Proceedings ofThe Tenth Arab Structural Engineering Conference13 15 November, 2006 KuwaitEditorsHusain Al-Khayat and Mohamed Abdel-RohmanSponsorsKuwait University (KU)Kuwait Society of Engineers (KSE) Kuwait Foundation for Advancement of Science (KFAS)Co-SponsorsKuwait Institute for Scientific Research (KISR) Kuwait National Petroleum Company (KNPC)American Society of Civil Engineers PrefaceThe main objective of the Arab Structural Engineering Conference (ASEC) is to provide a forum for the structural engineering researchers and engineers to discuss their recent research results and applications in the area of structural engineering. The conference is held every two or three years in an Arab Country. The first conference was held in 1985 in Egypt, the second conference was in 1987 in Jordan, the third conference was in 1989 in the United Arab Emirates, the fourth conference was in 1991 in Egypt, the fifth was in 1993 in Libya, the sixth was in 1995 in Syria, the seventh was in 1997 in Kuwait, the eighth was in 2000 in Egypt, the ninth was in 2003 in the United Arab Emirates. The current conference is the tenth which is held in Kuwait during the period from 13 to 15 November 2006. The conference was organized by the Department of Civil Engineering in Kuwait University and the Kuwait Society of Engineers. The main sponsors were Kuwait University (KU), Kuwait Society of Engineers (KSE) and Kuwait Foundation for the Advancement of Sciences (KFAS). The co-sponsors were Kuwait Institute for Scientific Research (KISR) and Kuwait National Petroleum Company (KNPC). The organizers invited five world known speakers from Australia, Turkey, UK and USA to present state of art papers in their specialties. The main topics of the papers presented in the conference are: Composite and steel structures Construction Management Damage assessment Materials Reinforced concrete structures Soil-structure interaction Structural analysis Structural behavior Structural design Structural repair Structural testingEach abstract or paper was subjected to the review process by two specialized referees. The total number of full-length papers which were received and met the deadlines was 86 papers from which 68 papers were accepted for the presentation and included in this proceedings.The organizing and scientific committees greatly appreciate the cooperation from the authors, reviewers and keynote speakers who shared in the success of this conference. Thanks to the members of the committees who accomplished their assigned tasks on time since the beginning of organizing this conference.Husain Al-Khaiat Mohamed Abdel-Rohman Chairman of the Conference Chairman of The Scientific CommitteeCOMMITTEESCONFERENCE CHAIRMANProf. Husain Al-Khaiat ORGANIZING COMMITTEEProf. Husain Al-Khaiat (Chairman) Prof. Mohamed Abdel-Rohman (KU) Dr. Naji Al-mutarey (KFAS) Dr. Hasan Kamal (KISR) Eng. Mohammed Al-Rasheedi / Ashwaq Al-Mudhaf (KSE)Eng. Ahmad Al-Dosari (KSE)SCIENTIFIC COMMITTEEProf. Mohamed Abdel-Rohman (Chairman) Prof. Husain Al-Khaiat Prof. Mohammed Naseer Haque Prof. Abdul Latif Al-khulaify Prof. Humayun Raibul-Hasan Kabir Dr. Khaldon RahalTHE PERMANENT ORGANIZING COMMITTEE FOR THE ARAB STRUCTURAL ENGINEERING CONFERENCES:Prof. Dr. Mahmoud Aly Reda Youssef (Egypt) (Chairman) Prof. Dr. Ahmad Atef Rashed (Egypt) Prof. Dr. Osman Mohamed Osman (Egypt) Prof. Dr. Husain Al-Khaiat (Kuwait) Prof. Dr. AbdelKader Cherrabi (Morocco) Dr. Amer Ali Al-Rawas (Oman)Dr. Khaled Kamal Naji (Qatar) THE ADVISORY COMMITTEE Abdul-Latif Al-Khaleefi, Kuwait University, KuwaitAbdul Q. M Ezzeldin Yazeed Sayed-Ahmed, University of Qatar, QatarAbdul Q. Melhem, University of Aleppo, Aleppo, Syria Ahmed Abdel raheem, Mansoura University, EgyptAhmed Mohamed Farahat, Cairo University, Egypt Ahmed Rashed, Cairo University, EgyptAli zregh, Al-Fateh University, Libya Alsanusi, Garyounis University, LibyaAmmar Bin Nakhi, Kuwait University, Kuwait Amr Sadek, Kuwait Institute for Scientific Research, Kuwait Azza M. Elleboudy, Banha University, EgyptBachir REDJEL , Univerisity of Annaba, Algeria Brahim NECIB, University of Constantine, AlgeriaHamayun Kabir, Kuwait University, Kuwait Hasan Kamal, Kuwait Institute for Scientific Research, KuwaitHashem Al-Tabtabai, Kuwait University, Kuwait Hossam Hodhod, Cairo University, EgyptHusain Al-Khayat, Kuwait University, Kuwait Ishac Ishac, Zagazig University, EgyptKamal Sharobim, Suez Canal University, Port Said, EgyptKhaldoun Rahal, Kuwait University, KuwaitMahmoud Aly Reda Youssef, Cairo University, EgyptMahmud Akkari, LibyaMohammad Al-Ani, University of Technology, IraqMohamed Abdel-Rohman, Kuwait University, KuwaitMohamed Terro, Kuwait University, Kuwait Mohammed Naseerul Haque, Kuwait University, Kuwait Moetaz Al-Hawary, Kuwait Institute for Scientific Research, Kuwait Nabil A.B. Yehia, Cairo University, EgyptNabil Kartam, Kuwait University, Kuwait Nabil S. Mahmoud, Mansoura University, Egypt Obada Al-Kayali, UNSW, AustraliaOsman Ramadan, Cairo University, EgyptParviz Koushki, Kuwait University, Kuwait Rana Alfares, Kuwait University, Kuwait Sami Tabsh, American University, Al-Sharqa, UAESanaa Al-Desouki, Cairo University, EgyptSayed Abdel-Salam, Zagazig University, EgyptS.Y. Barony, University of Al-Fateh, LibyaSuresh Shrivastava, McGill University, CanadaTed Stathopoulos, Concordia University; Montreal, CanadaTABLE OF CONTENTSKEYNOTE PAPERSCEMENTS AND CONCRETE MIXTURES FOR SUSTAINABLE DEVELOPMENT - STATE OF THE ARTpage 1P. KUMAR MEHTACivil and Environmental EngineeringUniversity of California, Berkeley, USATAILORING THE DESIGN OF CONTEMPORARY TALL BUILDINGS FOR WIND EFFECTS page 17AHSAN KAREEMDepartment of Civil Engineering and Geological SciencesUniversity of Notre DameNotre Dame, USAINTER-STORY DRIFT REQUIREMENTS FOR NEAR-FIELD EARTHQUAKESpage 35P. GLKANDisaster Management Research Center and Department of Civil EngineeringMiddle East Technical UniversityAnkara, TurkeyDURABILITY DESIGN A HOLISTIC CONCRETE CODE FOR THE 21ST CENTURYpage 49R.N. SWAMYDepartment of Mechanical Engineering, University of SheffieldSheffield, UKTHE EFFECT OF REINFORCEMENT TYPE ON THE DUCTILITY OF SUSPENDED REINFORCED CONCRETE SLABSpage 57R.I. GILBERTSchool of Civil and Environmental Engineering The University of New South WalesSydney, AustraliaTECHNICAL PAPERSComposite and Steel StructuresModeling of Local Buckling in Continuous Composite BeamsM. TEHAMI and M. HAMANE, University of Sciences and Technology of Oran, Algeriapage 69Modeling Effect of the Shear Connector-Welding Region on the Nonlinear Analysis of Composite BeamsA. F. KADHIM, University of Technology, Baghdad, Iraqpage 77Behavior Factor for Moment Resisting Steel Frames with End Plate ConnectionsA. I. RAMADAN, A. F. HASSAN, and S. A. MOURAD, Cairo University, Egyptpage 85Partial Interaction in Composite Beams Subjected to Torsion in Sagging Moment RegionA. M. EL-SHIHY, H. SHEHAB EL-DIN, H. FAWZY SHABAAN, S. A. A. MUSTAFA, Zagazig University, Zagazig, Egypt and S.S.J. MOY, Southampton University, UKpage 93Construction ManagementAnalyzing Engineering-Related Delays: An Expert System Approach M. M. MARZOUK, A.M. EL-DOKHMASEY AND M.E. IBRAHIM, Cairo University and ALEZZ Flat Steel, Egyptpage 105Damage AssessmentAssessment of Pounding Damage Potential for BuildingsM. M. MOKHTAR, A. F. HASSAN AND S. A. MOURAD, Cairo University, Egyptpage 113Prospective for Developing Rating and Monitoring Systems for Libyas Bridge NetworkMILAD M. ALSHEBANI, Alfateh University, Tripoli, Libyapage 121Characterisation and Analysis of Smart Materials Based on Adaptable Shape Memory AlloysB. NECIB, M. S. SAHLI, F. MILI, A. MERABET and E. FERKOUSUniversity of Mentouri Constantine, Constantine, Algeriapage 129New Sensors for Damage Detection Using Nano Photonic Bandgap MaterialsM.M. REDA TAHA, University of New Mexico, Albuquerque, USApage 141A Nouvelle Approach for Assessing the Possibility of Damage in StructuresM.M. REDA TAHA and E. ALTUNOK, University of New Mexico, Albuquerque, USApage 149MaterialsThe Effect of Using Urea and Urea-Formaldehyde Polymer on the Properties of ConcreteA. A. MAHMOUD, Ain Shams University, Cairo, Egyptpage 157Studying the Effect of Using Polymerized Alpha and Beta Naphthol with Formaldehyde on the Properties of ConcreteA. A. MAHMOUD and E. A. NASR, Ain Shams University, Cairo, Egyptpage 169Balancing Flowability and Stability of Self-Compacting ConcreteY. A. ABDEL-JAWAD QAWASMI, Jordan University of Science & Technology, Irbid, Jordanpage 177 - - - page 185Mechanical Behavior of Two-Stage (Pre-Placed Aggregate) ConcreteH. S. ABDELGADER, A. E. BEN-ZEITUN, A. F. SAUD and A. A. ELGALHUD Al. Fateh University, Tripoli, Libyapage 191 - - - page 199Effectiveness and Mechanism of Corrosion Inhibiting Admixtures A. M. K. ABDELALIM, G. E. ABDELAZIZ and Y. A. FAWZY, Banha University, Shoubra, Cairo, Egyptpage 205Development of Perlite-Gypsum-Slag-Lime Sludge Composite System for Building ApplicationM. S. MORSY, S. S. SHEBL and M. ABD EL GAWAD SAIF, Housing & Building National Research Center, Giza, Egyptpage 213A Draft Code for Designing Durable Concrete Structures in the Arabian GulfB. E. JOHN, M. N. HAQUE and H. AL-KHAIAT, Kuwait University, Kuwaitpage 223High Performance Concrete Using Slags as Mineral Additives and Steel FibresM. CHEMROUK, B. BOULEKBACHE, M. HAMRAT and T. TAHENI, University of Science & Technology, Houari, Boumediene, Algiers, Algeriapage 231Performance of Portland and Natural Pozzolana Cement Mortars Exposed to Sulfate EnvironmentsS. KENAI, University of Blida, Blida and M. GHRICI, University of Chlef, Chlef, Algeriapage 241Theoretical Simulation and Applied Measures of Roller Compacted Concrete (RCC) Strength: Case of Local Materials Quarries of TunisiaM. ZDIRI, M. BEN OUEZDOU and J. NEJI, National Engineering School of Tunis, Higher Institute for Technological Studies, Tunis Polytechnic School, Tunisiapage 249Ductility and Energy Absorption of Polyester Mortar M.M. EL-HAWARY, S.AL-OTAIBI AND A. ABDUL-JALEEL, KUWAIT INSTITUTE FOR SCIENTIFIC RESEARCH, KUWAITpage 257Reinforced Concrete StructuresMethod for Predicting Prestressing Force Needed to Close Crack in R.C. Beams Strengthened by External TendonsABDELSALAM M. AKASHA, Sebha University - Libyapage 265A Truss Model for Eccentric Shear Transfer at Edge-Column Slab ConnectionsA. G. SHERIF, Helwan University, Mataria, Cairo, Egyptpage 273Curvature and Displacement Ductilities of Reinforced Concrete