ACOUSTIC GRINDING

Cedima technology reduces noise pollution from concrete roadways

The expansion of European transport routes will pose a particular challenge in the coming years due to the increasing number of vehicles. The aim is to make the highways fit for the future and to consider the additional requirements resulting from the energy transition, climate change and increasing scarcity of raw materials. Specifically, the aim is to increase the grip of the surface while reducing rolling resistance, to minimize aquaplaning through optimized drainage and, finally, to noticeably reduce the rolling noise of the tires. In addition, the service life of the roadway or the road surface was to be noticeably extended compared to today's standards. In Germany, concrete roadways have been designed with an exposed aggregate concrete surface as a low-noise construction method since 2006. This process is cost-intensive but is not suitable for meeting all the requirements mentioned. Especially since various influences such as the type of aggregates, weather, temperature and age of the green concrete do not allow for a consistent quality of the surface with this production method.

Lengthways to the direction of travel

A new, promising method of structuring the surface of concrete surfaces is grinding. In this process, geometrically arranged grooves are ground longitudinally into the already hardened concrete in the direction of travel. Originally, this method was used to drain rainwater onto roadways and thus prevent dangerous aquaplaning. However, it soon became apparent that roads treated in this way emitted less rolling noise. In addition, grinding can be used not only for new roads, but also for existing concrete pavements.

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First test route on the A12 motorway

Cedima has been a member of the "Acoustic Grinding" committee of the Research Society for Road and Transport Engineering (FGSV) for several years. Together, with the support of Nord-Ost Autobahn GmbH, they have provided a lane of the directional carriageway and part of the hard shoulder over a length of approx. 120 m on a section of the A12 motorway near Fürstenwalde with a special groove profile. The noise emission was measured on this section before and after completion, and the long-term durability of the surface in running traffic is also to be investigated. The ground area on the hard shoulder serves as a reference surface.

Grooved profile created

Before the work began, unevenness and undulations in the already outdated lane had to be compensated. This task was accomplished by the company OAT by means of an excellent quality flatness grinding. The grooved profile was ground into the road surface by a fully hydraulic Cedima CF-6021 floor saw with grooving/grinding attachment kit. In this attachment kit, diamond cutting discs with specially profiled segments sit side by side on a shaft with a total width of 600 mm. These mill a precisely defined micro texture into the concrete surface. These are interrupted at regular intervals by cutting discs with a slightly larger diameter in order to create deeper grooves for drainage.

Clean road surface

Since traffic was not to be endangered or impaired during the work – traffic was diverted past via the emergency lane, or later via the right-hand lane – the cutting sludge had to be extracted and processed. For this purpose, a suction blade guard was mounted on the grinding attachment kit. The hydraulic extraction system of the CF-6021 was thus able to suck up almost all of the cutting sludge and forward it to the Cedima CBS-1500 sludge separator. This is capable of absorbing up to 1500 liters of contaminated cutting water per hour, filtering out the solids and returning the purified water to the work circuit. The filtered-out particles can then be disposed of as pressed filter cakes in an environmentally friendly manner as normal construction waste. Thanks to its own power generator, the CBS-1500 does not require any supply lines and is able to operate autonomously.

The first 125 meters

Milling was carried out over approx. 125 meters in 60 cm wide strips. The width of one lane is 3.75 m, in addition another strip was milled into the concrete of the emergency lane. In total, this results in a processed area of about 543 square meters. Milling began on the median strip of the roadway, while traffic continued the hard shoulder. For the total distance of 125 meters, the Cedima CF-6021 needed about 60 minutes, which corresponds to a feed speed of about 2 m/min and a milled area of about 1.2 m²/min. The work was carried out on two consecutive days, as the lane for through traffic had to be moved from the hard shoulder to the left lane overnight.

Significantly quieter

After completion of the work, the noise emission of the road surface was measured again with two reference tires and compared with the values from before the processing. This comparison showed a significant reduction in noise level of 3 dB(A). At first glance, that doesn't seem like much. However, in view of the fact that a reduction in the level of 10 dB(A) corresponds to a halving of the volume in the subjective human perception, the reduction in noise emission is nevertheless considerable.

Proof of shelf life

Now the test area on the A12 will have to prove its durability under real conditions in the coming months. If it passes, it would have taken a further step towards noise reduction. However, there is still a long way to go before it can be used across the board in road construction, which Cedima will continue to support in the coming years with technology and know-how.

This article was first published in issue 54 of the trade magazine "DER BETONBOHRER".
Published by Fachverband Betonbohren und Sägen Deutschland e.V.