Volume 7, No. 2 Special Issue: High-Strengrth and High-Performance Concrete edited by Prof. T. Ueda High performance Concrete: A Material with a Large Potential Joost Walraven Journal of Advanced Concrete Technology, 7(2) 145-156, 2009 High Performance Concrete is a material that was regarded as ?academic? for quite a number of years. Now, the profits of this material are becoming to be recognized. The high compressive strength is not the only advantage of this material. The fibers lead to small crack distances and give the material large ductility. The very dense material structure can as well result in high durability. This makes the material suitable for the design of lightweight slender structures with a long service life, as well as surprising architectural structures. On the other hand the material is appropriate for repair of structures, such as bridge decks. First applications show convincingly a large potential. At this moment an international committee (fib Task Group 8.6) works on producing an international recommendation. Mechanical Properties of Concrete and Reinforcement - State-of-the-art Report on HSC and HSS in Japan - Minehiro Nishiyama Journal of Advanced Concrete Technology, 7(2) 157-182, 2009 Sub-working group 1 of the Japan Concrete Institute (JCI) committee on Utilization of HSC and HPC (JCI-TC063A) has been working on collecting the information in the field of research as well as their practical use. The members of Sub-working group 1 are listed below. The committee published a report in the year 2006 in Japanese. The objective of the report is to present state-of-the-art information on concrete with strengths in excess of about 60 MPa and steel reinforcement, but not including concrete made by unordinary materials such as fibers or uncommon techniques. It addresses mainly on mechanical properties of high-strength concrete and high-strength steel reinforcement. A concise digest of the report has already been published as a keynote paper in the proceedings of 8th International Symposium on Utilization of HSC and HPC in October 2008 in Tokyo. This paper is based on the keynote paper with additional information on High Stength Steel, HSS, reinforcing bars in Japan. Development of Mechanical Properties of Ultra-High-Strength Concrete Subjected to Early Heat Curing Taku Matsuda, Hiroshi Kawakami, Takao Koide and Takafumi Noguchi Journal of Advanced Concrete Technology, 7(2) 183-193, 2009 Concrete cylinders with a design strength of 100 to 150 N/mm2 were subjected to thermal histories with different maximum temperatures simulating actual structures to examine the development of their mechanical properties. The tendencies of the mechanical properties of concrete subjected to a maximum temperature exceeding 45 to 60?C were found to significantly differ from those of concrete cured at lower temperatures. The authors thus propose a technique for estimating the compressive strength of concrete from the maximum curing temperature and effective age. We also report on investigation into the applicability of conventional prediction equations to the evaluation of static modulus and splitting tensile strength using compressive strength. and the decomposition of C-S-H by carbonation was thought to affect the salt weathering resistance. Seismic Testing and Performance of Precast High-Strength Concrete Beam-Column Joints Subjected to High-Axial Tension Hassane Ousalem, Hiroto Takatsu, Yuji Ishikawa and Hideki Kimura Journal of Advanced Concrete Technology, 7(2) 195-204, 2009 High-rise buildings are subjected in case of severe earthquakes and strong winds to intensive large axial and lateral loads, particularly at their lower stories, where the exterior columns experience varying high-axial loads. Herein, the seismic performance of two precast high-strength reinforced concrete exterior beam-column joints subjected to different varying highaxial levels is investigated while premature shear failure is generally 2 suspected. High-grade steel bars were used for reinforcement. Splice groutsleeves and mechanical anchors were used in columns and beams, respectively. The strength of concrete was 70 MPa. The maximum axial tension level in columns was 90% of the yield strength of main bars. Under high-axial tension, the tested subassemblies exhibited stable response, good dynamic characteristics, appropriate lateral force resistance and energy absorption capacity. They performed well within the lateral story drift angle of 3% where the successive failure modes (beam/column flexural yielding followed then by joint shear failure) confirmed the appropriateness of the design equations in AIJ and ACI regulations. Furthermore, the use of mechanical anchors proved to be very effective without any pushing on concrete toward the exterior face of the joint within the lateral story drift angle of 2%. Seismic Performance and Flexural Stiffness Variation of Assembled Precast High-Strength Concrete Beam Jointed at Mid-Span Using Transverse Bolts Hassane Ousalem, Yuji Ishikawa, Hideki Kimura, Tetsu Kusaka, Nobuyuki Yanagisawa and Keijiro Okamoto Journal of Advanced Concrete Technology, 7(2) 205-216, 2009 Assembled precast members and related connections should be economically feasible, bring ease of construction, and provide acceptable static properties as well as adequate dynamic characteristics in highly seismic zones. The seismic performance of an assembled precast high-strength concrete beam in high-rise buildings and its flexibility variation along the simple and innovative connection are discussed. The connection, located at beam mid-span zone, was tied up by transversely non-tensioned bolts. The simplicity of the form and developed mechanism were supposed suitable for construction sites. The experimental test results confirmed the adequacy of such assembles. The beam under reversed cyclic loading proved to be ductile and failure occurred outside the connection zone similarly to monolithic ordinary beams. The flexural stiffness varied along the connection length and reduced at the location where there was an abrupt change in the precast cantilever-beam cross-section under large loading. Therefore, this reduction, within design limits, would not affect the performance of the assembled beam. Self-Healing Capability of Fibre Reinforced Cementitious Composites Daisuke Homma, Hirozo Mihashi and Tomoya Nishiwaki Journal of Advanced Concrete Technology, 7(2) 217-228, 2009 In order to investigate the