ColumnsB. BOUSALEM AND N. CHIKH, University Mentouri Constantine, Algeriapage 281Post-Installed Reinforcing Bar Splices in Concrete BeamsY. K. AL-GHADANI, Building Permit Department, Muscat Municipality, Oman A. S. AL-HARTHY, Sultan Qaboos University, Omanpage 289Mechanical Reinforcing Bar Coupler Based on Bar DeformationsS.S. ALI-ELDIN and A.A. AL-TUHAMI, Zagazig University, Zagazig, Egyptpage 297Soil-Structures InteractionSafety of Skin Friction Drilled Shaft Foundations in Gravelly SoilsA. M. HARRAZ and M. M. EL-MELIGY, Mansoura University, Mansoura, Egyptpage 305Buckling Analysis of Piles Using The Finite Difference MethodABDULSALAM I. M. AL-JANABI, SALEH A. M. H. MIRAN and BALSAM J. M. FARID, University of Altahadi, Sirt, Libya page 313Optimum Structural Design of Counterfort Retaining WallsABDULSALAM I.M. AL-JANABI, AZIZA M.A. MELAD and MARIAM M.A. ABUALAWAFI, University of Altahadi, Sirt, Libyapage 323Behavior Improvement of Footings on Soft Clay Utilizing Geofoam G. E. ABDELRAHMAN and A. F. ELRAGI, Fayoum University, Fayoum, Egyptpage 333The Effect of Interface on the Performance of Piles in Expansive SoilsY. E. A. MOHAMEDZEIN, Sultan Qaboos University, Sultanate of OmanF. E. NOUR ELDAYEM, Al-Azhari University, Omdurman, Sudanpage 339Innovative Use of Piled Raft Foundation to Optimize the Design of High-Rise BuildingsY. M. EL-MOSSALLAMY, F. M. EL-NAHHAS and A. S. ESSAWY, Ain Shams University, Cairo, Egyptpage 347Effect of Flexibility of Spread Footings on Structural BehaviorS. W. TABSH, American University of Sharjah, Sharjah and A.R. AL-SHAWA, Toshiba Corporation, Abu Dhabi, UAEpage 359Structural AnalysisNonlinear Finite Element Analysis of Concrete Beams Reinforced with FRP RebarsH.M. IBRAHIM, Suez Canal University, Port Said, Egyptpage 369Selection of Optimum Lateral Load-Resisting System Using Artificial Neural NetworksM.H. ELGAMMAL, M.M. WAHBA and S.A. MOURAD, Cairo University, EgyptM.A. BADR EL DIN, EETC, Giza, Egyptpage 377Optimal Lateral Displacement Control of High-Rise Buildings Using the DPFs Method S.S. ABDEL-SALAM, O.E. SHALLAN and M.I. MOUSTAFA, Zagazig University,Egyptpage 385Elastic Stability of Ponded Clamped BeamsM. M. TAWIL, Academy of Graduate Studies, Janzur, Libyapage 393Analysis of Rectangular Plates: A Variational Symbolic ApproachHUSAIN JUBRAN AL-GAHTANI, King Fahad University of Petroleum and Minerals, Dhahran, Saudi Arabiapage 399Dynamic Analysis of Fixed Offshore Structures in Deep Water under the Action of Earthquake LoadR. A. OTHMAN and B. B. AL-ALOUSI, University of Baghdad, Iraqpage 405Effect of Shear Deformation on the Flexural Vibration of Multilayered BeamsA.M. SEGAYER, Al-Fateh University, Tripoli, Libya M.A. WAHAB and N.A. MAREIMI, High Institution of Global Professions, Rigdalin, Libyapage 413Analysis of Elastio-Plastic Deformations of Shells of Revolution by the Finite Element MethodA. ROUABHI, MHamed Bouguerra University, Boumerdes, Algrie, Algeriapage 423Structural BehaviorFracture Behavior of Flanged Reinforced Concrete Beams Experimental InvestigationN. M. WAHAB and N. A. B. YEHIA, Cairo University, Egypt page 431Mitigation of Progressive Collapse Initiation in High Rise BuildingsF.A. KASTI, Dar Al-Handash, Beirut, Lebanonpage 439Economic Feasibility and Structural Modeling of Post-Tensioned Flat SlabsA. S. ESSAWY, A. A. ABDELRAHMAN, and E. A. YEHIA, Ain Shams University, Egyptpage 449Behavior of High-Strength Reinforced Concrete L-Beams Subjected to Combined Shear and TorsionALAA ZOHERY, HAMED SALEM, WAEL ELDEGWY and AHMED FARAHAT, Cairo University, EgyptHAMDY SHAHEEN, Housing and Building Research Institute, Egyptpage 457Effect of Tension Reinforcement Ratio on Curvature and Displacement Ductility Indices of HSC BeamsS. F. KANSOUH, Helwan University, Mattaria, Cairo, Egyptpage 467Shear Behavior of Self Compacting Concrete BeamsS. F. KANSOUH, Helwan University, Mattaria, Cairo, Egyptpage 477Shear Behavior of High Strength Fiber Reinforced Concrete Beams Under Different Levels of Axial Compression ForcesIBRAHIM G. SHAABAN, Banha University, Shoubra, Cairo, Egyptpage 489Structural DesignDesign of Structures for TsunamisA. GHOBARAH, UAE University, AlAin, United Arab Emiratespage 497Shear-Torsion-Bending Interaction Using AASHTO-LRFD General Procedure KHALDOUN N. RAHAL, Kuwait University, Kuwait page 505MODELING TERRAIN EFFECTS And APPLICATION To The WIND LOADING OF BUILDINGSK. WANG, RWDI Inc., Guelph, CanadaT. STATHOPOULOS, Concordia University, Montreal, Quebec, Canadapage 515A Design Procedure for Proportioning Regular Earthquake Resistant RC FramesN. DJEBBAR and N. CHIKH, Constantine University, Constantine, Algeriapage 525Comparative Study of Quantity and Cost of a Multistory Building with Different R/C Floor SystemsJ.A. ABDALLA and S. EL-SAYEGH, American Univ. of Sharjah, United Arab EmiratesK. AL-SUWAIDI and S. BAJUBAIR, ADNOC, Abu Dhabi, United Arab Emiratespage 533Towards A New African Concrete Code (ACC) A. S. NGAB, Al Fatah University, Tripoli, Libyapage 543Structural RepairCFRP Strengthening of Prestressed-Precast Hollow Core Slabs to Resist Negative MomentsA. HOSNY and A. A. RAHMAN, Ain Shams University, Cairo, EgyptE. Y. SAYED-AHMED, Qatar University, Doha, QatarN. A. ALHLABY, Trust Group, Doha, Qatarpage 551Repair of Concrete Beams Reinforced with Debonded BarsH.A. ABDALLA, College of Technological Studies, KuwaitH. MOSTAFA and T. GAMAL EL-DEEN, Cairo University, Egyptpage 559Flexural Repair of Reinforced Concrete Beams - Experimental Investigation N. A. B. YEHIA, Cairo University, Egyptpage 567Behavior of Concrete Beams Repaired with Lightweight Epoxy MortarH. I. ABDEL-FATTAH, University of Sharjah, United Arab Emiratespage 575Strengthening of High Strength Concrete Columns with External Glass Fiber CompositeN. CHIKH and R. BENZAID, Constantine University, Constantine, AlgeriaB. BOUSALEM and N. DJEBBAR, Jijel University, Jijel, Algeriapage 581Retrofitting of RC Columns with Accessible and Inaccessible Faces Using the Mechanical Strengthening TechniqueA. A. AL-TUHAMI, Zagazig University, Zagazig, Egyptpage 589Strengthening of Masonry Walls Subjected to In-Plane and Out-of-Plane LoadsA. A. AL-TUHAMI and H. K. SHEHAB, Zagazig University, Zagazig, Egyptpage 601Structural TestingInfluence of Loading Rate on Axial Capacity of Pile Groups in Clay from Laboratory Model TestsA. I. AL-MHAIDIB, King Saud University, Riyadh, Saudi Arabiapage 611Experimental Study of Steel-Concrete-Steel Sandwich Beams with Partial Shear ConnectionH. M. HUSAIN, Tikrit University, Tikrit, IraqB. S. AL-NU'MAN and M. A. ZEBUN, Al-Mustansiriya University, Baghdad, Iraqpage 621Effect of High Temperature on Load-Slip Relationship of Shear Connectors in Sandwich BeamsM. A. ZEBUN, Al-Mustansiriya University, Baghdad, Iraqpage 629Load-Slip Relationship in Sandwich Beams Using Modified Push-Out TestM.A. ZEBUN, Al-Mustansiriya University, Baghdad, Iraqpage 637Buckling of Steel Portal Frames Considering Material Nonlinearity: An Experimental StudyG. ABU-FARSAKH, Al-Isra University and Y. HUNATI and H. QADAN, Jordan University, Amman, Jordanpage 645Full-Scale Dynamic Testing of the Alfred Zampa Memorial Suspension BridgeA.M. WAHBEH, J.P. CAFFERY, F.TASBIHGOO, California State Polytechnic University, Pomona, S.F. MASRI, University of Southern California, Los Angeles, J. CONTE, X. HE, B. MOAVENI, A. ELGAMAL, University of California at San Diego, La Jolla, California., USApage 657CEMENTS AND CONCRETE MIXTURES FOR SUSTAINABLE DEVELOPMENT STATE OF THE ART P. KUMAR MEHTA Civil and Environmental Engineering University of California, Berkeley, U.S.A. ABSTRACT: After a century of unprecedented and unrestricted industrial growth, now we are entering into an era of sustainable development. Portland-cement concrete is the most commonly used material today for the construction of buildings and infrastructure. However, future viability of the concrete industry is threatened not only by potential shortage of energy and materials, but also by unacceptable levels of environmental pollution from the solid, liquid, and gaseous wastes of the industry. This paper presents a state of the art report showing how the industry is responding to the challenge for sustainable growth by developing cements and concrete mixtures which consume less energy and natural resources, while reducing environmental pollution. INTRODUCTION In our industrial and urban world of today, portland-cement concrete is the most widely used material of construction for buildings and infrastructure. How long in the foreseeable future would concrete continue to dominate the field of construction materials? This depends on the response of designers and builders of concrete structures to the powerful forces that are shaping the world, namely global warming and sustainable development. The term, sustainability, entered into the public discourse with the issue of the Brundtland Report in 1987 by the U.N. Commission on Environment and Development. The Commission defined sustainable development as the ability to meet our needs without compromising the ability of future generations to meet their needs. Have we entered into an era of unsustainable growth. If so, when and how? What are the causes of global warming and related climate change, and how can they be mitigated? How are the sustainability issues affecting the construction industry in general, and the concrete construction practice in particular? A brief review of this background information is included in this paper which presents a global review of cements and concrete mixtures that are being developed as a part of the strategies for reducing the environmental impact of the concrete industry. SUSTAINABILITY ISSUES Since the end of the last ice age, some 10,000 years ago, the earths climate has remained reasonably stable. There is strong evidence that climate change attributable to radical planetary changes during the 20th century is now underway. Let us take a look at some of the changes that have occurred during the short span of the last 100 years: Human population, that had taken ten thousand years to grow to 1500 million, rose from 1500 to nearly 6000 million. Fueled by technology and cheap sources of energy, water, and minerals, the production rates of basic agricultural and industrial products increased 10 to 20 times. 