UTILIZATION OF STEEL SLAG FOR STABILIZATION OF A LATERITIC SOIL

ABSTRACT

A lateritic soil classified as sandy clay or (CL) and A-7-6 (5) according to Unified Soil Classification System (USCS) and AASHTO classification system respectively,was treated with up to 10% pulverized steel slag (an industrial waste product) by dryweight of soil. Elemental and chemical analysis of the steel slag was determined using x-ray fluorescence spectroscopy. Tests were carried out to determine the index properties, compaction characteristics (maximum dry density, MDD and optimum moisture content, OMC), strength characteristics (California bearing ratio, CBR and unconfined compressive strength, UCS) and permeability of the natural and treated soil. Test results show that Atterberg limits (liquid limit, plastic limit and plasticity index)
generally decreased, while specific gravity of soil " steel slag mixtures increased with higher steel slag content; MDD and OMC increased and decreased, respectively, with higher steel slag content. Generally, CBR and UCS increased up to 8% steel slag treatment of the soil. Permeability of soil " steel slag mixtures increased with higher steel slag content. Based on laboratory test results, an 8 % optimal stabilization of the A-7-6 soil with steel slag satisfactorily meets the Federal Republic of Nigerian General Specifications (Roads and Bridges) requirement for subgrade materials.

Table of Contents

CERTIFICATION ii
DEDICATION iii
ACKNOWLEDGEMENTS iv
LIST OF FIGURES viii
LIST OF TABLES ix
LIST OF ABBREVIATIONS AND ACRONYMS x
ABSTRACT xi

CHAPTER ONE
INTRODUCTION 
1.1 Preamble 1
1.2 Statement of the Problem 1
1.3 Justification for the Study 2
1.4 Aim and Objectives 3
1.5 Scope of the Study 3
1.6 Significance of Study 4

CHAPTER TWO
LITERATURE REVIEW 6
2.1 Background 6
2.2 What is Slag? 7
2.2.1 Slag Recycling 10
2.2.2 Utility and Usage of Slag Products 11
2.3 Efforts in Utilizing Slag 13
2.4 Production of Steel Slag 13
2.4.1 BOF Slag from Basic Oxygen Steelmaking 14
2.4.2 EAF Slag 17
2.4.3 Steel Slag Utilization 19
2.5 Properties of Steel Slag 20
2.5.1 Physical and Mechanical Properties 20
2.5.2 Chemical and Mineralogical Properties 23
2.6 Environmental and Health Considerations 27
2.7 Laterite and Lateritic Soils 27
2.8 Stabilization of Lateritic Soils 30

CHAPTER THREE
MATERIALS AND METHODS 33
3.1 Materials and Preparation 33
3.1.1 Steel slag 33
3.1.2 Soil 33
3.2 Methods 34
3.2.1 Chemical composition of steel slag 36
3.2.2 Natural moisture content 36
3.2.3 Sieve analysis 37
3.2.4 Specific gravity 38
3.2.5 Atterberg limits 36
3.2.6 Compaction characteristics 39
3.2.7 Strength characteristics 38
3.2.8 Permeability 39

CHAPTER FOUR
RESULTS AND DISCUSSION 40
4.1 X-ray Fluorescence 41
4.2 Natural Soil 41
4.3 Sieve Analysis 41
4.4 Specific Gravity 42
4.5 Atterberg Limits 43
4.6 Compaction Characteristics of Lateritic Soil Sample 45
4.7 California Bearing Ratio 47
4.8 Unconfined Compressive Strength 49
4.9 Permeability 51
4.10 Optimal Stabilization 52

CHAPTER FIVE
CONCLUSION AND RECOMMENDATION 53
5.1 Conclusion 53
5.2 Recommendation 54
REFERENCES 55
APPENDIX: LABORATORY RESULT SHEETS 61

LIST OF FIGURES
Figure 2.1: Types of Slag 7
Figure 2.2: Types of Ferrous Slag 8
Figure 2.3: Flow of Steel Slag Production (Nippon Slag Association, 2006) 10
Figure 2.4: Major Productive Use of Steel Slag in Europe 11
Figure 2.5: Steel Slag Utilization in Europe 11
Figure 2.6: A Typical BOF (National Slag Association, 2011) 14
Figure 2.7: Schematic of Operational Steps in Oxygen Steelmaking Process (BOF) (Fruehan, 1998) 15
Figure 2.8: Typical Composition after Sampling (Corus, 2011) 17
Figure 2.9: A Typical EAF (National Slag Association, 2011) 18
Figure 2.10: Schematic of Operational Steps in EAF Processes (Corus, 2011) 19
Figure 3.1: Steel Slag Sample Collection Site 34
Figure 3.2: Lateritic Soil Sample Collection Site 34
Figure 4.1: Particle Size Distribution of Soil 42
Figure 4.2: Variation of Specific Gravity with Slag Content 42
Figure 4.3: Variation of Average Liquid Limit with Slag Content 42
Figure 4.4: Variation of Plastic Limit with Slag Content 44
Figure 4.5: Variation of Plasticity Index with Slag Content 45
Figure 4.6: Variation of OMC with Slag Content 46
Figure 4.7: Variation of MDD with Slag Content 46
Figure 4.8: Variation of Unsoaked CBR with Slag Content 47
Figure 4.9: Variation of Soaked CBR with Slag Content 48
Figure 4.10: Variation of Swell Potential with Slag Content 48
Figure 4.11: Variation of Unconfined Compressive Strength with Slag Content 50
Figure 4.12: Variation of Undrained Shear Strength with Slag Content 50
Figure 4.13: Variation of Permeability with Slag Content 51

LIST OF TABLES
Table 2.1. Typical Use of Slag in Civil Engineering Applications (National Slag Ass.,
2011) 12
Table 2.2: Basic Oxygen Steelmaking Event Times (Fruehan, 1998) 16
Table 2.3: Applications of Steel Slag (Nippon Slag Association, 2006) 20
Table 2.4: Typical Physical Properties of Steel Slag 21
Table 2.5: Particle Size Distribution Results for BOF and EAF Slags 22
Table 2.6: Typical Mechanical Properties of Steel Slag 22
Table 2.7: Range of Metal Concentration in BOF and EAF Slags 24
Table 2.8: Typical Chemical Composition of Steel Slag 25
Table 2.9: Comparison of Chemical Comp. of Steel Slag and Portland Cement 27
Table 2.10: Properties of a Lateritic Soil (Okafor and Okonkwo, 2009) 30
Table 4.1: XRF Result of Steel Slag Sample 40
Table 4.2: Geotechnical Properties of Natural Soil 41
Table 4.3: Some Geotechnical Properties at Optimal Stabilization 52

LIST OF ABBREVIATIONS AND ACRONYMS
AASHTO American Association of State Highway and Transportation Officials
ASTM American Association for Testing and Materials
BOF Basic Oxygen Furnace slag
BS British Standards
CBR California Bearing Ratio
CERD Centre for Energy and Research Development
EAF Electric Arc Furnace slag
HERA Human Health and Ecological Risk Assessment
LL Liquid Limit
MDD Maximum Dry Density
OMC Optimum Moisture Content
OSC Optimum Steel-slag Content
PI Plasticity Index
PL Plastic Limit
SEM Scanning Electron Microscope
SSC Steel Slag Coalition
UCS Unconfined Compressive Strength
USC Unified Soil Classification System
XRD X-ray Diffraction
XRF X-ray Fluorescence

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