Materials for Civil and Construction Engineers 4th Edition PDF

 Materials for Civil and Construction Engineers FOURTH Edition Michael S. Mamlouk...

 Materials for Civil and Construction Engineers FOURTH Edition Michael S. Mamlouk John P. Zaniewski Boston Columbus Indianapolis New York San Francisco Hoboken Amsterdam Cape Town Dubai London Madrid Milan Munich Paris Montreal Toronto Delhi Mexico City São Paulo Sydney Hong Kong Seoul Singapore Taipei Tokyo A01_MAML0533_04_SE_FM.indd 1 12/8/15 2:54 PM  Vice President and Editorial Director, ECS: Director of Operations: Nick Sklitsis ­Marcia J. Horton Operations Specialist: Maura Zaldivar-Garcia Executive Editor: Holly Stark Creative Director: Blair Brown Editorial Assistant: Amanda Brands Art Director: Janet Slowik Executive Marketing Manager: Tim Galligan Cover Design: Black Horse Design Director of Marketing: Christy Lesko Manager, Rights and Permissions: Rachel Product Marketing Manager: Bram van Kempen Youdelman Field Marketing Manager: Demetrius Hall Printer/Binder: RR Donnelley/Crawfordsville Marketing Assistant: Jon Bryant Cover Printer: Phoenix Color/Hagerstown Team Lead Program and Product Management: Composition/Full-Service Project Management: Scott Disanno SPi Global Program Manager: Erin Ault Global HE Director of Vendor Sourcing and ­Procurement: Diane Hynes Copyright © 2017, 2011, 2008, 2005 by Pearson Education, Inc., Hoboken, New Jersey 07030. All rights reserved. Manufactured in the United States of America. This publication is protected by Copyright and permissions should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or ­likewise. To obtain permission(s) to use materials from this work, please submit a written request to Pearson Higher Education, Permissions Department, 221 River Street, Hoboken, NJ 07030. The author and publisher of this book have used their best efforts in preparing this book. These efforts include the development, research, and testing of the theories and programs to determine their ­effectiveness. The author and publisher make no warranty of any kind, expressed or implied, with regard to these programs or the documentation contained in this book. The author and publisher shall not be liable in any event for incidental or c­ onsequential damages in connection with, or arising out of, the furnishing, performance, or use of these programs. Library of Congress Cataloging-in-Publication Data Names: Mamlouk, Michael S. author. | Zaniewski, John P., author. Title: Materials for civil and construction engineers / Michael S. Mamlouk, John P. Zaniewski. Description: Fourth edition. | Hoboken : Pearson Education, Inc., Identifiers: LCCN 2015041953 | ISBN 9780134320533 Subjects: LCSH: Materials. Classification: LCC TA403.M246 2016 | DDC 624.1/8—dc23 LC record available at http://lccn.loc.gov/2015041953 ISBN 10: 0-13-432053-0 ISBN 13: 978-0-13-432053-3 A01_MAML0533_04_SE_FM.indd 2 12/8/15 2:54 PM  Contents Preface xv About the Authors xix One Materials Engineering Concepts 1 1.1 Economic Factors 2 1.2 Mechanical Properties 3 1.2.1 Loading Conditions 4 1.2.2 Stress–Strain Relations 5 1.2.3 Elastic Behavior 5 1.2.4 Elastoplastic Behavior 8 1.2.5 Viscoelastic Behavior 12 1.2.6 Temperature and Time Effects 18 1.2.7 Work and Energy 19 1.2.8 Failure and Safety 20 1.3 Nonmechanical Properties 22 1.3.1 Density and Unit Weight 22 1.3.2 Thermal Expansion 24 1.3.3 Surface Characteristics 25 1.4 Production and Construction 26 1.5 Aesthetic Characteristics 26 1.6 Sustainable Design 27 1.7 Material Variability 29 1.7.1 Sampling 30 1.7.2 Normal Distribution 31 A01_MAML0533_04_SE_FM.indd 3 12/8/15 2:54 PM  iv Contents 1.7.3 Control Charts 31 1.7.4 Experimental Error 34 1.8 Laboratory Measuring Devices 34 1.8.1 Dial Gauge 35 1.8.2 Linear Variable Differential Transformer (LVDT) 37 1.8.3 Strain Gauge 39 1.8.4 Noncontact Deformation Measurement Technique 40 1.8.5 Proving Ring 40 1.8.6 Load Cell 41 Summary 42 Questions and Problems 43 1.9 References 56 Two Nature of Materials 58 2.1 Basic Materials Concepts 58 2.1.1 Electron Configuration 58 2.1.2 Bonding 61 2.1.3 Material Classification by Bond Type 64 2.2 Metallic Materials 64 2.2.1 Lattice Structure 65 2.2.2 Lattice Defects 69 2.2.3 Grain Structure 70 2.2.4 Alloys 73 2.2.5 Phase Diagrams 73 2.2.6 Combined Effects 79 2.3 Inorganic Solids 79 2.4 Organic Solids 81 2.4.1 Polymer Development, Structure, and Cross-Linking 82 2.4.2 Melting and Glass Transition Temperature 85 2.4.3 Mechanical Properties 86 Summary 87 Questions and Problems 87 2.5 References 90 A01_MAML0533_04_SE_FM.indd 4 12/8/15 2:54 PM  Contents v Three Steel 91 3.1 Steel Production 93 3.2 Iron–Carbon Phase Diagram 96 3.3 Heat Treatment of Steel 99 3.3.1 Annealing 99 3.3.2 Normalizing 100 3.3.3 Hardening 101 3.3.4 Tempering 101 3.3.5 Example of Heat Treatment 101 3.4 Steel Alloys 101 3.5 Structural Steel 103 3.5.1 Structural Steel Grades 103 3.5.2 Sectional Shapes 106 3.5.3 Specialty Steels in Structural Applications 107 3.6 Cold-Formed Steel 112 3.6.1 Cold-Formed Steel Grades 112 3.6.2 Cold-Formed Steel Shapes 113 3.6.3 Special Design Considerations for Cold-Formed Steel 115 3.7 Fastening Products 115 3.8 Reinforcing Steel 117 3.8.1 Conventional Reinforcing 117 3.8.2 Steel for Prestressed Concrete 121 3.9 Mechanical Testing of Steel 122 3.9.1 Tension Test 122 3.9.2 Torsion Test 125 3.9.3 Charpy V Notch Impact Test 128 3.9.4 Bend Test 130 3.9.5 Hardness Test 131 3.9.6 Ultrasonic Testing 132 3.10 Welding 132 3.11 Steel Corrosion 135 3.11.1 Methods for Corrosion Resistance 136 3.12 Steel Sustainability 137 3.12.1 LEED Considerations 137 3.12.2 Other Sustainability Considerations 137 A01_MAML0533_04_SE_FM.indd 5 12/8/15 2:54 PM  vi Contents Summary 138 Questions and Problems 138 3.13 References 150 Four Aluminum 152 4.1 Aluminum Production 155 4.2 Aluminum Metallurgy 157 4.2.1 Alloy Designation System 159 4.2.2 Temper Treatments 160 4.3 Aluminum Testing and Properties 163 4.4 Welding and Fastening 168 4.5 Corrosion 169 4.6 Aluminum Sustainability 169 4.6.1 LEED Considerations 169 4.6.2 Other Sustainability Considerations 169 Summary 169 Questions and Problems 170 4.7 References 176 Five Aggregates 177 5.1 Aggregate Sources 178 5.2 Geological Classification 179 5.3 Evaluation of Aggregate Sources 179 5.4 Aggregate Uses 180 5.5 Aggregate Properties 181 5.5.1 Particle Shape and Surface Texture 183 5.5.2 Soundness and Durability 185 5.5.3 Toughness, Hardness, and Abrasion Resistance 186 5.5.4 Absorption 187 A01_MAML0533_04_SE_FM.indd 6 12/8/15 2:54 PM  Contents vii 5.5.5 Specific Gravity 189 5.5.6 Bulk Unit Weight and Voids in Aggregate 191 5.5.7 Strength and Modulus 192 5.5.8 Gradation 193 5.5.9 Cleanness and Deleterious Materials 208 5.5.10 Alkali–Aggregate Reactivity 209 5.5.11 Affinity for Asphalt 211 5.6 Handling Aggregates 212 5.6.1 Sampling Aggregates 212 5.7 Aggregates Sustainability 214 5.7.1 LEED Considerations 214 5.7.2 Other Sustainability Considerations 214 Summary 215 Questions and Problems 215 5.8 References 225 Six Portland Cement, Mixing Water, and Admixtures 227 6.1 Portland Cement Production 227 6.2 Chemical Composition of Portland Cement 228 6.3 Fineness of Portland Cement 230 6.4 Specific Gravity of Portland Cement 231 6.5 Hydration of Portland Cement 231 6.5.1 Structure Development in Cement Paste 233 6.5.2 Evaluation of Hydration Progress 233 6.6 Voids in Hydrated Cement 235 6.7 Properties of Hydrated Cement 235 6.7.1 Setting 235 6.7.2 Soundness 237 6.7.3 Compressive Strength of Mortar 238 6.8 Water–Cement Ratio 238 6.9 Types of Portland Cement 239 6.9.1 Standard Portland Cement Types 240 6.9.2 Other Cement Types 243 A01_MAML0533_04_SE_FM.indd 7 12/8/15 2:54 PM  viii Contents 6.10 Mixing Water 243 6.10.1 Acceptable Criteria 244 6.10.2 Disposal and Reuse of Concrete Wash Water 246 6.11 Admixtures for Concrete 247 6.11.1 Air Entrainers 247 6.11.2 Water Reducers 249 6.11.3 Retarders 253 6.11.4 Hydration-Control Admixtures 254 6.11.5 Accelerators 254 6.11.6 Specialty Admixtures 256 