1The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwait1The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwait Statistics show that there is a direct relationship between population growth, industrialization, and urbanization. At the beginning of the 20th century, nearly 150 million people lived in cities; now the number of people who are living in and around the cities has risen to approximately 3000 million. The world today also has 20 mega-cities of more than 10 million people each.2 This shows that a rapid urbanization of the planet has taken place. Not only the world is running out of cheap, non-renewable, sources of energy and materials but also the space for disposal of waste products of our civilization. According to Hawken et al1, only 6% of the total global flow of materials (i.e. 30 billion tonnes out of 500 billion tonnes a year), ends up in consumer goods; thus the yearly volume of industrial solid, liquid, and gaseous wastes that require disposal amounts to some 470 billion tonnes. In recent years, there is an increasing frequency and intensity in weather-related disasters in the world that are attributable to man-made global warming, caused by steadily rising concentration of greenhouse gases. Carbon dioxide, mostly produced by the combustion of fossil fuels, is the major greenhouse gas. According to a 2001 report by IPCC (Intergovernment Panel on Climate Change), carbon dioxide level in the atmosphere has risen well above the pre-industrial level of about 280 ppm to over 375 ppm and, with business-as-usual, an exponential rise is predicted during the next 100 years (Fig. 1). Fig. 1 Historical and future atmospheric CO2 concentrations. (From Mehta, P.K., Conc. Int., Vol. 23, No. 6, pp. 61-66, Oct 2001.) Due to our highly wasteful technology choices, we have reached a point when it is becoming increasingly clear that, in a finite planetary space the pursuit of unlimited industrial growth, unrestricted use of natural resources, and uncontrolled pollution of our life-supporting environment is a recipe for self-destruction. 2The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwait The status of the sustainability issue was recently summarized in a joint statement by representatives of science academies from 11 major countries of the world, namely Brazil, Canada, China, France, Germany, India, Italy, Japan, Russia, U.K., and U.S.A. The following excerpts are taken from this statement, which was published by the New York Times on June 7, 2005. There will always be uncertainty in understanding a system as complex as the worlds climate. However, there is now a strong evidence that significant global warming is occurring. The evidence comes from direct measurements of rising surface air temperatures and subsurface ocean temperatures, and from phenomena such as increases in global sea levels, retreating glaciers, and changes to many physical and biological systems. It is likely that most of the warming in recent decades can be attributed to human activities. This warming has already led to changes in the Earths climate. Increasing temperatures are likely to increase the frequency and severity of extreme-weather events such as heat waves and heavy rainfall. Increasing temperatures could lead to large-scale effects, such as melting of large ice sheets with major impact on low-lying regions throughout the world. We call on world leaders: to acknowledge that this threat of climate change is clear and is increasing to identify cost-effective steps that can be taken now to contribute to substantial and long-term reduction in net global greenhouse emissions to recognize that delayed action will increase the risk of adverse environmental effects and will likely incur a great cost. According to a more recent report, published in the April 3, 2006 issue of the Time Magazine, many climate scientists believe today that we have already crossed a tipping point beyond which the slow creep of environmental degradation has given way to a sudden and self-perpetuating collapse of the global climate. So far, the response of the world political and corporate leaders to stabilize and reduce the greenhouse-gas emissions has been rather mixed. According to the Kyoto Protocol, signed by 141 countries in February 2005, the signatory countries agreed to stabilize the GHG emissions by the year 2012 to a level that is at least 6% below the 1990 level. Among the industrially developed countries the U.S., which is responsible for nearly 25% of the worlds GHG emissions, did not sign the Kyoto Protocol. Some of the rapidly developing, large economies, such as China and India, also have not signed it. On the other hand, many states in the U.S., some 80 large cities around the world, and numerous multinational corporations have individually signed onto programs that intend to meet or beat the Kyoto targets. SUSTAINABILITY AND THE CONSTRUCTION INDUSTRY In the context of sustainability and global warming as two of the most powerful forces shaping our world, let us review the trends in the construction industry. Worldwide, buildings and other structures are a large consumer of energy and natural resources. They consume nearly 40% of the crushed stone together with sand and gravel, 25% virgin wood, 16% water, and 40% of the total energy.4 The most significant environmental impact of buildings is associated with their use, such as heating, cooling, lighting, ventilation, and waste disposal. In industrialized countries, green building design is a growing movement that places environmental considerations at the forefront of the design process in order to encourage ways of minimizing the use of energy and materials, and maximizing the recycling of waste. For instance, the U.S. Green Building Council has a certification program for buildings that involves a point rating system called the LEED (Leadership in Energy and Environmental Design) System. It has five main credit categories; 3The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwaitnamely sustainable site, water use efficiency, energy use efficiency, materials and resources, and indoor environmental quality. Environmental Impact of the Concrete Industry Energy and resources: Portland cement, the principal hydraulic cement used worldwide for modern concrete structures, not only is a product of an energy-intensive industry but also is responsible for large greenhouse-gas emissions that are associated with its production. Producing a tonne of portland-cement requires nearly 4 GJ energy, and the manufacture of portland clinker releases approximately 0.8 to 1 tonne carbon dioxide depending on the chemical composition of the fuel used for clinker burning. The worlds present annual production rate of 1800 million tonnes of cement and 14000 million tonnes of concrete, raises some serious issues about the environmental impact of the concrete industry. Assuming an average of 0.6 water-cement ratio and 75% aggregate content by mass, more than 1,000 million tonnes of potable water, and 11 billion tonnes of sand, gravel, and crushed rock are consumed worldwide for making concrete every year. Large quantities of additional water are required as wash-water for aggregate and ready-mixed concrete trucks, and for curing concrete. Therefore, among the manufacturing industries, the concrete industry is the largest consumer of natural resources in the world. The mining, processing, and moving operations, involving huge quantities of cement-making and concrete-making raw materials, require large amounts of energy besides leaving destructive footprints on the ecology of riverbeds and forests. Transport of huge volumes of cement, concrete mixtures, and precast concrete products also consumes considerable energy. Durability and resource productivity: Increase in the durability of a manufactured product means a more efficient use of energy and resources that have gone into its production. This approach, in the long term, provides an obvious solution for minimization of the environmental pollution, associated with wasteful consumption of the earths non-renewable resources. Hawken et al1 describe the Factor Ten Club movement toward enhancement of resource productivity. The club has challenged the nations of the world to achieve, within one generation, a ten-fold increase in the efficiency with which they use energy, natural resources and other materials. This would mean a 90% reduction in the consumption of energy and materials. The European Union has endorsed this approach as the new paradigm for sustainable development. Hawken and his co-authors wrote: Minimization of materials use, maximization of product durability, and reduction of the maintenance cost would not only increase customer satisfaction and product value but also the profitability of the business enterprise. The worlds ecosystems will be protected when both consumers and producers acquire a stake in improving the resource productivity. The report card on the durability of concrete in modern structures is not satisfactory. Whereas some of the ancient concrete structures built with Roman cements are still in good condition after nearly two thousand years, portland-cement based structures, usually designed for a service life of 40 to 50 years, often crack and start deteriorating soon after installation, thus requiring repair and replacement much earlier than their designed life. According to the April 1998 issue of ASCE News, the American Society of Civil Engineers gave the nations infrastructure a failing grade of D, and estimated that it will take more than a trillion U.S. dollars to fix the problems. In conclusion, the resource productivity of the concrete industry requires considerable improvement. 