Mountains and hills make up nearly 90 per cent of the Fujian Province topography in southeast China. This means that a large number of tunnels have been constructed and maintained for the region’s highways and roads to traverse its high-altitude ranges.
Concrete has been widely used for the tunnel pavement in the past. However, after several years of heavy use, these roads have suffered issues such as friction, broken slats and severe vibrations, which affect traffic flow and safety.
Transitioning from concrete to asphalt has been widespread in China, including in the Fujian Province. New tunnels there are now required to use asphalt rather than concrete pavements.
Xiamen Huate Group Co, a major road material solution provider in China, has been one of the country’s early warm mix asphalt (WMA) adopters. The company is also focusing on developing WMA as an effective application for the type of tunnel asphalt paving required for the mountainous Fujian Province.
“WMA is one of the most revolutionary technologies for the pavement installation industry in recent years,” says Xiangyu Zhang, Chief Engineer of Huate’s asphalt mix team. “As the Chinese government has been aiming at building a sustainable and energy-saving society, WMA has gained a lot of attention and is being applied to more and more projects in China.”
In June 2014, Huate, in cooperation with Dacheng Engineering Construction Co (DCEC), applied its WMA technology to the six-kilometre You-Che-Ling Tunnel on the Ningde-Lianjian Highway in the Fujian Province.
Mr. Zhang says that the major difficulty in using traditional hot mix asphalt (HMA) in such narrow, closed environments is the construction and safety risks arising from excessive heat emission and asphalt smoke. “The smoke would accumulate rapidly after 100 metres into the tunnel, which made the environment deteriorate and not suitable for construction,” he says. “In the past, high-powered ventilation facilities were used, but there were only little improvements.”
A poor working environment, high rate of equipment failure, worker exhaustion and harm to workers’ health are just some of the issues Huate identified with using HMA in the tunnel environment, not to mention the technical challenges of laying it in a humid and poorly ventilated site.
The engineers at Huate’s Research and Development (R&D) Centre, based in Xiamen City in southern China, devised an appropriate WMA solution for the project.
Yunrong Ma, Technical Director of the R&D Centre, explains that Huate’s warm mix binder technology used on the project is based on active surface technology.
Compared with attributes of traditional WMA, such as decreased viscosity and foaming, the active surface technology has different characteristics that make it applicable to a tunnel situation. “Through this technology, the binder surface tension is reduced to a lower temperature, which can make the bitumen easier to soak into aggregates to form good binding and anti-stripping capabilities,” she says. Another characteristic of the active surface technology is that a structural water film is formed in the bitumen colloid slurry during the paving and compacting process, largely improving the compaction performance. “After the construction, the active surface agent will gather around the interface of bitumen and aggregate, and not in the bitumen colloid slurry, which helps to avoid negative effects to the binder,” she adds.
“At the premise of guaranteeing the quality of bitumen binders, we focus on controlling the volatilisation point of nitric oxide and nitrogen dioxide (NOx) in bitumen as well as making mixing, paving and compacting possible under lower temperatures. This helps to enhance the working environment, protect workers’ health, reduce the emission of asphalt smoke and assure a high pavement quality.”
In July 2014, Huate manufactured the first batch of warm mix binder for a 200-metre trial section of the You-Che-Ling Tunnel.
Mr. Zhang says that during the trial, the mixing and initial compaction temperature was 30 degrees Celsius less than with traditional HMA.
WMA was used in the construction of the rest of the tunnel pavement following the successful trial. Mr. Zhang says that WMA became the fundamental solution for the project’s paving problems and, subsequently, workers could conduct continual paving works even in poorly ventilated areas.
“By using WMA technology, the compaction quality, compactness and flatness of the asphalt mix are largely improved, and the risk of water damage is greatly reduced,” he says.
The You-Che-Ling Tunnel was completed in keeping with the project’s schedule and resulted in a high quality pavement.
The WMA technology developed and implemented by Huate’s R&D Centre has an ongoing legacy on road projects in China. Its innovative solutions are being applied to projects around the globe.
Now, Huate is bringing the expertise of its R&D Centre to Australia, opening an office in Melbourne.
“We don’t have an engineer currently based in Australia, but our engineers are keen to travel globally to provide solutions to our customers based on their needs,” says Ms. Ma. “Like in Africa, when a contractor encounters some difficulties during the construction and looks to us for technical support, we will send an engineering team from China to help them identify the causes of the problems, design a solution and do some tests to make sure the solution works.”
Huate and its R&D Centre can provide customised, holistic solutions to its customers, including those in Australia. “Like we did on the You-Che-Ling Tunnel project, we can choose a basic bitumen and do the modification design to test to make sure it’s a suitable warm mix bitumen, then we do the aggregate grading design to make it fit with the specially-modified binder,” says Ms. Ma.
“Last, we do the performance test of the asphalt mix to make sure it meets the customer’s requirements and field conditions. We also provide the relative modifiers and agents as part of the solution.”
This process is the same in China, explains Ms. Ma. “Our R&D Centre is based in Xiamen City, but our engineers travel all over the country to provide different technical support to clients in different cities,” she says.
Ms. Ma adds Huate and its global engineering team provide on-site support services to help its customers solve the instant problems they encounter on site. “Whenever these engineers travel, the R&D centre is always a strong backup for them to solve different kinds of challenges.”
This story has appeared in the Roads & Civil Works February/March 2016 edition – get your copy here today!