A STUDY ON THE PRODUCTION OF HIGH QUALITY AGGREGATES FROM METSO BARMAC ROCK ON ROCK VERTICAL SHAFT IMPACT CRUSHER AND CONE CRUSHER
By
MAHATHIR BIN AMIR
Thesis submitted in fulfillment of the requirements for the degree of
Master of Science
ACKNOWLEDGEMENTS
Bismillaahirrahmanirrahiim,
My greatest gratitude to Allah S.W.T Almighty God, for the grace which enables me to complete my research. I would like to express my deep debt of inadequate acknowledgment to my main-supervisor, Prof. Dr. Khairun Azizi Binti Mohd Azizli for her guidance, supervision, assistance and encouragement throughout this work. Her patience and hard work have always been admired. I am also thankful to my co- supervisor, Dr. Hashim Bin Hussin for his encouragement and invaluable advice.
I am thankful to Universiti Sains Malaysia (USM) and my parents for the financial support, which enables me to pursue my studies. I am also thankful to Institute of Postgraduate Studies (IPS) for giving me the opportunity to conduct and complete my studies here. I would also like to express my indebtedness to Metso Minerals for loaning us the Metso Barmac Rock On Rock Vertical Shaft Impact Crusher.
My greatest gratitude and appreciation is extended to my father, En. Hamir Bin Hassan, mother Puan Sabariah Binti Mohd Rasid and all my family members for their sacrifice, continuous support and motivation. Many thanks also go to En. Kemuridan Bin Mat Desa for providing me his fullest effort, assistance and help. My sincere thanks are also directed towards other technical staff including En. Shahrul Ami, En. Rashid, and
the usage of the laboratory equipment. Thank you to my friends and everyone who has helped me in the completion of the thesis.
Mahathir Bin Amir
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS ii
TABLE OF CONTENTS iv
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF ABBREVIATIONS xv
LIST OF APPENDICES xvi
ABSTRAK xviii
ABSTRACT xix
CHAPTER 1- INTRODUCTION
1.1 Aggregates 1
1.2 Importance of Aggregate Shape in Asphalt Pavement 2
1.3 Problem Statement 5
1.4 Objective 8
CHAPTER 2 - LITERATURE SURVEY 10
2.1 Introduction 10
2.2 Cone Crusher 12
2.3.1 Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher 17
2.3.1.1 The unique principle of breakage 18
2.3.1.2 Breakage Mechanism 19
2.4 Aggregates as the Material for Construction 25
2.4.1 Sources of aggregates 25
2.4.2 Aggregates Characteristics 29
2.4.2.1 Influences of aggregates characteristics in hot mix asphalt 34
2.5 Asphalt Pavement 38
2.5.1 Asphalt Paving Materials 38
2.5.2 Asphalt Concrete Properties 41
CHAPTER 3 - MATERIAL AND METHODOLOGY 45
3.1 Feed sample 45
3.1.1 Sampling and Feed Preparation 45
3.1.2 Feed Characterization 47
3.2 Crushing Test Work 47
3.2.1 Rugged Marcy Gy-Roll Reduction Cone Crusher 48 3.2.1.1 Variations in Close Side Setting 48
3.2.1.2 Feed rate 49
3.2.1.3 Studies on Choke Feeding 51
3.2.2 Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) Crusher 52
3.2.2.1 Variations in Rotor Speed 53
3.2.2.2 Variations in Cascade Flow (%) 53
3.2.2.3 Studies on the Rock Build-up 55
3.3 Feed and Product Analysis 56
3.3.1 Sieve analysis 56
3.3.2 Shape Analysis 57
3.3.2.1 Flakiness Index (FI) 57
3.3.2.2 Elongation Index (EI) 57
3.3.3 Strength Analysis 57
3.3.3.1 Aggregate Impact Value (AIV) 58
3.3.3.2 Aggregate Crushing Value (ACV) 58
3.3.4 Determination of Void Content of Fine Aggregate 58
3.3.4.1 Uncompacted Void Content 58
3.3.4.2 Compacted Test Method 61
3.3.5 Chemical Composition analysis 62
3.3.6 Analysis of the Morphology Properties 62
3.3.7 Evaluation of Water Absorption of Coarse Aggregate 63
CHAPTER 4 - RESULTS AND DISCUSSIONS 65
4.1 Feed Characterization 65
4.1.2 Particle Shape 66 4.1.2.1 Elongation Index (EI) and Flakiness Index (FI) 66 4.1.2.2 Compacted and uncompacted void content (%) 68
4.1.3 Surface Properties of the Feed Sample 71
4.1.4 Constituents 72
4.1.5 Strength of Feed Sample 74
4.1.5.1 Aggregate Crushing Value (ACV) 74
4.1.5.2 Aggregate Impact Value (AIV) 75
4.1.5.3 Water Absorption 75
4.2 Crushing Test Work 77
4.2.1 Rugged Marcy Gy-Roll Reduction Cone Crusher 77 4.2.1.1 Effects of variations in feed rates (ton/hour) and Close Side
Setting, mm (CSS) on size of aggregates. 77 4.2.1.2 Effects of variations in feed rates (ton/hour) and Close Side
Setting, mm (CSS) on shape of aggregates. 83 4.2.1.2.1 Elongation Index (EI) and Flakiness Index (FI) 83 4.2.1.2.2 Compacted and uncompacted void content (%) of
Fine Aggregates. 87 4.2.1.3 Morphological Properties of the Crushed Products 92 4.2.1.4 Effects of variations in feed rates (ton/hour) and Close Side
Setting, mm (CSS) on strength of crushed aggregate
products 95
4.2.1.4.1Aggregate Crushing Value (ACV) and Aggregate 95
Impact Value (AIV)
4.2.1.5 Percentage of Water Absorption 99
4.2.2 Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher 102 4.2.2.1 Build-up Observation in the Crushing Chamber 102 4.2.2.2 Effects of variations in rotor speed (hertz) and cascade
opening (%) on size of aggregates. 104
4.2.2.3 Effects of variations in rotor speed (hertz) and cascade
opening (%) on shape of aggregates 108
4.2.2.3.1 Elongation Index (EI) and Flakiness Index (FI) 108 4.2.2.3.2 Uncompacted and compacted void content (%) of
fine aggregates 112 4.2.2.3.3 Morphological Properties of Crushed Products 117 4.2.2.3.4 Strength of Crushed Aggregate Products 121
4.2.2.3.5 Water Absorption 125
4.2.2.4 Comparisons of Products From Metso Barmac Rock on
Rock Vertical Shaft Impact Crusher and Cone Crusher 127
CHAPTER 5 - CONCLUSIONS AND FUTURE WORK 130
5.1 Feed Characteristics 130
5.2 Crushing Test Work 131
5.2.1 Cone Crusher 131
5.2.2 Metso Barmac Rock on Rock Vertical Shaft Impact Crusher 133
REFERENCES 136
APPENDICES 143
LIST OF TABLES
Page Table 2.1 : Some typical sedimentary rocks, with their composition 27
Table 2.2 : Examples of Metamorphic rocks 28
Table 2.3 : Minerals which are found in granite 30
Table 2.4 : Shapes of the particles 33
Table 2.5 : Types of surface texture 33 Table 3.1 : The feature of Rugged Marcy Gy-Roll Reduction Cone Crusher 48 Table 3.2 : The maximum feed rates in each close side setting 50 Table 3.3 : Feed rates for every close side setting 50 Table 3.4 : Crushing Test Work Conducted at different parameters 54 Table 3.5 : Control plate opening (mm) for different percentage of cascading
material 54 Table 3.6 : Proportion for Standard Graded Sample 59 Table 3.7 : Proportion for Individual Size Fraction 59 Table 4.1 : Mineralogical Composition of Feed Sample 73 Table 4.2 : Aggregate Crushing Value (ACV) and Aggregate Impact Value
(AIV) for Feed Samples 75
Table 4.3 : Percentage of Water Absorption for Feed Samples 76
LIST OF FIGURES
Page
Figure 1.1 : Expenditure and allocation for expansion of infrastructure
and public facilities (RM millions) 3
Figure 1.2 : Expenditure and allocation for development of housing and
urban services (RM millions) 3
Figure 2.1 : Important parts in the cone crushers 13 Figure 2.2 : Types of fracture mechanisms which are assumed to occur