6.12 Supplementary Cementitious Materials 256 6.13 Cement Sustainability 259 6.13.1 LEED Considerations 259 6.13.2 Other Sustainability Considerations 260 Summary 260 Questions and Problems 260 6.14 References 270 Seven Portland Cement Concrete 271 7.1 Proportioning of Concrete Mixes 271 7.1.1 Basic Steps for Weight and Absolute Volume Methods 273 7.1.2 Mixing Concrete for Small Jobs 290 7.2 Mixing, Placing, and Handling Fresh Concrete 293 7.2.1 Ready-Mixed Concrete 293 7.2.2 Mobile Batcher Mixed Concrete 294 7.2.3 Depositing Concrete 294 7.2.4 Pumped Concrete 298 7.2.5 Vibration of Concrete 298 7.2.6 Pitfalls and Precautions for Mixing Water 299 7.2.7 Measuring Air Content in Fresh Concrete 299 7.2.8 Spreading and Finishing Concrete 301 7.3 Curing Concrete 306 7.3.1 Ponding or Immersion 307 7.3.2 Spraying or Fogging 307 A01_MAML0533_04_SE_FM.indd 8 12/8/15 2:54 PM  Contents ix 7.3.3 Wet Coverings 308 7.3.4 Impervious Papers or Plastic Sheets 308 7.3.5 Membrane-Forming Compounds 308 7.3.6 Forms Left in Place 311 7.3.7 Steam Curing 311 7.3.8 Insulating Blankets or Covers 311 7.3.9 Electrical, Hot Oil, and Infrared Curing 311 7.3.10 Curing Period 312 7.4 Properties of Hardened Concrete 312 7.4.1 Early Volume Change 312 7.4.2 Creep Properties 314 7.4.3 Permeability 314 7.4.4 Stress–Strain Relationship 315 7.5 Testing of Hardened Concrete 317 7.5.1 Compressive Strength Test 317 7.5.2 Split-Tension Test 320 7.5.3 Flexure Strength Test 320 7.5.4 Rebound Hammer Test 322 7.5.5 Penetration Resistance Test 322 7.5.6 Ultrasonic Pulse Velocity Test 323 7.5.7 Maturity Test 324 7.6 Alternatives to Conventional Concrete 324 7.6.1 Self-Consolidating Concrete 325 7.6.2 Flowable Fill 327 7.6.3 Shotcrete 328 7.6.4 Lightweight Concrete 330 7.6.5 Heavyweight Concrete 330 7.6.6 High-Strength Concrete 332 7.6.7 Shrinkage-Compensating Concrete 332 7.6.8 Polymers and Concrete 333 7.6.9 Fiber-Reinforced Concrete 333 7.6.10 Roller-Compacted Concrete 334 7.6.11 High-Performance Concrete 334 7.6.12 Pervious Concrete 336 7.7 Concrete Sustainability 337 7.7.1 LEED Considerations 337 7.7.2 Other Sustainability Considerations 339 A01_MAML0533_04_SE_FM.indd 9 12/8/15 2:54 PM  x Contents Summary 339 Questions and Problems 340 7.8 References 355 Eight Masonry 357 8.1 Masonry Units 357 8.1.1 Concrete Masonry Units 358 8.1.2 Clay Bricks 363 8.2 Mortar 366 8.3 Grout 366 8.4 Plaster 367 8.5 Masonry Sustainability 367 8.5.1 LEED Considerations 367 8.5.2 Other Sustainability Considerations 367 Summary 369 Questions and Problems 369 8.6 References 372 Nine Asphalt Binders and Asphalt Mixtures 373 9.1 Types of Asphalt Cement Products 376 9.2 Uses of Asphalt 378 9.3 Temperature Susceptibility of Asphalt 381 9.4 Chemical Properties of Asphalt 384 9.5 Superpave and Performance Grade Binders 386 9.6 Characterization of Asphalt Cement 386 9.6.1 Performance Grade Characterization Approach 386 9.6.2 Performance Grade Binder Characterization 387 9.6.3 Traditional Asphalt Characterization Tests 392 A01_MAML0533_04_SE_FM.indd 10 12/8/15 2:54 PM  Contents xi 9.7 Classification of Asphalt 394 9.7.1 Asphalt Binders 394 9.7.2 Asphalt Cutbacks 400 9.7.3 Asphalt Emulsions 401 9.8 Asphalt Concrete 402 9.9 Asphalt Concrete Mix Design 402 9.9.1 Specimen Preparation in the Laboratory 403 9.9.2 Density and Voids Analysis 406 9.9.3 Superpave Mix Design 409 9.9.4 Superpave Refinement 418 9.9.5 Marshall Method of Mix Design 418 9.9.6 Evaluation of Moisture Susceptibility 426 9.10 Characterization of Asphalt Concrete 427 9.10.1 Indirect Tensile Strength 428 9.10.2 Asphalt Mixture Performance Tester 429 9.11 Hot-Mix Asphalt Concrete Production and Construction 433 9.11.1 Production of Raw Materials 433 9.11.2 Manufacturing Asphalt Concrete 433 9.11.3 Field Operations 434 9.12 Recycling of Asphalt Concrete 437 9.12.1 RAP Evaluation 437 9.12.2 RAP Mix Design 438 9.12.3 RAP Production and Construction 440 9.13 Additives 440 9.13.1 Fillers 440 9.13.2 Extenders 440 9.13.3 Polymer Modified Asphalt 441 9.13.4 Antistripping Agents 442 9.13.5 Others 442 9.14 Warm Mix 442 9.15 Asphalt Sustainability 444 9.15.1 LEED Considerations 444 9.15.2 Other Sustainability Considerations 445 Summary 445 Questions and Problems 446 9.16 References 454 A01_MAML0533_04_SE_FM.indd 11 12/8/15 2:54 PM  xii Contents Ten Wood 456 10.1 Structure of Wood 458 10.1.1 Growth Rings 458 10.1.2 Anisotropic Nature of Wood 460 10.2 Chemical Composition 461 10.3 Moisture Content 462 10.4 Wood Production 465 10.4.1 Cutting Techniques 466 10.4.2 Seasoning 467 10.5 Lumber Grades 468 10.5.1 Hardwood Grades 469 10.5.2 Softwood Grades 470 10.6 Defects in Lumber 471 10.7 Physical Properties 474 10.7.1 Specific Gravity and Density 474 10.7.2 Thermal Properties 475 10.7.3 Electrical Properties 476 10.8 Mechanical Properties 476 10.8.1 Modulus of Elasticity 476 10.8.2 Strength Properties 477 10.8.3 Load Duration 477 10.8.4 Damping Capacity 477 10.9 Testing to Determine Mechanical Properties 478 10.9.1 Flexure Test of Structural Members (ASTM D198) 479 10.9.2 Flexure Test of Small, Clear Specimen (ASTM D143) 481 10.10 Design Considerations 482 10.11 Organisms that Degrade Wood 483 10.11.1 Fungi 483 10.11.2 Insects 483 10.11.3 Marine Organisms 484 10.11.4 Bacteria 484 10.12 Wood Preservation 484 10.12.1 Petroleum-Based Solutions 485 10.12.2 Waterborne Preservatives 485 A01_MAML0533_04_SE_FM.indd 12 12/8/15 2:54 PM  Contents xiii 10.12.3 Application Techniques 486 10.12.4 Construction Precautions 486 10.13 Engineered Wood Products 487 10.13.1 Structural Panels/Sheets 488 10.13.2 Structural Shapes 491 10.13.3 Composite Structural Members 498 10.14 Wood Sustainability 498 10.14.1 LEED Considerations 498 10.14.2 Other Sustainability Considerations 501 Summary 502 Questions and Problems 502 10.15 References 508 Eleven Composites 510 11.1 Microscopic Composites 512 11.1.1 Fiber-Reinforced Composites 513 11.1.2 Particle-Reinforced Composites 516 11.1.3 Matrix Phase 516 11.1.4 Fabrication 517 11.1.5 Civil Engineering Applications 517 11.2 Macroscopic Composites 524 11.2.1 Plain Portland Cement Concrete 524 11.2.2 Reinforced Portland Cement Concrete 525 11.2.3 Asphalt Concrete 526 11.2.4 Engineered Wood 526 11.3 Properties of Composites 527 11.3.1 Ductility and Strength of Composite 528 11.3.2 Modulus of Elasticity of Composite 529 11.4 Composites Sustainability 534 11.4.1 LEED Considerations 534 11.4.2 Other Sustainability Considerations 534 Summary 535 Questions and Problems 535 11.5 References 540 A01_MAML0533_04_SE_FM.indd 13 12/8/15 2:54 PM  xiv Contents Appendix Laboratory Manual 542 1. Introduction to Measuring Devices 543 2. Tension Test of Steel and Aluminum 546 3. Torsion Test of Steel and Aluminum 549 4. Impact Test of Steel 552 5. Microscopic Inspection of Materials 555 6. Creep in Polymers 556 7. Sieve Analysis of Aggregates 560 8. Specific Gravity and Absorption of Coarse Aggregate 564 9. Specific Gravity and Absorption of Fine Aggregate 566 10. Bulk Unit Weight and Voids in Aggregate 568 11. Slump of Freshly Mixed Portland Cement Concrete 571 12. Unit Weight and Yield of Freshly Mixed Concrete 574 13. Air Content of Freshly Mixed Concrete by Pressure Method 576 14. Air Content of Freshly Mixed Concrete by Volumetric Method 578 15. Making and Curing Concrete Cylinders and Beams 580 16. Capping Cylindrical Concrete Specimens with Sulfur or Capping Compound 584 17. Compressive Strength of Cylindrical Concrete Specimens 586 18. Flexural Strength of Concrete 589 19. Rebound Number of Hardened Concrete 592 20. Penetration Resistance of Hardened Concrete 594 21. Testing of Concrete Masonry Units 597 22. Viscosity of Asphalt Binder by Rotational Viscometer 600 23. Dynamic Shear Rheometer Test of Asphalt Binder 602 24. Penetration Test of Asphalt Cement 604 25. Absolute Viscosity Test of Asphalt 606 26. Preparing and Determining the Density of Hot-Mix Asphalt (HMA) Specimens by Means of the Superpave Gyratory Compactor 608 27. Preparation of Asphalt Concrete Specimens Using the Marshall Compactor 