Proficiency Testing Australia has successfully completed the first large-scale proficiency study on 14mm Steel Furnace Slag Aggregate, which is the 33rd round of the aggregate proficiency testing program. The study aims to introduce sustainable and manufactured material alternatives to its programs.
Proficiency testing is a means of determining the performance of individual laboratories for specific tests or measurements and provides an external audit of their quality control procedures. A standard proficiency testing program compares the measuring results of different laboratories on identical samples.
Proficiency Testing Australia (PTA), one of Australia’s largest proficiency testing providers, services the construction materials industry by offering proficiency testing programs for aggregate, soils, concrete, rocks, cement, asphalt, and bitumen.
PTA recently announced the completion of its 33rd Aggregates Proficiency Testing Program. The program is accredited by International Accreditation New Zealand and was organised in collaboration with Australian Steel Mill Services (ASMS) for sample supply and Luke Murphy of Colas NSW for sample preparation, pretesting and technical assistance.
The program’s aim was to assess the laboratories’ abilities to competently perform the prescribed analyses on a 14mm steel furnace slag aggregate sample. It was the first proficiency testing program organised by PTA that did not use a natural quarry aggregate.
Overall, 87 laboratories participated in the program, demonstrating an interest among construction materials testing laboratories in testing alternative materials. The laboratories were provided with 17kg of 14mm steel furnace slag aggregate.
The program was designed to cover the following methods:
AS 1141.4 Bulk Density
AS 1141.6.1 Particle Density and Water Absorption of Aggregate
AS 1141.11.1 Particle Size Distribution
AS 1141.12 Material Finer than 75 µm
AS 1141.14 Particle Shape by Proportional Caliper (2:1 Ratio)
AS 1141.15 Flakiness Index
Prior to sample distribution, 10 samples were randomly selected and analysed for homogeneity, which was established for the prescribed tests.
PTA used a robust statistical approach to assess the laboratories’ testing performance which has provided understanding as to how steel furnace slag (SFS) aggregate performs under proficiency testing conditions in comparison to natural quarry aggregate.
Table A provides a comparison of the coefficient of variation (CV) between previous rounds and the most recent round in which 14 mm natural quarry aggregate was tested.
It is evident that steel furnace slag exhibits a larger variability of results than natural quarry aggregate, characterised by higher robust CVs for Particle Density and Water Absorption, Particle Size Distribution, Material Finer than 75 µm, Particle Shape and Flakiness Index.
Steel furnace slag is subject to a number of conditions that can affect its physical properties and, in turn, the results’ variability, including the production process, raw material chemical composition, and the rate at which it is cooled. In comparison, natural quarry aggregate sourced from a single geological deposit is more likely to have a relatively uniform composition.
While asphalt laboratories may test SFS aggregate on a regular basis and are familiar with the material, there are many laboratories that have not tested it prior to PTA’s program which may have attributed to the higher variability observed. Despite its variability, steel furnace slag exhibits many physical and mechanical properties that are appropriate for its application in the asphalt industry, making it a versatile and financially viable alternative to natural quarry aggregate.
WHAT IS STEEL FURNACE SLAG AGGREGATE?
Australian Steel Mill Services follows the Basic Oxygen Steelmaking process, which utilises the molten iron from a blast furnace with the addition of scrap steel and fluxes (burnt lime or dolomite), which promote fluidity and enable impurities to be removed in the form of slag. These fluxes are fed into a vessel, and a lance injects oxygen, enabling a reaction between constituents to produce steel and steel slag.
The steel is tapped from the vessel into a steel ladle, and the steel slag is poured into a slag pot. The slag pot is then handled by specialised equipment, and the slag is poured into pits for cooling. The steel slag is then removed from the pits and processed by ASMS into asphalt aggregates, road bases, fill materials and filter materials. The products produced are known as Steel Furnace Slag, and their ASMS product codes commence with ‘SFS”.
THE BENEFITS OF STEEL FURNACE SLAG
The application of steel furnace slag aggregates in road construction offers several notable benefits, particularly under the Transport for NSW Heavy Duty Asphalt specification in NSW. Its high density and angularity make it an excellent alternative to natural quarry aggregate for creating durable and stable asphalt pavements. These properties enhance the strength and load-bearing capacity of the pavement, making it ideal for heavy-duty applications. SFS also has a high Polished Aggregate Friction Value, which can improve the resistance of the asphalt-wearing surface, increasing safety for road users. Using this by-product in road construction aids in conserving natural aggregate resources and minimises environmental impact. The Colas NSW Tomago asphalt plant has incorporated steel furnace slag into its asphalt mixes for many years, to produce high-quality asphalt that meets stringent performance specifications. Using steel slag aggregate in heavy-duty asphalt under local specifications can deliver benefits to NSW’s road infrastructure.
For more information, visit pta.asn.au
Acknowledgments: This article was authored by Christian Foia from Proficiency Testing Australia, Luke Murphy from Colas NSW, and Mark Micallef from Australian Steel Mill Services.
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