Waste as meaningful substitute for natural sand

Today, the use of Washed Copper Slag (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.

(Holcim – Singapore) — 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 found a novel way of encapsulating copper slag into concrete, reducing the use of natural sand in cement production and avoiding landfilling that used to be the common way of disposing this “waste”.

It was all started in early 2007 when Indonesia banned sand exports over environmental concerns. The subsequent acute aggregate shortage hit the 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. The Product Development and Technical Services department was assigned to carry out the task of evaluating the use of one such available waste material called Washed Copper Slag (WCS) to partially replace the concreting sand. Holcim Singapore took initiatives to study and implement the potential on the use of recycled materials into ready-mix concrete.

Further use 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 and was disposed in landfills. However, there were environmental concerns about the leaching of heavy metals into soil and ground-water, and hence were dumped in landfill sites in the distant island of Pulau Semakau for decades which again had very little room for further landfills. Holcim Singapore found a novel way of encapsulating this waste into concrete thereby not only removing the environmental concern 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 produces no dust, has low crystalline silica (less than 0.1%) making it an environmentally friendly product, its usage was not explored to its full potential due to the conservative nature of the industry.

Conserving Resources

Together with Singapore’s Building and Construction Authority, Holcim had successfully developed “Holcim Green”, which is concrete using recycled granite from demolition debris and replacing part of the sand with WCS. The material has received Singapore’s “green label”, an award from Singapore Environmental Council honoring 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 the Singapore’s Aggregates standards which allows both natural and non-natural aggregates including recycled aggregates in concrete, thereby opening the door to the more use of recycled/waste materials in concrete production.

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