611 28. Bulk Specific Gravity of Compacted Bituminous Mixtures 614 29. Marshall Stability and Flow of Asphalt Concrete 616 30. Bending (Flexure) Test of Wood 618 31. Tensile Properties of Composites 624 32. Effect of Fiber Orientation on the Elastic Modulus of Fiber ­ einforced Composites 627 R Index 630 A01_MAML0533_04_SE_FM.indd 14 12/8/15 2:54 PM  Preface A basic function of civil and construction engineering is to provide and maintain the infrastructure needs of society. The infrastructure includes buildings, water treatment and distribution systems, waste water removal and processing, dams, and highway and airport bridges and pavements. Although some civil and construction engineers are involved in the planning process, most are concerned with the design, construction, and maintenance of facilities. The common denominator among these responsibilities is the need to understand the behavior and performance of materials. Although not all civil and construction engineers need to be material specialists, a basic understanding of the material selection process, and the behavior of materials, is a fundamental requirement for all civil and construction engineers performing design, construction, and maintenance. Material requirements in civil engineering and construction facilities are differ- ent from material requirements in other engineering disciplines. Frequently, civil engineering structures require tons of materials with relatively low replications of specific designs. Generally, the materials used in civil engineering have relatively low unit costs. In many cases, civil engineering structures are formed or fabricated in the field under adverse conditions. Finally, many civil engineering structures are directly exposed to detrimental effects of the environment. The subject of engineering materials has advanced greatly in the past few decades. As a result, many of the conventional materials have either been replaced by more efficient materials or modified to improve their performance. Civil and construction engineers have to be aware of these advances and be able to select the most cost-­ effective material or use the appropriate modifier for the specific application at hand. This text is organized into three parts: (1) introduction to materials engineer- ing, (2) characteristics of materials used in civil and construction engineering, and (3) laboratory methods for the evaluation of materials. The introduction to materials engineering includes information on the basic mechanistic properties of materials, environmental influences, and basic material classes. In addition, one of the responsibilities of civil and construction engineers is the inspection and quality control of materials in the construction process. This requires an understanding of material variability and testing procedures. The atomic structure of materials is covered in order to provide basic understanding of material behavior and to relate the molecular structure to the engineering response. The second section, which represents a large portion of the book, presents the characteristics of the primary material types used in civil and construction engineer- ing: steel, aluminum, concrete, masonry, asphalt, wood, and composites. Since the A01_MAML0533_04_SE_FM.indd 15 12/8/15 2:54 PM  xvi Preface discussion of concrete and asphalt materials requires a basic knowledge of aggre- gates, there is a chapter on aggregates. Moreover, since composites are gaining wide acceptance among engineers and are replacing many of the conventional materials, there is a chapter introducing composites. The discussion of each type of material includes information on the following: Basic structure of the materials Material production process Mechanistic behavior of the material and other properties Environmental influences Construction considerations Special topics related to the material discussed in each chapter Finally, each chapter includes an overview of various test procedures to intro- duce the test methods used with each material. However, the detailed description of the test procedures is left to the appropriate standards organizations such as the American Society for Testing and Materials (ASTM) and the American Association of State Highway and Transportation Officials (AASHTO). These ASTM and ­AASHTO standards are usually available in college libraries, and students are encouraged to use them. Also, there are sample problems in most chapters, as well as selected questions and problems at the end of each chapter. Answering these questions and problems will lead to a better understanding of the subject matter. There are volumes of information available for each of these materials. It is not possible, or desirable, to cover these materials exhaustively in an introductory single text. Instead, this book limits the information to an introductory level, concentrates on current practices, and extracts information that is relevant to the general educa- tion of civil and construction engineers. The content of the book is intended to be covered in one academic semester, although quarter system courses can definitely use it. The instructor of the course can also change the emphasis of some topics to match the specific curriculum of the department. Furthermore, since the course usually includes a laboratory portion, a number of laboratory test methods are described. The number of laboratory tests in the book is more than what is needed in a typical semester in order to provide more flexibility to the instructor to use the available equipment. Laboratory tests should be coordinated with the topics covered in the lectures so that the students get the most benefit from the laboratory experience. The first edition of this textbook served the needs of many universities and col- leges. Therefore, the second edition was more of a refinement and updating of the book, with some notable additions. Several edits were made to the steel chapter to improve the description of heat treatments, phase diagram, and the heat-treating effects of welding. Also, a section on stainless steel was added, and current infor- mation on the structural uses of steel was provided. The cement and concrete chap- ters have been augmented with sections on hydration-control admixtures, recycled wash water, silica fume, self-consolidating concrete, and flowable fill. When the first edition was published, the Superpave mix design method was just being intro- duced to the industry. Now Superpave is a well-established method that has been field tested and revised to better meet the needs of the paving community. This A01_MAML0533_04_SE_FM.indd 16 12/8/15 2:54 PM  Preface xvii development required a complete revision to the asphalt chapter to accommodate the current methods and procedures for both Performance Grading of asphalt bind- ers and the Superpave mix design method. The chapter on wood was revised to provide information on recent manufactured wood products that became available in the past several years. Also, since fiber-reinforced polymer composites have been more commonly used in retrofitting old and partially damaged structures, several examples were added in the chapter on composites. In the laboratory manual, an experiment on dry-rodded unit weight of aggregate that is used in portland cement concrete (PCC) proportioning was added, and the experiment on creep of asphalt concrete was deleted for lack of use. What’s New in This Edition The primary focus of the updates presented in this edition was on the sustainability of materials used in civil and construction engineering. The information on sustain- ability in Chapter 1 was updated and expanded to include recent information on sustainability. In addition, a section was added to Chapters 3 through 11 describing the sustainability considerations of each material. The problem set for each chapter was updated and increased to provide some fresh Exercises and to cover other topics discussed in the chapter. References