Volume 3, No. 1 Special section: Environmental Aspect Considerations edited by Prof. T. Noguchi The Way Concrete Recycling Should Be (Invited paper) Fuminori Tomosawa, Takafumi Noguchi and Masaki Tamura Journal of Advanced Concrete Technology, 3(1) 3-16, 2005 Providing excellent performances as a structural material, concrete has long been deemed essential for modern civilization and recognized as a material that will continue to maintain and support the development of human society. It is now being seen in a new light, as recycling of concrete in a completely closed loop has become technically feasible. This paper reviews the background to this development referring to the changes in the social systems and introduction of new technologies. In view of considerations for the global environment to be required in the future at every step of the production of concrete and concrete structures, this paper then overviews the method of identifying social needs for concrete structures, the way the production systems of structures should meet such social needs, lifecycle design techniques for structures, and techniques for expressing the environmental performance of structures with the background reasoning, as well as the importance of such techniques.The authors finally discuss what true recycling and truly recycling-oriented society are, based on the above-mentioned discussions. Environmental Design for Concrete Structures Koji Sakai Journal of Advanced Concrete Technology, 3(1) 17-28, 2005 Concrete is the most important materials employed in public works and building construction projects. The large amount of concrete production causes large energy consumption, resources depletion, CO2 emission, and other environmental impacts. This paper describes the environmental aspects of concrete, and proposes environmental design as a new design paradigm for concrete structures. It also shows a design example to indicate the rationality of environmental design. Modeling the Influence of Pore Structure on the Acoustic Absorption of Enhanced Porosity Concrete Narayanan Neithalath, Adam Marolf, Jason Weiss and Jan Olek Journal of Advanced Concrete Technology, 3(1) 29-40, 2005 This paper describes a model to predict the acoustic absorption of Enhanced Porosity Concrete (EPC). The acoustic absorption coefficient was determined experimentally using an impedance tube, while an electro-acoustic analogy was implemented to develop the predictive model, considering the pore structure of EPC as a series of resistors and inductors. The physical features of the pore network were experimentally characterized using image analysis and a pore volume characterization technique. A parameter termed ÒStructure factorÓ was introduced to account for the increased density of air that is not displaced by the acoustic wave pressure. The maximum acoustic absorption coefficient was found to decrease linearly with an increase in the structure factor. The development of this model and its correlation with physical measurements enable the prediction of acoustic absorption in EPC based on the geometric features of the pore structure. This model enabled a parametric study to be conducted to ascertain the effects of pore size, aperture size, porosity, and specimen thickness on acoustic absorption. An optimal pore to aperture diameter ratio was observed to exist, that maximizes acoustic absorption. The parametric study is believed to be able to aid in the design of EPC for acoustic absorption by better understanding the type of pore features that should be targeted for best performance. A Proposal of Concrete Structure Design Methods Considering Environmental Performance Kenji Kawai, Takafumi Sugimaya, Koichi Kobayashi and Susumu Sano Journal of Advanced Concrete Technology, 3(1) 41-51, 2005 In this paper, a concrete structure design considering environmental impact generated in the manufacture, construction, service, maintenance, demolition, and disposal and recycling processes of the structure is discussed. The environmental impact, including its reduction, is considered as a performance of the concrete structure as well as serviceability, safety, and durability of the structure, and two types of design methods that are a design verifying environmental performance and a design considering environmental performance are proposed. A design verifying environmental performance is available when an environmental performance is required to a concrete structure. In this design, the verification of the environmental performance is carried out and followed by its inspection in the planning stage, and also in the operation stage the inspection is performed. A design considering environmental performance is available whether