BROADER USE OF

STEEL SLAG AGGREGATES IN CONCRETE

JIGAR P. PATEL

Bachelor of Science in Civil Engineering

Maharaja Sayajirao University of Baroda, India

May 2006

Submitted in partial fulfillment of requirement for the degree

MASTERS OF SCIENCE IN CIVIL ENGINEERING

At the

CLEVELAND STATE UNIVERSITY

December, 2008
This thesis has been approved

For the Department of Civil and

Environmental Engineering and the

College of graduate studies by

Thesis Chairperson, Dr. Norbert Delatte

Department /Date

Dr. Paul Bosela

Department /Date

Dr. Lutful I. Khan

Department /Date
ACKNOWLEDGEMENT

First of all, I would like to thank my parents, my sister and all my friends for their 

blessings and supporting me throughout my education. I would like to thank the 

Department of Civil and Environmental Engineering at the Fenn College of Engineering 

at Cleveland State University.

I would like to thank to my advisor, Dr. Norbert Delatte. He not only provided 

support throughout this entire research but also throughout my entire graduate carrier. I 

would like to thank to the rest of my committee members Dr. Bosela and Dr. L.I.Khan. I 

would like to thank to my fellow graduate and undergraduate students who helped me 

with this project, which include Richard S. Obratil, Matthew A. Pastorelle, Vince Spisak, 

Daniel Fabriziana, and Tom Hyatt of Fenn College of Engineering at Cleveland State 

University and also the assistance of John Cleary of the Department of Civil Engineering 

at Case Western Reserve University. The help from Dave Epperly and Ali Kaddah in the 

lab was invaluable. I would also like to thank Mehul Maheria, Vikas Patel, Archan Shah, 

Mayur Patel, Hardika Gandhi, Dhaval Tamboli, Kinjal Mistry, Arpan Desai, Kuvleshay 

Patel, Jaimin Bhatt and many more friends for their support and co-operation during the 

research.
iv

 BROADER USE OF STEEL SLAG AGGREGATES IN CONCRETE 

JIGAR P. PATEL 

ABSTRACT 

 

Steel slag is an industrial byproduct obtained from the steel manufacturing 

industry. It is produced in large quantities during the steel-making operations which 

utilize Electric Arc Furnaces (EAF). Steel slag can also be produced by smelting iron ore 

in the Basic Oxygen Furnace (BOF). Steel slag can be used in the construction industry 

as aggregates in concrete by replacing natural aggregates. Natural aggregates are 

becoming increasingly scarce and their production and shipment is becoming more 

difficult. Steel slag is currently used as aggregate in hot mix asphalt surface applications, 

but there is a need for some additional work to determine the feasibility of utilizing this 

industrial by-product more wisely as a replacement for both fine and coarse aggregates in 

a conventional concrete mixture. 

Most of the volume of concrete is aggregates. Replacing all or some portion of 

natural aggregates with steel slag would lead to considerable environmental benefits. 

Most of the natural aggregates in the state of Ohio are shipped in from out of the state, 

whereas large steel slag deposits are locally available. The primary aim of this research 

was to evaluate the durability of concrete made with steel slag aggregates. This research 

has shown that replacing some percentage of natural aggregates by steel slag aggregates 

causes negligible degradation in strength. It is shown that as the amount of steel slag is 

increased beyond 75%; the workability of the concrete mixture became an important 

issue which eventually requires larger amounts of water reducing admixtures to achieve a 
v

minimum slump. The results showed that replacing about 50 to 75% of steel slag 

aggregates by volume for natural aggregates will not do any harm to concrete and also it 

will not have any adverse effects on the strength and durability. 
vi

TABLE OF CONTENTS 

ACKNOWLEDGEMENT .............................................................................................. iii 

ABSTRACT .................................................................................................................... iv 

LIST OF TABLES .......................................................................................................... vi 

LIST OF EQUATIONS ................................................................................................. vii 

CHAPTER I: INTRODUCTION ..................................................................................... 1 

1.1 Background............................................................................................................................. 1 

1.2 Purpose ................................................................................................................................... 3 

1.3 Scope ...................................................................................................................................... 4 

CHAPTER II LITERATURE REVIEW .......................................................................... 5 

2.1 Overview ................................................................................................................................ 5 

2.2 Concrete .................................................................................................................................. 5 

2.3 Aggregates .............................................................................................................................. 6 

2.4 Properties of Aggregates required for Mix design ............................................................ 7 

2.5 Non traditional aggregates ............................................................................................. 8 

2.6 Steel Slag and its production .................................................................................................. 9 

2.7 Current uses of steel slag ............................................................................................. 11 

2.8 Properties of Steel Slag ................................................................................................ 12 

2.8.1 Physical Properties ............................................................................................................ 13 

2.8.2 Chemical and Mineralogical composition ................................................................... 14 

2.8.3 Mechanical Properties ............................................................................................... 15

2.8.4 Effect on environment and health .............................................................................. 16

2.9 Problem associated with Steel slag aggregates ............................................................... 16

2.10 Aging of steel slag and Stockpiling of Steel slag aggregates ......................................... 17

2.11 Past studies on steel slag aggregates ............................................................................ 20
vii

CHAPTER III: EXPERIMENTAL DESIGN ................................................................ 25 

3.1 Overview .............................................................................................................................. 25 

3.2 Concrete Mix Design ............................................................................................................ 26 

3.3 Gradation .............................................................................................................................. 27 

3.4 Properties of concrete ........................................................................................................... 28 

3.5 Modulus of Rupture .............................................................................................................. 33 

3.6 Compressive Strength of concrete................................................................................. 33 

3.7 Splitting Tensile Strength of concrete ........................................................................... 34 

3.8 Change of length of Hardened Concrete ........................................................................ 35 

3.9 Resistance to Rapid Freezing and Thawing ................................................................... 35 

3.10 Research Plan ............................................................................................................ 37 

CHAPTER IV: MATERIALS ....................................................................................... 38 

4.1Overview ............................................................................................................................... 38 

4.2 Portland cement .................................................................................................................... 38 

4.3 Steel Slag .............................................................................................................................. 39 

4.4 Fine Aggregates .................................................................................................................... 41 

4.5 Coarse Aggregates ................................................................................................................ 41 

4.6 Chemical Admixtures ........................................................................................................... 42 

CHAPTER V: EXPERIMENTAL RESULTS ............................................................... 44 

5.1 Overview .............................................................................................................................. 44 

5.2 Gradations............................................................................................................................. 44 

5.3 Fresh concrete properties ............................................................................................. 46 

5.3.1 Workability ........................................................................................................................ 46 

5.3.2 Air Content ........................................................................................................................ 46 

5.3.3 Unit weight ........................................................................................................................ 48 

5.4 Hardened concrete properties ....................................................................................... 50 

5.4.1 Modulus of Rupture ........................................................................................................... 50 

5.4.2 Compressive strength for concrete specimens and Flexure beams ................................ 51 

5.4.3 Splitting Tensile Strength .......................................................................................... 54 

5.4.4 Freeze-Thaw Durability ............................................................................................ 57 

5.4.5 Change in length of concrete specimens ..................................................................... 69 
viii

CHAPTER VI: DISCUSSION ....................................................................................... 70 

6.1 Overview .............................................................................................................................. 70 

6.2 Overall Experimental observations ............................................................................... 70 

6.3 Compressive strength of concrete ................................................................................. 71 

6.4 Split Tensile strength ............................................................................................................ 72 

6.5 Flexural strength of concrete ................................................................................................ 73 

6.6 Freeze-thaw durability .......................................................................................................... 73 

6.7 Measurement of linear expansion or contraction of concrete specimens ............................. 76 

CHAPTER VII: CONCLUSION................................................................................................ 77 

7.1 Summary............................................................................................................................... 77 

7.2 Some limitations of test methods. ......................................................................................... 78 

7.3 Suggestion for Future research ............................................................................................. 79 

REFERENCES ........................................................................................................................... 81 
ix

LIST OF TABLES 

Table I: Typical Physical properties of steel slag ............................................................ 13 

Table II: Typical Steel Slag chemical compositon............................................................ 14 

Table III: Typical Mehanical properties of steel slag..........................................15 

Table IV: Concrete Mixture Proportions .......................................................................... 26 

Table V: Testing Program ................................................................................................. 37 

Table VI: Cement Compostion and Physical Properties. .................................................. 39 

Table VII: Steel Slag chemical compostion and properties .............................................. 40 

Table VIII: Measured slump and volume of addmixture .................................................. 46 

Table IX: Measured air content and volume of addmixture ............................................. 47 

Table X: Designed Unit weight and Measured unit weight .............................................. 49 

Table XI: Flexural strength of concrete ............................................................................ 50 

Table XII: 7 & 28 days compressive strength of concrete specimens .............................. 52 

Table XIII: 7 & 28 days compressive strength for flexure beam specimens .................... 53 

Table XIV: 7 & 28 days split tensile strength on concrete specimens .............................. 54 

Table XV: 7 & 28 days Split tensile strength on flexure specimens................................. 56 

Table XVI: Weight of specimens at various Freeze thaw cycles ...................................... 58 

Table XVII: Percentage Mass loss in %............................................................................ 59 

Table XVIII: Relative Dynamic Modulus ......................................................................... 60 

Table XVIII: Expansion length of concrete specimens .................................................... 69 
x

LIST OF FIGURES 

Figure 1: Schematic illustration of Basic oxygen furnace and Electric arc furnace........11 

Figure 2: Stockpilling of steel slag aggregates at Stein Inc .............................................. 19 

Figure 3: Fig show steel slag used for reasearch and sieve analysis test .......................... 27 

Figure 4: Air test being conducted on concrete sample .................................................... 29 

Figure 5: Slump test being conducted on concrete sample ............................................... 30 

Figure 6: Fig A & B shows compression test and split tensile test on concrete sample ... 31 

Figure 7: Freeze thaw test on concrete sample for durablity. ........................................... 32 

Figure 8: Sieve analysis result compared with FA and CA aggregates ............................ 45 

Figure 9: Comparison of replacement mixtures to ODOT class C paving mixture .......... 45 

Figure 10: Graph showing air content v/s volume of aggregates replaced by steel slag .. 47 

Figure 11: Graph showing Unit weight v/s volume of aggregates replaced by steel slag 49 

Figure 12: Graph showing Modulus of Rupture for concrete beams ................................ 51 

Figure 13: 7 & 28 days compressive strength of concrete specimens .............................. 52 

Figure 14: 7 & 28 days compressive strength of flexure beams ....................................... 53 

Figure 15: 7 & 28 days split tensile strength of concrete specimens ................................ 55 

Figure 16: 7 & 28 days split tensile strength for flexure beams ....................................... 56 

Figure 17: Relative Dynamic Modulus v/s nos of freeze-thaw cycles for 0% .................. 61 

Figure 18: Percentage Mass loss v/s nos of freeze thaw cycles for 0% ............................ 61 

Figure 19: Relative Dynamic Modulus v/s nos of freeze-thaw cycles for 25% ................ 62 

Figure 20: Percentage Mass loss v/s nos of freeze thaw cycles for 25% .......................... 62 

Figure 21: Relative Dynamic Modulus v/s nos of freeze-thaw cycles for 50% ................ 63 

Figure 22: Percentage Mass loss v/s nos of freeze thaw cycles for 50% .......................... 63 

Figure 23: Relative Dynamic Modulus v/s nos of freeze-thaw cycles for 75% ................ 64 

Figure 24: Percentage Mass loss v/s nos of freeze thaw cycles for 75% .......................... 64 

Figure 25: Relative Dynamic Modulus v/s nos of freeze-thaw cycles for 100% .............. 65 

Figure 26: Percentage Mass loss v/s nos of freeze thaw cycles for 100% ........................ 65 

Figure 27: Durability factor v/s freeze thaw cycle for 0 % replacement .......................... 66 

Figure 28: Durability factor v/s freeze thaw cycle for 25 % replacement ........................ 66 

Figure 29: Durability factor v/s freeze thaw cycle for 50% replacement ......................... 67 

Figure 30: Durability factor v/s freeze thaw cycle for 75 % replacement ........................ 67 

Figure 31: Durability factor v/s freeze thaw cycle for 100 mk1 % replacement .............. 68 

Figure 32: Durability factor v/s freeze thaw cycle for 100 mk2 % replacement .............. 68 

Figure 33: Photograph showing behaviour of 100% steel slag concrete specimen .......... 75 
xi

LIST OF EQUATIONS 

Equation I: Modulus of Rupture ASTM C 78...................................................................33 

Equation II Splitting Tensile strength ASTM C496 ...........................................34 

Equation III: length change ASTM C 15.......................................................................... 35 

Equation IV Relative Dynamic Modulus of elasticity ASTM C 666.........................36 

Equation V: Durability Factor ASTM C 666...................................................36 
 1

CHAPTER I 

INTRODUCTION 

1.1 Background 

Concrete is the most widely used material on earth after water. Many aspects of 

our daily life depend directly or indirectly on concrete. Concrete is prepared by mixing 

various constituents like cement, aggregates, water, etc. which are economically 

available. Concrete is unique among major construction materials because it is designed 

specifically for particular civil engineering projects. Concrete is a composite material 

composed of granular materials like coarse aggregates embedded in a matrix and bound 

together with cement or binder which fills the space between the particles and glues them 

together (Mindess et al. 2003). 

