As time goes on, the highway will become more and more noisy. To this end, German engineers are developing "silent concrete". This kind of concrete is particularly good at absorbing tire noise.
The noise of vehicles has recently been significantly reduced in about 1 km of a German highway. The reason is that the highway in this area is paved with open asphalt. The reason why it can reduce noise is that there are many tiny gaps in the road surface, which can "swallow" the sound produced by the rolling wheels.
Tests show that the use of this asphalt pavement with holes can achieve a significant reduction in noise. But they also have a big disadvantage, that is, over time, heavy trucks will produce a series of flange-grooves on the road surface. Compared with this, the concrete pavement is much stronger. But so far, no concrete technology can achieve similar noise reduction effect.
Therefore, the researchers of the Federal Transportation Bureau began to seek new ways to make concrete learn to "speak softly". The principle they use is similar to that of open-pore asphalt, which is also a tiny gap.
"There are many small voids in the open-cell concrete," the project manager said. She held in her hand a small gray square made up of many small stones connected to each other, with many gaps between the stones. These voids are formed because construction workers remove certain ingredients when producing concrete. "We didn't use sand or dust.". The function and principle of perforated pavement, whether asphalt or concrete, are the same. On the one hand, they act as a sound-absorbing material in the highway space, that is, they can absorb sound waves. "The noise of rolling wheels, especially in the high frequency part, will not be generated at all on the pavement paved with this material," said the acoustic expert of the Federal Transport Bureau. Acoustically, there is the so-called "exhaust effect", that is, when a tire rolls on the road surface, it will squeeze out the air at the contact point with the road surface and make a sound. If the surface of the road has many half-exposed voids, the exhaust effect no longer occurs. In this way, the purpose of avoiding noise is achieved. On the contrary, if the pavement is very tight, these noises will be generated.
Technicians can reduce the noise by about six decibels, or half, using this open-cell concrete. However, acoustics experts favor concrete not only because of its long service life, but also because its noise-reducing effect may last longer. Generally speaking, over time, the gap on the road will be blocked, and in the long run, the noise on the road will increase again. As far as open-pore asphalt pavement is concerned, it will be no different from ordinary asphalt pavement after almost eight years.
At present, perforated concrete pavement is not allowed to be used on expressways. Technicians must also first conduct long-term tests on secondary highways to ensure that it has a long enough service life. But they are quite sure about the effect of another kind of noise-reducing concrete. It is a kind of washed concrete with special treatment.
Highway experts said: "The specific generation process is to first pave ordinary washed concrete, and then brush its surface with a brush to remove the additives on it." After this treatment, there will be a smooth road surface, without obvious ups and downs, or potholes. Subsequently, the road workers milled a series of fine grooves longitudinally on such a surface. What was the result? "You can think of it as a plain with gullies," said the highway expert. The function of these grooves is that when the wheel rolls over, the air can flow in. After the wheel rolls away, it can be released again. In this way, the effect of the exhaust that generates the noise is mitigated. This kind of pavement also plays a role in reducing noise.
"In addition, if we can get a very smooth road surface, it will have a small load on the tires.". We have found that the issue of trench ventilation is very important, especially for the tires of large trucks. In other words, it is this longitudinal trenching method of road construction that is particularly advantageous mainly for truck transportation. In fact, the authorities have made plans to use this pavement on the right side of the highway, which is the main road for large trucks. Compared with open cell concrete, this kind of concrete has the advantages of easy production and low cost. Researchers plan to put it into practice on the highway after the final test on the test section this autumn.
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