Service life prediction of a reinforced concrete bridge exposed to chloride induced deterioration

Papadakis, Vagelis G. Techno-Press 2013 Advances in concrete construction Vol.1 No.3

While recognizing the problem of reinforcement corrosion and premature structural deterioration of reinforced concrete (RC) structures as a combined effect of mechanical and environmental actions (carbonation, ingress of chlorides), emphasis is given on the effect of the latter, as most severe and unpredictable action. In this study, a simulation tool, based on proven predictive models utilizing principles of chemical and material engineering, for the estimation of concrete service life is applied on an existing reinforced concrete bridge (${\O}$resund Link) located in a chloride environment. After a brief introduction to the structure of the models used, emphasis is given on the physicochemical processes in concrete leading to chloride induced corrosion of the embedded reinforcement. By taking under consideration the concrete, structural and environmental properties of the bridge investigated, an accurate prediction of its service life is taking place. It was observed that the proposed, and already used, relationship of service lifetime- cover is almost identical with a mean line between the lines derived from the minimum and maximum critical values considered for corrosion initiation. Thus, an excellent agreement with the project specifications is observed despite the different ways used to approach the problem. Furthermore, different scenarios of concrete cover failure, in the case when a coating is utilized, and extreme deicing salts attack are also investigated.

Sterile Necrosis of the Sternum: A Rare Complication Following Coronary Artery Bypass Surgery

Emmanouel Papadakis,Maria Kalliopi Konstantinidou,Meletios A. Kanakis 대한흉부외과학회 2017 Journal of Chest Surgery (J Chest Surg) Vol.50 No.6

We herein present the unique case of a 68-year-old male diabetic patient who developed sterile necrosis of the sternum 1 month after myocardial revascularization with the use of bilateral internal thoracic artery grafts. The sternum had been closed by the bilateral Robicsek wiring technique. The sternum was removed, and bilateral pectoralis major flaps were used to cover the defect. The patient had an uneventful recovery.

ILO 초국적 사회적 대화에 관한 전문가회의 논의내용, 결론문 및 ILO의 임무

Konstantinos Papadakis 한국노동연구원 2019 국제노동브리프 Vol.17 No.11

Spontaneous Prosthesis Leaflet Detachment and Loss During Aortic Valve Implantation

Emmanouel Papadakis,Thomas Martens,Meletios Kanakis 한국심초음파학회 2022 Journal of Cardiovascular Imaging (J Cardiovasc Im Vol.30 No.2

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Computer-aided approach of parameters influencing concrete service life and field validation

V. G. Papadakis,M. P. Efstathiou,C. A. Apostolopoulos 한국계산역학회 2007 Computers and Concrete, An International Journal Vol.4 No.1

Over the past decades, an enormous amount of effort has been expended in laboratory and field studies on concrete durability estimation. The results of this research are still either widely scattered in the journal literature or mentioned briefly in the standard textbooks. Moreover, the theoretical approaches of deterioration mechanisms with a predictive character are limited to some complicated mathematical models not widespread in practice. A significant step forward could be the development of appropriate software for computer-based estimation of concrete service life, including reliable mathematical models and adequate experimental data. In the present work, the basis for the development of a computer estimation of the concrete service life is presented. After the definition of concrete mix design and structure characteristics, as well as the consideration regarding the environmental conditions where the structure will be found, the concrete service life can be reliably predicted using fundamental mathematical models that simulate the deterioration mechanisms. The prediction is focused on the basic deterioration phenomena of reinforced concrete, such as carbonation and chloride penetration, that initiate the reinforcing bars corrosion. Aspects on concrete strength and the production cost are also considered. Field observations and data collection from existing structures are compared with predictions of service life using the above model. A first attempt to develop a database of service lives of different types of reinforced concrete structure exposed to varying environments is finally included.

Predictive modeling of concrete compressive strength based on cement strength class

V.G. Papadakis,S. Demis 사단법인 한국계산역학회 2013 Computers and Concrete, An International Journal Vol.11 No.6

In the current study, a method for concrete compressive strength prediction (based on cement strength class), incorporated in a software package developed by the authors for the estimation of concrete service life under harmful environments, is presented and validated. Prediction of concrete compressive strength, prior to real experimentation, can be a very useful tool for a first mix screening. Given the fact that lower limitations in strength have been set in standards, to attain a minimum of service life, a strength approach is a necessity. Furthermore, considering the number of theoretical attempts on strength predictions so far, it can be seen that although they lack widespread accepted validity, certain empirical expressions are still widely used. The method elaborated in this study, it offers a simple and accurate, compressive strength estimation, in very good agreement with experimental results. A modified version of the Feret’s formula is used, since it contains only one adjustable parameter, predicted by knowing the cement strength class. The approach presented in this study can be applied on any cement type, including active additions (fly ash, silica fume) and age.