Concrete plays a critical role in the design and construction of the nationís 

infrastructure. Almost three quarters of the volume of concrete is composed of 

aggregates. To meet the global demand of concrete in the future, it is becoming a more 

challenging task to find suitable alternatives to natural aggregates for preparing concrete. 
 2

Natural aggregates are obtained from natural rocks. They are inert, filler materials and 

depending upon their size they can be separated into coarse aggregates and fine 

aggregates. The coarse aggregate fraction is that retained on 4.75 mm (No 4) sieve, while 

the fine aggregates fraction is that passing the same sieve. According to some estimates 

after the year 2010, the global concrete industry will require annually 8 to 12 billions 

metric tons of natural aggregates (U.S.G.S and nationalatlas.gov, accessed Nov 2008). 

ìDuring the past 25 years, the production of crushed stone has increased at an average 

annual rate of about 3.3 percent. Production of sand and gravel has increased at an annual 

rate of less than 1 percent. Based on these numbers, by 2020 U.S. production of crushed 

stone, which is expected to increase by more than 20 percent, will be about 1.6 billion 

metric tons, while production of sand and gravel will be just under 1.1 billion metric tons, 

an increase of 14 percent. In essence the amount of crushed stone to be produced in the 

next 20 years will equal the quantity of all stone produced during the previous century i.e. 

about 36.5 billion metric tons.î (U.S. Geological survey) 

Therefore the use of alternative sources for natural aggregates is becoming 

increasingly important. Slag is a co-product of the iron and steel making process. Iron 

cannot be prepared in the blast furnace without the production of its co-product; blast 

furnace slag. Similarly, steel cannot be prepared in the Basic Oxygen Furnace (BOF) or 

in an Electric Arc furnace (EAF) without making its co-product; steel slag 

(www.nationalslag.org). The use of steel slag aggregates in concrete by replacing natural 

aggregates is a most promising concept. Steel slag aggregates are already being used as 

aggregates in asphalt paving road mixes due to their mechanical strength, stiffness, 

porosity, wear resistance and water absorption capacity. Studies and tests are being 
 3

conducted on ways to use this steel slag as an aggregate in concrete (Beshr and 

Maslehuddin et al. 2003). According to the National Slag Association, steel slag is 

currently used in bituminous asphalt paving, the manufacture of Portland cement, and in 

roadway construction as a base course, along with some agricultural applications. The 

only potential problem with steel slag aggregate is its expansive characteristics and 

undesirable reactions between slag and components of concrete. This might be a 

perception, but most of the information is anecdotal in nature rather than documented in 

published research studies. 

1.2 Purpose 

The purpose of this research was to explore the feasibility of utilizing the steel 

slag produced by steel mills in the Northeastern Ohio region as a replacement for natural 

aggregate in the concrete. Steel slag aggregates generally exhibit the potential to expand 

due to the presence of unhydrated free lime and magnesium oxides which hydrate in 

humid environments. If such a product is used in the concrete, it influences both the 

mechanical and physical properties of concrete along with its durability. Researchers in 

the past have successfully incorporated this industrial byproduct as aggregates for 

hydraulically bound mixtures for road bases. The use of this material as a construction 

aggregate is being studied, and further research is on going in the United States. 
 4

1.3 Scope 

The original scope of this research was to investigate the properties of concrete 

with steel slag aggregates. The fresh and hardened properties of concrete were tested with 

steel slag aggregates. The freeze-thaw resistance of concrete with steel slag aggregates 

was studied and the expansion of the concrete specimens was also examined. In addition 

to this research several tests were also included such as compressive strength, split tensile 

strength and the flexural strength of concrete with steel slag aggregates. For this research 

the percentage of the volume of natural aggregates normally used in concrete was 

replaced by steel slag. This replacement was done in 25% increments until all natural 

aggregates were replaced by the steel slag. Thus replacing the natural aggregates in 

concrete applications with steel slag would lead to considerable environmental benefits 

and would be economical. 
 5

CHAPTER II 

LITERATURE REVIEW 

2.1 Overview 

 This chapter discusses concrete in general as well as the effects of incorporating steel 

slag aggregates into the concrete mixture. Topics addressed include steel slag, how it is 

manufactured, its properties, comparison of steel slag aggregates with natural aggregates, 

and its feasibility for use as a replacement for natural aggregates in concrete. 

2.2 Concrete 

Concrete is a composite material which is composed of coarse granular materials 

called aggregates or filler embedded together in the form of a matrix with the help of the 

cement or binding material that fills the space between the aggregates particles and glues 

them together. Aggregates are usually obtained from natural rocks, either crushed stones 

or natural gravels. Cement binds the aggregates together. Other material like fly ash or 

ground granulated blast furnace slag may also be used as binding material. Aggregates 

are divided into two parts: fine aggregates and coarse aggregates. Fine aggregates are 

considered to be the material passing through 4.75mm (No 4) sieve (0.187 in square 
 6

opening) and are predominately retained on a No. 200 sieve. Natural coarse aggregates 

are generally crushed stones or gravels which are retained on the No.4 sieve. Finally, 

water is added to initiate the binding process. This makes the mix stiffer and forms the 

material called concrete, which can be used in construction and forms a basis of our 

modern society (Mindness.2002). 

2.3 Aggregates 

Aggregates provide dimensional stability and wear resistance for concrete. Not 

only do they provide strength and durability to concrete, but they also influence the 

mechanical and physical properties of concrete. Aggregates act as a filler material and 

lower the cost of concrete. Aggregates should be hard, strong, free from undesirable 

impurities and chemically stable. They should not interfere with the cement or any of the 

materials incorporated into concrete. They should be free from impurities and organic 

matters which may affect the hydration process of cement. The workability, strength, 

durability and moisture susceptibility of concrete are greatly influenced by the 

characteristics of aggregates. The size and grading of aggregates are important 

parameters in the design of a mix for a particular project because they can influence the 

workability of fresh concrete and its hardened strength. The porosity of aggregates and 

their absorption capacity affects the resistance of concrete to freezing and thawing 

(Mindness.2002). 
 7

2.4 Properties of Aggregates required for Mix Design 

Certain properties of aggregates must be known before designing a particular 

mixture for any construction project. These includes shape and gradation, moisture 

content, unit weight, specific gravity, void ratio and chemical properties 

For good workability the ideal aggregate particle should be close to spherical in 

shape, and well rounded with a relatively smooth surface. The shape of aggregates and 

particle characteristics greatly influences the cement paste requirements. Sufficient 

cement paste is required to coat the aggregates and to provide enough lubrication to 

decrease interaction between aggregate particles during mixing. The rough angular shape 

of crushed aggregates favorably influences the tensile strength of concrete by increasing 

the amount of surface area for bonding with cement paste and reducing high internal 

stress concentrations (Mindness.2003). 

 The particle size distribution and maximum size of aggregates affect the 

economy of overall concrete mixture, as they determine the amount of cement paste 

required for a particular concrete. The amount of paste depends on the amount of void 

space, which can be altered by incorporating different size particles. Sieve analysis is 

carried out to determine the grading of aggregates. 

Another property of aggregates is their ability to absorb water due to their 

porosity. Water can also be retained on the surface as adsorbed water in the form of a thin 

film. This adsorbed water must be considered in the mixture design, as extra water to be 

added into the mixture must be adjusted depending upon the water/cement ratio. 
 8

Generally aggregates are stockpiled before use in the construction and are in an air dried 

state (Mindness.2003). 

Soundness is also an important property of coarse aggregates. Aggregates are said 

to be unsound when their volume changes depends upon the change in environment i.e. 

due to chemical reactions. The resistance of concrete to freeze-thaw conditions depends 

on the high internal stresses developed when the water inside the aggregates freezes and 

causes a change in volume during cold weather. This leads to series of micro cracks in 

the concrete which will ultimately reduce the strength and weaken the concrete. A freezethaw test is conducted to determine the durability of concrete where the concrete 

specimens are subjected to a set amount of freeze-thaw cycles and changes in the weight 

of specimens are determined (Mindness.2003). 

2.5 Non-traditional Aggregates 

 A wide range of materials can be used as an alternative to natural aggregates. When 

any new material is used as a concrete aggregate, three major considerations are relevant: 

(1) economy, (2) compatibility with other materials and (3) concrete properties. 

(Mindness et al .2003). The economical use of non traditional materials in concrete 

depends on various factors, like transportation required to bring the materials from 

industry to the site of construction, quantity available, and the mix design requirements 

(Mindness et al .2003). Many sources are located very far from their potential markets 

for concrete with high transportation costs. The separation of any useful materials from 

undesired substances would be costly as well. Crushing the aggregates to particular sizes 
 9

is also an important issue. The aggregates should not react adversely with other 

constituents of the concrete mixture. They should not change the properties of the 

concrete adversely. The aggregates have vital role in concrete and provide strength and 

durability to concrete. The use of industrial byproducts in the concrete has received 

increasing attention in the recent years. Blast furnace slag is used as an aggregate for 

asphalt concrete and also as a cementitous material in concrete. Steel slag which is also 

an industrial byproduct has potential to be utilized as an aggregate in concrete as well. 

 

2.6 Steel Slag and its production: 

 Steel slag is a byproduct obtained either from conversion of iron to steel in a Basic 

Oxygen Furnace (BOF), or by the melting of scrap to make steel in the Electric Arc 

Furnace (EAF). The molten liquid is a complex solution of silicates and oxides that 

solidifies on cooling and forms steel slag. Steel slag is defined by the American Society 

for Testing and Materials (ASTM) as ìa non-metallic product, consisting essentially of 

calcium silicates and ferrites combined with fused oxides of iron, aluminum, manganese, 

calcium and magnesium that are developed simultaneously with steel in basic oxygen, 

electric arc, or open hearth furnacesî (Kalyoncu, 2001). The two states producing the 

most steel slag in the U.S. are Ohio and Indiana. The chemical composition and cooling 

of molten steel slag have a great effect on the physical and chemical properties of 

solidified steel slag. 
 10

 Steel furnace slag is produced in a Basic Oxygen Furnace (BOF) or Electric Arc 

Furnace (EAF) as a byproduct of the production of steel. In the Basic Oxygen Furnace 

(BOF), the hot liquid metal from the blast furnace, scrap and fluxes, which contain lime 

(CaO) and dolomitic lime, are charged to a furnace (Shi, 2004). A lance is lowered into 

the converter and then oxygen in injected with high pressure. The oxygen then combines 

with and removes the impurities as shown in Fig. 1(a). These impurities consist mainly of 

carbon in the form of gaseous carbon monoxide, silicon, manganese, phosphorous and 

some iron as liquid oxides, which combine with lime and dolomitic lime to form steel 

slag. At the end of the refining stage, the steel in the liquid form is poured into the ladle 

while the slag is retained at the top in the vessel and is then subsequently removed in 

separate slag pot. This slag is in molten state and is then processed to remove all free 

metallic impurities with help of magnetic separation and then sized into construction 

aggregates. 

 Unlike the Basic Oxygen Furnace (BOF) process, the Electric Arc Furnace (EAF) 

does not use hot metal, but uses cold steel scraps. Charged material is heated to a liquid 

state by means of an electric current. The electricity has no electrochemical effect on the 

metal, making it perfectly suited for melting scrap. During the melting process, other 

metals are added to the steel to give the required chemical composition. Meanwhile 

oxygen is blown into the EAF to purify the steel. This slag which floats on the surface of 

molten steel is then poured off. 
 11

 (A) (B) 

Fig 1 Schematic illustration of Basic Oxygen Furnace and Electric Arc Furnace 

(NSA accessed, 2008) 

 The main constituents of iron and steel slags are silica, alumina, calcium, and 

magnesia, which together make about 95% of the total composition. Minor elements 

included are manganese, iron, sulfur compounds and traces of several other elements 

(Kalyoncu, 2001). Physical characteristics such as porosity, density, particle gradation, 

are affected by the cooling rate of the slag and its chemical composition. 

2.7 Current Uses of Steel Slag: 

 Some of the current uses of steel slag according to the National Slag Association 

(NSA accessed, 2008) are as follows: 

1. Steel slag is used as an ideal aggregate in hot mix asphalt (HMA) surface mixture 

application due to its high frictional resistance and skid resistance characteristics. 