4The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwait CONCRETE TECHNOLOGY FOR SUSTAINABLE DEVELOPMENT In an earlier paper5, I identified the three main pillars of the foundation upon which the structure of a sustainable concrete industry can be built, namely the conservation of concrete-making materials by increasing the use of recycled industrial wastes, increasing the resource productivity of the industry by radical enhancement of durability of concrete products, and a holistic approach that gives top priority to environmental-friendly solutions in concrete design and construction practice. Described below are recently developed cement compositions and concrete mixtures that meet these guiding principles. Reduction of Portland Clinker in Cement In the short term, the two best strategies to obtain a major reduction in the carbon dioxide emissions associated with cement production, are to lower the clinker factor of the final product as much as possible by maximizing the proportion of mineral additions to clinker, and to increase the use of blended portland cements in general construction. Note that in some countries the mineral additions are batched directly with portland cement at the ready-mixed concrete plants. Portland cement, typically, contains 95% portland clinker and 5% gypsum. Production of blended portland-cements containing less than 95% portland clinker is a well-known method that is already helping to reduce the impact of the cement industry on energy and carbon-dioxide emissions. Today, in many countries, blended portland-cements containing 15 to 20% coal fly ash or limestone dust, or 30 to 40% granulated blast-furnace slag are being produced. In fact, in the European Union, portland cements market share has shrunk to nearly one-third of the total cement consumed by the construction industry. Although blended portland-cements are being increasingly produced worldwide, Jahren6 has estimated that, in the year 2002, the total volume of mineral additions was approximately 240 million tonnes in 1700 million tonnes of cement. This corresponds to 1460 million tonnes of clinker, or 0.86 clinker factor (i.e. the proportion of clinker per tonne of cement). Thus, the cement industry was responsible for generating some 1200-1400 million tonnes of carbon dioxide in the year 2002, which is approximately 6% of the total global emissions. Among the technically acceptable and economically available mineral additions, coal fly ash offers the best potential for achieving a considerable reduction in carbon emissions attributable to the cementitious materials in concrete. According to Jahren, in a 20 years perspective fly ash offers by far the most powerful tool toward sustainable development of the concrete industry. Recent estimates show that worldwide, approximately 500 million tonnes of fly ash are being produced every year. For a variety of reasons, the total consumption of fly ash by the cement and concrete industries is limited to about 75 million tonnes annually (15% of the available amount), and large volumes of the material are disposed by low-value applications or by ponding and landfills. As will be described below, we now have a proven technology to produce highly durable concrete products made with blended portland cements containing 50 to 60% ASTM Class F or Class C fly ash. Based on an estimate of 2500 million tonnes of cement consumption in the year 2020, Jahren has projected the following amounts of clinker additions that could possibly be used as a potential tool for the reduction of carbon dioxide emissions associated with cement production: 5The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwait Fly Ash = 500 million tonnes Limestone = 170 Blast-furnace slag = 75 Natural pozzolan = 50 Other ashes = 25______________ Total 820 million tones If we include 125 million tonnes of gypsum (5 % of cement) that is generally required for control of setting and hardening properties of cement, the total mineral additions in 2500 million tonnes cement amount to 945 million tonnes. This gives a clinker factor of 0.62 compared to 0.84, which is the estimated clinker factor today. Thus, a 27% reduction in the clinker factor, with a corresponding reduction in the carbon dioxide emissions (approx. 350 million tones/year), is achievable provided we vigorously pursue the strategies of maximizing the amount of mineral additions to cement and the use of such blended cements in the concrete construction practice. This approach will help the cement industry when the world governments make a serious commitment to pursue the goal of stabilizing the atmospheric concentration of carbon dioxide, and call upon every major industry to make significant emission-reductions that may go well beyond those prescribed by the Kyoto Protocol. Cement Standards of the World Worldwide, the prescriptive cement standards are under pressure to accommodate the need for reduction in carbon emissions associated with the cement production. For instance, the European Cement Specification, EN 197, covers 26 types of blended portland cements including some pozzolanic cements (Type CEM IV B) containing 26 to 55% by mass natural pozzolan or siliceous fly ash. This specification also includes composite cements (Type CEM V A) containing 18 to 30% blast-furnace slag plus 18 to 30% natural pozzolan or fly ash. By reducing the portland clinker factor to as low as 0.45 or 0.40, respectively, both these cement types are excellent examples of sustainable materials for general construction. In the U.S., ASTM has issued a new standard covering all hydraulic cements, which is not prescriptive but performance-based. According to ASTM C 1157-98, there are no requirements for blended portland cements with regard to the types of blending materials used, their proportion, and their chemical characteristics. The six cement types, with their key performance requirements are as follows: Type GU for general use (10 MPa compressive strength at 3-d, and 17 MPa at 7-d). Type HE for high early-strength (10 MPa at 1-d and 17 MPa at 3-d). Type MS for moderate sulfate resistance (max 0.1% expansion, ASTM Method C 1012). Type HS for high sulfate resistance (max 0.05% expansion, ASTM Method C 1012). Type MH for moderate heat of hydration (max .290KJ/kg, ASTM Method C 186). Type LH for low heat of hydration (max 250 KJ/kg, ASTM Method C 186). Reducing the Use of Natural Aggregate 6The 10th Arab Structural Engineering Conference, 13 -15 November 2006, KuwaitRubble from demolished concrete pavements, foundations, and floor slabs mostly contains stone particles coated with cement mortar. Brick and concrete masonry walls on crushing produce coarse fragments together with a large amount of fines, contaminated with hydrated cement paste and gypsum stucco. In early research, the size fraction that corresponds to fine aggregate, due to its very high water requirement, was found unsuitable for use in concrete mixture. The size fraction that corresponds to coarse aggregate grading is suitable but has a higher absorption capacity compared to natural aggregate particles and, therefore, yields concrete mixtures with a higher w/cem ratio and a correspondingly lower strength and elastic modules. European and Japanese researchers have published numerous reports on complete or partial substitution of natural coarse aggregate by recycled-concrete aggregate. Reported below are examples of recent research findings from Italy showing that the goal of complete utilization of the construction and demolition waste is attainable. For structural concrete mixtures, Corinaldesi and Moriconi7 reported that the strength loss associated with complete replacement of natural aggregate with a recycled-concrete aggregate (both coarse and fine fraction) was fully compensated by incorporation of fly ash and a water-reducing admixture in fresh concrete mixtures. In another study, Moriconi et al8 reported that the fine fraction from recycled concrete aggregate, when used as a partial replacement for cement in a masonry mortar, improved the bond strength between the mortar and fired-clay bricks. Although reliable estimates are not available, reportedly some 1,000 million tonnes a year of the construction and demolition waste is being generated worldwide.9 In Europe, nearly two-third of this waste consists of concrete, brick, and stone masonry rubble, and a large proportion of it can be easily processed for use as a substitute material for natural coarse aggregate in fresh concrete mixtures. In fact, it is reported that, in some countries such as the Netherlands, Belgium, Denmark, Italy, and U.K., relatively large amounts of the construction and demolition waste are already in use as recycled-concrete aggregate. However, in most countries including the U.S. huge quantities still end up in landfills. Reducing the Concrete Mixing Water The practice of using only the municipal drinking water for concrete mixing should not be followed blindly, especially in the areas of fresh water scarcity. Most recycled-waters from industrial and urban sources, or brackish and turbid waters from mining pits are suitable for making concrete unless proven otherwise by testing the concrete mixtures containing the questionable water. For instance, investigations at the Research Institute of German Cement Industry10 have shown that the use of wash water containing 18 kg/m3 or even larger content of fines from ready-mixed concrete plants, did not impair the compressive strength, elastic modulus, drying shrinkage, and creep characteristic of conventional concrete mixtures. This is a good example showing that, in order to achieve sustainability, a diversification of material resources will have to be encouraged instead of rigid adherence to absolute standards requiring that only municipal drinking water shall be used for mixing concrete. In the interest of sustainable development, in fact, many of such prescriptive standards can be eliminated in favor of performance standards. Also, to move toward a more efficient utilization of water, a number of steps can be taken by the concrete industry. First, many mix-proportioning methods, e.g., the ACI Committee 211 Guideline for Mix Proportioning, generally permit too much mixing water to obtain the desired consistency. By paying closer attention to the aggregate grading, and incorporation of a high proportion of standard fly ash and/or a high-range plasticizer into the fresh concrete mixture, it is usually possible to save up to 40% of the concrete mixing water. 