Complete Property Market Updates of Singapore

April 29, 2008

Recycling in construction sites

Filed under: Uncategorized — Propertymarketupdates @ 4:25 am

MATTHEW PHAN looks at what the building industry is doing to conserve water, energy and other resources

THE property market may have slowed, but the construction industry is still going at breakneck pace, with several national projects and plenty of private sector developments in the pipeline.

This is good for the economy, but perhaps less so for the environment – construction uses a lot of resources, such as concrete, steel, energy and water. How can builders mitigate this?

Water

Let’s start with water. Builders typically buy Newater from PUB, and the cost can run to several hundred thousand dollars per project, according to Pek Lian Guan, director at Tiong Seng Contractors.

This is ‘not high as a proportion of the total building cost’ but is ’still a fair amount in absolute numbers’, says Mr Pek.

Tiong Seng experimented with on-site water treatment and recycling in 2005 while working on City Developments’ Parc Emily condominium.

It ended up saving 21 swimming pools of water, says Mr Pek. This is about half of what it would have used otherwise, according to the PUB, which handed Tiong Seng one of its inaugural Watermark awards last year.

At sites, Tiong Seng sets up a temporary drainage system to collect used water and rainwater, channelling the flows to a holding area, where the water is treated using a portable membrane-based plant.

Clean or treated water is used for plastering, or recycled for washing. Rainwater is also treated before being discharged.

Tiong Seng spent $120,000 on the Cleansea plant, supplied by waste-water treatment specialist Hydroxyl, and another $80,000 for on-site piping and collection systems.

Hydroxyl’s plants are used in industrial facilities, but ‘I met them and asked whether they could be used for construction sites’, says Mr Pek. ‘They custom-made a prototype for us to do an on-site trial run.’

Housed in a 3m by 3m container, the plant is easily transported by crane from site to site, Mr Pek says. But the on-site piping may not be re-usable as it gets damaged during the two-year construction process.

Tiong Seng also implements ‘earth control measures’, such as covering exposed soil with protective sheets to protect it from erosion, which is a common problem at construction sites, says Mr Pek.

Typically, erosion can lead to muddy, silty run-off with Total Suspended Solids (TSS) levels in excess of 200, compared with less than 50 for clear drinking water, he explains.

In comparison, water from the Cleansea plant achieves TSS levels of under 10. Ironically, Tiong Seng has to train its workers not to drink the plant’s output, as the water is clear but may still contain biological contaminants.

Water conservation is another major area.

The level of use depends on the type and stage of construction, but there are typically two aspects of water use on a site, according to Simon Lee, executive director of The Singapore Contractors Association.

First, water is used in the wet works, or the concreting, plastering, testing for waterproofing and piping system, and while laying foundations. Second, water is used for site housekeeping, cleaning and washing, and at ancillary facilities like offices, living quarters or cookhouses.

On the whole, contractors manage resources by controlling their use, minimising waste and recycling where possible, says Mr Lee.

For example, it is normal practice to re-cycle water for the washing bay. Recycling makes ‘economic sense’ and ‘has always been practised by the prudent contractors’, though their input is ‘mainly in the construction processes and temporary works’, he says.

Prefabrication

In fact, sustainable construction starts at the design stage when the architects are thinking about what materials to use and how to put them together.

By using pre-fabricated components, or drywalls made partially of recycled material, builders can save water, energy and other resources.

Pre-casting, or offsite fabrication, means that not just beams and walls, but entire rooms, can be built in a factory, then transported to the construction site, where cranes fit them into buildings like Lego blocks.

‘Pre-fab takes place under controlled conditions, which minimises waste and ensures quality,’ says Vivien Heng, director at RSP Architects Planners & Engineers. ‘There is no need to worry about assembly on site. It saves time and manpower, and the site is safer, neater and less noisy because there are fewer things happening’, she says.

On the Tribeca project for City Developments, RSP is working with the contractor to use only pre-fabricated bathroom units (PBUs). ‘A PBU comes to the site like a box – everything is sealed. You just need to connect the pipes’, says Ms Heng.

Such units can also be designed using drywalls.

Made of gypsum, drywalls are used to finish the interior construction of walls or ceilings. They require no wet plaster, and can take just one or two days to install, compared to a week for masonry.

Although they weigh more than 85 per cent less than brick walls, drywalls can be insulated to achieve the same level of noise protection, according to the Building and Construction Authority (BCA).

Steel

As for structural frames, BCA has been encouraging builders to replace concrete with steel.

The latter requires no sand and has a very high strength-to-weight ratio, which allows for more flexible designs.

When connected by fasterners, steel frames are stronger than traditional systems, which allows savings on foundations and the crane capacity needed on site, according to BCA.

Steel frames are also easier and quicker to set up – which saves time on the construction site – and are fully recyclable.

Environmentalists may counter, of course, that steel manufacture is extremely carbon intensive. According to the Green Building Handbook: A Guide to Building Products and their Impact on the Environment, published in 2000, about three tonnes of carbon dioxide are emitted per tonne of steel if made from iron ore, and 1.6 tonnes of carbon dioxide if the steel is recycled.

Still, as most buildings in Singapore are high-rise, concrete or steel are pretty much the only two viable options, says RSP’s Ms Heng.

Recycled concrete

Sustainable construction also involves recycling materials – and a lot of what is demolished is reusable.

Virtually all the metal content, for example, from the structural steel to the metal doors of electrical rooms, is recyclable, according to Tang Kok Thye of ADDP Architects.

The other parts – crushed concrete, bricks, metal, ceramic tiles, wood and plastics – are termed Construction and Demolition (C&D) waste.

This is typically used for building temporary roads at construction sites or to lay the sub-base course – the deepest of four layers – of a road.

But local studies show that C&D waste can be processed into recycled concrete aggregate (RCA) and substituted for natural granite, according to an article by Ho Nyok Yong and Kelvin Lee of Samwoh Corp.

Writing in the first issue of BCA’s Sustainable Architecture newsletter, out this year, they also describe how to recycle asphalt pavements and incinerator ash.

By using RCA in place of natural granite when building roads, or in non-structural pre-cast concrete components like road kerbs and drains, contractors can save about 30 per cent, they say.

Overall, though, sustainability begins and ends with environmental consciousness and a sense of responsibility to use limited resources wisely, says RSP’s Ms Heng.

She describes how the contractor on the Tribeca project – which is located near the Grand Copthorne Waterfront Hotel – picked up some discarded carpets and used them as noise insulation for his power generators. ‘It’s an innovative, zero- cost solution stemming from awareness and a recycling mindset,’ she says.

Source : Business Times – 15 Apr 2008

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