The cubical nature of steel slag and its rough texture provides more resistance 

than round, smooth and elongated aggregates. 
 12

2. It is also used in making Stone Matrix Asphalt (SMA) because the particle-toparticle contact of the aggregate does not break down during the manufacturing, 

laying down, or compaction process. Illinois Department of Transportation 

(IDOT) has successfully specified steel slag SMA bituminous mixes on roadways. 

3. It is also used for manufacture of Portland cement. 

4. It is used in base application, construction of unpaved parking lots, as a shoulder 

material, and also in the construction of berms and embankment. 

5. It is also used in agriculture because it has minerals like iron, manganese, 

magnesium, zinc and molybdenum which are valuable plant nutrients. 

6. It is environment friendly. During the production of cement, the CO2 emissions 

are reduced as slag has previously undergone the calcination process. 

7. Steel slag aggregates are used for soil stabilization or soil improvement material 

and for remediation of industrial waste water run-off. 

2.8 Properties of Steel Slag 

The United States Department of Transportation and the Federal Highway 

Administration along with the Turner Fairbank Highway Research Center (TFHRC) have 

listed some of the properties of steel slag: 
 13

2.8.1 Physical properties

Steel slag aggregates are fairly angular, roughly cubical pieces having flat or 

elongated shapes. They have rough vesicular nature with many non-interconnected cells 

which gives a greater surface area than smoother aggregates of equal volume; this feature 

provides an excellent bond with Portland cement (NSA accessed Nov 2008).

Steel slag has a high degree of internal friction and high shear strength. The rough 

texture and shape ensure little breakdown in handling and construction (NSA accessed 

Nov 2008). Steel slag has high bulk specific gravity and less than 3% water absorption. 

Steel slag aggregates have high density, but apart from this feature most of the physical 

properties of steel slag are better than hard traditional rock aggregates. Below are listed 

some of the positive features of steel slag. (GeoPave, 1993) 

1. They are strong and durable. 

2. They have excellent angular shape which helps to develop very strong 

interlocking properties. 

3. They have high resistance to abrasion and impact. 

Table 1 lists some typical physical properties of steel slag. (TFHRC-Steel slag 

material description, accessed Nov 2008) 

Property Value

Specific Gravity > 3.2 - 3.6

Approx Dry rodded Unit Weight, kg/m3 (lb/ft3)

1600 - 1920 

(100 ñ 120)

Water Absorption up to 3%

Table I. Typical physical properties of steel slag. (TFHRC accessed 2008) 
 14

2.8.2 Chemical and Mineralogical composition 

Blast furnace slag usually contains four major oxides, namely lime, magnesia, 

silica and alumina. Minor elements include sulfur, iron, manganese, alkalis and trace 

amount of several others. The chemical composition of slag is generally expressed in 

terms of simple oxides calculated from elementary analysis determined from x-ray 

fluorescence. Table II shows the list of various ranges of compounds presents in steel 

slag from a typical oxygen furnace. (TFHRC-Steel slag material description, accessed 

Nov 2008). The mineralogical form of slag is highly dependent on the rate of cooling of 

slag in the steel making process. Most of the blast-furnace slag produced in the U.S. has 

compositions within the ranges as shown in table II. 

Constituent Composition (%) 

by TFHRC

Composition (%) by 

NSA 

CaO 40 - 52 42 

SiO2 10 ñ 19 15 

FeO 10 - 40 

(70 - 80% FeO, 20 - 30% Fe2O3) 24 

MnO 5 ñ 8 5 

MgO 5 ñ 10 8 

Al2O3 1 ñ 3 1-5 

P2O5 0.5 ñ 1 0.8 

S < 0.1 0.08 

Metallic Fe 0.5 ñ 10 - 

Table II. Typical steel slag chemical composition (TFHRC)

The rate of cooling of steel slag is generally kept lower so that the crystalline 

compounds are formed. The predominant compounds in steel slag are dicalcium silicate, 

tricalcium silicate, dicalcium ferrite, merwinite, calcium aluminate, calcium-magnesium 

iron oxides, some free lime and magnesia. Steel slag is mildly alkaline, with a solution 

pH generally in range of 8 to 10. However, the pH of leachate from steel slag can exceed 
 15

11, a level that can be corrosive to aluminum or galvanized steel pipes placed in direct 

contact with the slag. 

According to Department of Transportation (DOT) and Federal Highway 

Administration (FHA), the amount of free calcium and magnesium oxides is not 

completely consumed in steel slag. The hydration of unslaked lime and magnesia in 

contact with moisture is largely responsible for the expansive nature of most steel slag. 

The free lime hydrates very rapidly and can cause large changes in volume over a 

relatively short period of time, i.e. weeks, while magnesia hydrates much more slowly 

and contributes to long term expansion which may continue for many years. 

Free lime (Calcium oxide) (CaO) + water (H2O) = Calcium carbonates (CaCO3) 

 Magnesium oxide (MgO) + water (H2O) = Magnesium carbonates (MgCO3) 

2.8.3 Mechanical Properties 

According to TFHRC (www.tfhrc.gov) the processed steel slag has favorable 

mechanical properties for use as aggregates in construction; these include good abrasion 

resistance, good soundness characteristics, and high bearing strength. 

 Table III. Typical mechanical properties of steel slag. (TFHRC accessed 2008)

 

Property Value

Los Angeles Abrasion (ASTM C131), % 20 - 25

Sodium Sulfate Soundness Loss (ASTM C88), % <12

Angle of Internal Friction 40° - 50°

Hardness (measured by Moh's scale of mineral hardness)* 6 - 7

California Bearing Ratio (CBR), % top size 19 mm (3/4 inch)** up to 300

* Hardness of dolomite measured on same scale is 3 to 4. 

** Typical CBR value for crushed limestone is 100%.
 16

2.8.4 Effect on the Environment and Health 

 A Steel Slag Coalition (SSC) was formed in 1995 to provide a comprehensive 

study of steel slag. This coalition consisted of iron and steel manufacturers, slag 

processors, chemical laboratories and risk assessment teams, environmental scientists and 

toxicologists to conduct an industry-wide ìHuman Health and Ecological Risk 

Assessment (HERA)î on iron and steel slag. (NSA accessed Nov 2008). The result of 

this study confirmed that the iron and steel slag have no threats to human health or the 

environment when used in residential, agricultural, industrial and construction 

applications. ìSlag has also been effectively used to treat acid mine drainage discharge 

and is also useful in the removal of excess phosphorous from waste water discharges, 

thus rendering the waste water more ecologically beneficialî (Wagaman and Stanley, 

2005). 

2.9 Problems associated with Steel Slag aggregates 

Steel slag aggregates have two main features which are of concern to their use in 

construction, namely, volume expansion and high particle density. During the making of 

steel there is a small percentage of calcium and magnesium oxides which is left 

undissolved in the slag. These non hydrated calcium and magnesium oxides then later 

come in contact with moisture which leads to hydration process. The volume expansion is 

primarily caused by the reaction between the free lime in slag and water during the 

hydration process to produce calcium hydroxide. As a result there is a great increase in 

volume due to the difference of specific density of the hydration product. These changes 

in volume can occur either in a few weeks after production of slag or may occur many 
 17

years later if the slag is initially protected from contact with water (GeoPave, 1993). A 

general method usually used to overcome the expansion problem is to store the slag for 

aging in stockpiles for some four to six months before using it. 

Density of steel slag is also an important issue to be considered. Steel slag is a heavier 

material than natural rock types such as basalt, granite, or limestone. Thus, any given 

volume would require about 15 to 25% greater tonnage of steel slag than traditional 

natural aggregates which may create an economic disadvantage for steel slag in some 

applications where transportation costs are significant (GeoPave, 1993). 

2.10 Aging of Steel Slag and Stockpiling of Steel slag aggregates 

After initial crushing, the slag comes out from the factory and the potential 

expansion of oxidizing slag may then evaluated according to the ASTM D-4792 on 

samples taken at random from the stock piles. ASTM D-4792 is a test method for 

determining the compliance of steel slag and other materials containing components 

subjected to hydration. The test method consist of measuring the volume expansion of 

compacted specimens and to accelerate hydration reaction, the specimens are stored in 

water at 70 ± 3°C (158 ± 5°C) for minimum of 7 days. Three representative samples are 

taken from random location from the stock piles approximately 45kg (100 lbs) and 

samples are then reduced to testing size of two 18kg (40 lbs) according to ASTM C 702 -

Practice for reducing samples of aggregates to testing size. Sieve analysis of the samples 

is done. Three expansion test specimens should be prepared according to ASTM D 1883. 

After placing the stem and perforated plate surcharge weights 4.54 kg (10 lbs) is placed 
 18

and then it submerged in hot water for 30 minutes to allow thermal expansion of test 

apparatus and dial gage measurements are taken. For 7 days heated water is added 

continuously and the percentage expansion is calculated each day. An accelerated aging 

test is also sometimes carried out in which the specimens of 150 x 300mm are aged for 

28 days in a moist room (Manso et al. 2004 and Emery, 1984). These specimens are then 

submerged in water at 70°C and are kept for 32 days. After that the specimens are dried 

and kept for 90 days exposed to weather but direct impact of rain is avoided. These 

specimens when tested showed a considerable improvement in the compressive strength 

as compared to normal conventional concrete cured continuously in moist room from 28 

to 90 days (Manso et al. 2004). The objective of this test is to evaluate the hydration of 

the free lime and free magnesium of the slag aggregates in hot water. 

 

The steel slag used for this research was obtained from a company located in 

Cleveland Ohio. The steel slag was processed in compliance with Ohio Department of 

Transportation Construction and Material Specifications, 2005. Section 703.14 D gives 

the specifications regarding the stockpile requirements, which states that ì water is added 

to the stockpile material to provide a uniform moisture content not less than absorbed 

moisture and maintained in moist condition during the stockpiling period.î The minimum 

aging time was six months, but has been decreased to three months. The Expansion test 

can be performed according to Pennsylvania Department of Transportation PTM No.130 

Method of Test for Evaluation of Potential Expansion of Steel slag. PTM 130 is similar to 

ASTM D 4792 which is the Standard Test method for Potential Expansion of Aggregates 

from Hydration Reaction which is referenced for expansion testing of steel slag 
 19

aggregates in supplement 1071. The maximum allowable total expansion for the test is 

less than 0.5 %.( Bosela et al. 2007). The conditioning of the slag for its use as aggregate 

in concrete requires it to be crushed, homogenized, weathered and aged. The concrete 

obtained with oxidized slag as aggregates have good properties on hard and fresh state. 

Steel slag must be allowed to undergo the weathering process before using as an 

aggregate in construction because of its expansive nature. This is done in order to reduce 

the quantity of free lime to acceptable limits. The steel slag is allowed to stand in 

stockpiles for a period of at least 4 months and exposed to weather. During this 

weathering process, the steel slag is required to be in contact with water so that the 

hydration process between lime and water takes place. Hydration of free lime (CaO) or 

free magnesia (MgO) is responsible for expansive nature of steel slag. 

Figure 2: Stockpiling of steel slag aggregates at Stein Inc 2008 
 20

2.11 Past studies on Steel Slag aggregates 

The successful incorporation of steel slag as an aggregate in concrete has been 

studied in the past. Steel slag is an industrial byproduct and instead of disposing it in the 

landfill, the use of such product in the construction market would increase efficiency and 

economy. The physical and chemical characteristics of steel slag have been examined 

carefully. Due to its potentially expansive properties, it require special care if used in 

construction or other specific applications. The possibility of utilizing such product as a 

concrete aggregates with ecological benefits has been globally studied by several 

researchers like Anastasiou and Papayianni, (2006). 

They conducted several tests with slag aggregates in concrete and found out that 

the 28 day strength was increased by 21% with replacement of natural aggregates, while 

there was no increase in the setting time of concrete mixtures. The cement-aggregate 

interface seemed to be very dense without cracks or other discontinuities. The concrete 

that is produced with steel slag aggregates is of high specific gravity compared to 

conventional concrete. However the specific gravity can be increased or reduced 

proportionally by the combination of different types of aggregates (Anastasiou and. 

Papayianni, 2006). 

 A study on durability of the concrete made with Electric Arc Furnace slag as an 

aggregate was done by Manso and Gonzalez (2004), and the results showed that it was 

acceptable. The concrete mixes using conditioned EAF slag showed good fresh and 

hardened properties and acceptable behavior against aggressive environmental 

conditions. It was observed that the compressive strength was similar to that of traditional 

concrete. The durability was slightly lower than conventional concrete. The concrete had 
 21

good physical and mechanical properties, but results showed that special attention should 

be paid to the gradation and crushing process. The results showed that the high porosity 

of EAF slag aggregates affects concrete resistance to freezing and thawing but 

improvements in the field could be possibly obtained by adding air entraining 

admixtures. 

Comparison of steel slag and crushed limestone aggregate was done by 

Maslehuddin, et al, (2003). They studied the mechanical properties and durability 

characteristics of steel slag aggregate concrete in comparison with limestone aggregates. 