an environmental performance is required to a concrete structure or not. In this design, the verification or the selection of the environmental performance is carried out in the planning stage, and the inspection in the operation stage. As for a verification method, two types of methods are proposed according to diversity of environmental performance requirements. An Advanced Concrete Recycling Technology and its Applicability Assessment by the Input-Output Analysis Hirokazu Shima, Hisashi Tateyashiki, Ryuji Matsuhashi and Yoshikuni Yoshida Journal of Advanced Concrete Technology, 3(1) 53-67, 2005 While at present mostly recycled into road subbase, the amount of demolished concrete in Japan is expected to increase rapidly and exceed the demand of road subbase in the near future. To promote the recycling of concrete, a technology to produce high-quality recycled aggregate has been developed. This technology employs the heating and rubbing method. In order to investigate a future concrete recycling system, first of all, a specific model considering indices of economic activity is established to forecast the amount of demolished concrete in the future. Furthermore, an input-output table is extended by a detailed description of concrete-related industries such as construction, aggregate, cement, and ready-mixed concrete, and several concrete recycling processes have been added.The linear programming model connected to the input-output table assumes that the technology to be introduced in 2020. A subsidy for the high-quality recycled aggregate and a carbon tax are found to be effective to the early introduction of the technology.[PDF: 2.4MB] Corrosion Resistance of Functionally Graded Coatings on Plain Steel Rebars Jaesuk Ryou, Thomas Voigt, Maria S. Konsta-Gdoutos, Dominic J. Varacalle Jr., Thomas Mason and Surendra P. Shah Journal of Advanced Concrete Technology, 3(1) 69-75, 2005 The experimental results obtained on steel rebars with coatings of Si-based particles are described in this paper. It is well known that adding Si to metals generally increases their corrosion, oxidation, and erosion resistance. In addition, this paper presents impedance spectroscopy as an alternate technique in determining the corrosion activity of coated steel rebars. Impedance spectroscopy is an electrochemical measurement technique, which measures the response of a system to an applied alternating signal. A major benefit of the technique is its ability to monitor both the bulk and interfacial responses. This research was conducted to characterize the impedance response of several coatings on steel rebars, and in so doing, further understanding of the corrosion susceptibility of the systems. Chloride Binding of Cement Estimated by Binding Isotherms of Hydrates Hiroshi Hirao, Kazuo Yamada, Haruka Takahashi and Hassan Zibara Journal of Advanced Concrete Technology, 3(1) 77-84, 2005 Chloride binding behaviors of cement, which is important to estimate the chloride penetration into concrete, are investigated. Firstly chloride binding isotherms of major cement hydrates are examined and then a chloride binding isotherm of Cements are estimated from the binding isotherms of these hydrates. The results show that the monosulfate hydrate and C-S-H phases have significant chloride binding capacities, whereas ettringite and portlandite have no capacity to bind chlorides. The chloride binding by monosulfate hydrate is attributed to the formation of Friedel's salt and the binding isotherm shows a good fit to a Freundlich-type adsorption. The chloride-binding isotherm of C-S-H shows a good fit to a Langmuir-type adsorption. The binding capacity of C-S-H is saturated at about 0.6 mmol/g at high chloride concentration over than 2 M. Based on the chloride binding isotherm of monosulfate hydrate and C-S-H, the chloride binding isotherms of cements are shown to be realistically predicted. Development of Simulation Model of Chloride Ion Transportation in Cracked Concrete Ema Kato, Yoshitaka Kato and Taketo Uomoto Journal of Advanced Concrete Technology, 3(1)) 85-94, 2005 Chloride-induced deterioration is the most important deterioration phenomenon in reinforced concrete structures under marine environments. When a crack occurs in cover concrete, it may initiate and accelerate corrosion of steel reinforcement embedded in concrete. The performance of reinforced concrete structure may subsequently decrease even in the early stage of its service life. In this paper, for making clear the mechanism of chloride-induced deterioration, chloride ion transportation in cracked concrete was experimentally investigated and a simulation model for chloride ion transportation in cracked concrete was proposed. The zone having a crack was treated as the exposed surface of concrete in the proposed model of which chloride transportation was assumed to be governed by the density of chloride ion solutions in the crack. In addition, effects of crack width and an apparent diffusion coefficient through the crack on chloride ion transportation were numerically investigated and the applicability of the proposed model was discussed.