Cathodic Protection of Corroded Pre-stressed Tendons

The corrosion of reinforcement in concrete, whether conventional or pre-stressed, remains a significant cause for the loss of durability of reinforced concrete structures. Corrosion costs the UK economy between 3% to 4% of Gross National Product. This is, in turn, has resulted in the development of greatly enhanced methods of remediation and life extension. One possible approach is to use Cathodic Protection (CP) to control further deterioration. CP of reinforcing steel in concrete structures has proved to be effective for preventing or controlling corrosion and been used successfully for over 25 years. CP is able to stop corrosion in a reliable and economical way where the environment has caused reinforcement corrosion and subsequent concrete damage. However, concerns exist about the ability of CP to avert deterioration in pre-stressed structures due to hydrogen generation and subsequent embrittlement of the tendons. This research investigates the performance of pre-stressed steel tendon exposed to an impressed current cathodic protection (ICCP) at varying potentials on a long-term basis to establish its effect on strength and establish optimised criteria for CP that can be safely applied to deteriorated pre-stressed structures. Twelve timber moulds were manufactured for applying the pre-stressing technique to test specimens. Tendons measuring 5.4mm diameter were selected in both the galvanised and ungalvanised state. Two levels of pre-stressing have been investigated, namely low level (300-400 MPa) and high level (800-1200 MPa). Three different degrees of corrosion Stage I, II and III with target losses of cross-sectional of 0-1 %, 2-4 % and 4-7 % respectively, were employed to replicate in-situ conditions. The actual degree of corrosion was verified gravimetrically by weighing the tendons both before and after testing. The tendons were pre-stressed in two types of electrolyte, namely a saline solution and a sand/cement mortar representing mortar. Upon completion of the corrosion phase using an anodic impressed current method, Impressed Current Cathodic Protection (ICCP) was applied to the tendons at two levels of polarization, normal protection (ICCP-N) in the range of -650 to -750 mV vs Ag/AgCI/ 0.5M KCI and over protection (ICCP-O) ranging between -850 to -1300 mV vs Ag/AgCI/ 0.5M KCI for an extended period to both ungalvanised iv and galvanised pre-stressed steel tendons, to investigate its effect. The potentials of the pre-stressed steel tendon and potential decay resulting from the application of ICCP were monitored and analysed. The strain in the tendons was also monitored throughout the corrosion and ICCP phases to establish pre-stress losses. Finally, the mechanical properties were investigated and the tendon surfaces and fracture modes inspected using an Infinite Focus Microscope (IFM) and Scanning Electronic Microscope (SEM). The results confirmed that accelerated corrosion is a reliable technique for generating the corrosion of steel. ICCP can be used in the corroded pre-stressed tendons as the long-term application shows there is no significant effect on the surface or damage of the both types of tendons with low or high levels of pre-stress. There has been a long term loss in service stress which due to corrosion, due to ICCP or a combination of both. From the results, the loss is more likely to be corrosion induced rather than ICCP. A higher degree of corrosion leads to a higher loss in pre-stress in highly pre-stressed tendons, which is an additional loss that should be accounted for at the design stage

La formation continue des directeurs comme outil managérial d'introduction du changement en gestion scolaire

L'amélioration de la gestion scolaire est devenue une nécessité dans les systêmes éducatifs vue les contraintes des changements actuels, c'est pourquoi le développement du rôle du directeur est placé en priorité et c'est ainsi qu'on mise actuellement sur la formation continue de ce dernier. On cherche à  ce que cette formation contribue à  impliquer les chefs des établissements scolaires dans le processus de changement et à  assurer une transition réelle chez ces acteurs pour qu'ils s'engagent volontairement et effectivement dans l'innovation de la gestion de leurs écoles. L'expérience Marocaine montre que suite à  des processus continus de réforme, les décideurs sont devenus conscients de la nécessité de s'orienter dans un sens managérial et de considérer l'innovation dans la gestion scolaire et le rôle du directeur comme point de départ pour arriver à  une performance du systême. Parmi les outils exploités pour atteindre ces objectifs, la formation continue des directeurs est venue en premier lieu.  Cependant l'étude du terrain montre que cette formation comme conçue et dispensée n'a pas pu  assurer l'engagement total des chefs des établissements scolaires dans l'introduction du changement voulu

Capital immatériel et performance organisationnelle

The intangible capital has an essential place within the organization, it is a lever of value creation, it is an essential component of the value of a company. Knowledge management therefore enhances the value of intangible capital within the company, it allows to capitalize on the knowledge and experience of its organization and its employees, knowledge management therefore allows to exploit these assets in order to slow down the repetition of failures, to capitalize on good practices, to mitigate the low rate of learning, thus the silos are broken and the sharing of knowledge is promoted. By having a good knowledge management, an organization is perpetually listening to its customers while opting for customer segmentation and maintaining a relational frequency, i.e. a relationship with each of its customers, the organization also capitalizes on positive experiences that make the company unique in the eyes of customers.   JEL Classification: E22 Paper type: Theoretical ResearchLe capital immatériel à une place essentielle au sein de l’organisation, c’est un levier de création de valeurs, c’est une composante essentielle de la valeur d’une entreprise. La gestion des connaissances valorise donc le capital immatériel au sein de l’entreprise, elle permet de capitaliser sur le savoir et l’expérience de son organisation et de ses employés, la gestion des connaissances permet donc d’exploiter ces atouts afin de freiner les répétitions d’échecs, de capitaliser les bonnes pratiques, d’atténuer le faible taux  d’apprentissage, ainsi les silos sont cassés et le partage des savoirs est favorisé. En ayant une bonne gestion des connaissances, une organisation est perpétuellement à l’écoute de son client tout en optant pour la segmentation client et en maintenant une fréquence relationnelle c’est-à-dire une relation avec chacun de ses clients, l’organisation capitalise également des expériences positives qui rendent l’entreprise unique aux yeux des clients.   Classification JEL: E22 Type de l’article : Article théoriqu

