Steel corrosion in reinforced concrete is a major concern to transportation agencies nationwide because of the expenses incurred for repair and ultimate shortening of bridge life. Cathodic protection (CP), as a remedy, has been applied to reinforced bridges in the US since 1974. However, application of this technique is largely empirical, lacking fundamental understanding. In order to optimize the performance of a CP system, it is important to monitor the rebar potential with respect to a reliable reference electrode. Moreover, because of potential variation in the concrete, reference cell placement is fundamental to ensure effective protection. The work plan was divided into two parts: laboratory scale experimentation and computer simulation. In the experimentation section, the response of graphite probes was compared to that of an Orion silver-silver chloride electrode. Graphite probes behaved as well as the standard electrode. Furthermore, the home-made graphite probes behaved the same as the commercial ones. This will allow much greater experimental latitude since the home-made probes are much more economical than the commercial ones. A finite difference code was developed to assess the performance of cathodic protection. The potential distribution in a two dimensional geometry of a concrete block with a sprayed zinc anode at one boundary and an iron cathode at the other side was calculated under cathodic protection. The equations were solved by means of a Gauss-Seidel iterative method with the help of an overrelaxation factor. An interval halving method was used to solve for nonlinear boundary condition at the iron. The effects of concrete pore saturation, concrete cover, and applied potential were studied to determine the degree of protection and proper placement of the reference electrode in concrete. Furthermore, a sensitivity analysis was performed versus input parameters: concrete conductivity, oxygen mass transfer coefficient, and oxygen reduction polarization parameters. The results of the simulation showed that the center of the rebar is less protected than the other locations. Therefore, the reference electrode should be located as close to the center as possible. / Graduation date: 1995

Experiments were conducted to investigate the potential of using a quench and self-tempering heat treatment process with AISI 1117 steel to satisfy the mechanical properties of ASTM A 706 rebar. A series of quenching tests were performed and the resulting microstructure and mechanical properties studied using optical microscopy, microhardness measurement, and tensile tests. The presence of martensite throughout the samples contributed to the enhanced strength and strain-hardening ratio (tensile to yield strength) of the material. The experimental results showed that AISI 1117 is capable of meeting the ASTM standard. In addition to the experiments, a computer model using the finite difference method and incorporating heat transfer and microstructure evolution was developed to assist in future optimization of the heat treatment process.

Experiments were conducted to investigate the potential of using a quench and self-tempering heat treatment process with AISI 1117 steel to satisfy the mechanical properties of ASTM A 706 rebar. A series of quenching tests were performed and the resulting microstructure and mechanical properties studied using optical microscopy, microhardness measurement, and tensile tests. The presence of martensite throughout the samples contributed to the enhanced strength and strain-hardening ratio (tensile to yield strength) of the material. The experimental results showed that AISI 1117 is capable of meeting the ASTM standard. In addition to the experiments, a computer model using the finite difference method and incorporating heat transfer and microstructure evolution was developed to assist in future optimization of the heat treatment process.

The polarization performance of two types of commercial galvanic point anodes for protection of reinforced steel around patch repairs was investigated. Experiments included measurement of the polarization history of the anode under constant current impressed by galvanostatic circuits and in reinforced concrete slabs. The tests revealed, for both types of anodes, a potential-current function (PF) indicating relatively little anodic polarization from an open circuit potential at low current levels, followed by an abrupt increase in potential as the current approached an apparent terminal value. Aging of the anodes was manifested by a continually decreasing current output in the concrete tests, and by increasingly more positive potentials in the galvanostatic tests. Those changes reflected an evolution of the PF generally toward more positive open circuit potentials and, more importantly, to the onset of elevated polarized potentials at increasingly lower current levels. There was considerable variability among the performance of replicate units of a given anode type. Modest to poor steel polarization levels were achieved in the test yard slabs. Modeling of a generic patch configuration was implemented with a one-dimensional approximation. The model calculated the throwing distance that could be achieved by a given number of anodes per unit perimeter of the patch, concrete thickness, concrete resistivity, amount of steel and amount of polarization needed for cathodic prevention. The model projections and aging information suggest that anode performance in likely application scenarios may seriously degrade after only a few years of operation, even if a relatively optimistic 100 mV corrosion prevention criterion were assumed. Less conservative criteria have been proposed in the literature but are yet to be substantiated. Other investigations suggest a significantly more conservative corrosion prevention may apply instead. The latter case would question the ability of the point anodes to provide adequate corrosion prevention.

