Journal of Environmental Treatment Techniques 2015, Volume 3, Issue 3, Pages: 158-162

158

Application of Iron Slag at Different Pavement Layers

Zolfaghar Zarei, Mohammad Reza Baradaran

Department of Civil Engineering, Firoozabad Branch, Meymand Center, Islamic Azad University, Meymand, Iran.

Received: 16/07/2015 Accepted: 06/09/2015 Published: 30/06/2015

Abstract

Reusing waste material in the past decade has got too importance and the reason is emphasizing on environment laws and

reducing the pollution of industrial garbage. Steel-making operations has faced with this problem because of producing a large

amount of waste material during production which in the case of steel industries ability to recover and using this products, these

products create many problems in terms of pollution for environment with regard to their high production volume including slag,

dust, sludge, shell sheets and oxide layers in which slag has got the most importance than others because of high production rate.

Nowadays, broad research has performed in the world to recycling these side products which have resulted to solutions to recover

them. In Iran with regard to the increasing of steel and slag production, research on them and appropriate solutions to use in

different applications and reducing environmental pollution seems necessary. This paper addresses the investigation of iron slag

at different pavement layers and the influences like frictional resistance, track disruption and bearing strength that it produces.

Key words: Iron slag, frictional resistance, track disruption.

1 Introduction

Slag is a molten material which is created due to

interaction of molten materials, limestone, fuel and existing

oxide impurities in metal. During these interactions, the

impurities that mustn’t be in cast iron will be separated

from pig iron. Steel slag (iron) is side product during

production and steel manufacturing. This product is created

in one of the three types, fire furnace, basic-oxygen furnace

or electric arc furnace. This product is different from tall

furnace slag which is a product during iron making process

production in terms of chemical properties [3]. The

produced slag from steel making furnaces is usually cooled

by free air and a solid stony material will be created which

is similar with basalt in appearance. Basic-oxygen steel

slag and electric arc furnace slag both have similar

chemical and physical properties. Chemical composition of

blast furnace slags changes with regard to steel making

method and the quality of produced steel [4].

The positive characteristics of blast furnace include [4]:

1- Resistance and high stability against impact

2- The excellent angular shape of aggregate which creates

appropriate internal friction angle

3- High resistance against load, pressure and abrasion

4- High sliding resistance because of frictional strength

among aggregates

5- Bitumen absorption percentage due to high alkali

property

The mean of physical properties of blast furnace slags,

tall furnace slags and basalt stone are shown in Table 1 [4].

Corresponding author: Mohammad Reza Baradaran,

Department of Civil Engineering, Firoozabad Branch,

Meymand Center, Islamic Azad University, Meymand,

Iran. E-mail: mohamadrezabaradaran@gmail.com

2 Application of Blast Furnace Slag in Road

Surface

Surface layer in road pavement is a layer of high-grade

gender and rather with high strength that is located directly

in contact with vehicles. Surface layer in the high traffic

roads is made by high grade materials such as asphalt

concrete or cement concrete.

Table 1: Average of physical properties

Specifications

Iron slag

Tall furnace

slag

Basalt

stone

BOS

Slag

EAF

Slag

Density of materials

(Kg/m

)

3400

2600-2500

2850

Actual density (Kg/m

)

1700

1300-1200

1520

Resistance in dry

condition (KN)

250

275

100-85

350

Resistance in wet

conditions (KN)

230

240

90-65

Losanjeles resistance

13-15

43-37

sliding resistance

55-50

Relent

Impact resistant

Ductility factor

Water absorb

0.9

0.5

1.9

0.9

The improvement of surface performance in different

climate conditions and long-time heavy traffic has been the

main purpose of pavement designers and road-construction

engineers. Hence to improve the status of roads surface in

terms of friction and strength increase against other

destructions, various materials have been investigated in

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J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal of Environmental Treatment Techniques 2015, Volume 3, Issue 3, Pages: 158-162

159

laboratories that blast furnace slags have been also among

them and are utilized in asphalt surface and/or concrete

surface [5, 6]. Using slag in surfaces causes the increase of

sliding strength and also increasing strength against surface

rutting.

