Rust destroys bridges, erodes buildings, capsizes cargo ships: in Germany alone, this silent eater of metals costs more than 100 billion euros a year. Scientists and engineers are working hard to combat this, developing new protective coatings and detectors that can identify rust early on. At the same time, rust color is also considered by some to be a symbol of nobility, and has occupied a place in the fashion art world.
Nearly 11 o’clock on May 21, 1980, there was only a loud noise, and flying dust rose into the sky. The 600-ton curved roof of the Berlin Conference Hall in Germany suddenly collapsed, breaking the stairs at the entrance and burying the gate. Five people were injured and a journalist was killed. On December 12, 1999, the oil tanker “Erica” encountered a storm with 12-meter-high waves in the waters off Brittany, France. To pollution, tens of thousands of seabirds died.
These two disasters seem unrelated, but they actually have one thing in common, that is, they are both caused by rust. From a chemical point of view, rust is an oxide of iron, which is the product of the combined action of iron, oxygen and water in the air. Rust is the brother of rot and the brother of mold. It is everywhere, seemingly insignificant, but its destructive power cannot be underestimated. Rust has been a headache ever since humans freed iron from its encasement of rock and oxygen with the help of fire and charcoal. Once the conditions are right, iron that has been cast, wrought, or flattened will rust again, because oxygen, the most common substance on earth, reacts too easily with iron, the fourth most common substance. Rust, the silent attacker, erodes human achievement, destroys tall buildings, destroys bridges and vehicles. “In the quiet of the night, you can hear the rusting sound of a Ford car.” Americans love to joke like this. The French have been jokingly calling their Eiffel Tower the “Rust Tower” for years.
The World Corrosion Organization, a subsidiary of the United Nations, takes it as its mission to resist “quiet destruction”, and calculates that the annual expenditure caused by the corrosion of metal materials used in construction is about 3% of the gross domestic product of developed countries. From this point of view, in 2018, Germany’s expenditure on this topic reached more than 100 billion euros. Moreover, the “corrosion” here may only refer to the “rust of iron” in a narrow sense. Experts estimate that about 25% to 30% of losses can be avoided if builders, engineers and technicians always insist on rust prevention.
| Wicked Rust|
On a cloudy day in September 2019, a truck is parked in the emergency lane on the Bernbach valley bridge of the Saarland line motorway near the city of Aslar, Germany, with a working platform suspended from it and standing Three construction engineers in orange overalls. They are employees of the Hessen State Road Administration. According to German law, all engineering buildings must undergo a “big inspection” every six years, and all building components need to be carefully inspected. Three years after the “big inspection”, it will be a “small inspection” focusing on the defects found before. The work carried out on the Bernbach Valley Bridge this time is a “small inspection”.
In Germany, the problem of bridge safety is very worrying. There are about 39,500 bridges on motorways and federal arterials, tens of thousands more on smaller roads and more than 25,000 bridges on railways. Steel is present in all bridge construction, such as in supporting building elements or as reinforcement embedded in concrete. Some bridges have so many defects that they are no longer able to withstand the traffic load.
Of particular concern to transportation planners are prestressed concrete bridges. In Germany, 70% of the bridge area on highways and arterial roads is built with prestressed concrete construction technology. Architects love this way of building that seems to defy gravity, allowing houses to soar and boldly arch over valleys and rivers.
Prestressed concrete is more stable because of the steel wires and strands in it. But in the 1960s and 1970s when Germany aggressively expanded its infrastructure, road builders did not have a good grasp of this method. They used perishable rebar, undersized the bridges so easily they cracked, rusted easily when moisture seeped in, and some bridges had to be demolished or refurbished less than 20 years after they were built. The German Ministry of Transport has invested billions of euros in modernizing and strengthening bridges, and billions more will be needed.
The Saarland Line motorway was also born at the beginning of the application of prestressed concrete construction technology. It connects the Rhine-Ruhr economic area with the Rhine-Main metropolitan area and passes through a large number of valleys in the mountain section: from Dortmund to Asch There are a total of 73 bridges along the 260 kilometers of Finnburg, with an average of one bridge every 3.5 kilometers.
One of them is the Bernbach Valley Bridge. It is a box girder bridge, that is, a long hollow truss made of steel or concrete under the driveway as a beam: 191 meters long and 24 meters high. It was built in 1971. The Germany-wide “Road Information Base – Construction” documents the current state of each bridge. For this valley bridge near the city of Aslar, it reads: Both directions are unqualified, and the number of defects exceeds 203, including cracks, dislocations, hollows, water penetration… But this does not mean that Bernbach Valley The bridge may collapse at any time, but only to remind the relevant departments of the need to take timely action.