Numerous cases of premature concrete deterioration due to alkali-silica reaction and/or delayed ettringite formation have developed within highway infrastructure in the state of Texas over the past two decades. Although experimental research and in-situ load testing on an international scale has indicated that moderate levels of deterioration are unlikely to pose a threat to structural safety, the discovery of reinforcing bar fracture in Japan due to ASR-related expansion has called into question the integrity of heavily damaged structures. A two-part experimental program was conducted at The University of Texas at Austin relating to ASR/DEF-induced reinforcing bar fracture. Work conducted under TxDOT Project 0-6491 included the fabrication and monitoring of four concrete specimens. Methods were employed to simulate a fracture of the transverse reinforcement within the time frame of the study and the applicability of various NDT monitoring techniques to detect bar fracture was evaluated. Furthermore, a number of reinforcing bar samples were tested and analyzed to investigate (1) the development of reinforcing bar cracking due to the bending operation and (2) the progression of cracks after application of an expansive opening force on bars with 90° bends. Research findings and conclusions form a preliminary assessment on the potential for reinforcing bar fracture within affected infrastructure in Texas. / text

Το οπλισμένο σκυρόδεμα αποτελεί στις μέρες μας το πιο διαδεδομένο υλικό για την κατασκευή του φέροντος οργανισμού κτιριακών κατασκευών. Παρά την εξαιρετική επίδοση του οπλισμένου σκυροδέματος ως φέροντος υλικού, διαπιστώθηκε ότι στη διάρκεια ζωής των κατασκευών από οπλισμένο σκυρόδεμα, η οποία συχνά ξεπερνά τα 100 χρόνια, παρατηρείται μια βαθμιαία συσσώρευση βλάβης, ένας από τους κύριους παράγοντες της οποίας εντοπίζεται στη διάβρωση του σιδηροπλισμού. Tα τελευταία χρόνια το πρόβλημα της υποβάθμισης της φέρουσας ικανότητας του οπλισμού σκυροδέματος λόγω βλάβης διάβρωσης έχει προσελκύσει το ενδιαφέρον αρκετών ερευνητών παγκοσμίως. Όμως, μέχρι σήμερα ούτε η τεχνολογική σημασία της υποβάθμισης αυτής μπορεί να εκτιμηθεί ικανοποιητικά, κυρίως λόγω της έλλειψης σχετικών συστηματικών μελετών αλλά και επαρκών πειραματικών δεδομένων, ούτε οι φυσικοί μηχανισμοί που συμβάλλουν στην παρατηρούμενη υποβάθμιση των μηχανικών ιδιοτήτων έχουν γίνει πλήρως κατανοητοί. Κατά την εκπόνηση της παρούσας διδακτορικής διατριβής πραγματοποιήθηκε μια συστηματική μελέτη της μηχανικής συμπεριφοράς χαλύβων οπλισμού σκυροδέματος διαβρωμένων τόσο στο φυσικό τους περιβάλλον εντός του σκυροδέματος όσο και σε συνθήκες εργαστηριακής επιταχυμένης διάβρωσης. Με βάση τη σύγκριση της απώλειας μάζας σε συνάρτηση με το χρόνο έκθεσης στο διαβρωτικό μέσο που καταμετρήθηκε στο εργαστήριο, με την απώλεια μάζας δειγμάτων υλικού τα οποία είχαν διαβρωθεί φυσικά σε κατασκευές, κατέστη δυνατή η εξαγωγή ενός εμπειρικού συντελεστή επιτάχυνσης της βλάβης διάβρωσης όταν το υλικό διαβρώνεται με τη μέθοδο της αλατονέφωσης σε σχέση με τη βλάβη φυσικής διάβρωσης. Κατά την παρούσα εργασία εξετάστηκαν οι χάλυβες S400 και S500s, οι οποίοι χρησιμοποιήθηκαν ευρύτατα για κατασκευές του φέροντος οργανισμού κτιρίων στην Ελλάδα κατά το πρόσφατο παρελθόν, καθώς και