7The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwait Reducing the Curing Water It is a common practice in the construction industry to cure concrete structures by spraying liquid membrane-forming curing compounds. Usually, this method does not provide adequate curing when cements or concrete mixtures containing large volumes of pozzolanic materials are used. With cast-in-place concrete members that require moist-curing, many codes of construction practice recommend spraying of water or ponding methods that waste too much water. Large savings in the curing water can result from the application of textile composites with a water-absorbent fabric on one side and an impermeable plastic membrane on the other. The use of a small amount of lightweight aggregate fines, batched with a high degree of absorbed water, is another innovative method that provides internal curing of very low w/cem concrete mixtures, especially those containing high volume of cementitious materials. In the absence of proper moist-curing, these concrete mixtures, although designed for high performance, fail to perform because they tend to crack at early-age due to excessive self-desiccation, thermal shrinkage, and drying shrinkage. In a recently published review of several reports, Holm and Ries11 concluded: Blending light-weight aggregate containing absorbed water is significantly helpful for concretes made with a low ratio of water-cementitious material or concretes containing high volume of supplementary cementitious materials that are sensitive to curing procedures. This process is often referred to as water entrainment. DURABILITY OF CONCRETE Due to the large volume of energy and material resources consumed by the concrete industry today, and the limited quantities of recycled products that are available for replacement of concrete-making materials, the short-term solutions described above are no doubt helpful but they would be inadequate to bring this industry into an era of sustainable development unless, simultaneously, we also pursue the long-term solution. In general, to restore the ecological balance on the planet, it should be obvious that the long-term solution lies in a drastic reduction of the production rates of industrial products by a corresponding reduction in their consumption levels. A review of the global consumption patterns shows that, due to lack of durability, more than one-third of the freshly produced concrete ends up in the repair and replacement of structures that are deteriorating much faster than their expected service life of 50 years or more. Assuming that without any delay, we begin to build structures with highly durable concrete mixtures that endure for 500 years or more instead of 50. In fact, as described below, we do have the scientific knowledge base and a cost-effective, proven, technology to enhance the durability of ordinary concrete structures by a factor of 10 or more. Fig 2 illustrates how the immediate steps for radical enhancement of durability of concrete mixture would influence the consumption pattern of the material during the second half of the 21st century11. Principles Controlling the Durability From field experience with structures that have suffered from lack of durability we know that deterioration of concrete is seldom due to a single cause. Also, too often the principal cause of deterioration turns out to be different from the one for which the concrete mixture has been 8The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwaitdesigned. For example, in the 1970s and 1980s numerous cases of serious concrete deterioration of reinforced concrete structures, exposed to sea water or de-icing chemicals, were reported worldwide, and they were attributed to corrosion of the reinforcement11. Reportedly, in Saudi Fig 2. Forecast of future population growth and concrete consumption. (From Mehta, P.K., Concr. Int., Vol. 24, No. 7, pp. 23-28, July 2002.) Arabia, concrete mixtures designed with low C3A portland cement to resist sulfate attack, suffered damage not due to sulfate attack but due to the corrosion of the reinforcing steel. By following the sequence of changes that occur in the microstructure of ordinary concrete when reinforced structures are subjected to severe weathering conditions and corrosive sea water, Mehta and Gerwick12 proposed a theory of the concrete damage process that is also applicable to other commonly known physical-chemical phenomena responsible for deterioration of concrete, such as cycles of freezing and thawing, alkali attack on aggregate, and sulfate attack on cement paste. In a recently published paper13, the author has used the holistic approach to develop a three-stage concrete damage process and a cost-effective method of modifying the microstructure of concrete that could lead to radical enhancement of durability. Selected excerpts from this paper are as follows: Root causes of concrete deterioration: A high degree of water saturation is one of the three root causes for durability problems because, in almost every case, it precedes the occurrence of any visible damage to concrete structures. Water is not only the primary vehicle for transport of ions and gases into concrete but also is implicated in the expansion and cracking mechanisms in solids. Microcracks in concrete are another root cause because their growth and connectivity with macrocracks and voids marks the point in time when the stage of no damage ends, and the stages of initiation and propagation of damage begin as a result of loss in water-tightness. Being discontinuous and invisible to the human eye, microcracks are ignored by the strength-driven design and construction practice in the concrete industry. A search for the origin of microcracks will take us to the first root cause - the heterogenous microstructure of concrete as a result of 9The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwaitinhomogeneities in the hydrated cement paste. As described below, these inhomogeneities serve as potential sites for the formation of microcracks when concrete experiences tensile stresses from mechanical loading and environmental exposure conditions, e.g. cycles of freezing-thawing, heating-cooling, and wetting-drying. Microcracks their origin and significance: For a variety of well-known reasons, even with structural members designed for compressive loads, tensile stress and tensile cracking are unavoidable. The reinforcement of concrete with steel does not eliminate tensile cracks but it does restrict the crack-widths to 0.15 mm or less. The fine cracks, known as microcracks, are too small to be visible and quantified, and are therefore ignored in the structural design and construction practice. It is generally accepted that microcracks caused by settlement, plastic shrinkage, restrained thermal shrinkage and drying shrinkage, and accidental overloads would not have any adverse effect on the static behavior of concrete structures. However, due to the important role in determining the permeability and durability of concrete in service, it is important to understand the origin and growth of microcracks. Hydration reactions of portland cement minerals produce a multiphase product that consists primarily of an adhesive, poorly crystalline, C-S-H (calcium silicate hydrate) phase, and some well crystalline products including calcium hydroxide. In freshly mixed and compacted concrete, water films forming around the coarse aggregate particles raise the w/c in close proximity to these particles. In the interfacial transition zone between a coarse aggregate particle and cement mortar, the spaces with high w/c become filled with a porous framework of large, plate-like, oriented, and non-adhesive crystals of calcium hydroxide. In conventional concrete mixtures this is a weak area that is highly vulnerable to microcracking. Therefore, the tensile stress generated by differential movement between the cement paste and the aggregate is relieved by the formation of microcracks in the interfacial transition zone. It means that ordinary concrete contains microcracks in the interfacial transition zone even before a structure is loaded. Let us now examine the influence of microcracks on the behavior of concrete in a structure exposed to stress effects from mechanical loading and environmental loading under severe climatic conditions. From a typical strain-stress diagram of a concrete specimen loaded under compression it can be seen that, until about 50 percent of the ultimate stress, there is no significant change in the strain/stress ratio. However, beyond this point the stress/strain curve begins to deviate appreciably from the straight line, as increasingly higher strains are recorded with every unit of additional stress. This phenomenon is attributed to increase in the length, width, and number of pre-existing microcracks in the interfacial transition zone and the beginning of some microcracking in the mortar matrix. In the long run, the proliferation and growth of microcracks will have the effect of reducing significantly not only the elastic modulus and tensile strength, but also the water-tightness of concrete. Once concrete becomes saturated and any one of the four above-described expansive phenomena is initiated, the hydraulic pressure in the pore fluid would increase, enabling the microcracks to grow rapidly. The end result is a further loss of water-tightness of concrete followed by expansion, cracking, spalling, and loss of mass. Obviously, for a holistic approach to radical enhancement of concrete durability the formation of microcracks and their growth under service conditions has to be controlled. And for this purpose, we have to understand and control the microstructure of concrete. Three stages of the damage process: Let us consider the three-stage damage process graphically presented in Fig. 3. The growth of microcracks in the concrete microstructure may be looked upon as a kind of internal damage, because microcracks provide the bridges that interlink macrocracks and voids, and would eventually lead to a breach of water-tightness in concrete, 10The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwaitwhich is a necessary pre-requisite for the subsequent stages of damage. Before the advent of the two stages of initiation and propagation of damage, there exists a stage when there is no damage Fig. 3 A holistic approach illustrating the three-stages of concrete damage process13. whatsoever, i.e. not even internal damage to concrete (e.g., interlinked microcracks). It is proposed to call this a no-damage stage. The concept of no damage state is useful for achieving a radical enhancement in concrete durability. Clearly, without the growth in microcracks, there would be no increase in the permeability of concrete. Any method that successfully prolongs the Stage 1 of the damage process would have the effect of delaying the exposure of the structure to subsequent stages of damage. Thus, by holding the structure in the Stage 1 for a very long period of time, it is possible to achieve a radical enhancement in durability. Modifying the microstructure