Circular economy for construction materials

Le Sland is a by-product from SLN’s nickel smelter facility in New Caledonia.

A by-product from the production of nickel is being used as an aggregate in concrete applications and could soon be approved to Australian standards as a supplementary cementitious material. SLN Australia explains.

Beyond Zero Emissions, an internationally recognised Australian think-tank, estimated the production of Portland cement  (the most common cement product) is responsible for around 7.4 million tonnes of emissions in Australia. This equates to 1.3 per cent of national emissions.

In its ‘Rethinking Cement’ report released in 2017, it states clinker substitution is one of the ways cement production emissions can be reduced. This will require increasing the level of supplementary cementitious materials (SCM), which reduces the amount of limestone that needs to be calcined but upkeeps the quality of cement.

Further into the process at concrete batching plants cement is then mixed with SCM’s, sand aggregates and water to create the concrete product. Use of SCM’s at this stage can also reduce emissions.

While fly ash and slag are common clinker substitutions, SLN Australia has introduced a new product that can be produced as either a fine aggregate used in concrete, a supplementary cementitious material (SCM) for both cement and concrete applications or an addition for granular road building materials.

The product, Le Sland, is a by-product from SLN’s nickel smelter facility in New Caledonia. Currently around 20 million tonnes of the product is ready to be transported for use in Australia. There is also a 10,000 tonne stockpile available for sale at Port Kembla.

Le Sland can be used in general concrete, precast concrete or concrete blocks, road base, land reclaim and sand blasting applications.

Le Sland can also be used in Australia as a coarse sand substitute for use with other sand materials that complies with Australian Standard 2758.1, aggregates and rock for engineering purposes.

Yves Veran, Business Development Manager for SLN Australia, says Le Sland contributes to a reduction in the carbon footprint when used in its raw form or when ground to be used as a supplementary cementitious material.

SLN Australia has a commitment to circular economy principles in all its practices and Mr. Veran says this led the company to explore avenues for an alternative product to be used in the construction sector.

Michael van Koeverden (CQT Services Pty Ltd) is an independent technical expert that has been working with SLN Australia to evaluate the properties of Le Sland as both an aggregate and supplementary cementitious material.

“Because the SLN aggregate material is non plastic to the plasticity index test (PI), when it is combined with some clay-rich materials it can help to dilute  the clay (within the 0.425 milimetre / 425um fraction). This can make some materials available that may not have been previously available, due to clay content, which can improve quarry stock balance or turn an unwanted waste to a useful product by reducing PI,” Mr. van Koeverden says.

“The other benefit is it doesn’t contain a lot of fines at the bottom end which is very helpful when combining it with clay rich materials. It means you can produce a suitable overall fines combination that can be successfully used in concrete and other materials.”

Mr. van Koeverden says Le Sland is very consistent due to the processes involved in its production.

Natural products can vary, and he says the consistency of Le Sland could be an advantage for material compositions in a number of applications.

“Because of increasing demand our need to use clay rich sands, such as those within the Sydney Basin, is also increasing. I think the SLN product could help tremendously with concrete sand but in the roadbase area it’s also a very good filler,” he says.

“Road bases are bound by plasticity index or aggregate interlock so with high plastic materials out there the addition of this material could bring the plastic index down to an acceptable range.”

Zoe Schmidt, commercial and technical support to the SLN Team says when used as a premium sand in concrete products, improved chemical resistance, compressive and flexural strength, and structural characteristics can be achieved due to its chemical composition and dense, low permeable, structure.

SLN Australia has a commitment to circular economy principles in all its practices.

SLN Australia is a member and participant in the Australasian Pozzolan Association research program to develop a new standard for “pozzolans.” The Le Sland ground granular product is being evaluated.

Craig Heidrich, Executive Director of the Australasian Pozzolan Association says the association has been working with SLN Australia on a research and development program to investigate the pozzolanic characteristics of the Le Sland ground granular material through a series of material characteristic, mortar and concrete testing.

Mr. Heidrich says we have undertaken a significant testing program with an independent cement and concrete testing laboratory. All testing results will be released into the public domain so that results can be discussed with the standards committee technical members.

“The data will help us develop a standard with a series of parameters providing confidence to the market for the use of this material,” Mr. Heidrich says.

“Our materials industry is governed by having confidence around new materials because when you build, infrastructure engineers want to know these materials are going to perform as specified and will comply as well as be fit for purpose in the long term.”

Mr. Heidrich says part of the work being undertaken is to establish those standards and demonstrate that these materials can perform to the standard as minimum requirements.

The research project includes a three-stage evaluation.

“The first stage of that was a basic material characterisation, the second phase was mortar testing, then we move on to concrete testing. We will cast the product into concrete cylinders and evaluate those based on standard test methods,” Mr. Heidrich says.

“We have only just embarked on that third stage of testing and SLN’s Le Sland has been cast into concrete cylinders for further evaluation. The next standards committee meeting will review the interim results and discuss what the next stage will be,” Mr. Heidrich adds.

While Le Sland may be new to Australia, it has been used in New Caledonia and other Pacific Islands for many years.

“The most notable is approximately 1000 hectares of land reclaim used for industrial sites, commercial ports and the city centre, accounting for approximately 20 per cent on top of which Noumea city has been built,” Mr. Veran

“I think the construction industry is ready for new technology that falls within the circular economy and meets the targets posed to reduce Australia’s carbon footprint. SLN Australia is willing to explore opportunities with you to partner in meeting these targets,” Ms. Schmidt says.

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