A PILOT project has proved that ash from incinerators, disposed of in landfills, can be used to build roads which are as good as those made with the usual granite base.

The road, a 150 m stretch of Jalan Buroh, in Jurong, was constructed using 1,200 tonnes of bottom ash from incinerators as its base last January. This base was covered with asphalt.

The rest of Jalan Buroh, which extends more than 8.5 km, was widened using granite as the base.

The road was monitored for six months to see if it became uneven or developed cracks. Six groundwater standpipes were also installed near the road to help collect the groundwater for testing.

Repeated testing of the samples showed no contamination from the ash.

Before being used, the bottom ash was processed and screened carefully, and ferrous metals like lead, which can be toxic, were removed.

It was left to age for eight to 10 weeks, to stabilise it.

The project involved the National Environment Agency (NEA), the Public Utilities Board, the Land Transport Authority (LTA) and Hanson Pacific, a British firm with experience in processing ash for road-building in Europe.

It cost about $74,000, part of which came from the $20 million Innovation for Environmental Sustainability fund.

If huge quantities of incinerator ash can be used to build roads, it would mean generating wealth from waste by putting something that otherwise goes into the rubbish pit to productive use.

And it should take land-scarce Singapore a step closer to its goal of zero landfill, or recycling all waste rather than depositing them in landfills.

The NEA's chief executive officer, Brigadier-General Lam Joon Khoi, said the next step would be to work with the private sector to get the ash to the market.

He was speaking at a media briefing yesterday while several environmental conferences were being held simultaneously at Suntec City.

It had to be worked out if the ash could be sold at a competitive price, he added.

Contractors now pay between $17 and $18 for a tonne of natural aggregate imported from neighbouring countries.

Talks are now going on with companies interested in setting up a plant to process the ash. Recycling ash means not having to pay $77 for each tonne of it deposited at the Pulau Semakau landfill.

About 3,000 to 4,000 tonnes of the ash would be needed to construct 1 km of road, but BG Lam said that if the LTA were to rely on only recycled ash to build roads, it would use up between 30 and 40 per cent of the ash generated each year.

About 1,400 tonnes of ash is generated every day and the LTA estimates that it will construct 40 lane-km of road annually in the next three years.

The NEA is not stopping at roads. It is studying other possibilities of using the ash, such as for land reclamation.

For now, roads made of recycled material look set to be here in the next few years, especially because another pilot project has been launched to study the use of recycled steel slag as an asphalt substitute.