Use of slag in public flats to cut carbon emissions

Housing Authority will save money and lower pollution output by 3,700 tonnes of gas a year

Hong Kong’s annual carbon emissions will be cut by 3,700 tonnes, thanks to an environmentally friendly initiative of the Housing Authority.

The authority says it will save money and reduce its use of cement by mixing it with slag, a cheap by-product of steelmaking, in its annual construction of 15,000 flats.

The building material, known as granulated blast-furnace slag, is made by pulverising slag. The process produces 90 per cent less carbon than making cement.

The measure is one of the solutions identified in a carbon audit exercise the authority conducted for its upcoming public rental housing projects.

The saving of 3,700 tonnes of emissions is equivalent to the carbon dioxide intake of 16,000 trees.

“Our public rental homes house about 30 per cent of the city’s population. It is important to create a green living environment and have a greener housebuilding process,” said Ada Fung Yin-suen, deputy director of housing.

The cement industry accounts for 5 per cent of global carbon dioxide emissions.

The slag will come from two suppliers in Guangdong and costs 5 per cent less than cement.

The initiative will help save HK$600,000, according to Fung.

The authority will use slag in building public rental housing estates in Anderson Road, East Kowloon, and Hung Shui Kiu, Yuen Long.

The slag was used in infrastructure projects such as the Tsing Ma Bridge, but it is new to residential construction in the city.

Joseph Mak Yiu-wing, chief structural engineer of the Housing Department, said he hoped private developers would follow suit.

Separately, the department has completed a carbon audit exercise for 12 future projects in Kai Tak, Sheung Shui, Ngau Tau Kok, Sha Tin and Yuen Long.

The audit identified room for lowering carbon emissions by installing lighting systems powered by wind and solar power, among other measures.

joyce.ng@scmp.com