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Building a better way to reuse concrete

A Steel mesh sunshaded box of a building in the dusty industrial estate of Kranji Crescent has been hosting a steady stream of visitors from China, Mongolia, Israel and France over the past four months.

Mostly engineers, contractors and academics, they come to gawk, snap pictures and peer at the high-tech gadgets at the Eco-Green Building.

The three-storey property built by civil engineering and building material company Samwoh Corporation boasts an entire level with fully recycled aggregate - or loose granite - in its concrete structure. It is the first such building in South-east Asia.

The visitors are keen to find out what kind of research was done on the material and how the building was constructed.

Concrete is made from granite aggregate, sand, cement, and water. While cement itself cannot be recycled, there has been increasing interest in recycling aggregate because of the environmental costs of mining the material and shrinking landfill space.

Currently, recycled aggregate is mainly used to line the bottom of roads and cast into road kerbs, rather than used in building structures, due to concerns about its strength.

To date, recycled aggregate has been used in relatively small quantities in landmark projects like Melbourne’s Council House 2, a 10-storey office block; D�bendorf’s Forum Chriesbach, the office of the Swiss aquatic research institute Eawag; and Singapore’s 11 Tampines Concourse, an office building here by City Developments.

But it is not known if anyone has tried building an entire floor, including all its load-bearing structures, with concrete containing fully recycled aggregate. Samwoh, the Enterprise 50 winner last year, is among the first - if not the first - in the world to have done so.

Sustainable building expert Holger Wallbaum from the Swiss Federal Institute of Technology in Zurich, when contacted by The Straits Times, said: ‘This initiative is quite important to demonstrate the feasibility of such an approach, not only on the national level but also on the global scale as a lighthouse project.’

Indeed, the building is now being used by Samwoh to test and showcase new construction recycling technology. Fibre optic sensors embedded in its recycled concrete columns transmit live data about how much the material is being compressed from the weight of the building. It can show - in real time - whether the structure is functioning or failing.

But the latter is far from Samwoh’s mind, which has conducted at least three years of research on this material, says Samwoh’s technical director Ho Nyok Yong. The building now houses offices for two of Samwoh’s directors, and about 50 staff from its research and development, technical and operations divisions. It also has a construction recycling gallery that is open to the public from 9am to 5pm on weekdays by appointment.

The building, together with its new asphalt recycling plant and concrete production plant, will be officially opened on Monday by Senior Minister of State for National Development Grace Fu.

The venture represents the biggest leap of faith that any building owner here has taken with regards to the use of recycled concrete.

It also gives the beleaguered construction industry something to crow about, after weeks of being slammed for dragging down national productivity statistics and being slow to undertake research and development.

The Building and Construction Authority (BCA) wants demolition waste to go ‘upcycle’ so that they are used back in buildings rather than low-value material like kerbs. The Ministry of National Development helped fund Samwoh’s $4 million project with a $750,000 grant. About 2 million tonnes of construction and demolition waste are generated every year. The BCA estimates that about 1 million tonne of demolition waste - which yields about 600,000 tonnes of recycled aggregate - is recycled.

Samwoh shaved 10 per cent off the cost of concrete by using recycled aggregate in its Eco-Green building. But the bigger draw of recycling aggregate is how it could help Singapore hedge against supply disruptions like the one witnessed in 2007 after Indonesia abruptly banned the export of sand and detained ships carrying granite to Singapore.

Associate Professor Gary Ong from the National University of Singapore’s Department of Civil Engineering, says: ‘There is big demand for construction material and increasing concern of the environmental impact of quarrying. I can see material prices going only up.’

Concrete facts

-Concrete is the second-most consumed material after water. In 2006, an estimated 21 billion to 31 billion tonnes of concrete were used around the world.

-China and India produce and use over 50 per cent of the world’s concrete.

-Countries like the Netherlands and Japan recycle nearly all their waste concrete. In the Netherlands, landfill of concrete waste is banned.


Samwoh started small

The first level of its Eco-Green Building was made with concrete containing aggregate - or loose granite - with 30 per cent recycled content.

But emboldened by success, it built the second level with 50 per cent recycled aggregate. Growing in confidence, its top level used 100 per cent recycled aggregate.

Working with the Building and Construction Authority, it went beyond the limits of Singapore’s building code, which allows only up to 20 per cent of aggregate in concrete to be replaced with its recycled equivalent.

Samwoh had initially obtained a Ministry of National Development grant of $750,000 and help from Nanyang Technological University to build the $4 million building with 30 per cent recycled aggregate in its concrete. But test results - which came in halfway during construction - showed that it could go further than imagined.

Samwoh’s technical director Ho Nyok Yong, who has a doctorate in the efficient use of waste materials in structural concrete, says: ‘We wanted to see how far we could go. It’s just like being an athlete, you want to see how fast you can run. You want to push yourself to the limit.’

According to sustainable building expert Holger Wallbaum from the Swiss Federal Institute of Technology in Zurich, production of cement - which cannot be recycled - is responsible for the bulk of carbon emitted during concrete production.

Latest studies have shown that since a greater amount of cementitious materials need to be added to recycled aggregate to make concrete, using recycled concrete aggregates could result in a higher carbon footprint.

He says: ‘That means in some cases, we are facing a trade-off between the protection of natural resources (gravel) and the contribution to global warming.’

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