2.1 Skid resistance and friction properties

Resistance against slippery is defined as a reaction

force resists against vehicle sliding and prevents gliding of

tires on pavement level [7]. The aggregates that are used in

asphalt production have appropriate friction coefficient in

the first use of road surfaces but during time and with the

increase of vehicles traffic becomes smooth and their

roughness will be reduced. Some of reports indicate

disappearing 50% of initial roughness in the first two years

of pavement service. Hence using aggregates that have

resistance and rather high roughness has had special

importance in terms of roads safety. Physical properties and

surface texture of steel slag creates a friction coefficient at

surface layer that is usually more than natural aggregates

[8]. The individual composition of blast furnace slag which

is constituted by hard small structure causes the appearing

of pavement surface cover with proper long-time skid

resistance that usually is not the case in natural aggregates.

[8]

Young Gi et al. performed an experiment on a

component of one constructed road from blast furnace slag

in China under standard conditions to assess pavements

asphalt surface skid strength and they realized that the

performance of steel slag in terms of hardness and also

having roughness coefficient is too great. Table 2 shows the

experimental results [9].

Table 2: road experiment performance

Experiment

Period of service

month

The specific gravity

of the core samples

(gr/cm

)

2.511

2.520

2.524

2.525

Abrasion and

coefficient of

friction (BPN)

Depth textures

surface (mm)

1.2

0.9

0.8

2.2 Resistance against rutting

Rutting is often refers to permanent deformation that

happen in the path of vehicle wheels passing and parallel to

road longitudinal direction. The iteration of loading from

heavy vehicle passing and lack necessary pavement bearing

strength results in the creation of this kind of destruction.

Such a phenomenon happens often in tropical areas. It is

also possible that rutting in the path of wheels passing is

together with bump near to track. Regardless of aggregate

type and its processing method, aggregates in warm asphalt

admixture must create enough shear strength to resist

against frequent traffic pressure. When additional load is

applied on aggregate, a shear plane is developed in

aggregates particles and shear than to each other causes

deformation or rutting (figure 1-a). Rutting results happens

when shear tensions is more than aggregate shear resistance

along to this shear plane. (Figure 1-b) [5, 8].

Figure 1-a: aggregates shear than each other

Figure 1-b: rutting in the effect of applying additional load.

Shear resistance at asphalt admixtures depends on two

parameters: The internal friction angle of stony material

and also admixture adhering coefficient. But because slag

materials have cubic shape and their rough texture, the

prepared admixtures from these materials have more

resistance than natural flat and round aggregates. [8]

2.3 Stone matrix asphalt

Asphalt pavement has different types that one of them

is asphalt with open gradation. Blast furnace slag has broad

application in this kind of pavement.

Stone matrix asphalt is European pavement technology

that is designed to prevent from crushing and sliding from

heavy traffic pressure. This technology has focused on

preparing durable pavements that have lower sensitivity to

thermal cracks and creates one friction layer to reduce

water fracture phenomenon (hydroplaning).

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160

Figure 2: The cubic and round-sides shape of slag

aggregates.

Figure 3: Deformation of pavement before substitution

with SMA admixture along with iron slag.

Stone matrix asphalt is from coarse aggregate and

includes open gradation. In this matrix network, contrary to

superpave pavement samples, the aggregates with rough

texture are as close and sticking together contact. This issue

causes increasing appropriate internal friction angle and

high shear resistance. Tar in stone matrix asphalt is

typically from polymer type between 5-8 percent. Lower

fine aggregates are used in this admixture to ensure from

particle to particle contact and increasing the percent of

aggregate empty space. Using steel slag in stone matrix

asphalt has shown many successes. Because of steel slag

stability, aggregates contact is not vanished during

manufacturing. Moreover, aggregate steel slag is perfect for

the creation of friction at pavement surface. The thermal

characteristics of steel slags have many advantages to

protect against different temperatures.

3 Application of Iron Slag at Base and Sub-

Base Layer

Since slags are materials with sharp sides and similar to

crashed materials so they can be used as appropriate

aggregates in base and sub-base of roads. Steel slag

aggregates usually are used with the distances of 100km

from steel-making location, so the application and

availability of slag is an important problem and its utilizing

is not restricted in many sections. Where steel slag is

available, its utilizing in basic applications can be

considered and not only their gender, but also their type

must be closely assessed. The chemical property of steel

slag can be different between various mines and it is too

important that the properties of these materials will be

examined during using them. The chemical composition of

some steel slags causes inappropriate expansion surfaces.

Since mid-twentieth century, steel slags are used as

aggregate in many construction industries. The main use of

slags are for embankments, roads, rail-road upstream,

building materials, landscaping, cement replacement,

cement and soil stabilization. Madar et al. performed a

research on steel slag application in road construction.

