We often drive across the bridge. However, the biggest trouble when crossing the bridge is: when encountering road maintenance, traffic jams are often added; shortly after the road is repaired, bumps and bumps will appear, driving like a fellow ship. It is basically a maintenance cycle of 4-5 years, and the cycle of this cycle is still shortening.
Recently, with the completion of Wuhan Junshan Yangtze River Bridge super-high-performance concrete pavement, a new technology independently developed in China has also become a "net red". The biggest feature of this new technology is that it can greatly reduce the maintenance of the bridge deck and even achieve zero maintenance. The reporter from Science and Technology Daily came to the State Key Laboratory of Bridge Structural Health and Safety in Wuhan with curiosity and interviewed experts on the development and application of this technology.
Greatly improve bridge health and safety
The Junshan Yangtze River Bridge was opened to traffic on December 15, 2001, and has been in operation for 17 years. The bridge is a super-large expressway bridge across the Yangtze River shared by the Beijing-Hong Kong-Macau Expressway and the Shanghai-Chongqing Expressway.
The bridge currently has an average of 34,000 vehicles per day during peak periods, and more than 60% of them are large and medium-sized trucks. The high load, which is far beyond the design standard, puts huge pressure on the bridge deck. As early as 2010, the bridge was first repaired for about 100 days, and then repaired several times in the following years.
Tian Qixian, dean of the China Railway Bridge Science Research Institute and deputy director of the State Key Laboratory of Bridge Structural Health and Safety, introduced that there are many "sub-healthy" bridges like the Junshan Yangtze River Bridge in China. In recent years, the decks of large-span bridges in China mostly use orthotropic steel bridge decks, and the surface is paved with asphalt materials. However, with the economic development, the number of heavy-duty trucks has increased, and most bridge decks are subjected to loads far beyond the design. Not only the pavement is frequently damaged, but the lower steel plate is also prone to fatigue cracking and other symptoms.
Tian Qixian said, "The ultra-high-performance concrete composite bridge deck technology used in the Junshan Yangtze River Bridge this time can be used as a structural layer to reduce fatigue stress and avoid cracking of steel structures. Providing a permanent protection greatly improves the overall health and safety of the bridge structure. "
Project Chief Engineer Chen Luyi introduced: "Under normal circumstances, epoxy asphalt is removed and rebuilt every 5 years, and each maintenance period is 2-3 months, which has a great impact on traffic; ultra-high-performance concrete requires only 15 After the year, the wear layer on the surface is maintained (if the wear layer is not paved, it is maintenance-free), and the price is low (approximately one-twentieth of the epoxy asphalt), which takes only 2 days, which has a great impact on traffic small."
It will take 2 years to wear 2 mm
Tian Qixian said that materials are the foundation of the structure. For further development of the bridge structure, material innovation is essential. Therefore, improving the performance of concrete is the top priority.
Ultra-high-performance concrete is a new material that appeared in Europe in the 1980s. Compared with ordinary concrete, this type of concrete has ultra-high-strength properties and ultra-high durability. However, this material has two drawbacks: high shrinkage and the need for steam curing. "The easy-to-crack symptoms brought by high shrinkage make its scope of application severely restricted, and steam curing has also greatly increased the maintenance cost." Tian Qixian said.
In response to these two shortcomings, after nearly 6 years of exploration and thousands of tests, the team obtained a large amount of mixture data, and finally developed a low-shrinkage, non-steam curing ultra-high-performance concrete. Tian Qixian said: "Compared with ordinary concrete, the low-shrinkage, non-steam-curing ultra-high-performance concrete has 3 times higher compressive strength, 4-8 times higher tensile strength, 200 times higher toughness, and abrasion resistance after This means that if ordinary concrete wears 2 mm in 25 years, it will take 100 years for ultra-high performance concrete to wear 2 mm, which greatly reduces the maintenance costs in the future. " Performance concrete, they also developed ultra-high performance concrete composite bridge deck technology, which completely solved the problem of fatigue cracking of steel structure bridge deck.
Very wide application range
In 2016, the team first applied the ultra-high-performance concrete composite bridge deck technology to the Taiyuan City Photography Bridge.
After nearly two years of real-time health monitoring, the stress on the steel plate on the bridge deck has been greatly reduced compared to similar bridges, indicating that fatigue cracking of the steel plate will not occur.
Since then, this new technology has been used in Harbin Songhong Bridge, Yibin Jinsha River Public-railway Bridge, the Mongolia-China Railway Dongting Lake Bridge and the Public Security Yangtze River Bridge, as well as the current Junshan Yangtze River Bridge and other bridges.
"With the maturity of ultra-high-performance concrete technology, the cost of industrialized production will be further reduced, and its application scope will become wider. We are also currently conducting some new research. The next step will be to explore the ultra-high-performance concrete from several aspects. New applications, such as the combination of ultra-high-performance concrete and ordinary concrete. The durability of ordinary concrete can be improved by paving a layer of ultra-high-performance concrete, and the super-high-performance concrete on the surface can prevent its cracking, increase strength, and greatly reduce Follow-up maintenance costs. "Tian Qixian said, on the other hand, ultra-high-performance concrete can be applied to the parts of the structure with high stress, which can effectively improve the structural bearing capacity, reduce the weight of the bridge, and promote the diversification and lightweight of the structure of the bridge. Thinning. In addition, it can also try to apply ultra-high-performance concrete to some special buildings, such as the water front of a dam, the shell of a nuclear power plant reactor, and a sea-crossing bridge. The ordinary concrete used in these special occasions, because it is easy to crack, will cause water leakage or erosion of harmful substances, affecting the use function and life of the structure. If ultra-high-performance concrete is used, it can effectively prevent the occurrence of disease and extend the life of the building. .