Their results showed that the durability and physical properties of concrete with steel slag 

aggregates was better than limestone aggregates. They suggested that the use of steel slag 

aggregates in concrete was beneficial, particularly in areas where good quality aggregates 

are not available or have to be hauled from far off distances. Abrasion resistance, specific 

gravity, water absorption, chemical soundness, alkalinity, concentration of chloride and 

sulfates were tested and compared with lime stone aggregates. Shrinkage and expansion 

characteristics of steel slag and sand cement mortar specimens were evaluated and length 

was measured at periodic intervals. Their results showed that the compressive strength of 

steel slag aggregates increased with the proportion of coarse aggregates from 4550 psi 

(31.4 MPa) with 45% coarse aggregates to 6190 psi (42.7 MPa) with 65% coarse 

aggregates. The flexural strength and split tensile strength also increased while the water 

absorption capacity was reduced. They stated that the shrinkage of steel slag exposed to a 

dry environment was similar to limestone aggregate with no major expansion i.e. less 

than 0.05% as specified by ASTM C 33. The time of initiation of reinforcement corrosion 
 22

and time of cracking of concrete specimens was observed to be longer than with lime 

stone aggregates. 

Further study by Manso, Polanco et al (2006) reaffirmed that by proper mix 

proportions both the mechanical strength and durability of steel slag aggregate concrete 

can be improved. He conducted two tests for durability: 1) Autoclave test and 2) 

Accelerated aging test. Autoclave test is used to detect the presence of expansive 

compounds, free lime or magnesia in Portland cement, while accelerated ageing test is 

done based on ASTM D-4792. Results showed that the compressive strength was 

improved after testing. He conducted chemical reactivity test to observe the possible 

reactions between slag aggregates and other components of concrete. For the freeze-thaw 

test, three samples were stored in moist room for 28 days and subjected to 25 freezing 

and thawing cycles. They are then immersed in water at 4oC for 6 hours and maintained 

in frost storage at -17 oC for 18 hours. Variations in weights and compressive strength 

were recorded and results showed that Electric arc furnace slag concrete showed greater 

strength and lower water penetration. He also stated the use of air entraining admixtures 

increased the freeze-thaw resistance and durability of slag concrete was satisfactory. 

Industrial by-products like steel slag require a detailed study of its potential 

toxicity. There are several dangerous heavy metals and salts present in the steel slag. A 

leaching test is required prior before using the EAF slag as a filling material. Manso et al, 

(2006) conducted the leaching test for determining the possible attack of concrete in the 

environment. Analysis of leached water from crushed slag aggregates were used to detect 

the sulphates, fluorides and total chromium present in it. The results showed that smaller 

size of crushed slag produces higher concentration of dangerous substances in leached 
 23

water. The cloistering effect was found to be greater in larger sizes of crushed slag. He 

concluded that the use of EAF slag aggregate in concrete will help to reduce its potential 

toxicity and the results confirmed an important cloistering effect of cementitous matrix 

on the contaminants elements. Also some previous research was carried out at the 

Cleveland State University by (Obratil et al, 2008) who examined the effects of replacing 

various percentages of natural aggregates with steel slag in a standard concrete pavement 

mixture which showed satisfactory results. 

Research on freeze-thaw resistance of steel slag aggregate concrete was done by 

Takashi et al, (2007). Concrete specimens were prepared with steel slag aggregates, 

recycled aggregates and crushed stones and compared with each other. The size of steel 

slag aggregates used for the research ranged from 15-20mm. The samples were cyclically 

exposed to -18°C to 5°C, every 5 hours in water. Results showed that resistance to 

freezing and thawing of steel slag aggregates concrete was better than the recycled 

aggregates and almost same as crushed stone. Results also showed that compressive 

strength and resistance to freezing and thawing increased with increase in cement 

content. 

In Saudi Arabia, research was conducted to utilize locally available steel slag in 

concrete by Abdulaziz et al, (1996). The steel slag was used as coarse aggregates in 

concrete and comparison was made with crushed gravel. The results showed that the 

compressive and flexural strength for slag concrete was slightly higher than the natural 

gravel concrete. The splitting tensile strength and modulus of elasticity were higher, 

while drying shrinkage was lower than the natural gravel concrete. The results were 

encouraging since they showed no negative effects on short term properties of hardened 
 24

concrete. The slag was analyzed chemically and it did not show any presence of free lime 

or any other unstable substances, which can cause swelling effects. Four trial mixes were 

made with different water/cement ratio and compared with reference mix of crushed 

gravel as coarse aggregates. The Youngís modulus of elasticity E of steel slag aggregates 

concrete at 28 days was 5 x 106

 Psi (34.3 GPa) while it was 4 x 106 Psi (27.9 GPa) for 

gravel concrete. The improvement in strength properties of steel slag aggregate concrete 

may be due to shape of particles and surface texture, which provide better adhesion and 

bond between particles and the cement matrix.
 25

CHAPTER III 

EXPERIMENTAL DESIGN 

 3.1 Overview 

The main objective of this research was to utilize the steel slag aggregate in the 

concrete mixture and identify the properties of the mixture, its durability, expansion 

and also its fresh and hardened concrete properties. The research started by replacing 

the percentage of the volume of natural aggregates, normally used in the manufacture 

of concrete in Northeastern Ohio, with steel slag in increments of 25% until all the 

natural aggregates were replaced by the steel slag. 

All concrete mixing was performed in the Concrete Research Laboratory in the 

Fenn College of Engineering at Cleveland State University. Before mixing 

commenced, the gradation of steel slag samples was determined and compared with 

the natural aggregates. The experimental program consisted of first testing the fresh 

concrete properties, then forming specimens for the following tests: ASTM C 39: 
 26

Compressive Strength of Cylindrical Concrete Specimens. ASTM C 157: Length 

Change of Hardened Hydraulic-Cement, Mortar, and Concrete. ASTM C 78: 

Flexural Strength of Concrete. ASTM C 496: Splitting Tensile Strength of Cylindrical 

Concrete Specimens. ASTM C 666: Resistance of Concrete to Rapid Freezing and 

Thawing. 

3.2 Concrete Mix Design 

This research primarily focused on the Class C Option 1 Concrete mixture of the 

Ohio Department of Transportation (ODOT) because of its frequent use in road 

construction. Table IV show Concrete Mixture Proportions (Quantities per Cubic 

Yard (m3

) and Table V shows the Testing program along with the protocols and 

methods used during this research. 

Table IV: Concrete Mixture Proportions (Quantities per Cubic Yard (m3) 

Research Mixture Design 

 SSD Aggregate Weight 

Mixture 

Type 

Fine 

Aggregate 

Coarse 

Aggregate 

Steel Slag 

Aggregate 

Cement 

Content 

WaterCement 

Ratio 

 lb kg Lb Kg lb kg lb Kg Maximum 

ODOT Class C 1270 576 1610 730 - - 600 272 0.50 

25% 956 434 1171 531 844 383 600 272 0.50 

50% 638 289 781 354 1688 766 600 272 0.50 

75% 319 145 390 177 2531 1148 600 272 0.50 

100% - - - - 3375 1531 600 272 0.50 
 27

3.3 Gradations 

The steel slag aggregate was provided by Stein Inc. The initial visual examination 

of the steel slag samples suggested that it consisted of a mixture of both fine and coarse 

aggregates. Sixteen samples were taken and sieve analysis was done according to ASTM 

C 136. The average results of the percentage passing each screen for the steel slag were 

compared to the curves of the natural aggregates it was to replace. This data was also 

compared to the mixture curves determined for ODOT Class C option 1 pavement 

mixture. 

 

(A) 

FIG 3 (A) and (B) shows sieve analyses conducted to determine gradation. 
 28

(B) 

3.4 Properties of Concrete 

The properties of concrete are classified into two categories: fresh and hardened. 

The durability of concrete depends upon the mix design and durability of aggregates. The 

water-cement ratio and addition of admixtures greatly affect the durability of concrete. 

The properties which affect the strength and durability of a concrete structure change 

over the life of structure, increasing with time.

(A) Fresh Concrete Properties 

Fresh concrete properties include slump, unit weight and air content test. The 

slump of the concrete was tested following ASTM C143: slump of Hydraulic Cement 

Concrete. The slump test is empirical in nature, and it does not directly measure the 

workability of concrete mixture. Instead, it is used to ensure the uniformity between the 

different concrete batches for a given job (Mindess et al. 2003). ODOT specifies the 

maximum slump of four inches (100mm) for Class C mixture (ODOT 2005). The unit 
 29

weight test is a more reliable test and provides more valuable information than the slump 

test. The unit weight test will also give information related to air content, water content 

and changes in the aggregate proportion in the mixture. The unit weight of the mixture 

was tested according to ASTM C138: Density (unit weight), Yield, and Air Content 

(Gravimetric) of concrete. The air content test is the most important test for determining 

the durability of concrete in the freeze thaw conditions. The air content of the fresh 

concrete was performed following ASTM C231: Air Content of Freshly Mixed Concrete 

by the Pressure Method. ODOT specifies an air content of 6 ± 2% for Class C Option 1 

mixture. 

Air voids in the system protect the concrete from damage but also reduce the 

strength of the concrete mixture, and therefore great care should be taken not to entrain 

too much air (Mindess et al. 2003). Fig 4 illustrates how the air tests were conducted 

using the pressure method in the laboratory. Fig 5 shows the slump test conducted on the 

concrete sample with 100% steel slag aggregates without super plasticizers. 

Fig 4: Air test being conducted on the concrete sample .2008 
 30

Fig 5: Slump test being conducted on the concrete sample with 100% steel slag .2008

(B) Hardened concrete properties 

To determine the hardened properties of concrete, the Compression test 

(ASTM C 39), Splitting tensile test (ASTM C 496), Freeze-thaw durability test (ASTM 

C 666), and Modulus of rupture (flexural strength test) (ASTM C 78) were conducted. 

Concrete is much stronger in compression than in tension and so the compressive 

strength of concrete is an important property of the concrete (Mindess et al. 2003). It is 

very difficult to directly measure the tensile strength of concrete; therefore the splitting 

tensile test, an indirect method, was adopted. 
 31

 

 (A) (B) 

Fig 6: (A) shows the Compression test conducted on a concrete specimen with 

steel slag aggregates (B) Splitting tensile Test conducted on concrete specimen 

. 

 
 32

 Fig (A) 

 

 Fig (B) Fig (C) 

Fig 7: (A) shows the Fundamental transverse frequency was measured with 

resonance tester. Fig (B) Freeze-thaw test being conducted and concrete specimens are 

placed in the freeze-thaw machine and 300 freeze thaw cycle were carried out. Fig (C) 

Relative dynamic modulus of elasticity of concrete specimen was measured in concrete 

laboratory at CSU.
 33

3.5 Modulus of Rupture 

The modulus of rupture was tested at 7 days for each mixture. At the time of casting 

two specimens were molded following ASTM C 192. Beam specimens had a cross 

sectional area of six inches by six inches and were twenty inches long (152mm x 152mm 

x 508 mm). Specimens were stored in a water tank following ASTM C 511.The beam 

specimens were tested following ASTM C 78 using third-point loading and the Modulus 

of rupture calculated using the equation; 

Equation I: Modulus of Rupture (ASTM C 78) 

 

 

Where: 

R = The Modulus of Rupture. (MPa) 

P = The Maximum applied load indicated by the testing machine. (lbf) (N) 

L = The span length. (in) (mm) 

b = The average width of the specimen at the fracture. (in) (mm) 

d = The average depth of the specimen at the fracture (in) (mm) 

3.6 Compressive Strength of Concrete 

The concrete specimens were tested for compressive strength at 7 and 28 days. 

Specimens were made following ASTM C192 and stored in the water curing tank 

following ASTM C511. The cylindrical specimens prepared for the research were made 

with a diameter of four inches (102 mm) and a height of eight inches (203 mm). Two 

specimens were tested at each age, following ASTM C39, on a hydraulic loading 
 34

machine. The compressive strength was determined by dividing the ultimate applied load 

by the cross-sectional area of the cylinder. The type of fracture of the specimen and the 

compressive strength was also recorded and compared with ASTM C39. 