throughout the choked crushing of cone crusher 15 Figure 2.3 : Images showing the situation which will be happened whilst
an aggregate has been crushed by constraint force of a
crushing mechanism 16
Figure 2.4 : Metso Barmac Rock On Rock Vertical Shaft Impact Crusher 18 Figure 2.5 : Rock on rock crushing action in Metso Barmac Rock On
Rock Vertical Shaft Impact Crusher 20
Figure 2.6 : The flow of particle aggregates within Metso Barmac Rock
On Rock Vertical Shaft Impact Crusher 21 Figure 2.7 : Particles inside rotor are accelerated into the crushing
chamber and the rock-on-rock impact crushing appears 23 Figure 2.8 : Components of an Aggregate Shape: Shape (form),
Angularity, and Texture 32
Figure 2.9 : Asphalt mixture showing net or effective asphalt, absorbed
asphalt, and air voids 43
Figure 3.1 : Flow sheet for experimental procedures 46 Figure 3.2 : Close Side Setting of the cone crusher 49
Figure 3.3 : Cone crusher during choke feeding 51 Figure 3.4 : Diagram of a cone crusher during choked feeding 52 Figure 3.5 : Cascade percentage of control plate opening 54
Figure 3.6 : Void Content Analysis Apparatus 60
Figure 4.1 : Size distribution of feed samples 66
Figure 4.2 : Elongation Index of feed samples 67
Figure 4.3 : Flakiness Index of Feed Samples 68
Figure 4.4 : Uncompacted void content of feed samples 70 Figure 4.5 : Compacted void content of feed samples 70 Figure 4.6 : Morphological properties of feed sample. 72 Figure 4.7 : Size distribution analysis of feeds and products from cone
crusher at CSS 8 mm with increasing feed rate. 78 Figure 4.8 : Size distribution analysis of feeds and products from cone
crusher at CSS 10 mm with increasing feed rate. 79 Figure 4.9 : Size distribution analysis of feeds and products from cone
crusher at CSS 12 mm with increasing feed rate. 80 Figure 4.10 : Results of Flakiness Index for feeds and products from
crushing works at CSS 8mm, 10 mm and 12 mm with
increasing feed rate.86 84
Figure 4.11 : Results of Elongation Index for feeds and products from crushing works at CSS 8mm, 10 mm and 12 mm with
increasing feed rate. 85
Figure 4.12 : Results of Uncompacted Void Content for feeds and products from crushing works at CSS 8mm, 10 mm and 12 mm with
Figure 4.13 : Results of compacted Void Content for feeds and products from crushing works at CSS 8mm, 10 mm and 12 mm with
increasing feed rate. 89
Figure 4.14 : Morphological properties of feed sample and crushed
products of choke feeding crushing. 94
Figure 4.15 : Results of aggregate crushing value for feeds and products from crushing works at CSS 8mm, 10 mm and 12 mm with
increasing feed rate. 96
Figure 4.16 : Results of aggregate impact value for feeds and products from crushing works at CSS 8mm, 10 mm and 12 mm with
increasing feed rate 97
Figure 4.17 : Results of water absorption value for feeds and products from crushing works at CSS 8mm, 10 mm and 12 mm with
increasing feed rate. 101
Figure 4.18 : Rock Build-up in the crushing chamber of Metso Barmac
Rock On Rock Vertical Shaft Impact Crusher 103 Figure 4.19 : Size distribution for feeds and crushed products at various
rotor speeds (20 Hz to 60 Hz) and control plate opening 0%
at constant feed rate. 105
Figure 4.20 : Size distribution for feeds and crushed products at various rotor speeds (20 Hz to 60 Hz) and control plate opening 25%
at constant feed rate 105
Figure 4.21 : Size distribution for feeds and crushed products at various rotor speeds (20 Hz to 60 Hz) and control plate opening 50%
at constant feed rate 106
Figure 4.22 : Flakiness Index for feeds and crushed products at various rotor speeds (20 Hz to 60 Hz) and control plate openings
(0%, 25% and 50%) at constant feed rate. 109 Figure 4.23 : Elongation Index for feeds and crushed products at various
rotor speeds (20 Hz to 60 Hz) and control plate openings
(0%, 25% and 50%) at constant feed rate 110
Figure 4.24 : Uncompacted void content for feeds and crushed products at various rotor speeds (20 Hz to 60 Hz) and control plate
openings (0%, 25% and 50%) at constant feed rate. 113 Figure 4.25 : Compacted void content for feeds and crushed products at
various rotor speeds (20 Hz to 60 Hz) and control plate
openings (0%, 25% and 50%) at constant feed rate. 114 Figure 4.26 : Surface Texture of Feed and Crushed Products at 0%
Cascade, 25% Cascade and 50% Cascade for 60 Hertz Rotor
Speed. 118 Figure 4.27 : Aggregate crushing value for feeds and crushed products at
various rotor speeds (20 Hz to 60 Hz) and control plate
openings (0%, 25% and 50%) at constant feed rate. 122 Figure 4.28 : Aggregate impact value for feeds and crushed products at
various rotor speeds (20 Hz to 60 Hz) and control plate
openings (0%, 25% and 50%) at constant feed rate 123 Figure 4.29 : Percentage of water absorption for feeds and crushed
products at various rotor speeds (20 Hz to 60 Hz) and control
plate openings (0%, 25% and 50%) at constant feed rate 126
LIST OF ABBREVIATIONS
ACV Aggregate Crushing Value AIV Aggregate Impact Value c corners
CSS Close Side Setting e Edge
EI Elongation Index f Face
FI Flakiness Index
Hz hertz
tph tonne per hour
LIST OF APPENDICES
Page
Appendix 1 : Method of Flakiness Index (FI) 143
Appendix 2 : Method of Elongation Index (EI) 144
Appendix 3 : Method of Aggregate Impact Value (AIV) 145 Appendix 4 : Method of Aggregate Crushing Value (ACV) 146 Appendix 5 : Results of Flakiness Index for feeds and products from
crushing works at CSS 8mm, 10 mm and 12 mm with
increasing feed rate. 147
Appendix 6 : Results of Elongation Index for feeds and products from crushing works at CSS 8mm, 10 mm and 12 mm with
increasing feed rate. 148
Appendix 7 : Results of Uncompacted Void Content for feeds and products from crushing works at CSS 8mm, 10 mm and 12
mm with increasing feed rate. 149
Appendix 8 : Results of Uncompacted Void Content for feeds and products from crushing works at CSS 8mm, 10 mm and 12
mm with increasing feed rate. 150
Appendix 9 : Results of compacted Void Content for feeds and products from crushing works at CSS 8mm, 10 mm and 12 mm with
increasing feed rate 151
Appendix 10 : Results of compacted Void Content for feeds and products from crushing works at CSS 8mm, 10 mm and 12 mm with
increasing feed rate. 152
Appendix 11 : Results of aggregate crushing value for feeds and products from crushing works at CSS 8mm, 10 mm and 12 mm with
Appendix 12 : Results of aggregate impact value for feeds and products from crushing works at CSS 8mm, 10 mm and 12 mm with
increasing feed rate. 154
Appendix 13 : Results of water absorption value for feeds and products from crushing works at CSS 8mm, 10 mm and 12 mm with
increasing feed rate. 155
Appendix 14 : Flakiness and Elongation Index for feeds and crushed products at various rotor speeds (20 Hz to 60 Hz) and control plate openings (0%, 25% and 50%) at constant feed
rate. 156 Appendix 15 : Compacted void content for feeds and crushed products at
