steel slag asphalt the use of steel slag aggregate in asphalt

STEEL SLAG ASPHALT

The use of Steel Slag aggregate in asphalt

CONTENTS

Introduction

Steel Slag Aggregate

Steel Slag Asphalt Mixture

Environmental Considerations

Conclusion

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

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 Reenen’s Pass); and

Temperature ranges (Summer / Winter variation).

INTRODUCTION(TRAFFIC SPECTRUM AND LOADING)

INTRODUCTION(HEAVY TRAFFIC DAMAGE)

INTRODUCTION(MOISTURE DAMAGE/STRIPPING)

INTRODUCTION(GRADIENT E.G. VAN REENEN’S PASS)

INTRODUCTION(TEMPERATURE)

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

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.


WHAT IS STEEL SLAG??

It’s 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).


AGGREGATE PROPERTIES

The properties that have to be evaluated for the suitability of slag as anaggregate relate to the chemical, physical and mechanical nature of thematerial.

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.



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.



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;



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.


Property

BOF Slag

Dolerite Quartzite

Free Lime 1-15 N/A N/A pH 10 8 5 Particle Density 3.2 2.9 2.7 Water Absorption 1.5 0.8 0.3 Bulk Density 1800 1600 1500 Flakiness Index 7 20 23 Ten Percent Fines Value Wet Dry

460 490

315 350

236 299

Aggregate Crushing Value Wet Dry

7 -

13 11

20 15

Aggregate Impact Value 12 11-8 - Polished Stone Value 63 52 55 Los Angeles Abrasion Value 10 18 21

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.

STEEL SLAG ASPHALT MIXTURE (13,2mm AGGREGATE)

STEEL SLAG ASPHALT MIXTURE(9,5mm AGGREGATE)

STEEL SLAG ASPHALT MIXTURE(-3mm AGGREGATE)

STEEL SLAG ASPHALT MIXTURE(AGGREGATE)

3 mm to dust(300 samples over a 9 month period)

0

10

20

30

40

50

60

70

80

90

100

Number of grading tests

% p

assi

ng

4.75 2.36 0.6 0.075 4.75 (+5%) 4.75 (-5%) 2.36 (+5%)

2.36 (-5%) 0.6 (+5%) 0.6 (-5%) 0.075 (+5%) 0.075 (-5%)

STEEL SLAG ASPHALT MIXTURE(AGGREGATE)


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;


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 > 85% (well above required 75%);

– Film thickness 6,8 to 7,2 micron @ 5,2% binder.


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.

Rolled in stone SFC Continuously graded SFC 16mm Seal SFCN3-6X NB km 36,79 - km 39,95 0.40 N3-7X NB km 44,88 - km 47,61 0.38 N3-11 SB km 8,70 - km 15,10 0.44N3-6X NB km 43,08 - km 49,95 0.41 N3-7X SB km 53,20 - km 52,01 0.36N3-6X SB km 45,98 - km 38,87 0.47 N3-8X NB km 22,31 - km 23,67 0.35


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%

0

0.5

1

1.5

2

2.5

3

Steel Slag AC+4% SBS

Dolerite AC +4% SBS

Dolerite AC +4% SBS

SS/Dolerite AC+4% SBS

Quartzite AS 60/70 pen.

Quartzite SMA+4% SBS

Dolerite SMA 60/70 & Fib.

Mix Type Continuous Semi gapBinder Type SBS 60/70 SBS 60/70 & Fib.Aggregate Steel Slag Dolerite Dolerite Steel Slag/DoleriteQuartzite Quartzite Dolerite

MMLS3 DataAverage Voids (%) 3.1 3.3 3.6 - 7.2 7.2 -Average Rut Depth after 100k repetitions (mm) 1.2 1.3 1.8 2.9 2.2 2.6 1.7

SBSContinuous SMA


STEEL SLAG ASPHALT MIXTURE (ROLLED IN STONE)

STEEL SLAG ASPHALT MIXTURE (CONTINUOUSLY GRADED)

STEEL SLAG (16,0mm SINGLE SEAL)

ENVIRONMENTAL CONSIDERATIONS

ADVANTAGES

Reduces landfill;

Reduces the need to quarry;

Preserves our natural resources.

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.

CONCLUSIONS

Any Questions?

steel slag asphalt the use of steel slag aggregate in asphalt

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