Durability of reinforced concrete and the mechanical behavior of reinforced steel bar (Doctoral thesis)

Αποστολόπουλος, Αλκιβιάδης

Degradation of durability of reinforced concrete structures is becoming more and more a matter of concern for societies. In light of this, both the long and short life expectancy of a structure are synonymous terms of resistance. In other words, its ability to resist the detrimental environmental effect (physicochemical or mechanical) and any other deterioration process. The consequences of degradation of resistance of the structures, besides the known external visible phenomena, they take place as internal invisible phenomena such as: corrosion of steel rebar, bonding loss of concrete and steel rebar, impairment of the cross section and drop of mechanical properties of steel bar. In coastal areas, particularly, this kind of degradation takes place in stages throughout the years and is highly related to structural integrity and especially to the construction safety. Although the degradation of durability and corrosion of rebar are interdependent, parallel and time-dependent phenomena, are not included or quantitated in the regulation intervention (ΚΑΝΕΠΕ). The importance and necessity of this Thesis lies in the fact that the effects of reduced resistance of concrete in terms of the mechanical performance of corroded rebars have not been adequately studied. The analysis methodology that used, was based on the results of an extensive experimental program which included: • Experimental simulation of coastal environment through laboratory artificial salt spray corrosion of various categories steels rebars. • Production of reinforced concrete specimens, imposing conditions of corrosion and instrumental measurements for studying corrosion characteristics (measurement of half-cell potential values, mass loss, cracking across the specimens, depth and surface of pitting and metallographic analyzes). • Program of steel corrosion damage characterization (both bare and embedded rebars) in relation to time of exposure. • Program of tensile and low cycle fatigue tests (in order to simulate the seismic loads). • SEM and EDX analysis in corroded specimens, quantification - recognition of corrosion damage and identification of damage mechanisms. • Prediction of mechanical response of corroded BStIII (S420) rebars of existing structures under the effect of axial cyclic loads (in correspondence with strong seismic events). Conclusions Although corrosion of rebars causes a drop of strength properties roughly equivalent to the percentage reduction of mass loss, it leads to dramatic drop in ductility properties namely to deformation properties in maximum strength. For the same mass loss values, concrete embedded specimens presented stronger superficial severe localized pitting corrosion in contrast to bare specimens. This corrosion effect had a similar impact on the mechanical properties to both group of rebars. Chloride induced corrosion phenomena have significant effect on the mechanical behavior of dual-phase steel rebars, due to the interaction of external pitting and internally inclusions (MnS and FeS, pores, oxides). The characteristics of surface rebars fracture under (strong) seismic loads, reveal combinational action of various mechanisms failure phenomena. During strong axial rotations (seismic events), regions of internally sulfide inclusions, promote coalescence and propagation of cracks. Furthermore, the buckling phenomena accelerate the premature exhaustion of ductility of rebars. Based on the above-mentioned conclusions arises the need for "dense" technical inspections of reinforced concrete structures.
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Μηχανικών Επιστήμης Υλικών
Subject classification: Σκυρόδεμα
Keywords: Ανθεκτικότητα σκυροδέματος,Διάβρωση χλωριόντων,Οπλισμένο σκυρόδεμα,Διάβρωση χάλυβα οπλισμού,Μηχανικές ιδιότητες χάλυβα οπλίσμου,Εγκιβωτισμένος στο σκυρόδεμα χάλυβας οπλισμού,Απώλεια μάζας,Διάβρωση βελονισμών,Βάθος βελινισμού,Durrabillity of concrete,Cloride induced corrosion,Reinforced concrete,Corrosion of steel rebar,Mechanical properties of steel rebar,Sulfides in steal rebar,Embedded in concrete steel rebar,Mass loss,Pitting corrosion,Pit depth
URI: http://olympias.lib.uoi.gr/jspui/handle/123456789/28034
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