various rotor speeds (20 Hz to 60 Hz) and control plate
openings (0%, 25% and 50%) at constant feed rate. 157 Appendix 16 : Compacted void content for feeds and crushed products at
various rotor speeds (20 Hz to 60 Hz) and control plate
openings (0%, 25% and 50%) at constant feed rate. 158 Appendix 17 : Uncompacted void content for feeds and crushed products at
various rotor speeds (20 Hz to 60 Hz) and control plate
openings (0%, 25% and 50%) at constant feed rate. 159 Appendix 18 : Uncompacted void content for feeds and crushed products at
various rotor speeds (20 Hz to 60 Hz) and control plate
openings (0%, 25% and 50%) at constant feed rate. 160 Appendix 19 : Aggregate crushing value (ACV) and Aggregate Impact
Value (AIV) for feeds and crushed products at various rotor speeds (20 Hz to 60 Hz) and control plate openings (0%,
25% and 50%) at constant feed rate. 161 Appendix 20 : Percentage of water absorption for feeds and crushed
products at various rotor speeds (20 Hz to 60 Hz) and control plate openings (0%, 25% and 50%) at constant feed
rate. 162
KAJIAN PENGHASILAN AGREGAT BERKUALITI TINGGI OLEH PENGHANCUR METSO BARMAC HENTAMAN BATU KE BATU ACI
MENEGAK DAN PENGHANCUR KON
ABSTRAK
Kajian telah dijalankan untuk menilai prestasi penghancur kon dan penghancur Metso Barmac Aci Menegak ke atas penghasilan agregat berkualiti tinggi. Beberapa analisis telah dilakukan untuk mengkaji ciri-ciri bagi produk penghancuran seperti bentuk (Indeks Pemanjangan (IP); Indeks Kekepingan (IK); dan analisis kandungan lompang), taburan saiz, tekstur permukaan (Imbasan Mikroskop Elektron (IME)) dan kekuatan (Nilai Penghancuran Agregat (NPA) dan Nilai Hentaman Agregat (NHA)). Kajian juga dijalankan untuk mengenal pasti binaan-dalaman batuan yang baik dalam mempengaruhi mekanisma penghancuran. Produk penghancuran dari Suapan B menunjukkan keputusan yang lebih baik berbanding dengan produk penghancuran dari Suapan A. Penghancuran dengan tetapan bahagian tertutup iaitu 12mm dan pada kadar suapan 2.6 t/j dimana penghancuran ‘cekik’ berlaku, memberi penambahbaikan kepada ciri-ciri produk daripada segi bentuk dan tekstur permukaan dengan nilai IP dan IK masing-masing 31.25% dan 16.29%. Analisis NPA dan NHA menunjukkan nilai masing-masing 19.58%
dan 24.42%. Pengendalian penghancur Barmac pada kelajuan pemutar 60 Hz dan nisbah lataan 0% menghasilkan produk dengan nilai IP dan IK yang rendah iaitu masing-masing 19.96% dan 12.02% berbanding dengan penghancur kon. Nilai NPA dan NHA yang rendah turut diperolehi, iaitu masing-masing 15.61% dan 21.06%. Jelas bahawa penghancur Barmac berupaya untuk menghasilkan produk yang berkualiti tinggi daripada segi bentuk dan tekstur permukaan jika dibandingkan dengan penghancur kon.
A STUDY ON THE PRODUCTION OF HIGH QUALITY AGGREGATES FROM METSO BARMAC ROCK ON ROCK VERTICAL SHAFT IMPACT (VSI)
CRUSHER AND CONE CRUSHER
ABSTRACT
A study was conducted to evaluate the performance of cone crusher and Metso Barmac VSI crusher in producing high quality aggregates. Various analyses were completed to study the characteristics of crushed products such as shape (Elongation Index (EI);
Flakiness Index (FI); and voids content analysis), size distribution, surface texture (Scanning Electron Microscopy (SEM)) and strength (Aggregate Crushing Value (ACV) and Aggregate Impact Value (AIV)). A study was also conducted to evaluate a good rock build-up formation in influencing the crushing mechanism. Crushed products of Feed B displayed better results compared to the crushed products of Feed A. Crushing with CSS of 12mm and increasing the feed rate of the cone crusher to 2.6 t/h which was the choked feeding crushing, gave improvement to the characteristics of crushed products in terms of shape and surface texture with EI and FI values of 31.25% and 16.29% respectively.
ACV and AIV analyses showed values of 19.58% and 24.42% respectively. Operating the Barmac crusher at 60 Hz rotor speed and 0% cascade ratio was found to produce crushed products with lower percentage of EI and FI which were 19.96% and 12.02%
respectively compared to the cone crusher. Similarly, lower values of ACV and AIV were obtained, which were 15.61% and 21.06% respectively. Overall, Barmac crusher was capable to produce better quality of products in terms of shape and surface texture compared to the cone crusher.
CHAPTER 1
INTRODUCTION
1.1 Aggregates
Aggregates are from the natural rocks which are produced through the crushing process. It is used in construction sector such as roads, buildings and other structures.
Granite and limestone are the main sources for the aggregate industries in Malaysia. The qualities of aggregates which are used in concrete and asphalt mix depend on mineralogy and petrographic characteristics of the main rocks as well as the crushing machines used to produce these aggregates. Aggregates used in construction materials must adhere to certain standard specifications.
Physical characteristics of aggregates such as rock composition, hardness, size distribution, surface texture and shape are significant properties that influence the properties of concrete and asphalt pavement mixtures. The shape of aggregate for concrete plays an important role with the strength properties. Equidimensional shape of aggregate is the main choice because it is dense and strong. In reality, particles with equidimensional shape are difficult to obtain from the compression type of crushing process. Aggregate in the crushing products can be classified into six essential shapes which are rounded, irregular, flaky, angular, elongated; and flaky elongated. Particles
products. It is more difficult for the particles to break when forces are imposed from various directions. Hudson (1995) stated that cubical or equidimensional shape helped particles to arrange more packly and closely to fill the voids in the concrete mixtures.
The construction industry highly depends on the quarrying sector for its aggregates. In recent time, the construction sector demands better quality aggregate not only for its size grading, but also for the aggregate shape. The continuous growth experienced by the construction sector and aggregate industry through the years are due to the construction works as declared in the Ninth Malaysian Plan. Referring to Figures 1.1 and 1.2, the Malaysian Government plans to spend more than RM 70 billion for development of infrastructures (health and educational), public facilities, expanding of low and medium cost housing areas; city services and road developments. These developments are carried out not only in the urban areas, but will be expanded to rural areas so as to improve information system and the economic growth and upgrading the quality of residents’ life (Anon, 2006). These facts proved that the demand for aggregate as the raw material for construction purpose will increase to fulfill the requirement of the development sector.
