CORROSION INDUCED FAILURES IN PRESTRESSED CONCRETE STRUCTURES AND PREVENTATIVE MEASURES KORROSIONSBEDINGTE SCHÄDEN IN SPANNBETONKONSTRUK- TIONEN UND HIERAUS ABGELEITETE PRÄVENTIVMASSNAHMEN DOMMAGES EN CONSEQUENCE DE CORROSION DANS DES CONSTRUCTIONS EN BETON PRECONTRAINT ET DES MESURES PREVENTIVES
During the past 40 years in Germany some serious damages in postand pre-tensioned components have been occurred because of stress corrosion cracking of prestressing steel. Especially those problems caused a great stir, where the attendant circumstances of design, execution and building materials were not unusual. But the prestressing steel was unsuited to resist the inevitable conditions on construction site and inside the construction.
Etude et caractérisation par émission acoustique et mesures électrochimiques de la fragilisation par l'hydrogène des câbles de précontrainte : application aux ouvrages d'art
Il existe aujourd’hui un parc important d’ouvrages d’art vieillissants dont les possibilites de surveillance n’ont pas ete prevues des leur construction ce qui rend leur evaluation difficile. Concernant les ouvrages en beton precontraint, l’une de leurs principales causes de degradation est la corrosion des câbles de precontrainte en general et leur fragilisation par l’hydrogene en particulier. Dans ce but, l’emission acoustique (EA) peut etre une alternative pour l’inspection et le controle de ces ouvrages. L’objectif de ce travail est non seulement d’etudier le potentiel de l’EA a detecter l’endommagement des armatures de precontrainte provoque par fragilisation par l’hydrogene, mais aussi d’examiner l’adaptation de cette technique d’auscultation aux exigences structurelles des ouvrages. En couplant le suivi acoustique a des mesures electrochimiques, la validation de cette technique est realisee sur des structures de laboratoire a partir d’essais normalises et acceleres dans un milieu de thiocyanate d’ammonium. Les resultats obtenus montrent que l’EA est performante pour l’etude mecanistique et le controle de ce mode de corrosion. Ensuite des essais pilotes sur des structures complexes permettent de se rapprocher d’une auscultation sur ouvrage et egalement de caracteriser les limites de l’EA pour son application in situ.
Assessment of fractures in endodontically treated teeth restored with and without root canal posts using high-resolution cone beam computed tomography
Background Root fractures are a diagnostic challenge for dentists in endodontic treatment. This study aimed to determine the relationship between the characteristics of tooth fractures and the presence of root canal posts in endodontically treated teeth using high-resolution cone beam computed tomography (CBCT). Material and Methods Fifty high-resolution CBCT scans of endodontically treated teeth with a diagnosis of fracture were obtained, of which 30 were from women and 20 were from men. These scans were acquired with three Veraviewepocs 3D units and one 3D Accuitomo 170 unit, with a 40 × 40-mm field of view and 125 μm voxel size. The variables assessed included the type of fracture, extent of fracture, type of retention, post length, cause of endodontic failure, location of the lesion, and time required to detect the fracture (difficulty score). For data analysis, the chi-squared test, Student’s t-test, and multiple linear regression (α <0.05) were used. Results No association was found between the type of fracture and type of retention or between the type of fracture and its extent (P>0.05). On the other hand, the type of fracture significantly influenced the time required for its detection. Additionally, the most difficult plane for detecting the fracture and the difficulty score were associated, with statistically significant results. Conclusions The type of fracture in endodontically treated teeth was not associated with the type of post used for restoration. All of the CBCT systems used to detect tooth fracture showed the same efficiency. Key words:Cone-Beam CT, Tooth Fracture, Root Canal Post.