Renewing the urban landscape

http://www.straitstimes.com/Review/T...ry_343914.html

Feb 28, 2009

SCIENCE TALK

Renewing the urban landscape

Recyclable buildings and materials could reduce costs for S'pore

By Gary Ong Khim Chye


MORE than half the world lives in cities. According to the United Nations, the urban population is growing by an average of 1.6million people every 10 days. By 2030, two in three people will be city-dwellers.

Larger countries may still be able to afford the old model of urban sprawl, where the city boundary grows ever outwards.

In smaller countries like Singapore, however, evolving a city of the future will be very different.

When the Republic gained independence 44years ago, urban development focused on the country's needs: public housing to address a housing shortage, and infrastructure catering to low-technology and labour-intensive industries.

As Singapore's needs have evolved, so has the urban landscape.

The country has grown without choking on its own exhaust fumes, via measures such as limiting the car population and having an established and vigorously enforced environmental policy.

We are unique, and we need to develop our own holistic model and solutions for future sustainable urban development.

Sustainable construction refers to the adoption of building designs, construction methods and materials that are environmentally friendly.

It also means using materials and resources that have sustainable supplies.

The issue of sustainability came under the spotlight in 2007 when an unexpected disruption in the supply of sand and granite from Indonesia resulted in the prices of these materials tripling virtually overnight.

This is just one example of how over-dependence on imports of materials from overseas can put the construction industry in a stranglehold.

Research on sustainable development at institutions such as the National University of Singapore is ongoing.

A number of interesting projects are targeted at developing sustainable solutions to meet challenges unique to Singapore.

One project involves using microwave rays to increase the yield and quality of recycled materials.

This novel technique utilises microwave heating to separate the components of recycled concrete for reuse. Heating causes mortar, which sticks to the surface of granite particles, to peel off like the layers of an onion.

Such work aims to provide a sustainable supply of construction materials available locally, which can reduce an over-reliance on imported sand and aggregates, and temper the negative impact of any unexpected disruption in supply.

Another project funded by the National Development Ministry which is being worked on in conjunction with the Housing Board, is to design high-rise buildings which - like building blocks - can be disassembled and reused.

When en bloc fever reached a peak here last year, many older buildings were demolished to make way for new ones.

Unfortunately, there are no recyclable buildings here yet, so many were demolished even though they had plenty of service life left in them.

If they had been designed for disassembly, they could have been reincarnated as new buildings.

Currently, most of the recycled concrete aggregates from demolition debris have been used in land reclamation, roads, and in non-structural applications, such as in carparks and pavement slabs, as they cannot fully replace fresh stocks of aggregates used in constructing new structures.

Also, additional resources are needed to reuse them - they have to be sorted, then crushed, sieved and graded.

Reuse of precast concrete structural components in new buildings would actually take recycling a step further, by removing the need for these steps.

Premature demolition, which generates demolition waste for disposal, would be unnecessary, together with the need for fresh stocks of construction materials for the new building.

The Design for Disassembly (DfD) process involves the management of resources throughout the lifecycle of a building; from the extraction of raw materials, through manufacturing, design, construction and operation, to the eventual demolition.

The DfD building system takes full advantage of the flexibility, convertibility, addition and removal of future buildings.

With this concept in place, the next generation of buildings constructed in Singapore can be viewed as store houses of future building materials.

Spiralling construction costs are here to stay, due to increased global demand and the rising costs of construction materials and manpower.

With dwindling resources and an urgent need to preserve the environment, the concept of unlimited supplies of construction materials is no longer viable.

Stakeholders in the construction industry and members of the public must work together to develop a uniquely Singaporean model, so that future generations will also be able to live, work and play comfortably in Singapore.

The writer is deputy head (infrastructure and resources) at the National University of Singapore's Department of Civil Engineering.