1.2 Importance of Aggregate Shape in Asphalt Pavement
It is known that usage of aggregates that are equidimensional in shape will give better outcome on the product mixtures performance, because this property of aggregate is
1565.51290.0 3642.4
16540.5
2868.5 17303.1
3634.9
City Transportation Ports Rural Roads Public Facilities
Airports Roads Railw ays
Figure 1.1: Expenditure and allocation for expansion of infrastructure and public facilities (RM millions) (Anon, 2006)
9452
350.7 2256.5 117.6 9101.3
233.1 6844.8
Housing Rural Housing Low Cost Housing
Reunite for village Public Housing Housing for the Poors Government Housing
capable to control the performance of mixtures for the final products (Topal et al., 2005 &
Atkins, 2003).
Stronger aggregates with improvement in particle shape and textural characteristics tend to produce stronger asphalt pavement as the weak planes and structures are being reduced. Masad Eyad et al. (2003) stated that, if good performance of hot mix asphalt is required, the coarse aggregate which is used in the hot mix asphalt mixtures must have at least 85 percent of cubical or equidimensional particles. Cubical or equidimensional aggregates can increase the resistance strength of the hardened asphalt mixtures because they give much greater particle-to-particle mechanical bond and results in a larger adhesive force as they bind more securely between the particles and the asphalt cement mix. When forces are imposed on the hardened asphalt mix, frictional properties between aggregates themselves and asphalt cement mix as well can help to neutralize the absorption of the forces with the existence of good resistance to sliding of one particle over another (Atkins, 2003; Topal et al., 2005; Kaplan, 1959 & Masad Eyad et al., 2003). Asphaltic mixture properties that are affected by the shape and surface texture of aggregate includes, dynamic stiffness, stability, durability, permeability, resistance to moisture damage, air voids in the mixture, permanent deformation, fatigue resistance and the skid resistance of pavements (Topal et al., 2005).
1.3 Problem Statement
There are few factors that influence the production of cubical or equidimensional shape particles. Not only crusher and crushing techniques contribute to the production of good quality aggregates, but the rock and mineralogy were also affecting to the quality or characteristics of the product/aggregate. Based on the previous studies, it was proved that rock-on-rock crushing method was capable to reduce the production of flaky and elongated particles (Kojovic, 1995). Other researchers (Hosking, 1992; Jamkar et al., 2004
& Topal et al., 2005) found that product produced by impact crusher will give better shape compared to compression type of crusher.
In Malaysia, construction industries are completely dependent on the aggregate obtained from local quarries. Presently, most of the quarries are using conventional crushing method which is compression type of crushing machine to produce the aggregates. The usage of compression type of crusher influences the characteristics of aggregates produced by generating high percentage of poor quality aggregates.
According to Fernlund (2005), the production of aggregate with enhanced characteristics is highly emphasized because it gives a better outcome, life expectancy and safety to several engineering materials for housing, buildings, roads, bridges, dams and others.
Aggregates which are good in quality have improvements in their characteristics with more cubical or equidimensional shape and better graded or size distribution (Hammer, 1991). They are also free from weak planes which are easily fractured or damaged as
breakage method contained a lot of irregular, flaky and elongated particles. These types of shape will reduce the capability of the aggregate to arrange densely when used in concrete and asphalt pavement mixtures.
Cone crusher is a compression type of crushing machine. It is widely used in aggregate industry to produce the final saleable product (Moshgbar et al., 1995). It uses the principle of grinding rock between an eccentrically rotating mantle and a stationary concave liner. The material entering will be crushed between the two surfaces by compressive forces due to the eccentric motion (Napier-Munn et al., 1996 & Wills, 1995).
The high speed will cause the aggregate particles to shatter resulting from the great constraint forces (Bengtsson et al., 2006). In this research, focus shall be put on the operating variables (feed rate and close side setting, CSS) of a cone crusher, which those operating variables are capable to influence the provision of an effective breakage situation in producing aggregates with better physical characteristics. Besides, there is a situation where the operating variable of feed rate can be manipulated to create a condition known as "choke feeding". There are numerous reasons as to why this is employed by manufacturers. Besides reducing wares and damage on the mantel and concave parts of the crusher, choke feeding could improve the breakage imposed in the crushing chamber thus improving the cubicity of the product. Moreover it gives a more consistent product sizing (Bearman et al., 1998). Choke feeding provides the rock-to-rock crushing mechanism which is a unique breakage mechanism that influences the shape of the crushed aggregates. Interparticle collisions provide the breakage and fracture such as
crushing, shatter, shear, and compressive. The crushed aggregates are free from weak planes such as microfractures, mineral boundaries and jointing (Anon, 1994).
Impact crusher can give an alternative to the conventional methods that have been used widely. Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher is a type of impact crusher that uses a spinner or rock lined rotor that continuously accelerates and discharges the incoming aggregates outward onto a solid pack of rock lining in the crushing chamber, so that nearly all crushing energy is used in rock-to-rock impact crushing and attrition. The combination of high velocity impact crushing with high pressure attrition grinding is capable to produce high volumes of cubical and equidimensional products (Anon, 1994 & Briggs et al., 1996). The crushing action in the Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher concentrates on several aspects of aggregate particles such as areas of softer material, areas of planes of weakness, mineral boundaries and flat or thin edges of a particle. The process of autogeneous crushing occurring within the crushing chamber of the Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher varies from other type of crushers. The effectiveness of crushing works using impact crusher depends on the best condition of the three different operating variables which are crushing chamber build-up characteristics, rotor speed (hertz) and cascade ratio (%). Crushing under the optimum conditions is capable to provide a breakage that will destroy any weaknesses in the material, breaking elongated and flaky feed which are naturally produced through normal compression type of crushing operations; thus producing stronger aggregates.
The production of quality aggregate by both crushing machine shall be studied in this research. Cone crusher and Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) are chosen for this research as the representative of widely used crushing machine in aggregate producing industry of our country. Result analysis which displayed by both crushing machine can give picture clear regarding factors which give effect to production quality aggregate according to type of crusher used. The factors should be given high attention where this condition is able to provide safe and long lasting construction products, resulting from better aggregate quality.
1.4 Objective
The main objective of this research is to study the performance of two different types of crushers in producing high quality aggregates in terms of shape, surface texture and size grading to fulfill the requirements of asphalt pavement mixes.
Measurable objectives:
To study the breakage mechanisms in the cone crusher and impact crusher and evaluating the effects by changing the operating variables like feed rate (ton/hour), close side setting (mm), rotor speed (Hz) and cascade ratio (%) in controlling the production of products with good quality.
To investigate the influence of feed characteristics such as mineralogy, chemical and physical properties on the final products.
The results of this study are expected to provide more information and knowledge for better prediction and control of the quality aggregate for use in the production of better asphalt pavement.
CHAPTER 2
LITERATURE SURVEY
2.1 Introduction
Malaysia is among the countries that is experiencing rapid infrastructures growth.
Effective management of the material resources for construction purpose is highly demanded to ensure optimum production and usage of these construction material resources. One of the best solutions is to produce aggregates with high quality by upgrading the rock physical characteristics. Using high quality aggregates can produce better construction materials with improved quality and the advantage of avoiding carelessly and unappreciative usage of raw materials (Rajeswari, 2004).
Hot mix asphalt (HMA) is the most common pavement surfaces in use today. It is used on all types of roadway. Aggregates constitute the major part of the pavement structure. Aggregates have been reported as having considerable influence on strength and as well as the asphalt pavement performance. Moreover, it is relatively inexpensive and does not enter into complex chemical reactions with water and thus considered as inert mineral filler. Due to these characteristics, aggregates are considered as the most favorable filler ingredient in HMA, which determines many important properties of HMA.
Aggregates are obtained through crushing process on certain type of rocks.