were updated and increased in all chapters to provide students with additional reading on current issues related to different mate- rials. Many figures were added and others were updated throughout the book to pro- vide visual illustrations to students. Other specific updates to the chapters include: Chapter 1 now includes a more detailed section on viscoelastic material behav- ior and a new sample problem. Chapter 3 was updated with recent information about the production of steel. A sample problem was added to Chapter 5 about the water absorbed by aggre- gate in order to highlight the fact that absorbed water is not used to hydrate the cement or improve the workability of plastic concrete. Two new sample problems were added to Chapter 6 on the acceptable ­criteria of mixing water and to clarify the effect of water reducer on the p­ roperties of concrete. Chapter 7 was augmented with a discussion of concrete mixing water and a new sample problem. A section on pervious concrete was added to reflect the current practice on some parking lots and pedestrian walkways. Chapter 9 was updated with reference to the multiple stress creep recovery test, and the information about the immersion compression test was replaced with the tensile strength ratio method to reflect current practices. The selection of the binder was refined to incorporate the effect of load and speed. The section on the diameteral tensile resilient modulus was removed for lack of use. The sample problem on the diameteral tensile resilient modulus was also removed and replaced with a sample problem on the freeze-thaw test and the tensile strength ratio. A01_MAML0533_04_SE_FM.indd 17 12/8/15 2:54 PM  xviii Preface Chapter 10 was updated to include more information about wood deteriora- tion and preservation. The first two sample problems were edited to provide more accurate solutions since the shrinkage values used in wood are related to the green dimensions at or above the fiber saturation point (FSP), not the dry dimensions. The third sample problem was expanded to demonstrate how to determine the modulus of elasticity using the third-point bending test. Chapter 11 was updated to reflect information about the effective length of fib- ers and the ductility of fiber-reinforced polymers (FRP). The discussion was expanded with several new figures to incorporate fibers, fabrics, laminates, and composites used in civil engineering applications. The first sample problem was expanded to apply other concepts covered in the chapter. The laboratory manual in the appendix was updated to include two new exper- iments on creep in polymers and the effect of fiber orientation on the elastic modulus of fiber reinforced composites. The experiment on the tensile proper- ties of composites was updated. This would allow more options to the instruc- tor to choose from in assigning lab experiments to students. Acknowledgments The authors would like to acknowledge the contributions of many people who assisted with the development of this new edition. First, the authors wish to thank the reviewers and recognize the fact that most of their suggestions have been incor- porated into the fourth edition, in particular Dr. Dimitrios Goulias of University of Maryland, Tyler Witthuhn of the National Concrete Masonry Association, Mr. Philip Line of American Wood Council, Dr. Baoshan Huang of University of Tennessee, and Dr. Steve Krause of Arizona State University. Appreciation is also extended to Drs. Narayanan Neithalath, Shane Underwood, Barzin Mobasher, and Kamil Kaloush of Arizona State University for their valuable technical contributions. The photos of FRP materials contributed by Dr. Hota GangaRao of the Constructed Facilities Center at West Virginia University are appreciated. Appreciation also goes to Dr. Javed Bari, formerly with the Arizona Department of Transportation for his contribution in pre- paring the slides and to Dr. Mena Souliman of the University of Texas at Tyler for his contribution in the preparation of the solution manual. A01_MAML0533_04_SE_FM.indd 18 12/8/15 2:54 PM  About the Authors Michael S. Mamlouk is a Professor of Civil, Environmental, and Sustainable Engi- neering at Arizona State University. He has many years of experience in teaching courses of civil engineering materials and other related subjects at both the under- graduate and graduate levels. He has been actively involved in teaching materials and pavement design courses to practicing engineers. Dr. Mamlouk has directed many research projects and is the author of numerous publications in the fields of pavement and materials. He is a professional engineer in the state of Arizona. Dr. Mamlouk is a fellow of the American Society of Civil Engineers and a member of several other professional societies. John P. Zaniewski is the Asphalt Technology Professor in the Civil and Envi- ronmental Engineering Department of West Virginia University. Dr. Zaniewski earned teaching awards at both WVU and Arizona State University. In addition to materials, Dr. Zaniewski teaches graduate and undergraduate courses in pavement materials, design and management, and construction engineering and management. Dr. Zaniewski has been the principal investigator on numerous research projects for state, federal, and international sponsors. He is a member of several professional societies and has been a registered engineer in three states. He is the director of the WV Local Technology Assistance Program and has been actively involved in adult education related to pavement design and materials. A01_MAML0533_04_SE_FM.indd 19 12/8/15 2:54 PM  This page intentionally left blank A01_MAML0533_04_SE_FM.indd 22 1/18/16 9:37 PM  C h a p t e r 1 Materials Engineering Concepts Materials engineers are responsible for the selection, specification, and quality control of materials to be used in a job. These materials must meet certain classes of criteria or materials properties (Ashby and Jones, 2011). These classes of criteria include economic factors mechanical properties nonmechanical properties production/construction considerations aesthetic properties In addition to this traditional list of criteria, civil engineers must be concerned with environmental quality. In 1997, the ASCE Code of Ethics was modified to include “sustainable development” as an ethics issue. Sustainable development basically recognizes the fact that our designs should be sensitive to the ability of future gen- erations to meet their needs. There is a strong tie between the materials selected for design and sustainable development. When engineers select the material for a specific application, they must consider the various criteria and make compromises. Both the client and the purpose of the facility or structure dictate, to a certain extent, the emphasis that will be placed on the different criteria. Civil and construction engineers must be familiar with materials used in the con- struction of a wide range of structures. Materials most frequently used include steel, aggregate, concrete, masonry, asphalt, and wood. Materials used to a lesser extent include aluminum, glass, plastics, and fiber-reinforced composites. Geotechnical engineers make a reasonable case for including soil as the most widely used engineer- ing material, since it provides the basic support for all civil engineering structures. However, the properties of soils will not be discussed in this text because soil proper- ties are generally the topic of a separate course in civil and construction engineering curriculums. Recent advances in the technology of civil engineering materials have resulted in the development of better quality, more economical, and safer materials. These M01_MAML0533_04_SE_C01.indd 1 12/2/15 4:28 PM  2 Chapter 1   Materials Engineering Concepts materials are commonly referred to as high-performance materials. Because more is known about the molecular structure of materials and because of the continuous research efforts by