After the Second World War, governments of various countries poured huge funds into the modernization and creation of infrastructure: highways, bridges, railways. More than half a century has passed since then, and all this asphalt concrete legacy gradually begins to crumble, leading to economic losses and even human casualties, and it is expensive, long and ineffective to put trackmen with flaw detectors to all ends. We tell how scientists suggest listening, touching and looking at the road infrastructure in order to solve the problem of its aging.
According to the World Bank, roads today are the least invested infrastructure element on the planet. Compared to ports, railways, electric networks, water supply systems, telecommunications, airports, much less money is poured into this segment than necessary. Analysts believe that the road network of the planet by 2040 will receive less than $ 8 trillion needed for its modernization and development.
This means that roads, as well as road constructions (flyovers, bridges, tunnels) will be destroyed if we do not come up with more efficient and economical means of servicing them. Structural Health Monitoring (SHM) is now one of the most material and labor intensive industries.
We are missing:
- people, because the length of the infrastructure is such that it is impossible to effectively diagnose its condition by mobile means with the personal participation of specialists;
- technology, since flaw detection equipment itself quickly wears out, but at the same time is very expensive;
- time, because with the means it is impossible to ensure the necessary frequency of inspections, so as not to miss a fresh crack in the already seen column of the flyover.
Which direction to go? The general vector is as follows: SHM tools should be small, numerous, cheap, automated, interconnected and remote, and the flow of analytics from them should be continuous. In other words, the IoT revolution should also cover the SHM sphere, where there are many sensors and data collection practices, but there is no communication base for this. What means of monitoring roads and structures need to be integrated into the Internet of things? What does it look like? We show an example from the practice of Toshiba and our colleagues from other countries.
Listen: Acoustic Sensors in Bridges and Tunnels in Japan
In 2012, the arch of one of the many road tunnels collapsed in Japan. A 30-meter stretch of the ceiling mounts of the 4-kilometer tunnel collapsed on passing cars. As the examination subsequently showed, the reason was the banal aging of structures that have not been properly serviced since the 1970s. In a mountainous country, where there are more than 150 thousand bridges and tunnels, such accidents should not be allowed. Moreover, by 2033, about 63% of structures of this kind will celebrate their fifty or even more anniversary.
Toshiba Corporation, together with the University of Kyoto, has developed a technology for the acoustic analysis of concrete structures to visualize internal defects of bridge elements. It is based on acoustic emission, that is, stress waves that occur during dynamic processes in different materials. Simply put, any destruction generates sound (acoustic waves), such as, for example, a tree branch breaking before a fall. Of course, far from all these waves can be caught with the naked ear, therefore, special sensors “hear” the sound.
Acoustic emission sensors can be placed along the entire structure of bridges, tunnels and other structures. Telemetry can be obtained and analyzed almost continuously, and interference with traffic is almost not required. Source: Toshiba YouTube Channel
Internal damage to the material is reflected in the wave pattern, allowing you to understand exactly where in the concrete slab there is a crack, break, voids, etc. Moreover, the intensity of sound can predict the rate of further destruction of the material and its source. In this case, we do not need to physically affect the concrete or cut out any samples for study - everything passes within the framework of the non-destructive testing technique, which, by the way, we have already talked about .
By coloring the intensity of acoustic emission, you can understand in which part of the concrete structure there are already large faults, where they can appear, and where the material still maintains its integrity. Source: Toshiba
Sensors can be connected to a network, connected to geolocation systems, and the collected data can be analyzed in a data processing center remotely using energy-efficient long-range networks (LPWAN, BLE), as well as 5G for communication. No bypassers are required, and monitoring can go on almost continuously. True, the need for such a thorough analysis in the case of concrete, which has proven its durability since the days of Ancient Rome, is not always there, which can not be said about the road surface - the most vulnerable element of the infrastructure.
Touch: vibration sensors on German autobahns
As you know, in Germany one of the longest national road networks in the world, and it is logical that such an economy is not easy to care for. By 2030, the country's government intends to spend 270 billion euros on repairs and the construction of new lines of communication, of which 69% will go to modernize the existing infrastructure. Half of the allocated funds will be spent on roads, and it’s really difficult with them: only 177 km of roads are subjected to frequent diagnostic analysis in Germany, while 505 km are irregular. Meanwhile, the total length of the autobahns alone is 13 thousand km. Obviously, all these kilometers can not be bypassed and can not even go around on special diagnostic cars. Therefore, a group of scientists from the Karlsruhe Institute of Technology proposed an original solution - to turn personal cars of ordinary Germans into diagnostic cars.