of concrete: As mentioned above, the inhomogeneities present in the microstructure of hydrated cement paste (e.g., capillary voids and oriented layers of crystalline calcium hydroxide) are the primary source of microcracks in concrete. The interfacial transition zone next to the coarse aggregate particles (also next to the steel reinforcement) tends to contain a relatively large proportion of capillary voids and microcracks. Reducing the cement paste content in concrete, and elimination of the defects and inhomogeneities within the hydrated cement paste, are the obvious tools by which microcracks can be reduced. The use of low w/c, as mentioned by the ACI Building Code and other codes for durable concrete, enables a reduction in the volume and size of capillary voids, but this alone is not sufficient to reduce the proportion of the cement paste which is the source of microcracking from thermal shrinkage and drying shrinkage. To reduce the cement paste, both the water content and SERVICE LIFE, YEARS DAMAGE NO DAMAGE STAGE 1 STAGE 2 STAGE 3 GRADUAL LOSS OF WATER-TIGHTNESSEND OF SERVICE LIFE DAMAGE INITIATION NO LOSS IN WATER-TIGHTNESSDAMAGE PROPAGATION 11The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwaitthe cement content must be reduced as much as possible. Unfortunately, this is not mandated by building codes because a reduction in the cement content is accompanied by a corresponding reduction in early strength, which seems unacceptable to the strength-driven construction practice of today. In fully hydrated portland-cement pastes, approximately 24% of the hydration product by mass consists of oriented, heterogeneously distributed, and weakly bonded layers of calcium hydroxide crystals. They debond easily under the influence of tensile stress, and therefore serve as potential site for the formation of microcracks. By transforming all or most of the calcium hydroxide into the calcium silicate hydrate phase (the predominant phase produced by portland cement hydration), a much more homogenous hydration product would result. Thus, concrete mixtures with fewer microcracks can be produced by the use of blended portland cements containing a large proportion of pozzolanic cementitious materials. It is in this context that high-volume fly ash concrete mixtures, briefly described below, look most promising for the radical enhancement of durability of structures. HIGH-VOLUME FLY ASH CONCRETE MIXTURES The high-volume fly ash (HVFA) concrete developed by Malhotra14-18 and other researchers is an excellent example of a microstructurally homogeneous material that can be used for building highly durable concrete structures. Laboratory and field experience has shown that fly ash from modern coal-fired power plants, generally characterized by low carbon content and high fineness, when used in a large volume (typically 50-60% by mass of the total cementitious material) is able to impart excellent workability to concrete mixtures at a water content that is 15-20% less than without the fly ash. To obtain adequate strength at early age, further reductions in the mixing water content can be achieved with better aggregate grading and by the use of a superplasticizing admixture. Table 1 shows the mix proportions and typical properties of HVFA concrete used in some recently built structures in the U. S.15, 16 Petrographic examination of a HVFA concrete core, obtained from a massive unreinforced monolith foundation, 36 x 17 x 1.25 m, designed for a service life of 1000 years, revealed a very homogeneous microstructure with essentially no microcracks, capillary voids, and calcium hydroxide crystals3. The foundation is now seven years old, and to date has shown no cracking whatsoever. From laboratory test data on corrosion of steel reinforcement, alkali aggregate expansion, sulfate attack, and chloride permeability (ASTM C1202), Malhotra17 has confirmed the excellent durability characteristics of HVFA concrete mixtures. Mixture proportions, construction practice, and properties of HVFA concrete used for massive structures in North America and for pavements in India are described in a recent publication by Malhotra and Mehta18. According to the authors, proper moist-curing of HVFA concrete for at least a week is essential to achieve the desirable strength and durability characteristics. 12The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwait Table 1. Typical Mix Proportions and Characteristics of High-Volume Fly Ash Concrete Used in Some Recent Structures15,16 Structure San Francisco Bay Area Chicago Location and type Post-tensioned foundation Reinforced shear walls Residential beams, floors, walls Unreinforced piers Unreinforced foundations Mix- proportions, kg/m3 portland cement 160 195 150 125 105 Fly ash 195* 195* 150* 215** 195** Fine aggregate 849 859 890 780 820 Course aggregate: 25 mm, max. 872 - 1130 905 950 12 mm, max. - 864 - - - 9 mm, max. 267 228 - 300 300 Water 118 118 133 107 100 Superplast.L/m3 0.75 1.0 0 2.3 2.0 W/cm 0.30 0.33 0.44 0.31 0.33 Fly Ash/cm 0.55 0.50 0.50 0.63 0.65 Properties Slump, mm 150 175 150 150 150 Comp. Str. MPa 7-d 20 25 11 29 27 28-d 28 32 19 45 40 56-d 38 40 25 55 48 Chloride penetration ASTM C1202, Coulombs @ 90-d 1500 - - - 800 * ASTM Class F fly ash ** ASTM Class C fly ash 13The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwait CONCLUDING REMARKS There is no doubt that the current spell of global warming and extreme weather events, attributed primarily to the high rate of carbon dioxide gas emissions from our heavily industrialized and urbanized world, has emerged as a serious and credible threat to life on the planet. To bring the world back into a state of sustainable development, major efforts are needed by national governments, multinational corporations, and major industries. The concrete industry is responsible for considerable carbon emissions that are associated with the production of portland-cement clinker. Both short-term and long-term approaches need to be pursued without delay to bring this large industry into the era of sustainability. The short-term approach lies in partial replacement of concrete-making materials by recycling suitable industrial wastes. For instance, large amounts of coal fly ash, metallurgical slags, silica fume, and rice husk ash, individually or in combination, can be used as replacement materials for up to 50% of portland-cement clinker in blended cements. The long-term approach lies in reducing the consumption and production of fresh concrete through major enhancement of durability of concrete structures. The high-volume fly ash concrete system described in this paper is an example of the type of blended cements and concrete mixtures that would be increasingly used for building durable structures in the future. REFERENCES 1. Hawken, P., Lovens, E., and Lovens, H., Natural Capitalism-Creating the Next Industrial Revolution, Little Brown and Company, 1999, 369 pages. 2. United Nations Report, The State of the World Cities, U N Center for Human Settlements, New York, 2001. 3. Mehta, P.K., Reducing the Environmental Impact of Concrete, Concrete International, American Concrete Institute, 23 (10), 2001, pp. 61-66. 4. Shell, S. Environmental Impacts of Cement and Fly Ash, Unpublished Report, EHDD Architects, San Francisco, California, 1998. 5. Mehta, P.K., Concrete Technology for Sustainable Development, Concrete International, American Concrete Institute, 21 (11), 1999, pp 47-53. 6. Jahren, P., Greener Concrete-What are the Options?, Sintef Report, STF-A0860, August 2003, 84 pages. 7. Corinaldesi, V., and Moriconi, G., Role of Chemical and Mineral Admixtures on Performance and Economics of Recycled-Concrete Aggregate, ACI, SP 199, American Concrete Institute, 2001, pp. 869-884. 8. Moriconi, G., Corinaldesi, V., and Antonucci, R., Environmental-friendly Mortars: A Way to Improve Bond Between Mortar and Brick, Materials and Structures, Vol. 36, 2003. 9. Lauritzen, E.K., The Global Challenge for Recycled Concrete. Proc. Symp. On Sustainable Construction, Ed: R.K. Dhir, N. A. Henderson, and M. Limbachya, Thomas Telford, U.K., 1998, pp. 505-519. 10. Activities Report of the Research Institute of the German Cement Industry, Use of Recycled Water and Residual Concrete, Verein Deutscher Zementwerke, Dusseldorf, Germany, 2001-2003, p.100. 11. Mehta, P.K., and Monteiro, P. J. M., Concrete: Microstructure, Properties, and Materials, McGraw Hill, New York, 2006, pp. 176-195. 14The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwait12. Mehta, P.K., and Gerwick, B.C., Cracking-Corrosion Interaction in Concrete Exposed to Marine Environment, Concrete International, American Concrete Institute. 4 (10), 1982, pp. 45-51. 13. Mehta, P.K.,Durability of Concrete The Zigzag Course of Progress American Concrete Institute, STP 234, 2006, PP. 1-16. 14. Malhotra, V.M.,Superplasticized Fly Ash Concrete for Structural Applications, Concrete International, American Concrete Institute, 8 (12), 1986, pp. 28-31. 15. Manmohan, D., and Mehta,P.K., Heavily Reinforced Shear Walls and Mass Foundation Built with Green Concrete, ibid, 24 (8), 2002, pp. 64-70. 16. Mehta, P.K., and Manmohan, D., Sustainable High-Performance Concrete Structures, ibid, 28 (7), 2006, pp. 37-42.. 17. Malhotra, V.M., High-Performance High-Volume Fly Ash Concrete, ibid, 24 (7), 2002, pp. 30-34. 18. Malhotra, V.M., and Mehta, P.K., High-Performance High-Volume Fly Ash Concrete, Supplementary Cementing Materials for Sustainable Development, Inc. Ottawa, ONT, 2005, 120 pages. 