Despite the record, routine controls remain in place. Norbert Lor tied the climbing rope, stood in the elevator at the end of the workbench and went up two meters, just under the box girder. Four meters away from the bridge head, Lore kept beating with a hammer in his hand, and rusty steel bars soon appeared in the peeling concrete. Fortunately, they’re what engineers call “loose bars,” those added to strengthen the concrete, rather than “tight bars” that would compromise the bridge’s safety, so there’s nothing to worry about just yet. If the stability of the bridge is threatened, engineers immediately block that section of the road.
Lol marks the bridge with a circle drawn in red chalk. Achim Hofmann, 47, marks the exposed steel bars with short, wavy lines in what he calls “crack sketches.” This sketch is used to record building defects with an abbreviated notation with location and extent. In fact, concrete is the perfect “stainless” environment for iron and steel — a pH above 12, similar to ammonia. “In such a highly alkaline environment, the rebar will not rust,” Hoffman said.
However, bridges age, and various mechanisms may clear the way for rust to form, such as carbonation. Within a few years, carbon dioxide in the air will penetrate more and more into building materials, chemical reactions will occur between some components, and the range of acidic environments will gradually expand. Hoffman, a construction engineer, said: “If the pH value becomes 8, the steel will inevitably rust. Moreover, the more porous the concrete, the more serious the carbonation.” Add moisture, and the iron will be corroded. Moisture will inevitably get in through small cracks, and for a structure like the Bernbach Valley Bridge, there are too many gaps.
While the bridge quality inspectors were working under the box girder, there were still vehicles on the bridge. It was originally estimated that only 30,000 vehicles pass here every day, but now about 60,000 vehicles pass through here every day, more than 20% of which are trucks, some weighing 44 tons. Statistics show that each truck puts as much pressure on a bridge as 20,000 to 40,000 cars. To make matters worse, traffic here is on the rise.
Another problem with the Saarland Line motorway is that many valley bridges face north. “Antifreeze salt must be sprinkled in winter to maintain the trafficability of the road.” Hoffman said, “And antifreeze salt is the enemy of building steel.” Next, the metal is etched out of the hole. The most dangerous part is that even though the interior has been eroded by rust, the surface of the building is often free of dislocations and cracks, and no damage can be seen.
The workbench moved slowly, with constant bumps. 20 meters below the bridge body is the Bernbach River meandering through the bushes. For these building quality inspectors, the first thing to do when measuring is to ensure that they will not be dizzy. After the first pier, Michael Herder ascended with a small elevator and found a hollow point 58 meters from the bridge head. To remove loose building material, Herder used a percussion drill. “It’s very weak already,” he shouted to his colleagues. Debris kept falling and the hole is now 20cm deep. Herder took pictures and recorded them. As bad as it looked, Herder was relatively at ease. The damage was at the edge of the bridge’s arch and was not critical to the bridge’s load-bearing capacity, although it would be better to repair it. Four hours later, the trio finished work. The next day, they also inspected other parts of the bridge, looking for traces of rust.
| A History of Rust Research|
It seems to us that oxygen makes up as much as 20% of our environment for granted, but it has not always been the case. In ancient times, this gas existed in a free state in very small amounts. Until about 3 billion years ago—the exact date is still debated—cyanobacteria in the ocean brought about a new form of material exchange: They used solar energy to convert carbon dioxide into organic matter, and photosynthesis emerged. As a by-product of this process, oxygen is increasingly present in the air. The substance was toxic to the dominant organisms of the time, but life apparently survived the crisis, such as us humans and all other organisms that rely on this gas for their metabolism. So, rust is the price we pay for being able to breathe freely.
Masses of chemists, physicists, and engineers around the world have fought hard and persistently against this quiet destroyer. They search for new alloys that resist oxidation, look at what’s happening inside corroded metals at the atomic level, and develop new protective coatings and detectors that can identify rust early on.
Scientists from the Iron Research Department of the Max Planck Institute in Düsseldorf are also part of this. Their lab is housed in a brick building—although, given the subjects of their research, a steel building seemed more appropriate. Here, the sparkling rough world of a steelworker meets the delicate precision of a materials researcher. In the workshop halls, skilled workers fuse iron with elements such as vanadium, chromium, molybdenum or manganese to create new alloys. In the lab, scientists use atom probe tomography to peer inside metals, identifying how various atom types are arranged while tracking down traces of this ubiquitous metal eater. At first glance, the generation of rust follows a simple principle: humid air plus iron produces iron oxide, which is what we commonly call “rust”. “However, if you look more closely, you can see that the corrosion of iron and steel is actually a more complicated matter,” says electrochemist Michael Roveldel, who leads the “corrosion” working group. It’s complicated because the rust layer is made up of many different compounds of iron and oxygen as well as so-called “hydroxide ions” at the same time. They have famous names such as magnetite, goethite, and lepidosterite. “All of these rust products are several times larger than pure iron, and that makes rust very dangerous,” Loveldell said. It rises like dough, producing a lot of energy that could crack the concrete.
In addition, there is a lot of rain and condensation seeping into the pores. The transition between wet and dry phases determines the composition of the rust layer, explains Roveldel. It is a multiform, mutable adversary that erodes our infrastructure.