self-healing capability in fibre reinforced cementitious composites (FRCC), mechanical properties and surface morphology of crack in FRCC were studied. Three types of FRCC specimens containing (1) polyethylene (PE) fibre, (2) steel cord (SC) fibre, and (3) hybrid fibres composite (both of PE and SC) were prepared. These specimens, in which cracks were introduced by tension test, were retained in water for 28 days. The self-healing capability of the specimens was investigated by means of microscope observation, water permeability test, tension test and backscattered election image analysis. It was found that many very fine fibres of PE bridged over the crack and crystallization products became easy to attach to a lot of PE fibres. As a result, water permeability coefficient decreased and tensile strength was improved significantly. Therefore amount of the PE fibre per volume was indicted to have a great influence on self-healing. Furthermore, by means of backscattered electron image analysis, it was also shown that the deference of hydration degree in each FRCC has only little influence on the self-healing capability in case of the employed test series. Biaxial fracture behaviour of steel-span- and steel-fibre-reinforced concrete Elmar K. Tschegg Journal of Advanced Concrete Technology, 7(2) 229-238, 2009 The wedge splitting method according Tschegg has been used to determine the fracture-mechanical values for cubes (e.g. 150 x 150 x 150) under uniaxial (tension) and biaxial (compression + orthogonal tension) loading. The steel-fibre-reinforced concrete had fibre lengths of 15 to 60 mm and a volume content of 0.5 to 1%. The fracture behaviour and the influence of the fibre length and the fibre content on the fracture parameters can be explained qualitatively using a very simple model. Finally, some aspects relating to the biaxial fracture testing in steel-fibre-reinforced concrete which are of interest to engineers are discussed. Concrete Subjected to Variable Confinement, I: Experimental Evaluation Fatih Cetisli and Clay J. Naito Journal of Advanced Concrete Technology, 7(2) 239-249, 2009 A study of the axial response of plain concrete under varying confining pressure was conducted to examine the sensitivity of confining pressure on the compressive strength and deformability of concrete. The concrete was examined through the use of a novel triaxial cell with pressure controlled through dilation strain feedback. The study examined realistic levels of constant, linear elastic, elastic?perfectly plastic, and bilinear varying confinement typical of fiber reinforced polymer and steel jacketing applications. It was found that the axial stress-strain response of confined concrete is dependent on the variation of confining pressure applied. The assumption of constant confinement is not appropriate for concrete systems jacketed with passive confinement such as steel or FRP materials. These systems must be comprehensively examined under varying confinement using full-scale jacketed specimens or triaxial studies. The use of a triaxial cell was shown to provide an efficient and cost-effective means of evaluating confinement performance. Concrete Subjected to Variable Confinement, II: Modeling Fatih Cetisli and Clay J. Naito Journal of Advanced Concrete Technology, 7(2) 251-261, 2009 A unique model for estimating the axial response of concrete under varying or constant levels of confinement is developed. The proposed model is empirically developed from a companion experimental study of concrete tested under linear, elastic perfectly plastic, elasto-plastic with strain hardening, and constant triaxial confinement. The axial stress-strain response is divided into three regions separated by two characteristic response levels. The model is based on the variation of the confining pressure due to the lateral dilation of the concrete. An estimate of dilation with respect to axial strain is also developed. The model is shown to provide an accurate prediction of historical experimental studies of constant confinement tests on cylinders, FRP jacketed specimens, and columns confined with conventional lateral reinforcement or FRP jacket. Experimental Study on Bond-Strengthening Hooks for RC Beams Yuichi Sato, Katsuhiro Nagatomo and Yoshifumi Nakamura Journal of Advanced Concrete Technology, 7(2) 263-271, 2009 This paper presents an experimental investigation of bond-strengthening hooks as a new method to increase bond strength along flexural reinforcing bars in reinforced concrete (RC) beams. The proposed method attempts to increase confining stiffness around the flexural bars by placing U-shaped hooks and to prevent premature bond splitting failure. Ten specimens with varied amounts and sizes of the hooks were prepared to verify the strengthening effectiveness under monotonic four-point loading condition. The test result indicated that the hooks increased the bond strength along the flexural bars although the strengthening effectiveness was limited by effective number of anchors of hooks Nbe. This limit is determined by size of stress-transmitting zones of concrete around anchors of the hooks. The bond-strengthening effectiveness of hooks is equivalent to that of the conventional internal ties. The initial stiffness of bond stress-slip curve of flexural reinforcing bars strengthened with the hooks is 84.7 N/mm2 in average, which agrees with previous experimental studies. Resistance of Mineral Admixture Concrete to Acid Attack Shweta Goyal, Maneek Kumar, Darshan Singh Sidhu and Bishwajit Bhattacharjee Journal of Advanced Concrete Technology, 7(2) 273-283, 2009 The effect of an aggressive chemical environment on concrete prepared with ordinary Portland cement and silica fume, either as a binary combination or a ternary combination with fly ash, is investigated in the present study. The adverse environmental conditions are simulated by using either 1% sulfuric acid, 1% hydrochloric acid or 1% nitric acid. The corrosion process was monitored by measuring the mass loss and compressive strength for a period of one year. It was found that the course of action of acid attack is dependent on the type of acid and solubility of the calcium salt formed. The presence of mineral admixtures was found to lower the detrimental effect of all types of acids on concrete. Ternary mixes with OPC, silica fume and fly ash performed better than binary mixes containing only silica fume as supplementary cementitious material.