3.7 Splitting Tensile Strength of Concrete 

The splitting tensile strength of the concrete specimens was tested at 7 and 28 

days. The four inch (102 mm) and eight inch (203 mm) cylindrical specimens were 

molded at the same time as the compressive strength specimens. The specimens were 

tested on a hydraulic loading machine following ASTM C 496. The splitting tensile 

strength can be obtained from the following equations: 

Equation II: Splitting Tensile Strength (ASTM C 496) 

 

Where: 

T = splitting tensile strength (psi) (MPa) 

P = maximum applied load (lbf) (N) 

l = length (in) (mm) 

d = diameter (in) (mm)

 For this research the length (l) was equal to eight inches (203mm) and the 

diameter (d) of was taken as four inches (102 mm).The splitting tensile strength was 

equal to the maximum applied load divided by 50 (65,000). Two specimens were tested 

at 7 and 28 days for each experimental mixture. 
 35

3.8 Change of length of Hardened Concrete 

The testing program also included the determination of change in length of the 

specimens due to causes other than externally applied forces. Two prisms measuring 

4 x 4 x 10 inches (102 x 102 x 254 mm) were prepared for each mixture. Initial length 

measurements were taken after the specimen was removed from the mold 24 hours after 

casting. The prisms were placed into a lime bath until testing at 7, 28, 56, 90 and 120 

days. The length change was then calculated using the equation; 

Equation III: Length change (ASTM C 157) 

Where: 

=The change in length of specimen at any age (%) 

CRD = The difference between the comparator reading of the specimen and the reference 

 bar at any age 

G is the gage length (10 inches (250mm)). 

3.9 Resistance to Rapid Freezing and Thawing 

The resistance of the concrete due to rapid freezing and thawing cycles was tested 

according to ASTM C 666. The concrete prisms were placed into a Logan Freeze Thaw 

machine after curing for 14 days. At intervals of approximately 25 cycles the specimens 

were removed from the machine and their dimensions and weight were determined. The 

transverse frequency was then recorded utilizing an Olson Engineering Model RT-1 

Resonance Tester according to ASTM C 215. From this frequency measurement the 

relative Modulus of Elasticity was calculated by using the following equation; 
 36

Equation IV: Relative Dynamic Modulus of Elasticity (ASTM C 666) 

Where: 

Pc = Relative dynamic modulus of elasticity after c cycles of freezing and thawing (%). 

 N = The Fundamental transverse frequency at 0 cycles of freezing and thawing. 

N1 = The Fundamental transverse frequency after c cycles of freezing and thawing. 

ASTM C 666 specifies that the test ends after 300 cycles, or when the relative 

dynamic modulus of elasticity falls below 60%. The durability factor was then calculated 

using the equation; 

Equation V: Durability Factor (ASTM C 666) 

Where; 

DF = The Durability factor of the test specimen. 

P = The relative dynamic modulus of elasticity at N cycles (%). 

N = The Number of cycles at which P reaches the specific minimum value for 

discontinuing the test or the specified number of cycles at which the exposure is to be 

terminated, whichever is less, 

M is the specified number of cycles at which the exposure is to be determined (usually 

300) 
 37

3.10 Research plan 

 Table V show the testing program for the research. ASTM specifications for 

different test methods to be employed and number of samples to be prepared are also 

shown. 

Table V: Testing Program

Test Protocols and Methods Number of Tests specimens

Aggregate

Gradations ASTM C 136 12 samples

Fresh Concrete Properties

Workability ASTM C 143 2

Air content ASTM C 231 3

Unit weight ASTM C 138 3

Hardened Concrete Properties

Compressive strength ASTM C 39, 4î x 8î cylinders 2 ea. at 7 & 28 days, total of 4

Splitting tensile strength ASTM C 496, 4îx 8î cylinders 2 ea. at 7 & 28 days, total of 4

Flexural strength ASTM C 78, 6îx6îx20î beams 2 at 7 days

Expansive Properties

Length Change ASTM C 157 2

Durability

Freeze-thaw ASTM C 666, ASTM C 215 3 at 300 cycles

 
 38

CHAPTER IV 

MATERIALS 

4.1 Overview 

 This chapter provides the overview of materials used for this research. All the 

materials used during the research program remained the same, except different kind of 

coarse aggregates were used for flexure strength test and in the rest only the proportions 

were varied. All the materials aside from the steel slag were those utilized by ODOT 

District 12 in Northeastern Ohio on their highway projects. A water-cement ratio of 0.5 

was maintained constant during the course of the research program. 

4.2 Portland Cement

The cement used in this project was supplied by St. Maryís Cement Group. This 

is Type I Portland cement as classified by ASTM C150. The cement properties and its 

chemical composition were provided by St Maryís is shown in table VI. 
 39

Table VI: Cement Composition and Physical Properties 

Chemical Percent 

Loss on Ignition 1.6 % 

SiO2 20.45 % 

Fe2O3 2.77 % 

Al2O3 4.55 % 

CaO 61.81 % 

Free CaO 0.93 % 

MgO 3.15 % 

SO3 3.76 % 

K2O 0.53 % 

Na2O 0.30 % 

TiO2 0.28 % 

P2O5 0.17 % 

Mn2O3 0.09 % 

Insoluble Residue 0.13 % 

Total Alkali as Na2O 0.65 % 

Color Index 28.0

Calculated Compounds Percent 

C3S 51 % 

C2S 20 % 

C3A ñ ASTM 7 %

C3A ñ CSA 7.4 % 

C4AF 8 %

Physical Properties 

Fineness: Blaine 381 m2/kg

Retained in #325 sieve 4.0 % 

Autoclave Expansion 0.379 % 

4.3 Steel Slag 

The steel slag used in this research was provided by Stein Inc. and originated 

from Mittal Steel USA located in Cleveland, Ohio, which is involved in the manufacture 

of many types of steel. Stein Inc. also provided an analysis report compiled by 
 40

Alternative Testing Laboratories Inc. which provided information on the chemical 

composition of the steel slag along with the percent absorption and SSD Specific Gravity. 

 The steel slag provided was properly aged in a manner similar to that required by 

Pennsylvania Department of Transportation (PENNDOT) specification 703.2-4. This 

specification requires stockpiles to be kept uniformly moist for a period of at least six 

months. If the total expansion of the material is less than 0.50% than the material is 

ready to use, but if the expansion is greater than the 0.50% then additional curing of up to 

two months is necessary. 

TABLE VII: Steel Slag Chemical Composition and Properties 

(Courtesy: Alternative Testing Laboratories Inc)

Constituents Composition 

(%) by 

Stein. Inc 

Composition 

provided by 

TFHRC (%) 

Composition 

provided by 

NSA (%) 

Aluminum oxide (Al2O3) 5.84 1-3 1-5 

Calcium oxide (CaO) 30.7 40-52 42 

Chromium oxide (Cr2O3) 0.28 - - 

Iron oxide (FeO) 35.6 10-40 24 

Magnesium oxide (MgO) 9.95 5-10 8 

Manganese oxide (MnO) 3.99 5-8 5 

Phosphorus oxide (P2O5) 0.61 0.5-1 0.8 

Potassium oxide (K2O) 0.05 - - 

Silicon oxide (SiO2) 12.0 10-19 15 

Sodium oxide (Na2O) 0.09 - - 

Titanium oxide (TiO2) 0.65 - - 

Vanadium oxide (V2O5) 0.21 - - 

Water Absorption 3.37 0- 3 - 

SSD Specific Gravity 3.09 3.2-3.6 - 
 41

Table VII shows steel slag chemical compositions and properties. The values in 

the 2nd column were provided by Stein Inc and determined by Alternative Testing 

Laboratories. The values in the 3rd column are typical steel slag chemical compositions 

provide by TFHRC lab and 4th column had typical steel slag chemical compositions 

provide by NSA (accessed Nov 2008). 

4.4 Fine Aggregates 

The fine aggregate used for the research was Shalersville natural sand from 

Lafarge Corporation supplied by Cuyahoga Concrete and Stone. This Aggregate has 

absorption of 1.18%. The Bulk Specific Gravity of the fine aggregate was 2.60 while its 

SSD Specific Gravity was 2.63.

4.5 Coarse Aggregates 

Two types of coarse aggregates were used in this research. One was high 

absorption #57 Marblehead limestone with a nominal maximum size of 1 inch (25 mm), 

supplied by Cuyahoga concrete. These aggregates were used for making the freeze-thaw 

specimens, compressive test and tensile test specimens. The absorption of these coarse 

aggregates was 3.03%. The Bulk Specific Gravity provided by the supplier was 2.49 

with an SSD Specific Gravity of 2.57. The second type of coarse aggregates was the 

medium absorption coarse aggregate #57 Hanson Sandusky crushed limestone provided 

by Mack Concrete of Akron Ohio, which was used for making the flexural strength beam 

mixtures. This absorption of these aggregates was reported as 2.14% with an SSD 

Specific Gravity of 2.58. Two coarse aggregates were used because we had shortage of 
 42

#57 Marblehead limestones and none was left when we later decided to conduct the 

flexural strength test for the beam. 

4.6 Chemical Admixtures 

Two chemical admixtures were used in this research: high range water reducer 

and air entrainment admixture. The air entrainment admixture MB-AE 90 was applied to 

all mixtures, while a few mixtures required the use of the High range water reducer 

Glenium 3030 NS. These chemicals were provided by BASF/Master Builders. Glenium 

meets ASTM C494 requirements for Type A, water-reducing, and Type F, high-range 

water reducing, admixtures. The high range water reducing admixtures were added in the 

freeze thaw specimens with 100% steel slag aggregates and also in the flexural beams 

with 75% steel slag aggregates. The air entrainment admixture was MB-AE 90. MB-AE 

90 meets the requirements of ASTM C 260. 

Importance of chemical admixtures in the concrete 

All porous materials are susceptible to damage during freezing and thawing. 

Concrete can be made frost resistant by adding air entraining admixtures. These 

admixtures increase the amount of air in concrete during mixing. Depending upon the 

type of mixer, rate of mixing, time of mixing and amount of concrete to be mixed, the 

total required volume of air entraining admixtures is calculated and added accordingly. 

These air entraining admixtures form tiny bubbles, approximately spherical in shape and 

randomly dispersed throughout the mixture which help water to accumulate in them 

during the freezing condition and give space to water molecules to expand and reduce 
 43

high internal stresses and prevents micro cracks in concrete. (Mindness.2003). A well 

distributed system of small bubbles protects the whole paste volume. Bleeding and 

segregation are also reduced in the wet mixture and the concrete can be easily handled 

and transported. 

 However there are also some disadvantages of incorporating air into the concrete. 

If too much air is trapped in the paste, it weakens the concrete resulting in lower strength 

and possibly lower ductility. Proper care should be taken during mixing of concrete and 

the time elapsed between the mixing and casting into the mould to minimize the amount 

of entrapped air. A high amount of entrapped air would seriously affect the durability of 

concrete and its freeze-thaw resistance. 
 44

CHAPTER V 

EXPERIMENTAL RESULTS 

5.1 Overview 

The chapter discusses the results obtained from various tests. The results 

presented in this chapter are the average results when more than one sample each of 

mixture was tested. 

5.2 Gradations 

The sieve analysis of the steel slag samples revealed that the material was a 

combination of both fine aggregates and coarse aggregates. Figure 8 shows the results of 

sieve analysis of Steel slag obtained from Stein when compared with Shalersville fine 

aggregates and Marblehead #57 coarse aggregates. 

 Figure 9 illustrates the comparison between the replacement mixtures and the 

Class C pavement mixture. As can be seen in Figure 9 the overall mixture became finer 
 45

as more steel slag was used. The steel slag aggregates fractions lies between the fine 

aggregates and coarse aggregates.

FIGURE 8: Sieve analysis results compared with fine and coarse aggregates. 

FIGURE 9: Comparison of replacement mixtures to ODOT class C paving mixture. 
 46

5.3 Fresh concrete properties

5.3.1 Workability 

According to the ODOT Construction and Material Specifications Manual (2005), 

from Table 499.03-1 pg 264 the nominal slump for the Class C concrete paving mixture 

is 1 to 3 inches (25 to 75 mm). Values of slump and admixture added are shown in table 

VIII below. As Table VIII illustrates, the slumps for all the mixtures except the second 

100% mixture, met this specification. 