scientists and engineers, new materials such as polymers, adhe- sives, composites, geotextiles, coatings, cold-formed metals, and various synthetic products are competing with traditional civil engineering materials. In addition, improvements have been made to existing materials by changing their molecular structures or including additives to improve quality, economy, and performance. For example, superplasticizers have made a breakthrough in the concrete indus- try, allowing the production of much stronger concrete. Joints made of elastomeric materials have improved the safety of high-rise structures in earthquake-active areas. Lightweight synthetic aggregates have decreased the weight of concrete structures, allowing small cross-sectional areas of components. Polymers have been mixed with asphalt, allowing pavements to last longer under the effect of vehicle loads and envi- ronmental conditions. The field of fiber composite materials has developed rapidly in the past 30 years. Many recent civil engineering projects have used fiber-reinforced polymer compos- ites. These advanced composites compete with traditional materials due to their higher strength-to-weight ratio and their ability to overcome such shortcomings as corrosion. For example, fiber-reinforced concrete has much greater toughness than conventional portland cement concrete. Composites can replace reinforcing steel in concrete struc- tures. In fact, composites have allowed the construction of structures that could not have been built in the past. The nature and behavior of civil engineering materials are as complicated as those of materials used in any other field of engineering. Due to the high quantity of materi- als used in civil engineering projects, the civil engineer frequently works with locally available materials that are not as highly refined as the materials used in other engi- neering fields. As a result, civil engineering materials frequently have highly variable properties and characteristics. This chapter reviews the manner in which the properties of materials affect their selection and performance in civil engineering applications. In addition, this chapter reviews some basic definitions and concepts of engineering mechanics required for understanding material behavior. The variable nature of material properties is also dis- cussed so that the engineer will understand the concepts of precision and accuracy, sampling, quality assurance, and quality control. Finally, instruments used for measur- ing material response are described. 1.1 Economic Factors The economics of the material selection process are affected by much more than just the cost of the material. Factors that should be considered in the selection of the material include availability and cost of raw materials manufacturing costs M01_MAML0533_04_SE_C01.indd 2 12/2/15 4:28 PM  Section 1.2  Mechanical Properties 3 transportation placing maintenance The materials used for civil engineering structures have changed over time. Early structures were constructed of stone and wood. These materials were in ready supply and could be cut and shaped with available tools. Later, cast iron was used, because mills were capable of crudely refining iron ore. As the industrial revolu- tion took hold, quality steel could be produced in the quantities required for large structures. In addition, portland cement, developed in the mid-1800s, provided civil engineers with a durable inexpensive material with broad applications. Due to the efficient transportation system in the United States, availability is not as much of an issue as it once was in the selection of a material. However, transporta- tion can significantly add to the cost of the materials at the job site. For example, in many locations in the United States, quality aggregates for concrete and asphalt are in short supply. The closest aggregate source to Houston, Texas, is 150 km (90 miles) from the city. This haul distance approximately doubles the cost of the aggregates in the city, and hence puts concrete at a disadvantage compared with steel. The type of material selected for a job can greatly affect the ease of construc- tion and the construction costs and time. For example, the structural members of a steel-frame building can be fabricated in a shop, transported to the job site, lifted into place with a crane, and bolted or welded together. In contrast, for a reinforced concrete building, the forms must be built; reinforcing steel placed; concrete mixed, placed, and allowed to cure; and the forms removed. Constructing the concrete frame building can be more complicated and time consuming than constructing steel struc- tures. To overcome this shortcoming, precast concrete units commonly have been used, especially for bridge construction. All materials deteriorate over time and with use. This deterioration affects both the maintenance cost and the useful life of the structure. The rate of deterioration varies among materials. Thus, in analyzing the economic selection of a material, the life cycle cost should be evaluated in addition to the initial costs of the structure. 1.2 Mechanical Properties The mechanical behavior of materials is the response of the material to external loads. All materials deform in response to loads; however, the specific response of a material depends on its properties, the magnitude and type of load, and the geome- try of the element. Whether the material “fails” under the load conditions depends on the failure criterion. Catastrophic failure of a structural member, resulting in the collapse of the structure, is an obvious material failure. However, in some cases, the failure is more subtle, but with equally severe consequences. For example, pavement may fail due to excessive roughness at the surface, even though the stress levels are well within the capabilities of the material. A building may have to be closed due to excessive vibrations by wind or other live loads, although it could be structurally sound. These are examples of functional failures. M01_MAML0533_04_SE_C01.indd 3 12/2/15 4:28 PM  4 Chapter 1   Materials Engineering Concepts 1.2.1 Loading Conditions One of the considerations in the design of a project is the type of loading that the structure will be subjected to during its design life. The two basic types of loads are static and dynamic. Each type affects the material differently, and frequently the interactions between the load types are important. Civil engineers encounter both when designing a structure. Static loading implies a sustained loading of the structure over a period of time. Generally, static loads are slowly applied such that no shock or vibration is ­generated in the structure. Once applied, the static load may remain in place or be removed slowly. Loads that remain in place for an extended period of time are called sustained (dead) loads. In civil engineering, much of the load the materials must carry is due to the weight of the structure and equipment in the structure. Loads that generate a shock or vibration in the structure are dynamic loads. Dynamic loads can be classified as periodic, random, or transient, as shown in ­Figure 1.1 (Richart et al., 1970). A periodic load, such as a harmonic or sinusoidal load, repeats itself with time. For example, rotating equipment in a building can produce a vibratory load. In a random load, the load pattern never repeats, such as that produced by earthquakes. Transient load, on the other hand, is an impulse load that is applied over a short time interval, after which the vibrations decay until the Force Time (a) Force Time (b) Force Time F i g u r e 1. 1 Types of dynamic loads: (a) periodic, (b) random, and (c) (c) transient. M01_MAML0533_04_SE_C01.indd 4 12/2/15 4:28 PM  Section 1.2  Mechanical Properties 5 system returns to a rest condition. For example, bridges must be designed to with- stand the transient loads of trucks. 