15The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwait16The 10th Arab Structural Engineering Conference, 13 -15 November 2006, KuwaitTailoring Contemporary Tall Buildings for Wind Effects Ahsan Kareem NatHaz Modeling Laboratory Department of Civil Engineering and Geological Sciences University of Notre Dame Notre Dame, Indiana USA ABSTRACT: Globally, high-rise developments in urban settings have become a venue of choice for both business and residence. This has brought about trends toward structures with increasing heights, lighter and more slender construction whose performance is sensitive to complex wind environments. Most recent architectural trends exploit building shapes and configurations for aesthetic motives which result in buildings with asymmetrical aerodynamic profiles and coupled structural systems immersed in unsymmetric urban wind environment amid other buildings This has also posed new challenges in designing structural systems with adequate stiffness and damping to ensure acceptable performance in survivability, serviceability and habitability. Quantification of aerodynamic loads on these structures is central to the assessment of these performance limit states. This paper addresses related topics and emerging developments with a focus on recasting of the gust loading factor, widely used in all building codes and standards, introduction of 3-D gust loading factors, an example of aerodynamic loading data base and e-design, trends in codes and standards, importance of full-scale monitoring, issues related to coupled building response, aerodynamic tailoring of buildings, human comfort consideration and effectiveness of auxiliary damping systems. KEYWORDS: Tall buildings; Wind loads; Building Standards; Wind Tunnel; Damping, Damping devices 1 BACKGROUND Under the action of wind, tall buildings oscillate simultaneously in the alongwind, acrosswind and torsional directions (Fig. 1). The alongwind response has been successfully treated using quasi-steady and strip theories in terms of gust loading factors (Davenport 1967); however, the acrosswind and torsional loads cannot be treated in the same manner as alongwind loads, since they cannot be related in a straightforward manner to the fluctuations in the approaching flow. Accordingly, most current codes and standards provide little guidance for the acrosswind and torsional response. Unfortunately, for many high-rise buildings, these responses may exceed the alongwind in terms of both serviceability and survivability design considerations. Modern trends towards unconventional architectural shapes with innovative structural systems have led to buildings dynamically more sensitive to torsional loads resulting from asymmetrical wind pressures, and static and/or dynamic coupling among modes. There has been a significant focus over the years on developing load descriptions on buildings relying on 17The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwait17The 10th Arab Structural Engineering Conference, 13 -15 November 2006, KuwaitFigure 1 Aerodynamic loads on buildingshigh frequency force balance (HFFB), or synchronous scanning of multi-point pressures. The spectral and time-history information derived from these studies has been traditionally employed in a random vibration analysis framework for response predictions. In the case of slender structures, or those with complex coupled modes, reliance has been made on aeroelastic balance studies or multi-level aeroelastic model of structures to address the concerns surfacing from motion-induced loads and coupled motions, respectively. While these experimentally derived procedures met practical design needs, researchers have been active in developing analytical procedures based on the concept of the gust loading factor. These developments have led to initial formulations for 3-D gust loading factor. This paper highlights some recent developments with a potential of having a significant impact on the design of tall buildings in urban environment. These developments include recasting of the gust loading factor, 3-D gust loading factors, aerodynamic loading data base, codes and standards, full-scale monitoring, analysis of coupled building response and damping systems. Most of these topics will be discussed briefly here by including appropriate references. 2. ANALYSIS & DESIGN TOOLS This section highlights some recent developments in the analysis and design tools for tailoring contemporary tall buildings exposed to winds. 2.1 Scale Models in Wind Tunnel Scale model tests in wind tunnels are absolutely essential, especially when dealing with novel designs or designs for which dynamic and aeroelastic effects are difficult to anticipate. This primarily concerns long-span bridges and tall buildings, though wind sensitivity is not limited to these classes of structures. Regarding the instrumentation in scaled model testing, significant advances have taken place both in sensors and data acquisition systems. High sensitivity sensors at low cost have allowed synchronous scanning of pressures over building models for capturing individual point pressure variations as well as the integral loads. These scanning devices are a major leap forward 18The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwaitfrom earlier systems involving statistical integration with a limited number of pressure transducers or spatial averaging using pneumatic and PVDF films (Kareem 1982, 1989). These developments have made it possible to explore a space-time portrait of pressure field over building surfaces. Similarly, the HFBB has revolutionized wind tunnel testing of most high-rise structures, as it has evolved from earlier versions involving foil-strain gauged beam type balances to present day ultra-sensitive piezoelectric load cells (Kareem and Cermak, 1979, Tschanz and Davenport, 1983, Boggs and Peterka, 1989, Zhou et al. 2003). However, both pressure scanning systems and HFBB do not account for negative aerodynamic damping, which may become important for structures that experience significant lateral displacements. A comprehensive review of advanced monitoring techniques is described in Tamura (2002). Future developments in laser vibro-meters and GPS-like pseudolites -- indoor navigational systems -- would aid in further advancing our ability to measure structural displacements. Researchers would be able to draw similar benefits from advances in wireless accelerometers and load cells. The HFFB technique has widely been recognized for conveniently quantifying generalized forces on buildings with uncoupled mode shapes through measured base forces on stationary scaled building models (e.g., Kareem and Cermak 1979, Tschanz and Davenport 1983, Reinhold and Kareem 1986, Boggs and Peterka 1989). The generalized forces are then utilized for estimating dynamic response of buildings with given structural characteristics. The application of this technique to buildings with 3-D coupled mode shapes has been discussed in Irwin and Xie (1993), Yip and Flay (1995) and Holmes et al. (2003) for the estimation of resonant response. The HFFB measurements have also been utilized for identifying spatiotemporarily varying dynamic wind loads on buildings (Yip and Flay 1995, Ohkuma et al. 1995, Solari et al. 1998 and Xie and Irwin 1998). In these studies, analytical wind loading models with unknown parameters are assumed in the frequency domain in terms of their spectral descriptions (Yip and Flay 1995, Ohkuma et al. 1995 and Solari et al. 1998), or in the time domain in terms of their spatial distributions (Xie and Irwin 1998). These unknown parameters are then identified using the base force measurements. Once the dynamic wind loads are determined, any response component of interest can be subsequently analyzed using actual building dynamics without introducing any mode shape correction procedure. It has been pointed out that, akin to the traditional HFFB technique, the accuracy of these identification schemes depends on the efficacy of the assumed wind loading models (Chen and Kareem 2005). 2.1 New Gust Loading Factor/3-D Gust Loading Factors The gust loading factor has been used extensively to determine equivalent static wind loads (ESWL) on structures. In its most general form, the factor represents the ratio between the expected maximum mean value of a random variable and its mean value. Although this generalized definition is applicable to any load effect, the GLF, as it is traditionally envisioned, is actually based on the displacement response. The ESWL in this format is of the same distribution as the mean wind load, contradictory to the 19The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwaitcommon understanding of ESWL for flexible structures, where the resonant response dominates, thereby necessitating that the ESWL should distribute in accordance with the structural mass and mode shape. Consequently, when using the traditional GLF, structural displacements are determined with accuracy, while other response quantities, such as base shear, are not (Zhou and Kareem 2001). In response to this concern, a GLF cast in terms of base bending moments or MGLF is introduced (Zhou and Kareem 2001), which allows the mean base bending moment to be factored by the MGLF and distributed to the other floors in a manner similar to the convention used in earthquake engineering for the distribution of base shear. In addition to providing a realistic framework for gust loading factors, particularly for long period structures, the approach more importantly accommodates nonlinear and non-uniform mass distributions, circumventing the need for exact mode shape correction, resulting in a computationally efficient scheme that directly approximates non-ideal mode shapes. Further, this approach based on the base bending moment has been tailored for the acrosswind and torsional response calculations, using new aerodynamic loads database in an electronic frameworks (Zhou et al. 2003). This development offers a convenient and a reliable framework for the 3-D gust loading factor in a format very familiar to design engineers (Zhou et al. 2003 & Kareem and Zhou 2003). Another formulation of 3-D gust factors based on the quasi-steady theory and empirical description of loads is given in (Piccardo and Solari 2000). 