However, scientists have been studying rust prevention methods more than the details of rust formation. A classic method is galvanizing. Protecting steel with millimeter-thick layers of zinc is a traditional strategy because zinc is cheaper than iron and reacts more readily to oxygen and moisture. Even if there are scratches on the zinc layer, the iron will not be corroded, because the corrosion products produced after the zinc is oxidized will cover the scratches again.
Typically, another protective layer, such as lacquer, is added over the zinc layer. Anti-corrosion substances are often implanted during painting, such as zinc phosphate, which can repair the zinc layer if it is damaged. This method has a disadvantage: the humidity will gradually deplete the zinc phosphates, even if they are not used at all. In order to make zinc phosphate exist in sufficient amount in the long-term loss, they must be used in large quantities in the coating, so they may also enter the environment in large quantities, causing unnecessary environmental burdens, such as heavy metal pollution.
This has to get smarter, Loveldell said. The protective film they are developing can autonomously determine whether corrosion has occurred and only release effective substances when corrosion has actually occurred. Just like our body’s repair army – platelets and immune cells, they are only activated when the body is injured.
In Loveldell’s lab, “Kelvin detectors” are constantly measuring the voltage, which drops if corrosion occurs beneath the paint layer. The researchers implanted smart “healing substances” in the paint layer. They are housed in small boxes that sense changes in voltage, and when necessary pipes are opened and substances that end metal erosion are released. At the same time, the scientists at the Max Planck Institute were also working on a way to rebuild the damaged paint. “In this way, we have achieved a real ‘self-healing’.” Loveldell said.
From the car example, we can see that the efforts of these steel guardians are worthwhile. In the 1980s, when rust holes in the underside of the trunk or red eschar on the decklid seemed inevitable, the ability to paint and use a welding machine was a must-have skill for a driver. Now, car manufacturers guarantee that their products will not rust for 8 to 30 years. The anti-rust strategy is simple: perfect galvanized iron and improved paint, avoiding designs where moisture can pool, such as grooves in doors. At least in the car, the red attacker looks like a tiger with its teeth pulled out, and its prestige is no longer there.
| Beautiful Rust | Rust
isn’t a scary ghost for everyone, some people love this reddish-brown eschar so much they consider it a sign of nobility and even paint their cars the rust color.
Rust marks the past, living proof. Unlike a world increasingly dominated by digitization and illusion, this raw and eroded metal symbolizes the coldness of material reality. And at the Volklingen Ironworks, which welcomes tens of thousands of visitors every year, this feeling reaches its climax, where the contradiction between the destructive and aesthetic rust is very sharp. Pipes, elevators, iron furnaces, coke ovens, halls and workbenches can be seen here and there, and the colors are bright and colorful: fresh rust spots are orange, and when they age, they will turn reddish brown, brown and purple. Visitors love the hues and enjoy roaming freely here in relaxation.
In 1994, UNESCO listed the Volklingen Iron Works as a World Cultural Heritage Site. In 1986, the century-old steel mill stopped production, and the people of Volklingen endured the frustration and pain of unemployment, hoping to dismantle this rusty behemoth. Today, a large number of conservationists come to Saarland to learn how to renovate and maintain steel buildings.
The 58-year-old architect and urban planner Andreas Thiem has been leading the heritage building department of the Völklingen Steelworks since 2009. His office is what used to be the Furnace Office. Tim says there is good and bad rust, “good rust is an oxide film that protects the metal from further attack. bad rust is ‘puff pastry rust’ that stores moisture and can have a huge impact on our lives. impact. Whenever it rains, this rust increases.”
The requirements of UNESCO make cultural relics protectors face a practically unsolvable task: to maintain this world cultural heritage completely and truly. That means, they have to maintain the state of these rusts, but at the same time they can ruin everything. Tim knows that if he doesn’t intervene, if he doesn’t interfere, it will cause the building to collapse; if he wants to fully maintain the status quo, he must give up authenticity.
what does this mean? Next to the ironmaking furnace office is the charge hall, which used to store 12,000 tons of raw materials. Tim pointed to a pillar and said, “We had to cut off a section and replace it with a new one.” The chemical composition is as close as possible to steel as a substitute.
The architect feels a bit like a surgeon. “To save a patient’s life, surgeons sometimes have to be ruthless, even cruel, such as amputating a patient’s leg,” he said
. Rust was never a problem when steel mills were still producing. The ultra-high temperature of ironmaking furnaces, coke ovens, and hot blast stoves makes moisture nowhere to hide, and “bad rust” cannot be produced. By the time it was shut down, the steel mill was churning out millions of tons of iron and steel. The metal was used in buildings as steel beams, as wire in fences, as steel helmets worn in the trenches of Verdun, and as bullet casings that brought death. Many of them have gone through the classic path of iron elements: contact with the earth’s environment, return to the embrace of oxygen, return to the original, and become rust.