Crushing is the mechanical stage widely used in the aggregate-producing industry for the construction and development sector. The main objective is to reduce the particle size and dimension of rock materials (Wills, 1995; Tang et al., 2001 & Topal & Sengoz, 2005). It reduces the size of the rock particles to make them suitable for use in mixtures of concrete and hot mix asphalt. There are two main methods utilized in crushing for size reduction that are compression and impact.
There are a number of factors that can influence the shape of particles such as breakage energy, the rock type, and crusher type in terms of machine design. Impactors are capable to produce cubical particles compared to the compressive breakers. This kind of breakage method can influence the production of high quality aggregates in terms of improved shape and graded size. It takes place at a much shorter time scale, implying a dynamic crack propagation that leads to a much faster failure of the particles.
Furthermore, the impact generates compressive and tensile shock waves traveling throughout the particle. Consequently, the larger particles break more easily compared to the smaller particles because they contain larger micro-cracks. Compared to compressive breakers, the crushing trend of the jaw and cone crusher is causing a slow disintegration of the compression breakage. However, for the cone crusher (compressive breakers), the crushing technique of choked feeding crushing should be employed because it can reduce the production of particles with poor shapes (Kojovic, 1995). The choked feeding crushing occurs when the volume of material arriving at a particular cross-section is greater
than that leaving. There are numerous reasons as to why choked feeding crushing is recommended by manufacturers, the most common points include:
i. develops a uniform wear profile;
ii. gives a more consistent product sizing;
iii. maximises throughput;
iv. extends the liner life;
v. Improves the cubicity of the product (Bearman and Briggs 1998).
2.2 Cone Crusher
Cone crushers operate on the principle of compressive breakage. They are usually used in the mining and quarry sectors (for production of road stones or aggregates) which are widely used for secondary and tertiary crushing of rock (Moshgbar, et al., 1995 &
Yaxley & Knight 1999). They operate with dry feeds and their purpose is to reduce the ore to the size suitable for grinding.
The cone crusher (Figure 2.1) consists essentially of a spindle, a crushing head (a hard steel conical grinding element), spider and shell. During the crushing process, the material in the crushing chamber is subjected to a series of hammer-like blows and gradually nipping and compressing by both mantle and concave (Tang et al., 2001). Both mantle and concave which represent the jaws are moving relative to each other. The gradually actions allow particles to flow freely through the crushing chamber. Sometimes,
the smaller sizes go through the crusher without change, whereas larger particles are broken down to the desired size (Harold, 2003).
Figure 2.1: Important parts in the cone crushers (Wills, 1995).
Crushing process in the cone crusher occurs in the crushing chamber which is located between mantle and concave. Inside this chamber, aggregates will be shattered by the great compressive energy and will cause them to break undesirably to the smaller sizes.
The particles in the size range near to the crusher setting are mainly influenced by the crushing mechanism. For the fine particles, it is more difficult for the crusher surfaces to give the large impact of the compressive load, but only the coarse particles will receive larger percentage of the impact. There are two types of breakage actions which are imposed on the aggregates. They are the blows of the crushing head itself and the forces from the
Feed Spider
Shell
Crushing Head
Spindle Eccentric sleeve
Shell Spider
Discharge
The breakage condition of the crushing occupying a small number of aggregates is different than the breakage with lots of aggregates. The management of aggregate quantity involved in the crushing chamber is assisted by a distributing plate on the top of the cone which helps to centralize the feed, distributing it at a uniform rate to the entire crushing chamber where the controlled feed can give different crushing situations (Wills, 1995).
The quantity of aggregates will influence the breakage equilibrium in crushing chamber. This situation has a linkage with the amounts of the feed rate. Hosking (1992);
Jamkar & Rao (2004) and Topal & Sengoz (2005) state in their papers that poorer shape was generated by the crushers which were operated with slow feed rates (except impact breakers). Crushing with low feed rates will have a lot of voids among the aggregates, thus they are crushed freely and mostly manipulated by the breakage force of crusher’s head. However, the crushing mechanism will completely change as the feed rate increased to a higher value. Increasing the feed rate shall give a good improvement to the shape of the particles. While the chamber is full with particles, a large amount of the particles are compressed among themselves at the higher parts of crushing chamber. Feed particles start to fill the crushing chamber until it is fully packed. As the crushing chamber is crowded with aggregate particles, the rock-on-rock breakage mechanism shall occur. Antiparticle impacts between particles with same characteristics shall influence the particle breakage on weak planes such as mineral boundaries, jointing and microfractures (Anon, 1994). The breakage energy will be spread completely to all of the aggregates, resulting in ideal breakage mechanism. The energy impressed on the particles by the crusher head is also reduced since the travel of mantle and concave is restricted by the
aggregates which filled the crushing chamber. The decreasing breakage energy is shifted on the particles and it is utilized to smash among them. This crushing could produce better shape product compared to crushing by crusher head towards the aggregates itself in the crushing cavity. It causes extra amount of feed materials. Throughout this situation, there shall be various forms of breakage mechanism that occur on every aggregate such as shown in Figure 2.2.
Figure 2.2: Types of fracture mechanisms which are assumed to occur throughout the choked crushing of cone crusher (Anon, 1994).
The features of a cone crusher are important for providing a suitable situation of the crushing chamber. Normally, the crushing chamber’s capacity of a cone crusher is up to 1100 ton per hour (t/h-1) (Wills, 1995). A large capacity showing that the cone crusher has extra advantage of bigger crushing chamber for allowing it in receiving a high total feed. A stability of breakage energy occurred between the compressions and shattering of
been done and have shown that the existence of rock-on-rock breakage mechanism improves the physical conditions of the crushed aggregates. Without the presence of other aggregates, the huge breakage energy will be imposed directly on the aggregates in the crushing chamber. Consequently, poor characteristics of products with a lot of fines will be produced as shown in Figure 2.3. Once the crushing chamber is full with aggregates, then the impacts and frictions which take place between them are the important sources of strength that permit the aggregates to be processed and crushed without including high breakage energy of the crusher head. On the other hand, the effects gave by both attritions and abrasions are not too big as those in the crushing chamber of the impact crushers.
Figure 2.3: Images showing the situation which will be happened whilst an aggregate has been crushed by constraint force of a crushing mechanism (Tang et al., 2001).
Choked crushing is extremely suggested in the crushing process because it has some advantages on the aggregates. A high feed rate crushing controls the crushing mechanism in the crusher’s cavity. The choked crushing occurs when the volume of material arriving at a particular cross-section is greater than that leaving. The difference between these two
choked crushing, particles break each other (Wills, 1995). During the usual crushing action of a cone crusher, particle breakage in the cone crusher is influenced by constraint force of crusher’s surfaces. Poor shape of particles is produced from the collision between the particles and the crusher’s surfaces as the great energy of the crusher’s surfaces enforced the particles to shatter incompletely and undesirably. Besides, this interparticle comminution (choked crushing) can lead to excessive production of fines. Negatively, if choked crushing is severe, it can damage the crusher (Wills, 1995 & Tang et al., 2001).
2.3 Impact Crusher
Comminution in impact crusher is by impact rather than compression, by sharp blows applied at high speed to free-falling rock. Wills (1995) stated that the important difference between the states of material crushed by pressure, which can cause cracking later. However, impact causes immediate fracture with no residual stresses. The condition of stress-free for material crushed by impact force is particularly valuable in stones used for brick making, building, and road making, in which a binding agent, such as bitumen, is subsequently added to the surface. Thus, impact crushers have a wider use in the quarrying industry compared to that in the metal mining industry.
