AECOM New Zealand chose foamed bitumen primarily because of the high traffic volumes encountered in this location and the long life span offered by the foamed bitumen pavement.
“We worked with AECOM, Hiway Stabilisers and Winstone Aggregates to develop the best mix using the local materials on hand,” he says.
Downer laid Winstone’s General All Passing 65mm aggregate at a 170 – 600 mm depth as a sub basecourse. This was followed by a specialised Winstone Aggregates FB40 aggregate made specifically for foamed bitumen use. Downer topped it off with a waterproofing chip seal and 30mm porous asphalt over the top.
The specially formulated Winstone Aggregates basecourse is a modified M4 GAP40 with added fines that ensure the bitumen foams optimally.
For more information contact Winstone Aggregates on 0800 445 000.
Hiway Stabilizers has 3 purpose built Wirtgen recycler hoes for foamed bitumen work – the largest fleet in New Zealand. This is supported by industry leading technical experts who undertake site investigations and design the appropriate mix formula. Contact Hiway Stabilizers for more information on 09 426 3419 or visit their website www.hiways.co.nz