For this, the engineers proposed to equip the machines with inexpensive measuring instruments - an inertial sensor with a GPS module. The inertia sensor is located near the center of gravity of the vehicle. Acceleration and angular velocity recorders also collect data at a specific geographical point. The collected information can be automatically transferred to the server via Wi-Fi as soon as the car returns to the parking lot - this is if the owner of the car does not want the geography of his movement to be somehow recorded and stored. However, if the monitoring operator manages to ensure the safety of data, and the owner of the machine does not mind, then the inertial sensor and GPS-module can be integrated into the IoT ecosystem. This will allow you to receive information about the condition of roads in real time. For example, if a crack forms on the roadway due to a landslide, the road network operator will know about it as soon as the first machine connected to the system passes over the crack. Then, based on the machine learning algorithm and statistics calculated from the vibrations and dynamics of the vehicle, the system can classify the characteristics of the road and evaluate its condition.
The main thing is to place the sensor correctly, otherwise the data will be read incorrectly. Source: Masino, J., Frey, M., Gauterin, F., & Sharma, R. (2016). Development of a highly accurate and low cost measurement device for Field Operational Tests. 2016 IEEE International Symposium on Inertial Sensors and Systems.
In fact, the car turns into a mobile device, which "feels" the road surface for its evenness. The stronger and more often the vibrations, the worse the quality of the road. Equipping even a relatively small part of the cars will make it possible to cover most of the German roads with diagnostics. The technology is perfect for a well-equipped motorway in Germany, but in Russia, where railways are important, a different technique is used.
Take a closer look: fiber optic sensors and Russian railways
Russia ranks third in the world in terms of the length of railways after the United States and China - it is 85 thousand km (slightly more than two equators of the Earth). At the same time, most of the railways pass in hard-to-reach places with difficult climatic and geographical conditions, which makes the infrastructure deteriorate faster than in other countries.
Tracking the railways in Russia is not easy, because it requires a lot of flaw detection equipment, in fact, specialized trains equipped with numerous sensors. Their speed is low, cost is high, so they cannot give a continuous flow of information. And the diagnostic cars themselves are rapidly becoming obsolete: by 2020, the wear of this equipment will reach 84%.
How to replace them? Engineers of the Russian company Laser Solutions offer to monitor the condition of railways through distributed fiber-optic sensors. To measure environmental changes, a light signal is transmitted through a fiber optic cable. Since the speed of light in an optical fiber is known, the time delay between the pulse input and the recording of its reaching the end point may indicate physical effects on the cable - temperature, deformation, vibration, and acoustic vibrations. They locally change the characteristics of the origin of light. Thus, the fiber optic cable turns into a long sensor, which, as it were, “looks after” the infrastructure object throughout its entire length. Such a cable can be dug, for example, in the earthen base of the railway track - a vulnerable part of the railway infrastructure, because constant movements of the soil wear out and break the road. At critical sections of the tracks, fiber-optic deformation and temperature sensors are laid in the subgrade. A deformation sensor monitors the movement of the soil, and a temperature sensor is necessary for seasonal processes of thawing the earth.
So far, the length of sections of railway tracks controlled by fiber-optic sensors does not exceed 60 km, due to purely technical and well-known economic reasons - digging a high-tech cable where even copper wire can be stolen is fraught with negative consequences.
At the same time, it must be understood that in this and in the technologies described above, we are creating a separate infrastructure for monitoring the road transport infrastructure, which also requires maintenance - collecting and processing information, interpreting data, and responding. Someday, this parallel network of sensors, cables, data centers will have to be changed. To get out of this technological recursion, we need to teach the infrastructure self-healing.
“Heal yourself!”
In recent years, scientists have been trying to develop new building materials that can be restored (almost) on their own. So, at Delft University of Technology (Netherlands) created asphalt, which can be treated with induction heating. Asphalt is, roughly speaking, a mixture of gravel and sand, which sticks together thick and viscous bitumen. Gradually, under the influence of erosion, oxidation, temperature, and physical pressure, this “glue” wears out, after which the asphalt cracks and then becomes covered with holes. The Dutch suggested adding thin steel chips to bitumen, and then heating it from time to time using magnetic induction using a special road machine. At the same time, bitumen absorbs heat and regains viscosity, which holds together the elements of asphalt. According to scientists, this way of servicing asphalt will double its life time.
But as part of a treatment course for concrete, some scientists suggest prescribing special bacteria - sulfate-reducing microorganisms. They can be implanted into concrete at the construction stage and remain in suspended animation until the habitat changes, say, until microcracks appear. Then these bacteria come out of hibernation, begin to multiply and produce calcium carbonate and other substances that hold together the crumbling concrete.
So, the integration of all the sensors mentioned above into the Internet of things in the future will allow us to make monitoring truly continuous, which will virtually eliminate or significantly reduce the likelihood of technological accidents, reduce both the costs of maintenance and the construction of new infrastructure facilities, and also lead to release for more interesting tasks of tens of thousands of conditional trackmen around the world.