TABLE VIII: Measured Slump and Volume of Admixture 

Mixture 

Measured 

slump 

(in) 

Measured 

slump 

(mm) 

Volume of water 

reducing 

admixture (mL) 

Freeze-Thaw 0% 1.75 44.5 0 

Freeze-Thaw 25% 2.25 57.2 0 

Freeze-Thaw 50% 1.25 31.8 0 

Freeze-Thaw 75% 2.5 63.5 0 

Freeze-Thaw 100% 1.75 44.5 0 

Freeze-Thaw 100% Mk2 0.25 6.35 192 

Flexural 0% 2.25 57.2 0 

Flexural 25% 2.0 50.8 0 

Flexural 50% 1 1/16 27.0 40 

Flexural 75% 1 3/8 34.9 170 

5.3.2 Air Content 

Due to the cold climate experienced in Northeastern Ohio, ODOT specifications 

for Class C option 1 paving concrete mixture specifies an air content of 6 +/- 2%. The 

regular control mixture and the 25% replacement mixture each used 18 mL (0.6oz) of air 

entrainment. The 75% mixture used 12 mL (0.4oz) of air entrainment, whereas the 50% 

mix only used 6 mL (0.2oz). For observing the effects of putting air entrainment in 
 47

concrete some samples of 100% steel slag aggregates were prepared in which no air 

entraining admixtures were added. This 100% steel slag aggregates concrete mixture had 

a high amount of entrapped air and less entrained air. Table IX shows the air content for 

all the mixtures 

TABLE IX: Measured Air Content and Volume of Admixture 

Mixture 

Air 

Content 

(%) 

Volume of air entraining 

admixture (mL) 

Freeze-Thaw 0% 5.3 18 

Freeze-Thaw 25% 5.9 18 

Freeze-Thaw 50% 5.5 6 

Freeze-Thaw 75% 7.4 12 

Freeze-Thaw 100% 5.8 0 

Freeze-Thaw 100% Mk2 6.5 15 

Flexural 0% 5.9 18 

Flexural 25% 4.6 20 

Flexural 50% 5.1 25 

Flexural 75% 4.5 20 

Air content

0

1

2

3

4

5

6

7

8

0%

25%

50%

75%

100%

100mk2%

volume of aggregate replaced by slag 

in %

Air content in %

Freeze-Thaw

Flexure beam

FIGURE 10: Graph showing Air content v/s volume of aggregates 

replaced by steel slag 
 48

5.3.3 Unit Weight 

Unit weight or density of the fresh concrete can be determined by weighing a 

known volume of concrete. The sample is generally weighed immediately before the air 

content is determined. The presence of entrained air affects the unit weight, since air 

contributes volume, but not weight. The unit weight also gives an approximate indication 

of air content for concrete made with different materials. As can be seen in Figure 11, the 

measured unit weight was slightly higher in every instance than the desired design unit 

weight. Unit weight normally indicates the consistency in all phases of concreting 

operations. Both the designed unit weight and measured unit weight are reasonably close. 

Unit weight is a function of initial ingredients of concrete, mix proportions, initial and 

final water content, air content, volume changes, and degree of consolidation. Therefore 

with the change in the mixture proportions, there is a slight variation in the designed unit 

weight and measured unit weight. The unit weight test is the best tool to quickly find the 

uniformity of sample and possible significant changes in the mixture.
 49

FIGURE 11: Graph showing Unit weight of aggregates replaced by steel slag 

TABLE X: Table shows designed unit weight and measured unit weight for 

different mixtures 

Designed unit 

weight 

Measured Unit 

Replacement by steel weight slag Lbs/ft3 Kg/m3 Lbs/ft3 Kg/m3 

0% 139 2243. 145 2352 

25% 143 2324 151 2443 

50% 148 2405 154 2489 

75% 153 2486 155 2508 

100 % b 158 2567 168 2717 

100& 158 2567 168 2717 
 50

5.4 Hardened Concrete Properties 

5.4.1 Modulus of Rupture 

Beam specimens were prepared having a cross section of 6 inches by 6 inches and 

of 20 inches (152 x 152 x 508 mm) to determine the modulus of rupture. The modulus of 

rupture was also found at the end of 7 days by following ASTM C 78 using a third point 

loading on a hydraulic testing machine. The Ohio Department of Transportation (ODOT) 

specifies that if high early strength of concrete is required, the 3 day modulus of rupture 

must be above 600 psi (4.14 MPa) (ODOT Spec 2005, pg 264) . Figure 12 shows the 

results for the modulus of rupture for Class C concrete mixture. All specimens have 

modulus of rupture for 7 days above 600 psi (4.14MPa). 

TABLE XI: Flexural Strength of Concrete 

(Using Simple Beam with Third-Point Loading) 

 

Specimen

Identification

Maximum

load

applied

Modulus of

Rupture

(MOR)

(lbf) (psi) (MPa)

Control A 7389 684 4.72

Control B 8103 750 5.17

25a 6697 620 4.28

25b 7195 666 4.59

50a 6863 635 4.38

50b 7019 650 4.48

75a 6829 632 4.36

75b 7521 696 4.80
 51

FIGURE 12: Graph showing the Modulus of rupture for concrete beams 

5.4.2 Compressive Strength for concrete specimens and Flexure beams 

Cylinders were molded with a diameter of 4 inches (102mm) and a length of 8 

inches (203 mm) to determine the compressive strength of the concrete mixtures. The 

cylinders were tested at 7 and 28 days following the ASTM C 39. Ohio Department of 

Transportation (ODOT) specifies a minimum 28 day compressive strength of 4,000 psi 

(28 MPa) for Class C concrete mixtures. Table XII provides the compressive strength of 

concrete for 7 and 28 days. All the concrete mixtures exceeded the compressive strength 

requirements. Figure 13 shows that at the end of 28 days all the specimens have a 

compressive strength more than 4,000 psi (28 MPa) and thus met the ODOT 28 dayís 

requirement. The flexural beam specimens also demonstrated a compressive strength just 

above 4,000 Psi at the end of 28 days and those specimens also met the ODOT 

requirements. 
 52

Table XII: 7 & 28 days compressive strength of concrete specimens 

 

FIGURE 13: Graph showing the 7& 28 days Compressive Strength 

(Average of two samples A & B) 

Percentage 7 Days Compressive Strength 28 Days Compressive Strength

replaced Sample A Sample B Sample AB Sample BB

(Psi) (MPa) (Psi) (MPa) (Psi) (MPa) (Psi) (MPa) 

0 % 5090 35 5147 35 6212 43 5072 35. 

25% 4617 32 4623 32 4186 29 5141 35 

50% 4154 29 4277 29 5051 35 5140 35 

75% 3379 23 3358 23 4241 29 4288 30 

100 A% 3577 25 2869 20 4158 29 4474 31 

100 B% 4411 30 5416 37 6165 42 6069 42 

 
 53

TABLE XIII: 7 & 28 Days Compressive Strength for Flexure Beam Specimens 

FIGURE 14: Graph showing the 7& 28 days Compressive Strength of concrete for 

flexure beams (Average of two samples A & B) 

7 Days Compressive strength for 

Flex beams

28 Days Compressive strength for 

Flex beams Percentage 

replaced Sample C Sample D Sample C Sample D 

(Psi) (MPa) (Psi) (MPa) (Psi) (MPa) (Psi) (MPa) 

0 % 5468 38 5483 38 6471 45 6661 46

25% 5088 35 5177 36 4683 32 5317 37

50% 4465 31 4419 30 4432 31 4722 33

75% 3886 27 4416 30 5304 37 5265 36

 
 54

5.4.3 Splitting Tensile Strength 

 The splitting tensile strength of the concrete specimens was determined at 7 and 

28 days following ASTM C 496. As previously mentioned the specimens were molded at 

the same time as the compressive strength specimens. Cylinders were molded with a 

diameter of 4 inches (102 mm) and a length of 8 inches (203 mm). Figure 15 displays the 

average splitting tensile strength of the samples at 7 and 28 days. ODOT does not 

currently have any specification for splitting tensile strength. Table XIV shows the 7 and 

28 days splitting tensile strength on concrete specimens. The splitting tensile strength of 

concrete specimens at the end of 28 days was approximately about 500 psi. The splitting 

tensile test for the beams for flexural test also showed that after 28 days the splitting 

tensile strength was approximately 500 psi except the specimen which has 75 % of steel 

slag showed less splitting tensile strength.

TABLE XIV: 7 & 28 days Splitting Tensile Strength on Concrete Specimens 

* indicates that the specimens were not tested. 

Percentage 7 Days Split Tensile Strength 28 Days Split Tensile Strength

replaced Sample A Sample B Sample AB Sample BB

(Psi) (MPa) (Psi) (MPa) (Psi) (MPa) (Psi) (MPa) 

0 % 473 3.26 464 3.20 577 3.98 663 4.57

25% 541 3.73 531 3.66 485 3.35 565 3.90

50% 518 3.57 497 3.43 631 4.35 496 3.42

75% 373 2.57 * * 587 4.05 425 2.93

100 A% 420 2.89 375 2.59 457 3.15 563 3.88

100 B% 593 4.09 470 3.24 589 4.06 580 4.00

 
 55

FIGURE 15: Graph showing the 7& 28 days Splitting Tensile Strength of concrete 

(Average of two samples A & B) 
 56

TABLE XV: 7 & 28 days Splitting Tensile Strength on flexure Specimens 

FIGURE 16: Graph showing the 7& 28 days Splitting Tensile Strength of concrete 

for Flexure beams (Average of two samples A & B) 

7 Days Split Tensile Strength for 

Flexure beams

28 Days Split Tensile Strength for 

Percentage Flexure beams

replaced Sample C Sample D Sample C Sample D 

(Psi) (MPa) (Psi) (MPa) (Psi) (MPa) (Psi) (MPa) 

0 % 404 2.78 558 3.85 597 4.12 577 3.98

25% 471 3.24 434 2.99 499 3.44 532 3.67

50% 481 3.32 478 3.30 504 3.48 539 3.72

75% 434 2.99 392 2.70 439 3.02 501 3.46

 
 57

5.4.4 Freeze-Thaw Durability 

The freeze-thaw durability of various concrete mixtures with replacement of steel 

slag in different increments was tested following ASTM C 666. Table XVIII shows the 

results for the relative dynamic modulus Figures 17, 19, 21, 23 and 25 shows plots of 

relative dynamic modulus with respect to the number of Freeze-thaw cycles of different 

concrete specimens with steel slag aggregates. Figures: 18, 20, 22, 24 and 26 shows plots 

of percent mass loss with respect to the number of freeze-thaw cycles for different 

concrete specimens with steel slag aggregates. The result shows that the percentage mass 

loss is small and trends are hard to define. Table XVI shows the initial weight of the 

specimens at various Freeze-thaw cycles and Table XVII provides data for percent mass 

loss. 

Visual examination showed that if a particular sample maintains a dynamic 

modulus of elasticity above 60% through 300 freeze thaw cycles, the relative dynamic 

modulus of elasticity will be the same ( i.e. the variables N and M in the equation V will 

be equal to 300). During this research, all the samples performed in the same manner so 

the durability factor of each specimen is the same as the dynamic modulus of elasticity. 

It can be stated from the results that the relative dynamic modulus drops as the 

number of freeze thaw cycles increases. The control specimen, 25a and 75 % steel slag 

specimen did not showed any sign of disintegration. The samples which had no air failed 

in the initial cycles, as their relative dynamic modulus was less than 60 %, and were 

removed from the freeze-thaw testing machine. 
 58

There might be a possibility of an experimental error while taking readings of the 

frequency from the testing machine during the 204 cycles for 25% replacement (as shown 

in figure 28), because the trend of the dynamic modulus is constant thereafter. 

Table XVI: Weight of the specimens at various Freeze-thaw cycles. 

Weight of the Specimens at various Freeze-thaw cycles in lbs

Cycles 0 25 44 77 97 118 149 174 204 244 262 274 300

Control A 16.6 16.8 16.8 16.8 16.8 16.8 16.9 17 16.8 17 16.8 16.6 16.8

Control B 16.4 16.2 16.5 16.4 16.5 16.5 16.9 16.6 16.6 16.6 16.4 16.5 16.5

NA-A 17.0 17.2 17.3 17.2 FAILED −− −− −− −− −− −− −− −−

NA-B 17.0 −− −− −− 17.0 17.0 17.1 17.1 17.2 17.2 FAILED

25a 17.4 17.5 17.6 17.6 17.4 17.6 17.7 17.6 17.6 17.6 17.6 17.4 17.4

25b 17.4 17.4 17.5 17.5 17.6 17.5 17.6 17.5 17.6 17.6 17.6 17.4 17.2

25c 17.4 17.5 17.5 17.6 17.5 17.6 17.6 17.6 17.6 17.6 17.6 17.4 17.4

50a 18.0 18.0 18.0 17.9 18.0 18.0 18.0 17.9 17.9 17.8 17.6 17.5 17.4

50b 18.1 18.1 18.2 18.3 18.2 18.2 18.1 18.2 18.1 18 18 17.8 17.7

50c 18.2 18.2 18.3 18.2 18.2 18.4 18.3 18.4 18.1 18.2 18 18 17.8

75a 17.6 17.9 18.0 17.7 17.9 17.9 17.9 17.9 17.8 17.8 17.9 17.6 17.5

75b 17.6 17.8 17.8 17.8 17.9 17.9 17.8 17.9 17.8 18 17.9 17.7 17.6

75c 17.6 17.8 17.9 17.7 17.8 17.8 17.8 17.8 17.6 17.9 17.8 17.6 17.5

100a 19.4 19.5 19.6

100b 19.3 19.4 19.5

100c 19.5 19.5 19.7

FAILED

Specimen Failed 

FAILED

FAILED 

100-B-a 19.5 19.6 19.6 19.4 19.6 19.4 19.2 19.1 18.8 19.2 18.8 18.6 18.5

100-B-c 19.5 19.6 19.6 19.4 19.5 19.3 19.1 19 19 18.8 18.8 18.6 18.6

100-B-d 19.7 19.7 19.8 19.8 19.6 19.4 19.3 19.1 19 18.8 19 18.8 18.6
 59

TABLE XVII: Percent Mass Loss 

Percent Mass Loss (%) 

