Gulf Construction Online - Acoustic barriers the way forward

GRC

Installing absorptive noise barriers in Malaysia.

Acoustic barriers the way forward

With the increase in urbanisation worldwide, it is becoming necessary to take measures to suppress noise pollution caused by traffic in commercial and residential areas. One solution is the use of GRC noise barriers, says Ian J Morrison, Vetrotex Cem-FIL of the UK.

01 MARCH 2001

Glassfibre reinforced concrete (GRC) based on AR (alkali resistant) glassfibre reinforcement has been used worldwide since the early 1970s.

One of the earliest trials of the practical use of GRC - by the former UK Building Research Station - was a sound barrier on the M4 motorway near London. The barrier consisted of simple flat panels in grey GRC. The barrier worked acoustically but was not very attractive to look at.

As the experience of the industry developed, more complex and attractive panel forms became possible and over the past 10 years, one of the growing applications has been the use of GRC acoustic barriers.

Throughout the world, new highways and mass transit rail systems compete for space in already developed urban areas. The result is that major traffic routes move increasingly closer to commercial and residential areas. With public opinion gaining importance, it is necessary to take measures to suppress noise pollution. One solution is the use of GRC noise barriers.

The most effective barriers are absorptive and consist of a front face made in the form of a grille, borrowed Middle Eastern sunscreen technology, and a solid back face.

One of the practical benefits of GRC as a sound barrier is the relatively low weight of the panels. It is well known that transmission loss through a panel is dependent on the "Mass Law". Lightweight panels would, therefore, seem not to be a good idea. However, dispersion and diffraction of sound from the top and ends of acoustic barrier systems means that there is little or no benefit in further increases in surface mass above the typical 20 kg/sq m for 10-mm-thick flat sheet GRC.

GRC acoustic barriers have been used for many years in Europe, and their use in Asia is now growing. Some of the reasons that GRC is chosen include:

Light weight - which enables rapid erection without heavy lifting gear, causes minimum traffic disruption and exerts a greatly reduced load on elevated structures;

Durability and maintenance - GRC will not rot or corrode, and is resistant to biological attack, is not affected by freeze/thaw, road salts or vehicle fumes, has no embedded steel, so no spalling or staining, has a hard dense surface, thus offering good anti-graffiti properties, and is maintenance-free;

Flexibility of design - it makes aesthetic solutions possible and is more attractive and acceptable to residents;

Non-combustible, as it is based on cement, sand and glassfibre; and

Excellent acoustic performance - it has a high surface density and can be shaped to form reflective, dispersive or absorptive panels.

GRC panels can be fabricated by many producers worldwide. The ability of GRC to be moulded to intricate shapes means that acoustic barriers can be formed to suit local aesthetic requirements without compromising the technical acoustic requirements.

The transition from the boring, simple flat panels of 30 years ago to the sophisticated forms and shapes of today's systems is a general reflection of the progress of the GRC industry.

Vetrotex Cem-FIL, which supplies Cem-FIL AR glassfibre reinforcement, has been active in the promotion of this concept and further information may be obtained from them directly or at www.cem-fil.com.