The vast amount of copper slag, a by-product obtained during smelting and refining of copper, was for many years treated as waste with no further use thereafter. Holcim Singapore has found a novel way of encapsulating copper slag into concrete, reducing the use of natural sand in cement production and avoiding the accumulation of copper slag in landfill.
In early 2007, Indonesia banned sand exports over environmental concerns. The subsequent acute aggregate shortage hit the Singapore construction industry hard, as sand and granite are concrete?s primary ingredients.
Holcim Singapore took up the challenge to turn this difficult time in construction into an opportunity to innovate. Its product development and technical services department was assigned to evaluate the potential of waste materials such as washed copper slag (WCS) as partial replacements for concreting sand.
FURTHER USES FOR COPPER SLAG
Originally imported from Japan, copper slag was used as an abrasive material for removing rust and marine deposits from ships through sandblasting. After repetitive recycling and reuse, the copper slag lost its original abrasive property and with no good use thereafter was disposed in landfills.
However, there were environmental concerns about the leaching of heavy metals into soil and groundwater, and so the slag was dumped in landfill sites on the distant island of Pulau Semakau.
Holcim Singapore found a novel way of encapsulating this waste into concrete, thereby not only removing the environmental concerns about WCS, but also finding a value-added and meaningful substitute for natural sand. Copper slag is similar to sand in grading and its hard, non-absorptive, non-reactive properties make it an ideal fine filler material for concrete after it is suitably washed to remove all impurities.
Even though WCS does not produce dust, it has a low crystalline silica (less than 0.1 per cent) that makes it an environmentally friendly product. Its usage was not explored to its full potential due to the conservatism of the Singapore construction industry.
CONSERVING RESOURCES
Together with Singapore?s Building and Construction Authority, Holcim successfully developed ?Holcim Green?, concrete which uses recycled granite from demolition debris and replaces part of the sand with WCS. The material has received the Singapore Environmental Council?s ?green label?, an award that honours products that are environmentally friendly and conserve resources.
Today, the use of WCS as a substitute for sand in the production of concrete is widespread in Singapore with the majority of the ready-mixed concrete companies using it. The new application of WCS as a partial substitute for sand also triggered the change of Singapore?s Aggregates standards.
The Aggregates standards which permit both natural and non-natural aggregates, including recycled aggregates in concrete, open the door to the potential use of more recycled/waste materials in concrete production.
Source: Holcim
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