Cycles 25 44 77 97 118 149 174 204 244 262 274 300 

Control A -0.01 0.00 -0.01 -0.01 -0.01 -0.02 -0.02 -0.01 -0.02 -0.01 0.00 -0.01 

Control B 0.01 -0.01 0.00 -0.01 -0.01 -0.03 -0.01 -0.01 -0.01 0.00 -0.01 -0.01 

avg 0.00 0.00 -0.01 -0.01 -0.01 -0.02 -0.02 -0.01 -0.02 -0.01 0.00 -0.01 

NA-A -0.01 -0.02 -0.01 - - - - - - - - - 

NA-B 0.00 0.00 - - 0.00 -0.01 -0.01 -0.01 -0.01 - 

25a -0.01 -0.01 -0.01 0.00 -0.01 -0.02 -0.01 -0.01 -0.01 -0.01 0.00 0.00 

25b 0.00 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 0.00 0.01 

25c -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 0.00 0.00 

avg 0.00 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 -0.01 0.00 0.00 

50a 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.01 0.01 0.02 0.03 0.03 

50b 0.00 -0.01 -0.01 -0.01 -0.01 0.00 -0.01 0.00 0.01 0.01 0.02 0.02 

50c 0.00 -0.01 0.00 0.00 -0.01 -0.01 -0.01 0.01 0.00 0.01 0.01 0.02 

avg 0.00 0.00 0.00 0.00 -0.01 0.00 0.00 0.00 0.01 0.01 0.02 0.03 

75a -0.02 -0.02 -0.01 -0.02 -0.02 -0.02 -0.02 -0.01 -0.01 -0.02 0.00 0.01 

75b -0.01 -0.01 -0.01 -0.02 -0.02 -0.01 -0.02 -0.01 -0.02 -0.02 -0.01 0.00 

75c -0.01 -0.02 -0.01 -0.01 -0.01 -0.01 -0.01 0.00 -0.02 -0.01 0.00 0.01 

avg -0.01 -0.02 -0.01 -0.02 -0.01 -0.01 -0.01 -0.01 -0.02 -0.01 0.00 0.00 

100a -0.01 -0.01 

100b -0.01 -0.01 

100c 0.00 -0.01 

Specimen Failed 

100-B-a -0.01 -0.01 0.01 -0.01 0.01 0.02 0.02 0.04 0.02 0.04 0.05 0.05 

100-B-c -0.01 -0.01 0.01 0.00 0.01 0.02 0.03 0.03 0.04 0.04 0.05 0.05 

100-B-d 0.00 -0.01 -0.01 0.01 0.02 0.02 0.03 0.04 0.05 0.04 0.05 0.06 

avg 0.00 -0.01 0.00 0.00 0.01 0.02 0.03 0.03 0.03 0.04 0.05 0.05 
 60

TABLE XVIII: Relative Dynamic Modulus 

Table XVIII shows the relative dynamic modulus of elasticity of the various concrete 

specimens incorporated with steel slag aggregates. The lowest relative dynamics modulus of 

elasticity was 64. ASTM C 666 specifies that the test ends at 300 cycles or when the relative 

dynamic modulus of elasticity falls below 60 %. It shows that the concrete specimens performed 

well during the Freeze-thaw environments and no major change was observed in concrete 

specimens with 75% steel slag aggregates. Figures 27 to 32 show the plot of Durability 

Relative Dynamic Modulus (Pc)

Cycles 25 44 77 97 118 149 174 204 244 262 274 300

Control A 100 100 100 100. 100 100 100 100 100 100 100 100

Control B 94.0 100 100 100 100 100 100 100 100 100 100 100

Average 97.0 100 100 100 100 100 100 100 100 100 100 100 

NA-A 88.6 72.8 34.6 - 

NA-B - 94.2 88.6 88.6 72.8 54.1 - 

25a 100 100 100 100. 100 100 100 100 100 100 100 100

25b 94.0 94.0 94.0 94.0 94.0 94.0 94.0 72.0 94.0 94.0 94.0 94.0

25c 94.0 94.0 94.0 94.0 94.0 94.0 94.0 94.0 94.0 94.0 94.0 94.0

Average 96.0 96.0 96.0 96.0 96.0 96.0 96.0 88.7 96.0 96.0 96.0 96.0 

50a 100 100 100 93.4 93.4 93.4 93.4 87.1 81.0 75.1 75.1 64.0

50b 100 100 100 100. 100 100 100 100 93.4 93.4 93.4 87.1

50c 93.7 93.7 93.7 93.7 93.7 93.7 93.7 93.7 87.5 87.5 81.6 75.9

Average 97.9 97.9 97.9 95.7 95.7 95.7 95.7 93.6 87.3 85.3 83.4 75.7 

75a 100 100 100 100. 100 100 100 100 100 100 100 100.0

75b 100 100 100 100. 100 100 100 100 100 100 100 100.0

75c 100 100 100 100. 100 100 100 100 100 100 100 100.0

Average 100 100 100 100 100 100 100 100 100 100 100 100 

100a 63.5 - 

100b 79.7 - 

100c 80.4 34.4

Specimen Failed 

100-B-a 93.4 93.4 93.4 93.4 93.4 87.1 87.1 87.1 86.4 86.0 85.0 84.7

100-B-c 100.0 100.0 93.2 93.2 86.7 86.7 86.2 86.0 85.5 85.5 84.0 84.0

100-B-d 100.0 100.0 93.4 93.4 93.4 93.4 93.4 93.2 93.2 93.0 93.0 88.6

Average 97.8 97.8 93.3 93.3 91.1 89.0 88.9 88.8 88.4 88.2 87.3 85.8
 61

factor v/s freeze thaw cycles for various percentage increments of different concrete 

mixtures with steel slag aggregates. 

Figure 17: Relative Dynamic Modulus v/s Number of Freeze-thaw cycles for 

average 0% steel slag aggregates concrete mixture 

Relative Dynamic Modulus v/s Number of Freeze-thaw 

cycles

80

85

90

95

100

105

110

0 50 100 150 200 250 300

Number of cycles

Relative Dynamic

Modulus

Figure 18: Percentage Mass Loss v/s Number of Freeze-thaw cycles 

 Average 0% steel slag aggregates concrete mixture 

Percentage Mass loss v/s Number of Freeze-thaw cycles

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0 50 100 150 200 250 300

Number of cycles

Percent Mass Loss %
 62

Figure 19: Relative Dynamic Modulus v/s Number of Freeze-thaw cycles for 

average 25% steel slag aggregates concrete mixture 

Relative Dynamic Modulus v/s Number of Freeze-thaw 

cycles

80

85

90

95

100

105

110

0 50 100 150 200 250 300

Number of cycles

Relative Dynamic

Modulus

Figure 20: Percentage Mass Loss v/s Number of Freeze-thaw cycles 

 Average 25% steel slag aggregates concrete mixture 

Percentage Mass loss v/s Number of Freeze-thaw cycles

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0 50 100 150 200 250 300

Number of cycles

Percent Mass Loss %
 63

Figure 21: Relative Dynamic Modulus v/s Number of Freeze-thaw cycles for 

average 50% steel slag aggregates concrete mixture 

Relative Dynamic Modulus v/s Number of Freeze-thaw 

cycles

74

79

84

89

94

99

104

109

0 50 100 150 200 250 300

Number of cycles

Relative Dynamic

Modulus

Figure 22: Percentage Mass Loss v/s Number of Freeze-thaw cycles 

 Average 50% steel slag aggregates concrete mixture 

Percentage Mass loss v/s Number of Freeze-thaw cycles

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0 50 100 150 200 250 300

Number of cycles

Percent Mass Loss %
 64

Figure 23: Relative Dynamic Modulus v/s Number of Freeze-thaw cycles for 

average 75% steel slag aggregates concrete mixture 

Relative Dynamic Modulus v/s Number of Freeze-thaw 

cycles

75

80

85

90

95

100

105

110

0 50 100 150 200 250 300

Number of cycles

Relative Dynamic

Modulus

Figure 24: Percentage Mass Loss v/s Number of Freeze-thaw cycles 

 Average 75% steel slag aggregates concrete mixture 

Percentage Mass loss v/s Number of Freeze-thaw cycles

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0.03

0 50 100 150 200 250 300

Number of cycles

Percent Mass Loss %
 65

Figure 25: Relative Dynamic Modulus v/s Number of Freeze-thaw cycles for 

average 100% steel slag aggregates concrete mixture 

Relative Dynamic Modulus v/s Number of Freeze-thaw 

cycles

80

85

90

95

100

105

110

0 50 100 150 200 250 300

Number of cycles

Relative Dynamic

Modulus

Figure 26: Percentage Mass Loss v/s Number of Freeze-thaw cycles 

 Average 100% steel slag aggregates concrete mixture 

Percentage Mass loss v/s Number of Freeze-thaw cycles

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 50 100 150 200 250 300

Number of cycles

Percent Mass Loss %
 66

Figure: 27 Durability Factor v/s Freeze Thaw cycle for 0% replacement 

Durability Factor vs. Freeze-Thaw Cycle for 0% Replacement

0

10

20

30

40

50

60

70

80

90

100

25 44 77 97 118 149 174 204 244 262 274 300

Freeze-Thaw Cycle #

Durability Factor

Specimen A Specimen B Average

Figure: 28 Durability Factor v/s Freeze Thaw cycle for 25% replacement 

Durability Factor vs. Freeze-Thaw Cycle for 25% Replacement

0

10

20

30

40

50

60

70

80

90

100

110

25 44 77 97 118 149 174 204 244 262 274 300

Freeze-Thaw Cycle #

Durability Factor

Specimen A Specimen B Specimen C Average
 67

Figure: 29 Durability Factor v/s Freeze Thaw cycle for 50% replacement 

Durability Factor vs. Freeze-Thaw Cycle for 50% Replacement

0

10

20

30

40

50

60

70

80

90

100

110

25 44 77 97 118 149 174 204 244 262 274 300

Freeze-Thaw Cycle #

Durability Factor

Specimen A Specimen B Specimen C Average

Figure: 30 Durability Factor v/s Freeze Thaw cycle for 75% replacement 

Durability Factor vs. Freeze-Thaw Cycle for 75% Replacement

0

10

20

30

40

50

60

70

80

90

100

110

25 44 77 97 118 149 174 204 244 262 274 300

Freeze-Thaw Cycle #

Durability Factor

Specimen A Specimen B Specimen C Average
 68

Figure: 31Durability Factor v/s Freeze Thaw cycle for 100% mk1 replacement 

Durability Factor vs. Freeze-Thaw Cycle for 100% mk1 Replacement

0

10

20

30

40

50

60

70

80

90

100

110

25 44 77 97 118

Freeze-Thaw Cycle #

Durability Factor

Specimen A Specimen B Specimen C Average

Figure: 32 Durability Factor v/s Freeze Thaw cycle for 100% mk2 replacement 

Durability Factor vs. Freeze-Thaw Cycle for 100% mk2 Replacement

0

10

20

30

40

50

60

70

80

90

100

25 55 95 113 125 151 175 200 225 250 275 300

Freeze-Thaw Cycle #

Durability Factor

Specimen A Specimen B Specimen C Average
 69

5.4.5 Change in length of concrete specimens 

Table XVIII shows the change of length of the concrete specimens and is 

compared to the initial length at the start of the test procedure. All the specimens were 

kept at the normal room temperature in the water basin. The result shows that the change 

in length of concrete specimens was negligible at the end of 120 days. The control 

specimens showed a sign of expansion but there was slight contraction in length in the 

specimens with 100% steel slag. 

Table XVIII: Expansion length of concrete specimens 

Specimen 

Initial 

CRD 

CRD 

7 

Days

Length 

Change

CRD 

28 

Days

Length 

Change

CRD 

90 

Days

Length 

Change 

CRD 

120 

Days

Length mixture Change (%) 

ID# (in.) (in.) (%) (in.) (%) (in.) (%) (in.) (%) 

Control 

A ctrl-A 0.0459 0.0462 0.003 0.0459 0.000 0.0430 -0.029 0.0493 0.034 

Control 

B ctrl-B 0.0558 0.0561 0.003 0.0556 -0.002 0.0525 -0.033 0.0574 0.016 

25% 25-A 0.0000 0.0000 0.0000 0.0000 0.000 0.0900 0.900 0.000 0.000 

25% 25-B 0.0208 0.0207 -0.001 0.0186 -0.022 0.0196 -0.013 0.0232 0.024 

50% 50-A 0.0045 0.0055 0.01 0.0044 -0.001 0.0041 -0.004 0.0079 0.034 

50% 50-B 0.0004 0.0001 -0.003 0.0000 -0.004 0.0009 0.005 0.0027 0.023 

75% 75-A 0.0295 0.0285 -0.01 0.0262 -0.033 0.0266 -0.029 0.0315 0.02 

75% 75-B 0.0000 0.0000 0.0000 0.0000 0.000 0.0990 0.99 0.000 0.000 

100% 100-A 0.0496 0.0320 -0.176 0.0279 -0.217 0.0000 -0.496 0.0355 -0.141 

100% 100-B 0.0298 0.0112 -0.186 0.0095 -0.203 0.0000 -0.298 0.0107 -0.191 
 70

CHAPTER VI 

DISCUSSION 

6.1 Overview

 This chapter discusses the results of the experiments conducted. The strength of 

concrete with steel slag aggregates is analyzed, the resistance of concrete under freezing 

and thawing environments is evaluated and change in length of concrete specimens 

discussed. 