2.3.1 Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher
Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher was invented by
Rock Vertical Shaft Impact (ROR) crusher is the only thoroughly field, proven, successful rock-on-rock vertical shaft impactors (Anon, 1994). Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher is ideal for third and fourth stage crushing machines (Anon, 1994). Figure 2.4 shows the Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher.
Figure 2.4: Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher (Anon, 2006)
2.3.1.1 The unique principle of breakage
Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher is a machine for crushing the complete range of ores, rocks and minerals. Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crushers are unique amongst all other vertical shaft impactors because they incorporate pure rock-on-rock crushing principle technology, not using impeller shoes or impact anvils to achieve reduction in the size. Accordingly, the invention of the Metso Barmac Rock-On-Rock Vertical Shaft Impact Crusher rock-on-rock crushing
principle has revolutionised material reduction of the aggregates and minerals industries worldwide in the last two decades (Anon, 1994; Anon, 2006).
Rotor is one of the most important components in Metso Barmac Rock-On-Rock Vertical Shaft Impact Crusher. It is in the crushing chamber and surrounded by rock lining. Rotor works as a tool which acts as a high velocity dry stone pump to project incoming aggregate outward onto a solid pack rock lining of the same aggregate as a continuous rock stream as shown in Figure 2.5, so that nearly all crushing energy is used in rock-to-rock impact crushing and attrition (Anon, 2006 & Anon, 1994). They combine high velocity impact crushing with high pressure attrition grinding that tends to produce high volumes of cubical products and quality sand (Anon, 1994 & Briggs & Bearman, 1996). Rotor is run by the specialized motor via a drive belt placed outside of the crusher.
The speed of the rotor can be increased from the lowest to the maximum value, where the speeds are controlled by the central controlling machine. The selection of rotor speed is based on the 3 stages of speed which are the minimum speed, 20 hertz, the central speed, 40 hertz, and the maximum speed, 60 hertz.
2.3.1.2 Breakage Mechanism
Figure 2.6 shows the interior parts of the crusher and the aggregate flow into the crusher as the feed material. The material entering into the crusher will go through the feed hopper first at the upper part of the crusher. The feed hopper will centralize the flow of
Figure 2.5: Rock on rock crushing action in Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher (Anon, 2006)
Then, the feed material passes the control plate. Control plate is an important part that controls the cascade of the feed that flows into the crushing chamber. Control plate works to separate the feed to two types of flow which are rotor flow and cascading flow.
The amount of particles in each flow depends on the control plate settings. The closing of the control plate can be set using the cascade control. Control plate with a big opening allows a huge part of feed to go into the rotor’s chamber, while control plate with small opening causes the feed retained to fall into the rotor’s chamber, thus falling directly into the crushing chamber as cascading material. Increasing the cascade flow decreases the reduction ratio achieved whilst increasing the capacity of the crusher (Anon, 1994). The position of the choke on the control plate controls flow of the material into the rotor (Anon, 1994). Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher uses the patented cascade feed system to introduce a second stream of material, in a controlled quantity, into the crushing chamber turbulence, causing a supercharging of particle
Figure 2.6: The flow of particle aggregates within Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher (Anon, 1994)
This improves the energy transfer between the particles (Anon, 2006). Control plate divides the flow to two different types of flows which are a flow into the rotor and a flow
The rotor accelerates the materials and continuously discharges them into the crushing chamber. As shown in Figure 2.7, particles exit the rotor with velocities range from 50-85 m/s (165-275 ft/s) and accelerated into the crushing chamber with increasing kinetic energy of the particles. Reduction process of abrasion and attrition begins as particles are forced across the rock lining of the rotor. In the crushing chamber, material from the rotor and the cascading material meet and crash together. Besides, they hit the cascading material and patented rock lined rotor as well. Material from the rotor is continuously discharged into the crushing chamber and this process replenishes the rock lining, while at the same time maintains a rock-on-rock chain reaction of crushing and grinding (Anon, 1994).
The particle cloud appears in the crushing chamber which is driven by the material ejected from the rotor. It swirls around the crushing chamber in a highly turbulent manner. As particles bump, rub and grind together, much reduction by impact, attrition and abrasion occurs before losing sufficient velocity. The particles are retained for 5-20 seconds before losing energy and falling out of the crushing chamber as products.
Accordingly, they drop out of the particle cloud and leave the crushing chamber.
Typical residence times for particles in the crushing chamber are between 5 and 20 seconds. Since the size reduction process relies on random interparticle collisions, it follows that crushing efficiency will be improved by increasing the particle cloud density in the crushing chamber thereby increasing the likelihood and frequency of collisions (Anon, 1994).
Figure 2.7: Particles inside rotor are accelerated into the crushing chamber and the rock-on- rock impact crushing appears (Anon, 2006; Anon, 1994)
There are four types of fracture mechanisms occurring in the Metso Barmac Rock on Rock Vertical Shaft Impact (ROR) crusher which are:-
• Impact/shatter
• Cleavage
• Attrition
• Abrasion
These fracture mechanisms are due to the high intensity interparticle and particle-to-rock lining collisions occurring within the rotor and crushing chamber. Particle breakage is
Cascading material flowing into the crushing chamber
Rotor accelerates particles, increasing the kinetic energy
of the particles.
Principle crushing action is impact reduction as high speed particles
from rotor collide with particles already in crushing chamber.
fractures. The crushed product is usually free of weak planes, cubically shaped and often has the valuable mineral exposed or liberated (Anon, 1994).
The type of fracture mechanism that prevails depends entirely on the nature of the collision and the speed at which it takes place. Energy for the reduction process is imposed on each particle as kinetic energy as it is accelerated through the rotor and expelled into the particle cloud in the crushing chamber. The velocity of each particle leaving the rotor is dependent on the rotational velocity of the rotor. The size and mass of individual particles leaving the rotor varies according to the size distribution of the feed material, therefore the energy level of individual particles will vary from a maximum for the largest, dense particles to almost zero for very fine particles. As these energised particles enter the particle cloud in the crushing chamber, a chain reaction of particle collisions and energy transfer occurs. Large, dense, high energy particles when colliding with smaller or weaker particles will deliver a severe impact causing shattering and rapid reduction. The lower energy medium sized particles and daughter particles from earlier impacts deliver a less severe impact, chipping and wearing down other particles they come into contact with. The smallest particles, the fines and" dust, although having little kinetic energy are traveling at high velocities and effectively sand blast anything they come into contact with.
2.4 Aggregates as the Material for Construction
2.4.1 Sources of aggregates
Aggregates may be of natural, processed or synthetic origin (Topal & Sengoz, 2005). For the natural, they can be obtained from natural gravel or from processed crushed rocks in quarries. However, as the supply of natural gravel in many countries is decreasing due to the lack of availability or legal restrictions, the use of crushed rock material is becoming more and more important. The crushed rocks or aggregates are produced from the quarry industries. They are very important in producing aggregates of specified sizes via a process of crushing and screening for development works (Hosking, 1992; Tang et al., 2001 and Bearman & Briggs, 1998). Processed aggregates from bedrock are obtained by crushing and screening quarried rock, oversize gravel and boulders (Topal & Sengoz, 2005 & Harold, 2003). Sources of aggregates for construction include:-
a. Natural sand and gravel deposits b. Crushed rock
c. Slag and mine refuse d. Rubble and refuse
e. Artificial and processed materials
f. Pulverized concrete and asphalt pavements
g. Other recycled and waste materials (Harold, 2003).
