Turning Black Into Gold Singapore Copper Slag Story


It was all started in early 2007 when Indonesia banned sand exports over environmental concerns. Construction was hit hard by the skyrocketing prices resulting from concrete supply disruptions due to unavailability of sand. Sand and granite are concrete's primary ingredients. With acute aggregate shortages and price increases over 140%, concrete had to be sold at prices that were almost double or triple of the normal prices earlier, causing the Construction Industry to be almost paralyzed by the ban.

Every year, Singapore used about 6 to 8 million tons of sand, most of which came from Indonesia before the export ban. It was needed mainly for land reclamation and concrete manufacturing. The ban came with different reasons - from political to environmental. Construction growth in the island country being a necessity for economic progress spurred the Government into ringing the alarm bell for embarking on a sustainable construction program.

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 took initiatives to study and implement the potential on the use of recycled materials into ready-mix concrete.

Copper slag made a perfect match to be reused. 400,000 tons of WCS needed to be disposed annually. 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, sent to landfill. 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 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. WCS is similar to sand in grading and its hard, non-absorptive, inert / 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 it full potential due to the conservative nature of the industry and no one to take the lead in resource recovery.

The Building Construction Authority (BCA) which subsequently took the lead to further promote the use of alternative / substitute materials, then acknowledged the use of WCS, and even extended 100% WCS use to all non structural concrete without the need for official approval from BCA. Currently, the BCA approves the use of WCS in the production of structural concrete for up to 10% replacement of sand by mass.

Holcim's environmentally-friendly product, 'Holcim Green' was launched on 26 May 2007. It had subsequently received credit from the Singapore Environmental Council by way of a GreenLabel certificate - the Singapore's eco-label that is given to products that are environmentally friendly and conserves resources. The Green Label helps build public awareness while they make assertive choices on their purchases to engage in the green environmental movement.

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. It is also one of the main recyclable materials in the recently published BCA Guidebook on recycled materials. The new application of WCS as a partial substitute for sand also triggered the change of the Singapore's Aggregates standards from the old SS 31 to the new SS EN 12620:2008 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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