Concrete Moves To Cut Waste

CEMENT and concrete have a shade of green. But that is all the green that most of us can associate with the building materials.


Not Dr Sujit Ghosh. Ask the CEO of cement manufacturing firm Holcim about the green efforts of the company and he can talk to you at length on how Holcim has changed the green practices in the industry here. It is no empty boast, for Holcim - an early pioneer in using recycled material to produce ready-mixed concrete, now an accepted practice in the construction industry - has won the Singapore Environmental Achievement Award for 2008-09.

How did this come about?

Some time after Dr Ghosh took over the reins at Holcim, a friend who was working for a recycling company asked him if he could find any good use for copper slag sand.

"That was the beginning. My research revealed that about 300,000 to 400,000 tonnes of copper slag sand waste came from the ship repair industry every year. After processing this waste according to National Environment Agency standards, the material is sent to the landfill year after year as no one had any good use for it. This strengthened my resolve to find a solution," says Dr Ghosh, 45.

His company, which is headquartered in Switzerland, supported his efforts.

"By the middle of 2006, after extensive testing and development, we had a product that was not only a substitute for sand, but, in fact, was a far superior substitute for sand."

The real battle, however, lay ahead. Dr Ghosh had to convince the industry, the regulators and the end-users. It was not easy.

"Most give up here. Eventually, the uphill battle was won, somewhat facilitated by the subsequent sand-ban from Indonesia in 2007 which made people think seriously about resource recovery and reuse, and the eventual support provided by the Building and Construction Authority (BCA), to help promote this alternative to sand. It gives me a great sense of self-satisfaction when I hear these days that no copper slag sand is sent to landfills and the material is in high demand as builders get 'green points' from BCA for using concrete that is made with copper slag sand as a partial substitute for natural sand," says Dr Ghosh, with justifiable pride.

Singapore's shipyards import copper slag which is used for sand blasting - the copper slag is pumped at high force to blast rust and marine organisms from the hulls of ships that are dry docked for repair - from Japan.

After repeated use, the slag loses its abrasive strength and becomes waste material.

Seeing how Holcim could turn a waste material into useful "sand", the NEA asked Dr Ghosh to help find a use for incinerator ash, another waste product that adds to the Semakau landfill. Holcim then joined hands with the National University of Singapore (NUS) to see what could be done and the outcome looks promising.

The ash (or what is left after incineration) comes out as solid chunky material.

This is broken down into stone-like pieces, or aggregates, and can be a substitute for stone chips in concrete. Holcim, which supplies about a quarter of Singapore's requirement of concrete, is working towards making this a reality.

The washed copper slag and the ash generated in Singapore cannot fully replace the annual requirement of sand and stones used in concrete.

They can at best substitute a month's supply. But Dr Ghosh is glad that it will reduce the load on the landfill and therefore extend its life.