The method of extraction will depend upon the type of material and its location. At one extreme, extraction consists simply of digging a material such as gravel from the ground and, at the other, blasting solid rock (Hosking, 1992). A deposit might be composed of many different types of mineral particles—such as limestone, sandstone, and granite - depending on the original bedrock source of the particles. Underwater deposits are also used for aggregates. The material is recovered using dredges, excavation equipment mounted on barges, or by buckets dragged through the deposit with the use of dragline systems. Many deposits are covered by an overburden of lower-grade weathered material that has to be removed before extraction begins. This may be replaced after extraction or used for less demanding engineering purposes (Hosking, 1992 & Harold, 2003). The initial step in the development of a pit is the stripping of top soil, vegetation, and other unsuitable material from the surface of the deposit. Holes are drilled from the surface. The raw materials extracted from the quarry, gravel pit or other sources are usually processed to the required sizes by crushing in various types of rock crushers and screening to produce a range of aggregates (Harold, 2003 & Hosking, 1992). These aggregates are often processed through a washing plant, which cleans the dust off the particles and also removes any silt and clay particles and alters the gradation of the aggregate in other ways (Harold, 2003).
There are three major classes of rock which are sedimentary, igneous and metamorphic.
Sedimentary rocks are formed from the solidification of chemical or mineral sediments deposited under ancient seas. They are usually layered because the original material was deposited in this manner (Harold, 2003). Some typical sedimentary rocks, with their composition, are given in Table 2.1.
Table 2.1: Some typical sedimentary rocks, with their composition (Harold, 2003)
Limestone Calcium carbonate
Dolomite Calcium carbonate and magnesium carbonate Shale Clay Sandstone Quartz
Gypsum Calcium sulphate
Conglomerate Gravel
Chert Fine sand
Limestone and dolomite are common sedimentary rocks. They are softer than igneous rocks but are still acceptable as aggregates for most purposes. Shale, being composed of clay grains, is very weak and disintegrates easily when exposed to the weather. It is a poor aggregate. Chert is often found as an impurity in other rock deposits, and may also disintegrate when exposed to weathering (Harold, 2003).
Metamorphic rocks are igneous or sedimentary rocks that have been changed (meta- morphosed) due to intense heat and pressure. Examples are listed in Table 2.2. Igneous and metamorphic rocks are usually very hard and make excellent aggregates for most purposes (Harold, 2003). Aggregates have a lot of uses such as:-
a. in building, as blocks, slabs, flags, setts, roofing slates b. damp-proof courses
a. Aggregate for concrete, terrazzo, plasters, tarmacadam, mastic asphalt, etc
d. Abrasives (Everett, 1972)
Table 2.2: Examples of Metamorphic rocks (Harold, 2003) Slate From shale
Marble From limestone Quartzite From sandstone
Gneiss From granite
Granite is the most abundant igneous rock. Granites are a mosaic of crystals, sometimes several inches in length. It is composed of three main mineral constituents, feldspar, quartz and mica. The principal constituent is feldspar. It is dull white to deep red in colour. Other ingredients are small grains of grey quartz and mica, which contribute
‘sparkle’. These three homogeneous mineral components occur in varying proportions in different granites, and even in different parts of the same granite mass. Sometimes hornblende and, less frequently, augite, is present (Wills, 1995 & Everett, 1972). Granites are usually strong and have very high failing strength in compression. Being extremely resistant to knocks and abrasion, granite is eminently suitable for roadway kerbs, bridge cutwaters, jetties, spur stones, bollards and heavy-duty paving as slabs or setts. Most granite is virtually impermeable and serves as damp-proof courses provided the vertical joints between blocks are designed to prevent water movement Hosking, 1992 (Everett, 1972 & Hosking, 1992). Table 2.3 shows the brief description of mineral which are found in granite.
2.4.2 Aggregates Characteristics
Aggregatesare granular mineral particles and they are used either in combination with various types of cementing material to form concretes or alone as road bases, backfill and others (Harold, 2003). The majority of aggregates used in buildings and road construction are obtained from naturally occurring deposits or processed quarry rocks. Some typical uses of aggregates are Portland cement concrete, asphalt concrete, asphalt surfaces, road bases and subbases, railroad ballast, trench backfill, fill under floor slabs, concrete blocks, water filtration beds, drainage structures, riprap, and gabion material (Harold, 2003). In the road construction, aggregates can be separated into two types which are coarse aggregates and fine aggregates.
Many studies have emphasized the role of aggregate properties in controlling the performance of the mixtures for the final products (Masad Eyad et al., 2003, Topal, and Sengoz, 2005 & Harold, 2003). The properties which have been mentioned are size gradation, shape, surface texture, durability, cleanliness, toughness and absorption.
Size gradation is one of the external characteristics of the particles of mineral aggregates which is important (Buchanan, 2000). The effect is significant in the quarrying industry since it affects the quality of construction aggregates (Kojovic, 1995). Size gradation means the arrangement of sizes owned by an aggregate sample. The aggregate samples which will be used in some construction mixes must have appropriate size grading to
combination of size grading will make available a perfect mixes, thus bring into being a fine, compact and long-lasting products. Aggregates with a complete condition of the size grading will have an advantage for filling up the voids among the other ingredients contained in the mixes. Consequently, there will be strong bonds between materials in the blend. For an example, during surface treatment (either surface dressings or chippings in asphalt), aggregates used as chippings must fulfill the requirement of controlled grading and shape in order to give a suitable surface texture and to facilitate laying. The experiment which is used to evaluate the size distribution of an aggregate sample is the sizing analysis (Masad Eyad et al., 2003).
Table 2.3: Minerals which are found in granite (Everett, 1972)
Minerals Description
Feldspar Usually the chief ingredient in igneous stones. It is dull white to deep red in colour
Quartz An extremely hard and durable crystalline form of silica, usually transparent and colourless, but sometimes grey, pink, yellow or purple.
Mica
A silicate of aluminum with potassium (muscovite mica), which with the further inclusion of iron and magnesium (biotite mica) is soft and cleaves very easily into very thin flakes.
Hornblende Essentially a silicate of calcium, magnesium and iron occurs as almost black six-sided prismatic crystals.
Augite Similar to hornblende but having eigth-sided crystals.
Iron pyrites A sulphide of iron occurring in small specks of cubes of brassy colour and liable to decompose rapidly.
Olivine An iron magnesium silicate, is black, green or yellow in colour.
Asbestos Is made up of various incombustible fibrous minerals related to either hornblende of olivine
Besides size grading, the shape property is also the external characteristics of mineral aggregates (Buchanan, 2000). The shape is significant in the quarrying industry since it affects the quality of construction aggregates (Kojovic, 1995). It will result in better management of resources and increase the life of the engineering product (concrete and asphalt pavement) and thus result in economic savings (Fernlund, 2005, Herrin &
Goetz, 1954; Benson, 1970; Ishai & Gelber, 1982; Kuo & Freeman, 1998 and Maerz, 2004). Particle geometry in aggregates is proficient to improve the strength of the main materials in the engineering products. The shape of each particle which is sufficiently complete, with flat and level surfaces, also corners with a fine arrangement, will finally produce a strong combination to strap up the materials that are contained in concrete and asphalt pavement mixtures and in the next step; influencing as well the performance of finished mixes (Harold, 2003; Topal & Sengoz, 2005; Kaplan, 1959 & Masad Eyad et al., 2003). Masad Eyad et al., (2003) stated that, the particle geometry can be fully expressed in terms of three independent properties: shape (or form), angularity (or roundness), and surface texture (Masad Eyad et al., 2003). A schematic diagram that illustrates the differences between these properties is shown in Figure 2.8. Shape or form, the first order property, reflects variations in the proportions of a particle. It also affects the degree of compaction of samples and stress distribution (inside them) in response to loading.