1.2.2 Stress–Strain Relations Materials deform in response to loads or forces. In 1678, Robert Hooke published the first findings that documented a linear relationship between the amount of force applied to a member and its deformation. The amount of deformation is proportional to the properties of the material and its dimensions. The effect of the dimensions can be normalized. Dividing the force by the cross-sectional area of the specimen normalizes the effect of the loaded area. The force per unit area is defined as the stress s in the specimen (i.e., s = force/area). Dividing the deformation by the orig- inal length is defined as strain ε of the specimen (i.e., e = change in length/original length). Much useful information about the material can be determined by plotting the stress–strain diagram. Figure 1.2 shows typical uniaxial tensile or compressive stress–strain curves for several engineering materials. Figure 1.2(a) shows a linear stress–strain relationship up to the point where the material fails. Glass and chalk are typical of materials exhibiting this tensile behavior. Figure 1.2(b) shows the behavior of steel in tension. Here, a linear relationship is obtained up to a certain point (proportional limit), after which the material deforms without much increase in stress. On the other hand, alu- minum alloys in tension exhibit a linear stress–strain relationship up to the propor- tional limit, after which a nonlinear relation follows, as illustrated in Figure 1.2(c). Figure 1.2(d) shows a nonlinear relation throughout the whole range. Concrete and other materials exhibit this relationship, although the first portion of the curve for concrete is very close to being linear. Soft rubber in tension differs from most materi- als in such a way that it shows an almost linear stress–strain relationship followed by a reverse curve, as shown in Figure 1.2(e). 1.2.3 Elastic Behavior If a material exhibits true elastic behavior, it must have an instantaneous response (deformation) to load, and the material must return to its original shape when the load is removed. Many materials, including most metals, exhibit elastic behavior, at Stress Stress Stress Stress Stress Strain Strain Strain Strain Strain (a) (b) (c) (d) (e) F i g u r e 1. 2 Typical uniaxial stress–strain diagrams for some engineering ­materials: (a) glass and chalk, (b) steel, (c) aluminum alloys, (d) concrete, and (e) soft rubber. M01_MAML0533_04_SE_C01.indd 5 12/2/15 4:28 PM  6 Chapter 1   Materials Engineering Concepts least at low stress levels. As will be discussed in Chapter 2, elastic deformation does not change the arrangement of atoms within the material, but rather it stretches the bonds between atoms. When the load is removed, the atomic bonds return to their original position. Young observed that different elastic materials have different proportional con- stants between stress and strain. For a homogeneous, isotropic, and linear elastic mate- rial, the proportional constant between normal stress and normal strain of an axially loaded member is the modulus of elasticity or Young’s modulus, E, and is equal to s E = (1.1) e where s is the normal stress and ε is the normal strain. In the axial tension test, as the material is elongated, there is a reduction of the cross section in the lateral direction. In the axial compression test, the opposite is true. The ratio of the lateral strain, εl, to the axial strain, εa, is Poisson’s ratio, - el v = (1.2) ea Since the axial and lateral strains will always have different signs, the negative sign is used in Equation 1.2 to make the ratio positive. Poisson’s ratio has a theoreti- cal range of 0.0 to 0.5, where 0.0 is for a compressible material in which the axial and lateral directions are not affected by each other. The 0.5 value is for a material that does not change its volume when the load is applied. Most solids have Poisson’s ratios between 0.10 and 0.45. Although Young’s modulus and Poisson’s ratio were defined for the uniaxial stress condition, they are important when describing the three-dimensional stress– strain relationships, as well. If a homogeneous, isotropic cubical element with linear elastic response is subjected to normal stresses sx, sy, and sz in the three orthogonal directions (as shown in Figure 1.3), the normal strains εx, εy, and εz can be computed by the generalized Hooke’s law, sx - v(sy + sz) ex = E sy - v(sz + sx) ey = E sz - v(sx + sy) ez = (1.3) E sz sy sx Figure 1.3 Normal stresses applied on a cubical element. M01_MAML0533_04_SE_C01.indd 6 12/2/15 4:28 PM  Section 1.2  Mechanical Properties 7 Sample Problem 1.1 A cube made of an alloy with dimensions of 50 mm * 50 mm * 50 mm is placed into a pressure chamber and subjected to a pressure of 90 MPa. If the modulus of elasticity of the alloy is 100 GPa and Poisson’s ratio is 0.28, what will be the length of each side of the cube, assuming that the material remains within the elastic region? Solution Ex = [Sx - n(Sy + Sz)]/E = [ -90 - 0.28 * (-90 - 90)]/100,000 = - 0.000396 m/m Ey = Ez = - 0.000396 m/m 𝚫x = 𝚫y = 𝚫z = -0.000396 * 50 = - 0.0198 mm Lnew = 50 - 0.0198 = 49.9802 mm Linearity and elasticity should not be confused. A linear material’s stress–strain relationship follows a straight line. An elastic material returns to its original shape when the load is removed and reacts instantaneously to changes in load. For exam- ple, Figure 1.4(a) represents a linear elastic behavior, while Figure 1.4(b) represents a nonlinear elastic behavior. For materials that do not display any linear behavior, such as concrete and soils, determining a Young’s modulus or elastic modulus can be problematical. There are several options for arbitrarily defining the modulus for these materials. Figure 1.5 shows four options: the initial tangent, tangent, secant, and chord moduli. The ini- tial tangent modulus is the slope of the tangent of the stress–strain curve at the ori- gin. The tangent modulus is the slope of the tangent at a point on the stress–strain curve. The secant modulus is the slope of a chord drawn between the origin and an arbitrary point on the stress–strain curve. The chord modulus is the slope of a chord drawn between two points on the stress–strain curve. The selection of which modulus to use for a nonlinear material depends on the stress or strain level at which the material typically is used. Also, when determining the tangent, secant, or chord modulus, the stress or strain levels must be defined. Table 1.1 shows typical modulus and Poisson’s ratio values for some materials at room temperature. Note that some materials have a range of modulus values rather Loading Loading Stress Stress Unloading Unloading Strain Strain F i g u r e 1. 4 Elastic behavior: (a) linear and (b) nonlinear. (a) (b) M01_MAML0533_04_SE_C01.indd 7 12/2/15 4:28 PM  8 Chapter 1   Materials Engineering Concepts Initial Tangent tangent modulus modulus Chord modulus Stress Secant modulus Strain Figure 1.5 Methods for approximating modulus. than a distinct value. Several factors affect the modulus, such as curing level and proportions of components of concrete or the direction of loading relative to the grain of wood. 1.2.4 Elastoplastic Behavior For some materials, as the stress applied on the specimen is increased, the strain will proportionally increase up to a point; after this point, the strain will increase with little additional stress. In this case, the material exhibits linear elastic behavior Table 1.1 Typical Modulus and Poisson’s Ratio Values (Room Temperature) Material Modulus GPa (psi * 106) Poisson’s Ratio Aluminum 69–75 (10–11) 0.33 Brick 10–17 (1.5–2.5) 0.23–0.40 Cast iron 75–169 (11–23) 0.17 Concrete 14–40 (2–6) 0.11–0.21 Copper 110 (16) 0.35 Epoxy 3–140 (0.4–20) 0.35–0.43 Glass 62–70 (9–10) 0.25 Limestone 58 (8.4) 0.2–0.3 Rubber (soft) 0.001–0.014 (0.00015–0.002) 0.49 Steel 200 (29) 0.27 Tungsten 407 (59) 0.28 Wood 6–15 (0.9–2.2) 0.29–0.45 M01_MAML0533_04_SE_C01.indd 8 12/2/15 4:28 PM  Section 1.2  Mechanical Properties 9 Stress Stress Stress Strain Strain Strain Plastic Elastic strain strain (elastic recovery) (a) (b) (c) F i g u r e 1. 