2.3 Equivalent Static Wind Loads There are a number of equivalent static load descriptions available in the literature, e.g., (Holmes 2002, Solari and Repetto 2002, Davenport 1985, and Kasperski 1992). Recently, a new framework for evaluating the equivalent static wind load (ESWL) for any given peak response of a building characterized by uncoupled and coupled motions in the three primary directions was presented in Chen and Kareem (2003, 2004, 2005 and 2005a). This includes a new description of the background loading based on the gust loading envelope, whereas the resonant component was described in terms of the inertial loading. In this scheme, the proposed background load based on the gust loading envelope offered a very simplified load description in comparison with the load-response-correlation approach whose spatial distribution exhibits a clear dependence on the response component of interest (Kasperski 1992). It also provided a physically more meaningful and efficacious description of the loading as compared to the conventional gust response factor approach. The ESWL for the total peak response was then expressed as a linear combination of the background and resonant components. It was demonstrated that the proposed equivalent static load in terms of the external fluctuating wind load and the inertial load description provided a convenient and meaningful load description for future applications to building codes and standards. Buildings with either complex geometric shapes or structural systems with non-coincident centers of mass and resistance, or both, may undergo three dimensional (3-D) coupled motions when exposed to spatiotemporarily varying dynamic wind loads. To capture these dynamic load effects, Chen and Kareem (2005) presented a framework for 20The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwaitthe analysis of 3-D coupled dynamic response of buildings and modeling of the equivalent static wind loads (ESWLs). This framework took into account the correlation among wind loads in principle directions and the inter-modal coupling of modal response components. The wind loading input for this scheme may be derived either from multiple point synchronous scanning of pressures on building models or through high-frequency force balance (HFFB) measurements. The ESWL for a given peak response was expressed as a linear combination of the background and resonant loads, which respectively reflect the fluctuating wind load characteristics and inertial loads in fundamental modes of vibration. The nuances of utilizing HFFB measurements for buildings with 3-D coupled mode shapes were elucidated with a focus on the evaluation of the generalized forces including mode shape corrections, the background and resonant responses, and the associated ESWLs. Utilizing a representative tall building with 3-D mode shapes and closely-spaced frequencies, the framework for the analysis of coupled dynamic load effects and modeling of 3-D ESWLs was demonstrated in (Chen and Kareem, 2005 and 2005a). 2.4 Aerodynamic Loads Database Most standards and codes traditionally have relied on reductive formats and simplifications, which lead to tables and plots to describe wind loads on structures. The level of accuracy inherent in codified information in this format and the uncertainty associated with interpolation or extrapolation of information may compromise the overall accuracy in the code-specified load effects. This has recently led to the initial development of database-assisted design procedures, which offer convenient meshing with existing analysis software. Primarily, such databases rely on wind tunnel-derived data, which may be couched in analysis portals to provide desired loads effects. One such example, concerning tall buildings, manages information via an e-database of aerodynamic wind loads. This was introduced by Zhou et al. (2003), based on HFBB measurements on a host of isolated tall building models, and is currently accessible to the Figure 2 Input portal for aerodynamic data base21The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwaitworldwide Internet community via Microsoft Explorer at the URL address http://aerodata.ce.nd.edu, which has been modified in light of recent advances in web-based and file manipulation tools Through the use of this interactive portal, users can select the geometry and dimensions of a model building, from the available choices, and specify an urban or suburban condition. Upon doing so, the aerodynamic load spectra for the alongwind, acrosswind or torsional response is displayed with a Java interface permitting users to specify a reduced frequency of interest and automatically obtain the corresponding spectral value. Based on recent advances in data management, mining and software tools, this interactive database was revised to enhance, for the purposes of analysis and design, the accessibility, organization, dissemination and utility of wind tunnel data (Kwon et al. 2005). The revised website offers more attractive and user-friendly features to allow on-line determination of equivalent static wind loads and accelerations for survivability and habitability designs, respectively (Fig. 2). It also offers the users with the options of either using the NatHaz database or introducing user supplied data or utilizing analytical description of the spectra. These changes were achieved using a combination of several web-based programming tools and popular software. When coupled with the subsequent Figure 3 Aerodynamic database output22The 10th Arab Structural Engineering Conference, 13 -15 November 2006, KuwaitFigure 4 Output of building load effectssection on design, a comprehensive tool for computation of the wind-induced response of tall buildings suitable for possible inclusion in codes and standards as a design guide in the preliminary stages is offered. For example, in Fig. 3 a typical output from the database for a building is provided. The final base bending moments and rooftop accelerations are listed in Fig. 4. Other databases in different formats at various stages of development exist e.g., Cheng and Wang, et al. 2005 and Ning et al. 2005). 2.5 Codes/Standards The ultimate end of the research is to enhance the performance and safety of the built environment under wind. International codes and standards represent the most direct manner by which this research comes together in a form that dictates the daily design and construction of civil engineering structures. Most international codes and standards utilize some form of the traditional displacement-based gust loading factor for assessing the dynamic alongwind loads and their effects on tall structures. Although deriving themselves from a similar theoretical basis, considerable scatter in the predictions of codes and standards have been reported, e.g. (Kijewski and Kareem 1998). Unfortunately, the globalization of the construction industry and the prospect of 23The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwaitdeveloping unified international codes and standards make it increasingly important to better understand the underlying differences, prompting an in-depth investigation by Zhou et al. (2002). The major international codes and standards (Zhou et al. 2002): the US Standard (ASCE 7-98), the Australian Standard (AS1170.2-89), the National Building Code of Canada (NBC-1995), the Architectural Institute of Japan Recommendations (RLB-AIJ-1993) and the European Standard or Eurocode 1993 were compared. It was found that the varying definitions of wind field characteristics, including mean wind velocity profile, turbulence intensity profile, wind spectrum, turbulence length scale, and wind correlation structure, were the primary contributors to the scatter in predicted response quantities. An example presented in Zhou et al. (2002) highlights these differences. Current efforts are underway in trying to bridge these differences for better agreement between the predictions based on different major codes and standards. In the following section, some recent developments and future prospects related to codes/standards and design tools are discussed. 3 COUPLED BUILDING RESPONSE Buildings with complex geometric shapes or structural systems with non-coincident centers of mass and resistance, or both, may undergo three dimensional (3-D) coupled motions when exposed to spatiotemporarily varying dynamic wind loads. It is also worth paying attention to buildings with similar dynamic properties in orthogonal directions as a small change in structural property may shift the principal axes. In some cases the analysis may be performed along the principal axes to avoid analysis based on 3-dimensional mode shapes. In these cases proper care must be exercised to take into account the building principal axes, the force balance orientation and necessary correlations. Accordingly, the prediction of coupled building response requires analysis frameworks that take into account the cross-correlation of wind loads acting in different primary directions and the inter-modal coupling of modal responses (e.g., Chen and Kareem 2005, Kareem 1985, Tallin and Ellingwood 1985, Shimada et al. 1990 and Flay et al. 1999). The coupled building response analysis based on HFFB measurements have been studied in Irwin and Xie (1993), Yip and Flay (1995), Holmes et al. (2003), and Chen and Kareem (2005). The inter-modal coupling is often considered by utilizing the complete quadratic combination (CQC) rule to combine the modal responses for the estimate of total dynamic response. It is worth emphasizing that the modal correlation coefficient of two adjacent modes estimated by the closed form formulation given in (Der Kiureghian 1980) is only valid when the generalized forces are fully correlated as for the case of buildings experiencing a single earthquake excitation input. The modal correlation coefficient of two adjacent modes depends not only on the frequencies and damping ratios, but also on the correlation/coherence of the generalized forces (Chen and Kareem 2005a and 2005b). This important consideration of the CQC rule for partially correlated generalized forces associated with multiple inputs of loadings has not been completely recognized in the analysis of wind load effects on buildings and other structures (e.g., Xie et al. 2003). This lack of understanding may significantly impact the accuracy of the response analysis. 24The 10th Arab Structural Engineering Conference, 13 -15 November 2006, Kuwait4 FULL-SCALE BUILDING RESPONSE MONITORING Although scale model studies, traditionally employed to quantify wind loads on buildings, are often useful, they are at times unable to capture the underlying characteristics of structural response and require validation from full-scale observations. In the new era of high-rise buildings design challenges continually rise that motivate the need for better understanding of the dynamic behavior of these structures through full-scale monitoring. Recent interest in structural health monitoring has increased activity in the area of full-scale monitoring. While there are numerous examples of such studies around the world, one such example concerns the Chicago monitoring project, for which the measured characteristics of tall buildings under a wide range of wind environments are being correlated with the behavior predicted via analyses performed as a part of the des