Angularity, the second order property, reflects variations at the corners, that is, variations superimposed on shape (Masad Eyad et al., 2003). Table 2.4 shows a brief description of the shapes of particle in aggregate.
Surface texture is used to describe the surface irregularity at a scale that is too small to affect the overall shape (Masad Eyad et al., 2003). Surface texture depends on the hardness, grain size and pore characteristic of the parent material, as well as on the degree to which forces acting on the particle surface have smoothed or roughened it.
Figure 2.8: Components of an Aggregate Shape: Shape (form), Angularity, and Texture (Masad Eyad et al., 2003).
The classification of the surface texture is based on the degree to which the particle surfaces are rough, smooth or polished (Topal & Sengoz, 2005). These three properties can be distinguished because of their different scales with respect to particle size, and this feature can also be used to order them. Any of these properties can vary widely without necessarily affecting the other two properties (Masad Eyad et al., 2003). Table 2.5 contains a brief elaboration of the types of surface texture found in aggregate samples.
Table 2.4: Shapes of the particles (BS 812: Part 1: 1975)
Classification Description
Rounded Fully water-worn or completely shaped by attrition, having approximately an equidimensional shape
Irregular Naturally irregular, or partly shaped by attrition and having rounded edges, lacking any symmetry
Angular Possessing well defined edges formed at the intersection of roughly planar faces, Sharp-edged or having roughly polyhedral shape Flaky Material of which the thickness small relative to the other two
dimensions, Plate-like
Elongated Material, usually angular, in which the length is considerably larger than the other two dimensions
Flaky and elongated
Material having the length considerably larger than the width and the width considerably larger than the thickness
Table 2.5: Types of surface texture (BS 812: Part 1: 1975)
Surface texture Characteristics
Glassy Conchoidal fracture
Smooth Water-worn, or smooth due to fracture of laminated or fine-grained rock
Granular Fracture showing more or less uniform rounded grains
Rough Rough fracture of fine-or medium-grained rock containing no easily visible crystalline constituents
Crystalline Containing easily visible crystalline constituents Honeycomb With visible pores and cavities
2.4.2.1 Influences of aggregates characteristics in hot mix asphalt
The degradation of road surfaces such as cracking and deflection can be related to deformations of underlying layers (base, subbase and subgrade). Consequently, the characterisation of these layers received much of the attention during the last 15 years. As high-quality pavements are needed to meet increases in traffic volume and load, the suitability of aggregates to be used in asphaltic mixtures depends on their properties of shape (angular/cubical) and rough surface texture. Generally when cubical particles are used in hot mix asphalt (HMA), it tends to lower its resistance to permanent deformation (rutting). It is the shape and texture which actually determines the resistance of HMA mixes in which they are used to permanent deformation. This is because particle shape, angularity and surface texture affect the dilation of the aggregate structure, the strength of the aggregate particles, the mechanical bond between the aggregate surface with cementing materials, frictional properties and the resistance to sliding of one particle over another (Harold, 2003; Topal & Sengoz, 2005; Kaplan, 1959 & Masad Eyad et al., 2003). Asphaltic mixture properties that are affected by the shape, angularity and surface texture of aggregate include:
i. dynamic stiffness ii. stability
iii. durability iv. permeability
v. resistance to moisture damage vi. air voids in the mixture
vii. Permanent deformation, fatigue resistance and the skid resistance of pavements (Topal & Sengoz, 2005; Herrin & Goetz, 1954; Benson, 1970; Ishai & Gelber, 1982; Kuo & Freeman, 1998 and Maerz, 2004).
Field (1958), and Kandhal and Wenger (1973) found a considerable increase in hot mix asphalt mixtures Marshalls stability due to an increase in the percentage of crushed coarse particles. The use of crushed coarse aggregates caused a significant increase in the Marshall stability of the dense-graded mix stability compared with uncrushed coarse aggregates. The crushed particles are considered to have high number of angularity compared to the uncrushed particles. Aggregates with an angular and cubical with rougher particle surface texture have much greater particle-to-particle contact and results in a larger adhesive force as they bind more securely between the particles and the asphalt cement mix compared to a not cubical and smooth particle surface texture. Rough faces on the aggregate particles also allow higher friction strength to be developed if some load would tend to force one particle to slide over an adjacent particle. Consequently, when asphaltic aggregate mixtures with highly stable and resistance to shearing forces are needed, it is specified that both the coarse aggregate and the fine aggregate must be angular and cubical with rough surface textured crushed stone (Fernlund, 2005; Topal, & Sengoz, 2005 & Harold, 2003). Kandhal et al. (1991) recommended that, if good performance of hot mix asphalt is required, the coarse aggregate which is used in the hot mix asphalt mixtures must have at least 85 percent of particles with two or more fractured faces for heavy-duty wearing and binder courses.
Many highway agencies now limit the amount of not cubical particles in HMA for heavy duty pavements in order to minimize permanent deformation. In the year 1935, there was general agreement among surveyors and road engineers that flaky and elongated material was undesirable in aggregates intended for road use (Hosking, 1992). Flaky particles have a thickness (smallest dimension) of less than 0.6 of their nominal size this size being taken as the mean of the limiting sieve apertures used for determining the size fraction in which the particle occurs while elongated needle-shaped particles have a length (greatest dimension) of more than 1.8 of their nominal size, this size being taken as the mean of the limiting sieve apertures used for determining the size fraction in which the particle occurs. The flaky and elongated particles have long been considered to be undesirable in hot mix asphalt because they have a tendency to break or degrade (especially in open-graded mixtures) during the construction process, tend to develop poor resilient properties in the mix, reduce the durability of road surfaces caused by the weaker bonding and are likely to fail or break under applied traffic and bending stresses more easily than cubical or angular particles. (Kojovic, 1995; Harold, 2003; Buchanan, 2000; Topal, & Sengoz, 2005 & Masad Eyad et al., 2003).
In the Superpave mix design system, an aggregate particle is determined to be flaky and elongated if the maximum (length) to minimum (thickness) dimension ratio is greater than 5. Many specifications restrict the percent of elongated or flaky particles allowed in aggregates or require that a percent of the particles have at least one fractured face or side that has been broken in a gravel crusher (Harold, 2003). An example was the published BS 594:1935 "Rolled Asphalt. Fluxed Lake Asphalt" where it was required that the
aggregate used "shall be angular but not flaky (Hosking, 1992). Other specifications require particles to have two or more fractured faces (Harold, 2003). Stephens and Sinha (1978) reported that HMA mixes containing 30 percent or more flat particles (longest axis to shortest axis is more or equal to three) maintained higher voids content compared to some other blends with less percentage of flat particles.
Additionally, the workability and optimum bitumen content of the mixture are affected by the shape, angularity and surface texture of aggregates. Rounded, smooth textured aggregate has a much better workability than rough textured and angular aggregate (Topal, & Sengoz, 2005). Changes in the angularity of coarse aggregates had a greater effect on the workability than changes in flakiness index (Masad Eyad et al., 2003). The ease of movement of one aggregate particle relative to another is related to the number of contact point between the aggregate particles. The more asphaltic mixtures are workable, the more they are compactable. Researches show that easily compactable asphaltic mixtures can rut easily and quickly under traffic. In contrast, mixtures with low workability prove to be less prone to rutting under same conditions. Because of this reason, in recent years highway engineers have preferred less workable asphaltic mixtures. Angularity of aggregates is a primary factor affecting the workability of asphaltic mixtures (Topal, & Sengoz, 2005).
The shape and surface texture of aggregates may vary from highly angular and rough to fully rounded and smooth, because it is the result of parameters, like:
i. The dominant factor was found to be the reduction ratio (ratio of size of feed to the size o
