This is an example of a highly successful acoustic solution for a metal industrial building containing an extremely loud noise source.
Over time, hardened concrete builds up inside the drum of concrete mixer lorries and this reduces capacity and increases vehicle weight and fuel consumption. So the hardened concrete needs to be removed periodically. The traditional way of removing it is for a man to crawl inside the lorry drum and use a pneumatic hammer drill (like a road drill) to loosen the concrete. This is extremely noisy. It also generates a lot of dust (which is a carcinogen) within a small confined space with limited ventilation, so it is a hazardous job.
The disadvantages of this manual operation led a company to develop a new method of removing the concrete. This uses a water jet at very high pressure (20,000 psi) to free the concrete from the drum interior. The water jet is on a long boom that is operated remotely by an operator from outside the lorry drum. Being outside the drum makes the process much safer, considerably reducing the operator's exposure to dust and noise. The water jet method also saves a lot of time. It can take several hours to clean a lorry drum manually, whereas a water jet clean typically takes 45 minutes, according to ReadyJet, the company that provides the service in the UK.
You can see the traditional method of removing hardened concrete in this video: manual mixer drum cleaning / chipping and compare it with the new cleaner water jet method in the video: ReadyJet safer concrete removal by water jet.
There are more details about the water jet system on safer concrete removal for mixer drums.
When ReadyJet started up their water jet cleaning service in the UK, they built a new steel-clad industrial style building at a site near Heathrow airport. They installed their water jet equipment inside this tall, thin metal building. Concrete mixer lorries reverse into the building for the cleaning operation. You can see the steel building in the photograph above.
When they carried out the first trial run, Readyjet received noise complaints from a company that carries out lorry trailer repairs in an external yard beside the steel water jet building. So we were asked to investigate and help with an acoustic solution to reduce the high noise transmitted outside the water jet building.
Trailer repair workers often work as close as 3 metres from the side of the water jet building. Our noise survey found that with the water jet running, the noise here was 94 dBA (with all the water jet building doors closed). With the water jet off, the noise here was 59 dBA with no trailer repair activities and 69 dBA with general repair activities in the yard. So the water jet was increasing noise levels in the repair yard by 25 - 35 dBA (even though the water jet was enclosed inside a building). It was also exposing trailer repair workers to a noise level that was 9 dBA above the 85 dBA legal limit of the Control of Noise at Work regulations (for 8 hour exposure). The water jet noise in the yard was so high that it made it impossible for trailer repair workers to communicate.
ReadyJet plans to operate its water jet cleaning service at night in future. There are houses nearby so it is highly likely that night operation would have woken up nearby residents and caused noise nuisance complaints.
Using the data obtained from the noise survey, we designed an acoustic solution and noise insulation treatment for the steel industrial building containing the water jet equipment. We considered a range of materials / panels and designs to determine the best option that provided the necessary noise reduction at minimum cost. The acoustic solution / noise insulation treatment was designed to provide the very high noise reduction needed to allow night operation without causing noise nuisance to residents. It was also designed to avoid the water jet causing noise nuisance and interfering with communication for workers in the adjacent trailer repair yard. To achieve a very high noise reduction, a number of different materials were used, some to provide noise insulation, and some to provide acoustic absorption of the sound.
The treatment was highly successful, reducing the water jet noise outside the building by 30 - 32 dBA. This is a massive sound reduction. It meant that in the adjacent trailer repair yard, the water jet noise was not even audible, whereas it had been extremely loud before. This made it easy for trailer repair workers to communicate in their yard. At 3 metres from the side of the water jet building, the water jet noise was 62 dBA after treatment, which is only slightly higher than the daytime background noise when there are no trailer repair activities in the yard. Prior to installation of the acoustic insulation solution, the water jet noise inside the building was 120 dBA. So the acoustically treated building achieved a remarkable sound reduction of almost 60 dBA. This is an extremely high noise reduction for an industrial building constructed of profiled steel panels.
Furthermore, the water jet noise has been reduced to such a large extent that the company can operate at night in future without causing nuisance to local residents.
You can see more examples of our highly successful sound reduction projects on acoustic solutions for all types of building.
There are more examples of our high performance noise insulation solutions on soundproofing industrial buildings.