6 Stress–strain behavior of plastic materials: (a) example of ­loading and unloading, (b) elastic–perfectly plastic, and (c) elasto–plastic with strain hardening. followed by plastic response. The stress level at which the behavior changes from elastic to plastic is the elastic limit. When the load is removed from the specimen, some of the deformation will be recovered and some of the deformation will remain as seen in Figure 1.6(a). As discussed in Chapter 2, plastic behavior indicates perma- nent deformation of the specimen so that it does not return to its original shape when the load is removed. This indicates that when the load is applied, the atomic bonds stretch, creating an elastic response; then the atoms actually slip relative to each other. When the load is removed, the atomic slip does not recover; only the atomic stretch is recovered (Callister, 2006). Several models are used to represent the behavior of materials that exhibit both elastic and plastic responses. Figure 1.6(b) shows a linear elastic–perfectly plastic response in which the material exhibits a linear elastic response upon loading, fol- lowed by a completely plastic response. If such material is unloaded after it has plasticly deformed, it will rebound in a linear elastic manner and will follow a straight line parallel to the elastic portion, while some permanent deformation will remain. If the material is loaded again, it will have a linear elastic response followed by ­plastic response at the same level of stress at which the material was unloaded (Popov, 1968). Figure 1.6(c) shows an elastoplastic response in which the first portion is an elastic response followed by a combined elastic and plastic response. If the load is removed after the plastic deformation, the stress–strain relationship will follow a straight line parallel to the elastic portion; consequently, some of the strain in the material will be removed, and the remainder of the strain will be permanent. Upon reloading, the material again behaves in a linear elastic manner up to the stress level that was attained in the previous stress cycle. After that point the material will follow the original stress–strain curve. Thus, the stress required to cause plas- tic deformation actually increases. This process is called strain hardening or work hardening. Strain hardening is beneficial in some cases, since it allows more stress to be applied without permanent deformation. In the production of cold-formed steel framing members, the permanent deformation used in the production process M01_MAML0533_04_SE_C01.indd 9 12/2/15 4:28 PM  10 Chapter 1   Materials Engineering Concepts can double the yield strength of the member relative to the original strength of the steel. Some materials exhibit strain softening, in which plastic deformation causes weakening of the material. Portland cement concrete is a good example of such a material. In this case, plastic deformation causes microcracks at the interface between aggregate and cement paste. Sample Problem 1.2 An elastoplastic material with strain hardening has the stress–strain relationship shown in Figure 1.6(c). The modulus of elasticity is 25 * 106 psi, yield strength is 70 ksi, and the slope of the strain-hardening portion of the stress–strain diagram is 3 * 106 psi. a. Calculate the strain that corresponds to a stress of 80 ksi. b. If the 80-ksi stress is removed, calculate the permanent strain. Solution (a) E = (70,000/25 * 106) + [(80,000 - 70,000)/(3 * 106)] = 0.0028 + 0.0033 = 0.0061 in./in. (b) Epermanent = 0.0061 - [80,000/(25 * 106)] = 0.0061 - 0.0032 = 0.0029 in./in. Materials that do not undergo plastic deformation prior to failure, such as con- crete, are said to be brittle, whereas materials that display appreciable plastic defor- mation, such as mild steel, are ductile. Generally, ductile materials are preferred for construction. When a brittle material fails, the structure can collapse in a cata- strophic manner. On the other hand, overloading a ductile material will result in distortions of the structure, but the structure will not necessarily collapse. Thus, the ductile material provides the designer with a margin of safety. Figure 1.7(a) demonstrates three concepts of the stress–strain behavior of elasto- plastic materials. The lowest point shown on the diagram is the proportional limit, defined as the transition point between linear and nonlinear behavior. The second point is the elastic limit, which is the transition between elastic and plastic behavior. However, most materials do not display an abrupt change in behavior from elas- tic to plastic. Rather, there is a gradual, almost imperceptible transition between the behaviors, making it difficult to locate an exact transition point (Polowski and Ripling, 2005). For this reason, arbitrary methods such as the offset and the exten- sion methods, are used to identify the elastic limit, thereby defining the yield stress (yield strength). In the offset method, a specified offset is measured on the abscissa, and a line with a slope equal to the initial tangent modulus is drawn through this M01_MAML0533_04_SE_C01.indd 10 12/2/15 4:28 PM  Section 1.2  Mechanical Properties 11 Elastic limit 0.2% offset 0.5% extension yield strength yield strength Stress Stress Proportional limit Strain, % Strain, % 0.2% 0.5% (a) (b) F i g u r e 1. 7 Methods for estimating yield stress: (a) offset method and (b) extension method. point. The point where this line intersects the stress–strain curve is the offset yield stress of the material, as seen in Figure 1.7(a). Different offsets are used for different materials (Table 1.2). The extension yield stress is located where a vertical projec- tion, at a specified strain level, intersects the stress–strain curve. Figure 1.7(b) shows the yield stress corresponding to 0.5% extension. Sample Problem 1.3 A rod made of aluminum alloy, with a gauge length of 100 mm, diameter of 10 mm, and yield strength of 150 MPa, was subjected to a tensile load of 5.85 kN. If the gauge length was changed to 100.1 mm and the diameter was changed to 9.9967 mm, calculate the modulus of elasticity and Poisson’s ratio. Solution S = P/A = (5850 N)/[P(5 * 10-3 m)2] = 74.5 * 106 Pa = 74.5 MPa Since the applied stress is well below the yield strength, the material is within the elastic region. Ea = 𝚫L/L = (100.1 - 100)/100 = 0.001 E = S/Ea = 74.5/0.001 = 74,500 MPa = 74.5 GPa El = change in diameter/diameter = (9.9967 - 10)/10 = - 0.00033 N = - el/ea = 0.00033/0.001 = 0.33 M01_MAML0533_04_SE_C01.indd 11 12/2/15 4:28 PM  12 Chapter 1   Materials Engineering Concepts Table 1.2 Offset Values Typically Used to Determine Yield Stress Material Stress Condition Offset (%) Corresponding Strain Steel Tension 0.20 0.0020 Wood Compression parallel to grain 0.05 0.0005 Gray cast iron Tension 0.05 0.0005 Concrete Compression 0.02 0.0002 Aluminum alloys Tension 0.20 0.0020 Brass and bronze Tension 0.35 0.0035 1.2.5 Viscoelastic Behavior The previous discussion assumed that the strain was an immediate response to stress. This is an assumption for elastic and elastoplastic materials. However, no material has this property under all conditions. In some cases, materials exhibit both viscous and elastic responses, which are known as viscoelastic. Typical viscoelastic materials used in construction applications are asphalt and plastics. Time-Dependent Response Viscoelastic materials have a delayed response to load application. For example, Figure 1.8(a) shows a sinusoidal axial load applied on a viscoelastic material, such as asphalt concrete, versus time. Figure 1.8(b) shows the Applied load (a) Time Time lag Resulting deformation (b) Time Figure 1.8 Load-deformation response of a viscoelastic material. M01_MAML0533_04_SE_C01.indd 12 12/2/15 4:28 PM  Section 1.2  Mechanical Properties 13 Direction of particle motion Direction of wave propagation Consecutive times t1 t2 t3 t4 t5 t6 F i g u r e 1. 