STEEL SLAG ASPHALT

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STEEL SLAG ASPHALT

• The use of Steel Slag aggregate in asphalt

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CONTENTS

• Introduction
• Steel Slag Aggregate
• Steel Slag Asphalt Mixture
• Environmental Considerations
• Conclusion

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ACKNOWLEDGEMENTS

• N3TC Philip du Plessis
• Multiserve Nick Jones, Koos Jan van
  Brouwershaven
• Ilanga Aspahlt Jan van der Merwe
• Levy Company John Yzenas
• Rand Roads Mike Kohlberg
• Illinois Department of Transportation
• USA Steel Slag Association
• Australian Steel Slag Association

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INTRODUCTION

• WHY DO WE NEED AN ALTERNATIVE PRODUCT??
• Changes in traffic spectrum
• Changes in traffic loading
• Heavy traffic damage (rutting and shoving)
• Moisture damage (Wet environments)
• Gradient (e.g. Van Reenens Pass) and
• Temperature ranges (Summer / Winter variation).

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INTRODUCTION(TRAFFIC SPECTRUM AND LOADING)
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INTRODUCTION(HEAVY TRAFFIC DAMAGE)
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INTRODUCTION(MOISTURE DAMAGE/STRIPPING)
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INTRODUCTION(GRADIENT E.G. VAN REENENS PASS)
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INTRODUCTION(TEMPERATURE)
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INTRODUCTION

• WHAT ARE WE HOPING TO ACHIEVE??
• Improved Deformation Characteristics i.e.
  strength and stability
• Improved Durability i.e. moisture sensitivity
• Improved Skid resistance i.e. polished stone
  value, SCRIM values

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STEEL SLAG AGGREGATE

• WHAT IS STEEL SLAG??
• It is a by product of the steel making process,
• It has a complex chemical structure, comprising
  oxides and silicates that are formed through the
  oxidation of impurities within the steel by the
  addition of lime and fluorspar
• On completion of the steel making process, the
  liquid slag is separated and poured into purpose
  built hot slag carriers.
• The slag is then cooled before further
  processing, which includes weathering, crushing,
  and screening
• The weathering process is an essential part of
  the handling of steel slag, as it enables the
  hydration of any uncombined free lime (CaO) or
  free magnesia (MgO) present in the material.

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STEEL SLAG AGGREGATE

• WHAT IS STEEL SLAG??
• Its chemical composition is primarily calcium
  silicates together with oxides and compounds of
  iron, manganese, alumina and other trace
  elements.
• Steel slag is mildly alkaline with a solution pH
  generally in the range of 8 to 10 (highest
  measured at 12,6).

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STEEL SLAG AGGREGATE

• AGGREGATE PROPERTIES
• The properties that have to be evaluated for the
  suitability of slag as an
• aggregate relate to the chemical, physical and
  mechanical nature of the
• material.
• Hardness / toughness, resistance to abrasion
• The high Fines Aggregate Crushing Test (10
  FACT)
• Low Aggregate Crushing Value (ACV)
• Low Los Angeles Abrasion Value
• Indicate high density and crushing strengths of
  the steel slag aggregate.

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STEEL SLAG AGGREGATE

• AGGREGATE PROPERTIES
• Particle shape and surface texture, stability and
  skid resistance
• Cubical shape
• Rough surface texture rough
• The Flakiness Index (FI) of the steel slag
  aggregate is markedly lower than those for the
  dolerite and quartzite aggregates
• A Polished Stone Value (PSV) of 63 for the steel
  slag aggregate indicates a high resistance to the
  surface of the aggregate polishing under the
  action of traffic.

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STEEL SLAG AGGREGATE
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STEEL SLAG AGGREGATE
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STEEL SLAG AGGREGATE
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STEEL SLAG AGGREGATE

• AGGREGATE PROPERTIES
• Specific gravity and water absorption
• Particle density of the steel slag aggregate
  compared to natural aggregates (dolerite
  quartzite) is more dense and heavier material by
  approximately 20
• Steel Slag typically has a higher water
  absorption than dolerite and quartzite

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STEEL SLAG AGGREGATE

• AGGREGATE PROPERTIES
• Durability, resistance to stripping
• Steel slag, with a pH of between 8 and 10, has a
  strong affinity to bitumen and therefore displays
  a greater degree of binder retention.
• Rough surface texture, improves stripping
  resistance.
• This is very important in the prevention of
  stripping of the binder and moisture damage.