6.2 Overall experimental Observations 

 No major difficulty in handling the concrete which incorporated steel slag 

aggregates was encountered except at 75% or higher replacement percentages. There 

were no major changes in the fresh or hardened properties of concrete with steel slag 

aggregates. The size and grading of steel slag aggregates were similar to natural 

limestone aggregates. Using different ranges of sizes of aggregates enable the smaller 

particles to pack between larger particles, and thereby reducing the void spaces and 

lowering the cement paste requirements. The shapes of the steel slag aggregates were 
 71

more or less angular in nature, which made the concrete mixture workable. The water 

absorption capacity of steel slag aggregates was more than that of limestone, which 

sometimes made the concrete mixture less workable and so water reducing admixtures 

were added accordingly. One of the important aspects in the concrete mixture is the 

amount of air voids in the matrix. Air voids helps the water to seep into the pores, which 

in turn reduce high internal stresses and thereby reduce micro cracking in the structure. 

Proper amount of air entraining admixtures are added to introduce air bubbles in the 

concrete mixture. The reason for failing of concrete samples with 100% steel slag 

aggregates might be due to presence of excessive entrapped air and less entrained air in 

the mixture during the mixing of concrete. Proper amount of air entraining admixtures 

were added accordingly depending upon required air content. During the research, it was 

found that, as the percentage of steel slag aggregates in concrete increased, the mixture 

became stiffer and more water or admixtures was required to make the concrete more 

workable. 

 

6.3 Compressive strength of concrete 

Most properties of concrete are directly related to its compressive strength. The 

compression test on the concrete specimens was carried out according to ASTM C39. 

The samples were properly molded and cured. The specimens were loaded at a control 

rate in the compression machine. The results can be seen from the Table XII. The control 

mixture had both 7 and 28 day strength of more than 5,000 psi (35 MPa). The specimen 

with 50% steel slag aggregates in concrete had 28 days compressive strength of 5,000 psi 

while specimen with 100% steel slag aggregate had about 6000 psi (40 MPa). The 100% 
 72

steel slag aggregate sample gave good strength than the rest; the reason might be the 

water-cement ratio. The mixture was very harsh and water reducing admixtures were 

added to get minimum slump. The higher strength might be due to the cement paste and 

the bond strength at the paste-aggregates boundary. Variability of test method might be 

the reason. The rate of loading and progress of crack around the aggregate particles might 

be the reason of greater strength. The rest of the specimens had 28 day strength more than 

4,000 psi (28 MPa) which exceeded the minimum strength requirements from ODOT 

specifications. Some additional cylinder samples were prepared from the mixture for 

flexural beams and compression tests were carried out. The results for 7 and 28 days 

compressive strength for flexure beams are shown in fig 14. The specimen with 75% 

steel slag aggregates showed strength of more than 5,000 psi. This shows that concrete 

with steel slag aggregates achieves similar strength compared to conventional concrete. 

 

6.4 Splitting Tensile strength 

 The splitting tensile test is an indirect way of estimating the tensile strength of 

cylindrical concrete specimens. Since the concrete is much weaker in tension than in 

compression, the failure would be at a much lower load than in compression. The 

cylinders were tested according to ASTM C 496. The results of 7 & 28 days splitting 

tensile strength are shown in Fig 15. The control mixture showed splitting tensile strength 

after 28 days around 600 psi while all other specimens had around 500 psi (3.5 MPa). For 

the ordinary structural concrete the tensile strength is around 400 psi (3 MPa) 

(Mindness 2002). 
 73

6.5 Flexural Strength of concrete 

 The flexural strength of concrete with steel slag aggregates was tested according 

to ASTM C 78. The flexural beams were prepared, cured in the standard manner and 

tested using the three point loading method. The theoretical maximum modulus of 

rupture R is then calculated from simple beam bending formula for third-point loading 

shown in Equation I. The testing was done after 7 days and results are plotted in Fig 

12. The trend was similar to the control mixture. All the mixtures gave a modulus of 

rupture more than 600 psi (4.14 MPa) in 7 days. This test is very useful since concrete 

pavements tend to be loaded in bending rather than in axial tension. The flexure test gives 

better representation of concrete property. It can be noted that the flexure test gave higher 

values than the tension test, the reason may be that in tension test total volume of 

specimen is stressed while in flexure test only a relatively small volume of material near 

the bottom of the beam is subjected to high stress. The flexural strength for a structural 

concrete is around 800 psi (6MPa). This shows that the concrete with steel slag 

aggregates performs well (Mindness 2002). 

6.6 Freeze-Thaw Durability 

 The freeze-thaw durability test is used to predict the durability of concrete in 

freeze-thaw environments. Deterioration of the concrete and D cracking are primarily 

caused by the expansion of water in the paste of concrete mixture or in aggregates during 

its conversion from liquid phase to solid phase in cold environments. Concrete beam 

specimens were prepared and tested for freeze thaw according to ASTM C 666 in an 
 74

automated freezing and thawing machine. The change in the resonant frequency 

according to ASTM C 215 and change of mass of each specimen was monitored at 

regular intervals. A small hammer is used to create vibrations inside the specimens and 

the response is recorded by accelerometer attached to the specimen. A resonance tester 

was used to measure the frequency. Testing was done at regular intervals, usually 15 to 

30 cycles. The dynamic modulus of elasticity was determined by measuring the 

fundamental transverse frequency of the sample at each test interval. The equation to 

determine relative dynamic modulus of elasticity is show in Equation IV. 

 According to ASTM C 666, the freeze-thaw resistance test is considered 

complete when either the specimen is subjected to 300 freeze-thaw cycles or when the 

dynamic modulus of elasticity drops below 60 %. The results showed that the control 

mixtures did not undergo any change in the durability factor and the relative dynamic 

modulus for the control mixture was 100 percent throughout 300 cycles. Similarly the 

concrete mixture which had 75% of volume replaced by steel slag aggregates also did not 

undergo any change in durability factor. The worst relative dynamic modulus (Pc) was 

found to be approximately 64 percent. The concrete specimen which had 100% (A) steel 

slag aggregates in it failed during the initial Freeze-thaw cycles as the relative dynamic 

modulus was less than 60%. The reason for the failure of that specimen was that no air 

entraining admixture was added into the concrete during its preparation and a high 

amount of entrapped air was found during mixing. The 100% (B) specimen with proper 

air entrainment showed a relative dynamic modulus after 300 cycles of 85 percent and 

was still in a good shape with no major deterioration. 
 75

All concrete specimens suffered some mass change (loss). During the freeze-thaw 

environment there is an increase in series of micro cracks in the sample which will reduce 

the fundamental transverse frequency and which will ultimately change the mass of the 

specimens. Scaling deterioration of the sample is expected and will reduce the mass. The 

results showed that this mass loss was very small. Loss in mass leads to lower frequency 

and lower durability factor. 

Figure: 33 Photograph (A) showing the behavior of 100% A steel slag specimen 

with no air entraining admixtures under the freeze-thaw machine and (B) shows series of 

micro cracks and deterioration of the concrete after 44 cycles. 

Figure: 33(A) 100 % steel slag aggregate specimen A (Top) 

Figure: 33(B) 100 % steel slag aggregate specimen A (Bottom) 
 76

6.7 Measurement of linear expansion or contraction of concrete specimens. 

This test was conducted in order to observe the change in length of concrete 

specimens with steel slag aggregates. There was a perception that steel slag aggregates 

have expansive properties under moist conditions. The specimens were prepared and 

initial length measurement readings were taken before placing in the water bath. All the 

specimens were maintained at same temperature range and then compared. The change in 

length of the concrete specimens can be calculated from Equation III. The change in 

length of various concrete specimens with steel slag aggregates were taken at 7, 28, 90 

and 120 days as shown in Table XVIII. The control specimens showed an increase of 

0.034% at end of 120 days. The concrete specimen with 25%A and 75%B showed no 

change in length at 120 days. All specimens observed slight expansion under saturated 

conditions except the specimen with 100% steel slag aggregates showed an average 

shrinkage of 0.166%. 
 77

CHAPTER VII 

CONCLUSIONS AND RECOMMENDATIONS 

7.1 Summary 

The main aim of this research was to study the behavior of concrete and changes 

in the properties of concrete with steel slag aggregates by replacing the use of natural 

aggregates. Steel slag is a byproduct and using it as aggregates in concrete will might 

prove an economical and environmentally friendly solution. The demand for aggregates 

is increasing rapidly and so as the demand of concrete. Thus, it is becoming more 

important to find suitable alternatives for aggregates in the future. 

A through literature review was conducted to study and investigate the properties 

of steel slag aggregates. The results showed that it has properties similar to natural 

aggregates and it would not cause any harm if incorporated into concrete. A comparison 

was made between concrete having natural coarse aggregates and concrete with various 

percentages of steel slag aggregates replaced by volume. The results of this research were 

encouraging, since they show that using steel slag as coarse aggregates in concrete has no 

negative effects on the short term properties of hardened concrete. 
 78

The results of the research program can be summarized as follows: 

1. Compressive strength, flexural strength and splitting tensile strength for steel slag 

aggregates concrete were similar to conventional concrete. The strength may be 

affected with time and so long term effects on hardened properties of concrete 

require further investigation. 

2. Durability of steel slag aggregates concrete under freeze-thaw environment was 

the main goal in this research, as there was a belief that the steel slag aggregates 

have expansive characteristics and would cause cracking in concrete. The results 

proved that if up to 50 to 75 % of steel slag aggregates are incorporated in the 

traditional concrete, there would not be much change in the durability of concrete. 

3. The slight improvement in strength may be due to shape, size and surface texture 

of steel slag aggregates, which provide better adhesion between the particles and 

cement matrix. 

4. Proper care should be taken during the aging of steel slag and during the 

stockpiling of steel slag. 

7.2 Some Limitations of testing methods 

It should be kept in mind that most of the research was conducted in the 

laboratory environment. There are chances of experimental error which influences the 

results of the tests. The freeze-thaw test is designed in such a way that concrete 

specimens are subjected to repeated cycles of freezing and thawing in a very short period 

of time. There is a rapid rate of cooling in the freeze thaw machine. The prescribed 

cooling rate during the test method is about 6 to 15°C per hour; this is much higher than 
 79

what concrete would be subjected in the field. Chilling the specimens within a specified 

period of time, so as to allow many samples to be tested to 300 cycles, generally is not 

what happen actually in the field. Therefore concrete that passes this severe laboratory 

test should be durable in the field. 

The tests for hardened concrete are susceptible to variation according to the 

specimen sizes, difference in geometry, rate of loading, temperature at time of testing and 

other factors. It should be kept in mind that small concrete specimens do no particularly 

represent the strength of concrete in the structure; they only give comparative data. 

7.3 Suggestions for future research 

1. A much more extensive field study on a concrete structure made with steel slag 

aggregates used in the mixture should be conducted and changes in durability and 

mechanical properties should be investigated and correlated to laboratory results. 

2. Further investigation on resistance of concrete with steel slag aggregates to attack 

by sulfates; alkali silica reactions, carbonation, sea water attack, harmful 

chemicals and resistance to high temperatures are needed. The behavior of steel 

slag aggregate concrete under corrosive environments and its fire resistance 

capacity should also be investigated. The results of such studies would directly 

benefit the construction industry and broader use of steel slag in concrete would 

improve overall properties and cost effective solution. 

3. The long term behavior of concrete with steel slag aggregates should be studied 

and its compatibility with reinforcing steel should be analyzed in the future. 
 80

4. It is also suggested to do Petrographic examinations of concrete samples with 

steel slag aggregates to get insight of the actual behavior of concrete. The 

relationship between entrained air and entrapped air in concrete should be studied. 

5. A comprehensive chemical analysis of steel slag aggregates should to be carried 

out before using in construction. 

6. Due to presence of several dangerous heavy metals and salts in the steel slag 

aggregates, leaching tests should be carried out to verify its environmental 

compatibility.
 81

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