Silence is golden: the benefits of using precast concrete for noise barriers

Roads & Infrastructure Magazine explores how precast concrete noise barriers are protecting residents from detrimental traffic noise.

Environmental noise can impact sleep, reduce work performance, potentially increase stress and anxiety levels and reduce enjoyment of home life, according to the Victorian Environment Protection Authority (EPA).

The EPA surveyed more than 1200 residents across Victoria in its 2007 EPA Noise Surveys and measured noise at 50 sites around Melbourne. It found that almost half of the people surveyed were disturbed or annoyed by environmental noise, with the main source being road traffic noise due to its prevalence and high noise levels.

Additionally, the survey found the percentage of residents that had been exposed to and annoyed by traffic noise had increased since 1986, which the EPA says indicates that more people are living nearby busier roads. According to the survey, similar studies in Brisbane, South Australia, Canada, Hong Kong and the UK found that Victorians experienced similar environmental noise impacts compared with cities around the country and world.

Very loud traffic can reach up to 90 decibels, eight times as loud as ordinary conversation, according to the US National Institute on Deafness and Other Communication Disorders. To protect residents from this noise, VicRoads has applied a limit of 68 decibels in residential areas. Roads and Maritime Services (RMS) has also implemented a Noise Abatement Program to ensure external noise levels are at least 65 decibels during the day and 60 decibels in the night.

One method used to reduce these noise levels in NSW is to install noise barriers and architectural acoustic treatments along the road corridors of freeways, tollways or transitways that have an annual average daily traffic volume of more than 40,000 vehicles.

There are three basic types of noise barriers: reflective, dispersive and absorptive barriers. Reflective barriers are usually tall walls that attempt to block noise and reflect it to reduce the overall noise level. Dispersive barriers are similar and redirect traffic noise upwards or downwards based on their inclination and pattern. Absorptive barriers dissipate the sound waves through a membrane or passage and are generally not effective for wide easements.

Sarah Bachmann, National Precast Concrete Association Australia CEO, says road authorities and construction companies often use precast concrete to create these roadside barriers because of the benefits of the product.

“There are numerous advantages of constructing noise walls with precast concrete. Being manufactured offsite in a controlled factory environment guarantees a high-quality product, excellent finishes and a fast construction time,” Ms. Bachmann says.

“Installation is simplified and safer as fewer tradespeople are required onsite. In addition, precast has the added benefits of being sustainable, as well as durable and low maintenance.

“The countless options of high quality surface finishes that are on offer also ensure a pleasing aesthetic solution.”

Ms. Bachmann adds that noise walls are able to be designed with custom moulds and patterns using form liners or void formers to create a number of shapes.

“Any finish is available too, whether that be a reflective polished finish or a textured finish, as well as pigments, stains or paints able colour the surface and images that can be carved into the surface,” she explains.

“Combining these gives the designer unlimited options, to the extent where noise walls can actually be used to improve an area’s liveable qualities.”

Shell Cove silencer

Shell Cove is a $1.5 billion residential development located 20 kilometres south of Wollongong. The project was beginning to extend towards the Bass Point Quarry, which provides crushed basalt for Sydney’s concrete production.

The main access road to the quarry in the area required a 2.5-kilometre noise wall to protect residents from the nearby noise.

RMS encourages the concept of adding art to the design of a noise wall to provide aesthetically pleasing designs for local communities, which was done by adding texture and colour to the precast panel.

A black pigment was added to the concrete mix to reference the local basaltic rock while providing the benefit of being low maintenance.

Keith McComasky, Managing Director of builder Trade West, says the construction team recognised early on the benefits of using precast construction instead of smaller lightweight panels. “Precast panels offer fast installation and we were able to lift fewer panels as opposed to many,” he says. “They are durable in the long term, as well as being less susceptible to damage during transport and installation. And they are supplied as the finished product. In terms of finishing, the coloured panels don’t require any messy finishing trades after installation”.

Glass-Reinforced Concrete

One type of precast material which can excel as a noise barrier as a lightweight alternative is glass reinforced concrete (GRC), a composite material that has alkali-resistant glass fibres randomly distributed throughout it.

GRC walls have been used by road authorities throughout Australia, on roads including the Monash Freeway in Victoria and the M4 in Paramatta. Around 1400 GRC panels were used on the M4 to line the noise barriers along the sides of the viaduct and along the on and off-ramps.

Des Pawelski, Managing Director of Adelaide-based GRC manufacturer Asurco Contracting, says GRC panels were chosen because of their weight, coming in at about one-10th the weight of an equivalent precast concrete panel.

“In this particular case, because of how the M4 was designed, it would not have been possible to retrofit regular precast concrete as noise barriers, as they would have been too heavy,” he explains.

“One of GRC’s biggest advantages is the fact it is possible to transport 20 to 30 panels in one go and they are easier to install once they’re on site. This meant there were minimal traffic flow disruptions during the noise wall’s installation, which is important as the M4 is one of the busiest roads in the country. Only a single lane was closed while the panels were installed.”

The durability benefits of precast in addition to its aesthetic possibilities make its concrete it excel when used for noise barriers, according to Ms. Bachmann, who predicts an increased uptake by road authorities around the country.

“I see more road authorities and developers of civil projects using the application as they see what’s been done elsewhere,” she adds. “They have been used widely in the eastern states to create some impressive designs and their durability can’t be outdone by any other product.”