[PDF: 0.5MB] Emergency Retrofit of Shear Damaged Extremely Short RC Columns Using Pre-Tensioned Aramid Fiber Belts Tetsuo Yamakawa, Mehdi Banazadeh and Shogo Fujikawa Journal of Advanced Concrete Technology, 3(1) 95-106, 2005 The seismic retrofit on existing RC buildings, which are vulnerable to seismic excitation, remains an active area of research. Emergency retrofit is necessary for rehabilitation of damaged RC buildings immediately after earthquake attack. The emergency retrofit must be convenient and dry process, because it must be hurried up. From such viewpoints, an emergency retrofit of RC columns damaged in the earthquake is proposed in this study. By introducing the pretension force into the aramid fiber belt, the emergency retrofit also acts as a shear strengthening as well as axial capacity recovery method, while the damaged RC columns are transversely confined with the aramid fiber belt prestressing. It is possible to recover the earthquake performance sufficiently by the emergency retrofit, if the damage due to earthquake is within the moderate level and if the column can sustain the vertical load. Multi-Mechanical Approach to Structural Performance Assessment of Corroded RC Members in Shear Kukrit Toongoenthong and Koichi Maekawa Journal of Advanced Concrete Technology, 3(1) 107-122, 2005 For explicitly taking into account corrosion cracks in structural safety performances, a multi-mechanical model is presented to deal with materialized corrosive substances around steel bars and equilibrated damage in structural concrete. The multi-mechanics of corrosive product and cracked concrete are integrated with a nonlinear multi-directional fixed crack modeling so that corrosion cracks in structural concrete can be simulated in a unified manner. Structural analysis of corroded RC beams is carried out for experimental verification of the multi-mechanical model in terms of shear capacity and ductility. RC beams, which primarily fail in shear or flexure, are discussed and special attention is addressed to conversion of failure modes and the absolute capacity. Consideration of inherent cracking on corroded RC members is proven to be crucial for structural performance assessment and the anchorage failure of longitudinal reinforcement is found to cause considerable decay of member capacity.[PDF: 2.5MB] Computational Performance Assessment of Damaged RC Members with Fractured Stirrups Kukrit Toongoenthong and Koichi Maekawa Journal of Advanced Concrete Technology, 3(1) 123-136, 2005 A mechanical effect of fractured web reinforcement on structural safety was experimentally investigated by intentionally avoiding hooks or anchorage devices at extreme ends of stirrups, which is a replica of broken web steel by corrosion or alkali-aggregate reaction of concrete. Significant reduction in shear capacity was experimentally found without yield of reinforcement when web steel anchorage was incomplete. The marked difference in failure crack patterns was also observed in comparison with the sound one. The longitudinal cracks were ultimately formed along main reinforcement where unprocessed edges of stirrups lie. A non-linear finite element analysis was employed to investigate and simulate failure processes and the static capacity. The bond deterioration zone of web reinforcement was computationally assumed to be ten times diameter of steel bars from the cut-off trimming of steel bars. This simple assumption in nonlinear computation was verified acceptable for performance assessment of damaged reinforced concrete with fractured stirrups. Estimation of Corrosion in Reinforced Concrete by Electrochemical Techniques and Acoustic Emission Veerachai Leelalerkiet, Toshimitsu Shimizu, Yuichi Tomoda and Masayasu Ohtsu Journal of Advanced Concrete Technology, 3(1) 137-147, 2005 Deterioration of reinforced concrete caused by corrosion of reinforcing steel under chloride environment is experimentally studied. Onset of corrosion and nucleation of cracking are estimated by acoustic emission, comparing with the chloride content. Corroded areas are evaluated by the half-cell potential and the polarization resistance. To compensate the potentials, the inverse boundary element method (IBEM) is applied. Results show that AE parameters can effectively evaluate the onset of corrosion and the nucleation of