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JOHN VERCOE of New Zealand roading network, generally city streets requiring smoother and less noisy surfaces. Vercoe, a polymer chemist who used to lead Exxon’s bitumen research facility in France, says that Road Science’s stock-in-trade is materials testing – understanding the fundamental properties of base courses, bitumen emulsions and polymer binders, then altering their characteristics to better match them to particular situations. But when Vercoe came to the company seven years ago, research into chipseal methods had stagnated – surprising, given that chipseal dominates roading networks in New Zealand, Australia and South Africa. As asphalt rules elsewhere, there was little chipseal knowledge to be gained from the rest of the world. But the paints and cosmetics industries, long noted for innovation, offered promising leads. “The biggest emulsions business in the world is cosmetics,” says Vercoe. “When it comes to the control of the material properties of emulsions, the cosmetics industry would be at least 25 years ahead of roading emulsions.” Take hand cream in a tube, for example. Even with the lid open and the tube upturned, nothing will spill out. When you gently squeeze – or apply pressure – the cream flows. Rub your hands and it spreads easily. “These cosmetics researchers can control thinness and thickness to the nth degree,” says Vercoe, and that’s not easy to achieve with most substances. Take traditional bitumen: it’s thick and viscous, like tomato sauce, and has to be heated to 180 °C to become watery enough to spray. This means it’s a burns risk, runs off slopes and is ruined by rain. It also has to be sprayed in the warmer months of the year. By finding a way to adjust the particle sizes of the bitumen emulsion droplets, Road Science has created an emulsion that can be sprayed at 80°C, cures faster, contains (at most) half the kerosene of standard products of its type, is more weather-resistant and stores for longer. It can also be sprayed in air temperatures as low as 10°C. Rotorua District Council (RDC) was keen to try it. “The council was able to undertake sealing in September, when the weather would generally preclude using traditional bitumen,” says Vercoe. “That meant the Downer sealing crews and equipment were utilised during that period when they would normally be parked up. All the sealing was done before the heat of summer and the peak tourist season, which meant there was no loose chip flying around.” Engineer John Ryan of Sigma Consultants, RDC’s network consultant, said that he valued the speed of the initial curing, which meant less risk of damage to the road. Less kerosene in the mix also meant less risk of the road bleeding and “black tarry stuff sticking to your tyres and going everywhere”. The next thing Vercoe wants to achieve is bitumen that can be sprayed cold, like paint. “If we can do that, there are massive benefits for this industry in energy savings, storage, and health and safety.” So far, his team is successfully spraying emulsions at 70-90°C in the field and down to 60°C in the company’s state-of-the-art laboratory. By making some changes to the spray machinery, Vercoe’s hoping to get down to 40°C or even 25°C. He’s also endeavouring to make bitumen emulsions that will store as long as paint, which generally stores for 12 months. “Then all the issues with regard to bitumen emulsion separation and stability disappear.” Creative problem-solving is in the Road Science DNA. In 2010, Auckland Transport came to the company with a problem involving the iconic Tamaki Drive, which was cracking and failing. The base course was unstable and the asphalt very thin, due to fixed kerb and channel heights and services buried at a shallow depth. And, of course, the budget was tight. Auckland Transport asked Road Science to research a thin but stronger surface. The company’s chemists found that by adding a particular polymer to the DID YOU KNOW? The chipseal method is a Kiwi invention. It was developed in 1935 by Levin-born Frederick Melrose Horowhenua Hanson, a maverick, decorated veteran of both world wars who rose to become Commissioner of Public Works. In 1935, while working for the Government, he perfected the scientific approach to laying chipseal, offering a way to build affordable roads in a young, agricultural country with a small population. The ministry that Hanson headed later became part of Downer, Road Science’s parent company. Says Road Science technical manager John Vercoe: “We’re proud of the progress we have made building on Frederick Hanson’s technology. It’s chipseal roads that make our country tick.” 38 / DOWNER / IN BLACK & WHITE


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