Transient Forces on Pipe Bends by the Propagation of Pressure Wave

Woo, Hyo-Seop,Papadakis, C.N.,Kim, Won Korea Water Resources Association 1995 Korean journal of hydrosciences Vol.6 No.-

External forecs acting on a pipe bend change when a transient pressure wave propagates through the bend. Analytical expressions are derived to compute the changes of these forces which depend mainly on static pressure rather than fluid momentum. This analysis reveals that the change of the vertical component of the force acting on a pipe bend with an angle larger than 90 may reverse in direction during the passage of a pressure wave through the bend.

A software-assisted comparative assessment of the effect of cement type on concrete carbonation and chloride ingress

S. Demis,V.G. Papadakis 사단법인 한국계산역학회 2012 Computers and Concrete, An International Journal Vol.10 No.4

Utilization of supplementary cementing materials (SCM) by the cement industry, as a highly promising solution of sustainable cement development aiming to reduce carbon dioxide emissions, necessitates a more thorough evaluation of these types of materials on concrete durability. In this study a comparative assessment of the effect of SCM on concrete durability, of every cement type as defined in the European Standard EN 197-1 is taking place, using a software tool, based on proven predictive models (according to performance-related methods for assessing durability) developed and wide-validated for the estimation of concrete service life when designing for durability under harsh environments. The effect of Type II additives (fly ash, silica fume) on CEM I type of cement, as well as the effect of every Portland-composite type of cement (and others) are evaluated in terms of their performance in carbonation and chloride exposure, for a service life of 50 years. The main aim is to portray a unified and comprehensive evaluation of the efficiency of SCM in order to create the basis for future consideration of more types of cement to enter the production line in industry.

Sustainable concrete mix design for a target strength and service life

Julia G. Tapali,Sotiris Demis,Vagelis G. Papadakis 사단법인 한국계산역학회 2013 Computers and Concrete, An International Journal Vol.12 No.6

Considering the well known environmental issues of cement manufacturing (direct and indirect levels of CO2 emissions), clinker replacement by supplementary cementing materials (SCM) can be a very promising first step in reducing considerably the associated emissions. However, such a reduction is possible up to a particular level of SCM utilization, influenced by the rate of its pozzolanic reaction. In this study a (4-step) structured methodology is proposed in order to be able to further adjust the concrete mix design of a particular SCM, in achieving additional reduction of the associated levels of CO2 emissions and being at the same time accepted from a derived concrete strength and service life point of view. On this note, the aim of this study is twofold. To evaluate the environmental contribution of each concrete component and to provide the best possible mix design configuration, balanced between the principles of sustainability (low environmental cost) and durability (accepted concrete strength and service life ). It is shown that such a balance can be achieved, by utilising SCM by-products in the concrete mix, reducing in this way the fixed environmental emissions without compromising the long-term safety and durability of the structure.

Inflammatory Bowel Disease: Updates on Molecular Targets for Biologics

( Konstantinos H. Katsanos ),( Konstantinos A. Papadakis ) 대한간학회 2017 Gut and Liver Vol.11 No.4

Therapy for inflammatory bowel disease (IBD) has changed, with several new agents being evaluated. The era of anti-tumor necrosis factor (anti-TNF) antibody therapy saw remarkable progress in IBD therapy. Some patients, however, do not respond to anti-TNF treatment, or their response decreases over time. This phenomenon highlights the need to identify new molecular targets for therapy in IBD. The targets of new therapeutic molecules in IBD must aim to restore immune dysregulation by the inhibition of proinflammatory cytokines (TNF-α, interleukin [IL]-6, IL-13, IL-17, IL-18, and IL-21) and augmentation of the effect of anti-inflammatory cytokines (IL-10, IL-11, and transforming growth factor β) and to pursue new anti-inflammatory targets, such as regulatory T-cell therapy, Smad7 antisense, Janus-activated kinase inhibition, Toll-like receptor stimulation, leukocyte adhesion, and blockade of T-cell homing via integrins and mucosal addressin cellular adhesion molecule-1. In addition, potential molecular targets could restore mucosal barrier function and stimulate mucosal healing. Despite these potential targets, the value and clinical significance of most new molecules remain unclear, and clinical efficacy and safety must be better defined before their implementation in clinical practice. This article aims to review the promising and emerging molecular targets that could be clinically meaningful for novel therapeutic approaches. (Gut Liver 2017;11:455-463)