9 Delay of propagation of compression and dilation waves in a Slinky®. resulting deformation versus time, where the deformation lags the load—that is, the maximum deformation of the sample occurs after the maximum load is applied. The amount of time delayed of the deformation depends on the material characteristics and the temperature. The delay in the response of viscoelastic materials can be simulated by the move- ment of the Slinky® toy in the hand of a child, as illustrated in Figure 1.9. As the child moves her hand up and down, waves of compression and dilation are devel- oped in the Slinky. However, the development of the waves in the Slinky does not happen exactly at the same time as the movements of the child’s hand. For example, a compression wave could be propagating in one part of the Slinky at the same time when the child is moving her hand upward and vice versa. This occurs because of the delay in response relative to the action. Typical viscoelastic civil engineering materials, such as asphalt, have the same behavior, although they are not as flexible as a Slinky. There are several mechanisms associated with time-dependent deformation, such as creep and viscous flow. There is no clear distinction between these terms. Creep is generally associated with long-term deformations and can occur in metals, ionic and covalent crystals, and amorphous materials. On the other hand, viscous flow is asso- ciated only with amorphous materials and can occur under short-term load dura- tion. For example, concrete, a material with predominantly covalent crystals, can creep over a period of decades. Asphalt concrete pavements, an amorphous-binder M01_MAML0533_04_SE_C01.indd 13 12/2/15 4:28 PM  14 Chapter 1   Materials Engineering Concepts material, can have ruts caused by the accumulated effect of viscous flows resulting from traffic loads with a load duration of only a fraction of a second. Creep of metals is a concern at elevated temperatures. Steel can creep at tem- peratures greater than 30% of the melting point on the absolute scale. This can be a concern in the design of boilers and nuclear reactor containment vessels. Creep is also considered in the design of wood and advanced composite structural mem- bers. Wood elements loaded for a few days can carry higher stresses than elements designed to carry “permanent” loads. On the other hand, creep of concrete is associ- ated with microcracking at the interface of the cement paste and the aggregate parti- cles (Mehta and Monteiro, 2013). The viscous flow models are similar in nature to Hooke’s law. In linearly viscous materials, the rate of deformation is proportional to the stress level. These materials are not compressible and do not recover when the load is removed. Materials with these characteristics are Newtonian fluids. Figure 1.10(a) shows a typical creep test in which a constant compressive stress is applied to an asphalt concrete specimen. In this case, an elastic strain will develop, followed by time-dependent strain or creep. If the specimen is unloaded, a part of the strain will recover instantaneously, while the remaining strain will recover, either completely or partially, over a period of time. Another phenomenon typical of time-dependent materials is relaxation, or dissipation of stresses with time. For example, if an asphalt concrete specimen is placed in a loading machine and subjected to a constant strain, the stress within the specimen will initially be high, then gradually dissipate due to relaxation as shown in Figure 1.10(b). Relaxation is an important concern in the selection of steel for a prestressed con- crete design. In viscoelasticity, there are two approaches used to describe how stresses, strains, and time are interrelated. One approach is to postulate mathematical Stress Strain Time Time Creep Elastic rebound Stress Strain Relaxation Elastic Recovery strain Time Time (a) (b) Figure 1.10 Behavior of time-dependent materials: (a) creep and (b) relaxation. M01_MAML0533_04_SE_C01.indd 14 12/2/15 4:28 PM  Section 1.2  Mechanical Properties 15 relations between these parameters based on material functions obtained from laboratory tests. The other approach is based on combining a number of discrete rheological elements to form rheological models, which describe the material response. Rheological Models Rheological models are used to model mechanically the time- dependent behavior of materials. There are many different modes of material defor- mation, particularly in polymer materials. These materials cannot be described as simply elastic, viscous, etc. However, these materials can be modeled by a combina- tion of simple physical elements. The simple physical elements have characteris- tics that can be easily visualized. Rheology uses three basic elements, combined in either series or parallel to form models that define complex material behaviors. The three basic rheological elements, Hookean, Newtonian, and St. Venant, are shown in ­Figure 1.11 (Polowski and Ripling, 2005). The Hookean element, as in Figure 1.11(a), has the characteristics of a linear spring. The deformation d is proportional to force F by a constant M: F = Md (1.4) This represents a perfectly linear elastic material. The response to a force is instantaneous and the deformation is completely recovered when the force is removed. Thus, the Hookean element represents a perfectly linear elastic material. A Newtonian element models a perfectly viscous material and is modeled as a dashpot or shock absorber as seen in Figure 1.11(b). The deformation for a given level of force is proportional to the amount of time the force is applied. Hence, the rate of deformation, for a constant force, is a constant b: # F = bd (1.5) F F t t 0 0 d d F F t t 0 0 (a) (b) F FO FO F d 0 (c) F i g u r e 1. 1 1 Basic elements used in rheology: (a) Hookean, (b) New- tonian, and (c) St. Venant. M01_MAML0533_04_SE_C01.indd 15 12/2/15 4:28 PM  16 Chapter 1   Materials Engineering Concepts The dot above the d defines this as the rate of deformation with respect to time. If d = 0 at time t = 0 when a constant force F is applied, the deformation at time t is Ft d = (1.6) b When the force is removed, the specimen retains the deformed shape. There is no recovery of any of the deformation. The St. Venant element, as seen in Figure 1.11(c), has the characteristics of a sliding block that resists movement by friction. When the force F applied to the ele- ment is less than the critical force FO, there is no movement. If the force is increased to overcome the static friction, the element will slide and continue to slide as long as the force is applied. This element is unrealistic, since any sustained force sufficient to cause movement would cause the block to accelerate. Hence, the St. Venant ele- ment is always used in combination with the other basic elements. The basic elements are usually combined in parallel or series to model material response. Figure 1.12 shows the three primary two-component models: the Maxwell, Kelvin, and Prandtl models. The Maxwell and Kelvin models have a spring and dashpot in series and parallel, respectively. The Prandtl model uses a spring and St. Venant elements in series. In the Maxwell model [Figure 1.12(a)], the total deformation is the sum of the deformations of the individual elements. The force in each of the elements must be equal to the total force (F = F1 = F2). Thus, the equation for the total deformation at any time after a constant load is applied is simply: F Ft d = d1 + d2 = + (1.7) M b In the Kelvin model, Figure 1.12(b), the deformation of each of the elements must be equal at all times due to the way the model is formulated. Thus, the total deforma- tion is equal to the deformation of each element (d = d1 = d2). Since the elements are in parallel, they will share the force such that the total force is equal to the sum of the force in each element. If d = 0 at time t = 0 when a constant force F is applied,