Chemical-physical characteristics of steel slags in

comparison to existing natural aggregate demonstrated the

suitability of air-slacked steel slag to use in the base and

sub-base of pavement. Pavement designing based on

analytic methods shows clearly that using established

layers with slag in base and sub-base layers results in the

small improvement of tensile strain at tar sub-mix and also

low compressive tension at above sub-grid. This

improvement causes the reduction of fraction and wheel

path depression at pavement and finally the increase of

pavement life-time. Haldi studied the different

characteristics of slag including density and the amount of

water absorption, mechanical strength, friction properties

and expansion and he concluded that steel slag can be an

appropriate aggregate for embankments, base and sub-base,

and the upstream of rail-road etc. [8, 10].

Figure 4: using slag in base and sub-base layer

Industrial countries prefer using steel slag in

bituminous pavement because of the extraordinary stability,

long life-time and high friction strength which provides a

safe surface. The operation of road construction has shown

that slag can be mixed simply and if compressed correctly,

a major difference will be obtained rather to common

materials. Also it has demonstrated proper strength

characterization, volume stability, durability and free

draining. Also it has a thorough cubic angular shape and

with high internal friction angle to natural stones and is

appropriate as asphalt mixture aggregate; contrary to

natural stones, slag tends to preserve high friction

resistance than time, climate factors and abrasion against

traffic. Gradated clean slag satisfies structural and physical

necessities of all road layers in general. Steel slag specially

is used as the material of road shoulder without pavement.

The cement properties of steel slag in road shoulder results

to a durable, stable and hard road shoulder which is too

more durable than the shoulders of the roads that are made

from other aggregates [8, 10].

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161

Researches on slag in Ahvaz yielded following results

[11].

1. In the areas that sub-grid soils or underside layers are

from clay, mixing them slag with these soils amends their

properties and can be used in streets and roads

embankment.

2. For bypass roads and streets with low traffic, the

admixture of slag with local soil and limestone can be used

as sub-base layer and the ratios of materials is 50% slag

and 40% soil and 10% limestone.

3. The use of slag or admixture of slag and soil or slag, soil

and limestone is possible for roads and streets with low

traffic with ratios of 50% slag, 40% soil and 10% limestone

[11].

3.1 Application of blast furnace slag as ballast

Since 1900, some of slags from melting metals as

ballast have been used in rail-road lines. In the lines in

which trains move with high velocity, the aggregates of

slags are utilized as sub-ballast and coarser particles in

ballast construction. Slag ballasts due to high porosity have

appropriate draining property. The separation of aggregates

in them happens too hard. The reasons are hardness, shape

and better interlock of slags. Slags have proper resistance

against wetting and drying, melting and freezing and abrupt

changes of temperature and bearing chemical and corrosive

materials and this is another reason to use them as ballast

[10].

Figure 5: using slag in ballast

3.2 Application of blast-furnace slag at pavement layers

stabilization

Advantages

1. Remarkably increases soil dry bulk weight.

2. Increases soil CBR more than cement and limestone.

3. The lowest settlement from vehicles loading happens on

stabilized soil with slag.

4. Its resistance increase is not dependent on time and gives

the best results in short term.

5. Due to its free initial materials is the first grade in terms

of economic efficiency.

6. To stabilize with slag there is no need to long-term

humidity in soil.

7. With regard to the change in soil gradation due to adding

slag, it results in decreasing soil plasticity and efficiency

increase.

Disadvantages

1. Increases fluidity level and paste mark and raises soil

plasticity and reduces soil efficiency [12].

4 Conclusions

With regard to the high production rate of slags, these

products create many problems in terms of pollution for

environment which using it in road construction can help to

reduce pollution.

Steel slag aggregate have base property (pH between 8

and 10). Steel slag in reaction with bitumen creates a

resistance composition against humidity. So it shows

appropriate strength against stripping phenomenon. Steel

slag has sharp edges and rough surface. This issue helps the

interlock among aggregates and increases the resistance

against permanent deformation.

Asphalt admixtures including steel slags because of

having sharp edge, pitted and high hardness surface have

high friction strength. Steel slag has high polished stone

value (PSV). High number of aggregate PSV raises friction

resistance and increasing the safety of asphalt admixture

level and surface stack. Using slag in pavement increases

the resistance against rutting and reduces surface

depression. Cubic shape property of slag material and its

rough texture causes more resistance than smooth and

round edge aggregates. Using slag in different pavement

layers is possible.

References

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Environmental impacts of steel slag reused in road

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Journal of Environmental Treatment Techniques 2015, Volume 3, Issue 3, Pages: 158-162

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