Kamal H. Khayat

Bio: Kamal H. Khayat is an academic researcher from Missouri University of Science and Technology. The author has contributed to research in topics: Self-consolidating concrete & Compressive strength. The author has an hindex of 54, co-authored 330 publications receiving 9306 citations. Previous affiliations of Kamal H. Khayat include University of Science and Technology & Université de Sherbrooke.

Workability, testing, and performance of self-consolidating concrete

Abstract: Self-consolidating concrete (SCC) is a new category of high-performance concrete that exhibits a low resistance to flow to ensure high flowability and a moderate viscosity to maintain a homogeneous deformation through restricted sections, such as closely spaced reinforcement. This paper reviews the benefits of using SCC to facilitate the casting of densely reinforced sections and improve productivity and onsite working conditions. Workability requirements necessary to secure self-consolidation and the principles involved in proportioning such highly flowable concrete are discussed. Field-oriented tests useful in evaluating the deformability, filling capacity, and stability of SCC are presented. The performance of concrete mixes proportioned according to two main approaches needed to ensure high deformability, low risk of blockage during flow, and proper stability are compared. Such approaches involved the proportioning of concrete with a moderate water-to-cementitious material ratio (w/cm) of 0.41 and using a viscosity-enhancing admixture to increase stability, as well as mixes without any viscosity-enhancing admixture, but with lower w/cm of 0.35-0.38 to reduce free water content and provide stability. Mixes with both moderate and high contents of ternary cementitious materials were evaluated. The performance of each concrete was compared to that of a flowable concrete with 250-mm slump.

Viscosity-enhancing admixtures for cement-based materials — An overview

Abstract: Viscosity-enhancing admixtures, also known as anti-washout admixtures, are water-soluble polymers that increase the viscosity and cohesion of cement-based materials. Such enhancement of the liquid-phase viscosity is essential in flowable systems in order to reduce the rate of separation of material constituents and improve the homogeneity and performance of the hardened product. Viscosity-enhancing admixtures are mostly used along with a high-range water reducer to obtain a highly fluid, yet cohesive cement-based material that can flow readily into place with minimal separation of the various constituents of different densities and minimal intermixing with the surrounding water whenever cast under water. This paper reviews the types and modes of action of commonly used viscosity-enhancing admixtures and highlights their influence on the rheological properties of water and cement paste. An overview of the influence of various types of viscosity-enhancing admixture on high-range water reducer demand, resistance to water dilution, static and forced bleeding, segregation, settlement, setting time, and air entrainment is presented. The influence of such admixtures on bond to anchored reinforcing bars, frost durability, mechanical properties, and rapid-chloride permeability is also highlighted. Special applications where such relatively new admixtures can significantly enhance performance are highlighted, including their incorporation in concrete intended for underwater placement and repair, self-consolidating and segregation-free concrete for abovewater construction, and structural grout for filling post-tensioning ducts.

Mechanical Properties of Ultra-High-Performance Concrete Enhanced with Graphite Nanoplatelets and Carbon Nanofibers

Abstract: Effects of graphite nanoplatelets (GNPs) and carbon nanofibers (CNFs) on mechanical properties of ultra-high-performance concrete (UHPC) are investigated. A non-proprietary UHPC mixture composed of 0.5% steel micro fibers, 5% silica fume, and 40% fly ash was used. The content of the nanomaterials ranged from 0 to 0.3% by weight of cementitious materials. The nanomaterials were dispersed using optimized surfactant content and ultra-sonification to ensure uniform dispersion in the UHPC mixture. As the content of nanomaterials is increased from 0 to 0.3%, the tensile strength and energy absorption capacity can be increased by 56% and 187%, respectively; the flexural strength and toughness can be increased by 59% and 276%, respectively. At 0.2% of GNPs, the UHPCs exhibited “strain-hardening” in tension and in flexure.

Influence of silica fume content on microstructure development and bond to steel fiber in ultra-high strength cement-based materials (UHSC)

Abstract: The use of silica fume can significantly enhance mechanical properties of concrete given its beneficial filling and pozzolanic effects. In this study, a simple and effective double-side pullout testing method was adopted to characterize the interfacial bond properties, which include pullout load-slip relationship, bond strength, and pullout energy, of steel fiber-matrix in ultra-high strength cement-based material (UHSC) with 0–25% silica fume by the mass of binder. The effects of silica fume content on flowability, heat of hydration, compressive and flexural strengths, hydration products, and pore structure of matrix at different curing time were evaluated as well. Backscatter scanning electron microscopy (BSEM) and micro-hardness measurement were used to examine the quality of interfacial transition zone (ITZ) around the fiber. In terms of the results, the optimal silica fume content could be in the range of 15%–25%. UHSC mixtures with these dosages of silica fume showed significant improvement in pullout behavior. Its bond strength and pullout energy at 28 d could increase by 170% and 250% compared to the reference samples without any silica fume. The microstructural observation verified the findings on the macro-properties development. Formation of more and higher strength of hydration products and refinement of ITZ around the fiber ensured higher micro-hardness, and thus improved the bond to fiber.

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

American Society for Testing and Materials

Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

Design and Control of Concrete Mixtures

Abstract: This updated, definitive reference book on concrete technology covers the fundamentals and detailed information on freshly mixed and hardened concrete for Canada The properties of concrete as needed in concrete construction are presented, including strength and durability All concrete ingredients are reviewed for their optimal use in designing and proportioning concrete mixtures Applicable standards from the American Society for Testing and Materials, Canadian Standards Association and American Concrete Institute are referred to extensively Individual chapters address: (1) fundamentals of concrete; (2) Portland, blended and other hydraulic cements; (3) fly ash, slag, silica fume and natural pozzolans; (4) mixing water; (5) aggregates for concrete; (6) admixtures for concrete; (7) fibers; (8) air-entrained concrete; (9) designing and proportioning normal concrete mixtures; (10) batching, mixing, transporting and handling concrete; (11) placing and finishing concrete; (12) curing concrete; (13) hot weather concreting; (14) cold-weather concreting; (15) volume changes of concrete; (16) control tests for concrete; (17) high-performance concrete; and (18) special types of concrete