Corrosion induced losses in pre-stressed tendons

The diameter of single tendons in pre-stressed concrete is typically around 5mm, corrosion combined with high levels of pre­stress can lead to a catastrophic, sudden rupture if not discovered in time. However, even if corrosion is present but not severe enough to cause rupture, a loss in pre-stress may result which may influence the load carrying capacity of the member This paper investigates the loss in pre-stress of tendons subjected to different levels of corrosion and different level of pre-stress. Twelve timber moulds were manufactured as a base for applying the pre-stressing technique. Ungalvanised tendons measuring 5.4mm diameter were pre-loaded to two extreme target levels of stress, namely 30% and 80% of ultimate tensile strength (UTS) and surrounded by mortar. Accelerated corrosion of 0% (control), 3% and 6% target loss of cross-sectional area were applied to replicate in-situ conditions. The strain in the tendons was continuously monitored throughout the corrosion process via vibrating wire strain gauges. The results show that the lightly pre-stressed tendon (30% UTS) exhibited a negligible change in pre-stress for 0% and 3% corrosion which increased to 17MPa when the degree of corrosion was doubled to 6%. Similarly, a decline in the initial high target level of pre-stress of 80% UTS was recorded as 9 MPa for 3% corrosion but when the corrosion doubled to 6%, the loss in pre-stress increased by a factor of 7 to 63MPa reduction. This indicates that higher degrees corrosion coupled with higher levels of pre-stress leads to higher losses of pre-stress and this should be accounted for as an additional loss at the design stage

LES APPROCHES DU LEADERSHIP EN MANAGEMENT DES ORGANISATIONS : ANALYSE COMPARATIVE DES FONDEMENTS, DES APPORTS ET DES LIMITES

In order to understand and explain the phenomenon of power in organizations, several theories have tried to develop models that focus primarily on the characteristics of the manager or leader in the organization. All these theories belong to global approaches that are oriented to wards different visions: traits approch, behavioural, contingency, transformational and many others that can beassociated or which sometimes complete them. In this synthes is work, the aimis to present a critical reflection on the main approaches in styles of organizational management and leadership, we will study all these approaches by looking for relations of heterogeneity, contradiction or Complementarity by highlighting the basic hypotheses and foundations of each approach as well as the context of its emergence. For the same goal, we will develop the inputs and limits of the models of these approaches

Étude de la dynamique stationnelle des populations des culicidés dans la province de Sidi Slimane (Maroc)

La province de Sidi Slimane (Maroc) par son climat et sa position dans la plaine du Gharb en tant qu’une zone d’inondation, engendre une grande variété de gîtes larvaires culicidiens. Les autorités sanitaires de la province adoptent la stratégie nationale qui vise essentiellement le maintien de l’élimination des maladies parasitaires à transmission vectorielle et notamment le paludisme autochtone qui repose en grande partie sur la lutte contre le vecteur. Cette lutte ne peut être efficace sans la bonne connaissance de la répartition de ce vecteur dans l’espace et dans le temps. Dans ce travail nous avons suivi l’évolution spatiotemporelle de 06 espèces de la famille de culicidae (1 espèce d’Anophèles, 5 espèces de Culex) dans huit (08) stations au cours d’un cycle hydrologique de l’année 2011 dans la province de Sidi Slimane (Maroc). Les différents peuplements étudiés sont largement dominés par Cx. pepiens aussi bien spatialement que temporellement. C’est une espèce ubiquiste et printano-automnale. CX.hortensis est une espèce printanière. Cx. theileri est une espèce qui enregistre son maximum d’abondance en printemps. CX. laticinctus évolue également dans un gîte permanent presque durant toute l’année, An. labranchiae, CX.medestus, espèces qui ont des exigences quant au type de gîtes à coloniser.Mots-clés : culicidae, spatio-temporel, anophèles, culex, Sidi Slimane, MarocStudy of the population dynamics of stational culicidées in the province of Sidi Slimane (Morocco)The province of Sidi Slimane (Morocco) by its climate and its geographical situation in the plain of Gharb,which is known as a zone of flood, engenders a big variety of mosquitos larvae breeding grounds. The sanitary authorities of the province adopt the national strategy That aims essentially at eliminating the parasitic diseases at vector transmission , particularly, the autochtonous malaria , That takes the largest part in the fight .However The fight against this vector cannot be effective without a good knowledge of distribution in space and time. In this work we followed the spatiotemporelle evolution of 06 culicidae family species (1 species of Anophèles, 5 species of Culex). In eight (08) stations during a hydrological cycle of the year 2011 in the province. The various studied settlements are largely dominated by Cx. pepiens spatially and temporally as well ubiquist and printano-autumnal. CX.hortensis is a spring species. Cx. theileri is a species which records its maximum of abundance in spring. CX.laticinctus also evolves in the permanent of breeding places almost during all the year. An. labranchiae, CX.medestus, is species which have certain requirements as for the type of breeding places with colonize.Keywords : culicidae, spatio-temporel, anophèles, culex, Sidi Slimane, Morocco