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STEEL SLAG AGGREGATE
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STEEL SLAG ASPHALT MIXTURE

• MIX DESIGN
• Continuously graded mix
• Aggregate used
• 13,2 mm
• 9,5 mm
• -3 mm
• Polymer modified binder
• SBS binder used for high seasonal temperature
  fluctuations and high stability flexibility
  mixes for high traffic.

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STEEL SLAG ASPHALT MIXTURE (13,2mm AGGREGATE)
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STEEL SLAG ASPHALT MIXTURE(9,5mm AGGREGATE)
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STEEL SLAG ASPHALT MIXTURE(-3mm AGGREGATE)
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STEEL SLAG ASPHALT MIXTURE(AGGREGATE)
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STEEL SLAG ASPHALT MIXTURE(AGGREGATE)
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STEEL SLAG ASPHALT MIXTURE

• MIX PROPERTIES
• Strength and Stability
• the cubical shape of the aggregate enables the
  formation of strong interlocking structures
  within the asphalt mixture, which exhibit high
  stiffness and excellent resistance to permanent
  deformation
• Stability of 15,1 kN
• Flow of 3,7 mm
• Stability / Flow Ratio of 4,1
• Indirect Tensile Strength (ITS) of 1288 kPa

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STEEL SLAG ASPHALT MIXTURE

• MIX PROPERTIES
• Durability
• Attributable to such things as air voids in the
  mixture, binder film thickness and moisture
  sensitivity. However, one of the superior
  properties of steel slag is its ability to retain
  the binder coating
• Steel slag, with a pH of around 10, has a strong
  affinity to bitumen and, therefore, displays a
  greater degree of binder retention
• Voids In Mix (VIM) designed to be 4,1
• Voids in Mineral Aggregate (VMA) of 16,8
• Voids Filled with Binder (VFB) of 72
• Air permeability below 1,0 x 106 cm3 / second.
• Immersion Index of gt 85 (well above required
  75)
• Film thickness 6,8 to 7,2 micron _at_ 5,2 binder.

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STEEL SLAG ASPHALT MIXTURE

• MIX PROPERTIES
• Skid Resistance
• A polished stone value of 63 classifies the steel
  slag as a high specification aggregate and is
  generally used for the higher risk sites
• It is usual for an aggregate having a PSV in this
  range to have a poor abrasion value
• Steel slag, however, also has excellent
  resistance to abrasion
• An unusual combination of properties, making
  steel slag a safe and durable alternative to
  natural aggregates.
• Grip tester friction measurements.

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STEEL SLAG ASPHALT MIXTURE

• ADDITIONAL TESTING
• Gyratory compaction
• Average voids 3,1 after 300 gyrations (minimum
  2,5 after 300 gyrations)
• Wheel tracking using MMLS3
• The MMLS performance test results indicate that
  the steel slag asphalt has better resistance to
  deformation than the Dolerite asphalt and SMA
  samples evaluated.
• Soluble deleterious material test
• Unwashed sample 85
• Washed sample 100

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STEEL SLAG ASPHALT MIXTURE
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STEEL SLAG ASPHALT MIXTURE (ROLLED IN STONE)
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STEEL SLAG ASPHALT MIXTURE (CONTINUOUSLY GRADED)
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STEEL SLAG (16,0mm SINGLE SEAL)
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ENVIRONMENTAL CONSIDERATIONS

• ADVANTAGES
• Reduces landfill
• Reduces the need to quarry
• Preserves our natural resources.

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CONCLUSIONS

• Steel slag produces a high quality aggregate
  which can benefit asphalt materials in a number
  of ways.
• Steel Slag aggregate can out perform natural
  aggregates in terms of
• Shape
• Resistance to crushing
• Skid resistance and
• Durability and
• Adhesion.
• Steel Slag in asphalt mixtures improves
  properties of the mix in terms of
• Stability
• Resistance to permanent deformation
• Durability and
• Skid resistance.
• To date approximately 90,000 tons placed on N3.

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CONCLUSIONS

• Any Questions?