cracking, which are remarkably comparable to chloride concentration. The decrease in the half-cell potential is observed, following high AE activities. It is concluded that AE technique give an earlier warning of corrosion than the half-cell potential measurement. In addition, crack types at onset of corrosion and nucleation of cracking are identified from AE parameters. Corroded areas estimated by IBEM solutions are in good remarkable agreement with those of visual inspection, although results of electrochemical techniques are marginally successful. Evaluation of Ultimate Strength of Post-Tensioned Anchorage Zones Young Mook Yun Journal of Advanced Concrete Technology, 3(1) 149-159, 2005 The anchorage zones of post-tensioned concrete members can be divided into local and general zones. The current study estimated the ultimate strengths of post-tensioned beams tested to anchorage failure using the AASHTO LRFD approximate stress analyses/design method, the critical section concept in which the strengths of the node-strut interface and local zone-general zone interface are examined, the bearing strength equation which considers the confinement effect due to reinforcing bars, and the nonlinear strut-tie model approach which incorporates nonlinear techniques in the selection, analysis, and verification processes of a strut-tie model, thereby evaluating their respective validity in the analysis and design of post-tensioned anchorage zones. The ultimate strengths of the post-tensioned beams in the nonlinear strut-tie model approach were estimated by checking the occurrence of a nodal zone failure mechanism, the structural instability of the selected strut-tie model due to the strength reduction of the struts and ties during the incremental loading steps, and conformity to the strut-tie model's geometric compatibility condition. The 21 May 2003 Zemmouri (Algeria) Earthquake: Damages and Disaster Responses Hakim Bechtoula and Hassane Ousalem Journal of Advanced Concrete Technology, 3(1) 161-174, 2005 A large number of reinforced concrete buildings collapsed or heavily damaged during the 6.8 magnitude earthquake that struck northern Algeria on 21 May 2003. A technical survey campaign was lunched to assess damages and losses in the most affected areas at Algiers and Boumerdes prefectures. Reinforced concrete frame structures and apartment buildings were the most damaged categories. Buildings with shear walls or steel frames performed well. Analyses of collected data showed that damage was randomly distributed in different localities. Results and observations highlighted the following deficiencies: poor quality materials, poor quality constructions, insufficient element sizes and dimensions, lack of good detailing and poor design. This paper also reviews the seismic hazard preparedness and disaster responses, like emergency relief, administrative, technical and scientific issues, and social issues. Finally, lessons from the catastrophic event and future needs are summarized. Inventory Survey of the 2003 Zemmouri (Algeria) Earthquake: Case Study of Dergana City Hassane Ousalem and Hakim Bechtoula Journal of Advanced Concrete Technology, 3(1) 175-183, 2005 Soon after the May 21, 2003 Zemmouri (Algeria) earthquake that had stricken mainly Boumerdes and Algiers prefectures, inventory investigations were conducted on the existing constructions and facilities in order to evaluate losses and damages that affected the areas. This paper presents observations and analyses concerning a locality judged be typical and might be considered as a case for the whole affected prefectures. A recent small-urbanized zone of around 4km2 located in Algiers prefecture and near the border of Boumerdes prefecture was investigated in detail by the authors. A total of 725 buildings were evaluated. Analysis of the collected data showed that damage was randomly distributed on the area. This result would strengthen the assumptions of poor materials quality and lack of good details and design, as regards to other assumptions, for instance soil conditions effect. Reinforced concrete constructions were the most affected among other types where about 18% of constructions suffered moderate to heavy damage. Data analyses showed that the most affected constructions are those in the range from 5 to 6 stories while constructions with one story did not suffer any damage. Typical observed damages were, mainly, due to poor longitudinal and/or transversal reinforcements in the columns, very poor concrete quality, lack of shear reinforcements at beam-column joints, soft stories, pounding and also formation of short columns. Restoration of facilities and retrofitting practice on damaged buildings are reviewed in some cases.