ο χάλυβας B500c ο οποίος από τα τέλη του 2006 χρησιμοποιείται στην Ελλάδα σχεδόν αποκλειστικά. Για την εξασφάλιση μια επαρκούς πειραματικής βάσης, πραγματοποιήθηκαν περισσότερες από 500 δοκιμές εφελκυσμού σε διαβρωμένα και μη διαβρωμένα δοκίμια. Οι μηχανικές δοκιμές εφελκυσμού έδειξαν ότι οι ιδιότητες αντοχής του διαβρωμένου υλικού παρουσιάζουν μικρή μόνο υποβάθμιση. Παρά ταύτα, η μείωση της διατομής των ράβδων του σιδηροπλισμού λόγω βλάβης διάβρωσης οδηγεί σε αύξηση των εφαρμοζόμενων τάσεων, αφού το βάρος των δομικών στοιχείων των κατασκευών προφανώς δεν μεταβάλλεται. Αυτό έχει ως συνέπεια τη σημαντική μείωση των συντελεστών ασφαλείας. Αντίθετα με τις ιδιότητες αντοχής, παρατηρήθηκε μια σημαντική μείωση στην παραμόρφωση θραύσης του διαβρωμένου υλικού. Η παραμόρφωση θραύσης και η ειδική ενέργεια παραμόρφωσης είναι κρίσιμες τεχνολογικές ιδιότητες σε συνθήκες σεισμού. Για την κατανόηση των φυσικών μηχανισμών που συμβάλλουν στην παρατηρούμενη υποβάθμιση των μηχανικών ιδιοτήτων, διεξήχθη εκτενής μεταλλογραφική μελέτη καθώς και μελέτη των επιφανειών θραύσης του διαβρωμένου υλικού. Παρατηρήθηκε ότι η διάβρωση είναι ομοιόμορφη, ενώ κατά το μήκος των δοκιμίων εντοπίστηκαν περιοχές με εντονότερη και άλλες με λιγότερο έντονη διάβρωση. Επιπλέον, η ανάλυση των επιφανειών θραύσης έδειξε πλήρως όλκιμη συμπεριφορά θραύσης των δοκιμίων ακόμη και στο έντονα διαβρωμένο υλικό. Επομένως, μπορεί να εξαχθεί το συμπέρασμα ότι η υποβάθμιση των μηχανικών ιδιοτήτων εφελκυσμού του χάλυβα οπλισμού οφείλεται κυρίως στην ανομοιομορφία που παρουσιάζει η διατομή του σιδηροπλισμού κατά μήκος των ράβδων του υλικού λόγω της βλάβης διάβρωσης, με συνέπεια αφενός την τοπική συγκέντρωση τάσεων και αφετέρου την καταπίεση της ομοιόμορφης παραμόρφωσης κατά τον εφελκυσμό του υλικού. Τέλος, στην εργασία αυτή παρουσιάζεται μια μέθοδος με την οποία προσομοιώνεται η βλάβη λόγω διάβρωσης με μια τεχνητή εγκοπή. Η μέθοδος αυτή στηρίζεται στις παραδοχές ότι η ολκιμότητα του υλικού παραμένει αμετάβλητη λόγω της διάβρωσης και η παρατηρούμενη μείωση στην παραμόρφωση θραύσης οφείλεται στην καταπίεση της ομοιόμορφης παραμόρφωσης λόγω των εγκοπών που προκαλεί η διάβρωση στο υλικό οι οποίες διευκολύνουν τη δημιουργία του λαιμού. Επίσης γίνεται η παραδοχή ότι η παρατηρούμενη μείωση των ιδιοτήτων αντοχής οφείλεται στη συγκέντρωση τάσεων που προκαλούν οι εγκοπές αυτές. Δοκιμές εφελκυσμού σε δοκίμια με εγκοπές γνωστής γεωμετρίας έδειξαν ότι η μέθοδος αυτή μπορεί να χρησιμοποιηθεί με ικανοποιητική ακρίβεια για τον υπολογισμό των ιδιοτήτων εφελκυσμού του υλικού χωρίς την ανάγκη πραγματοποίησης μηχανικών δοκιμών. / Reinforced concrete is currently the most common material used for the construction of the load bearing elements of structures. Although this composite material performs exceptionally well, it has been noted that during the life span of reinforced concrete structures, which often exceeds 100 years, a gradual damage accumulation takes place. One of the most influential factors of this damage has been attributed to the corrosion of steel reinforcement. Recently, the degradation of the load bearing ability of steel reinforcement has been an issue under research by several researchers worldwide. Yet to date, the technological importance of this degradation caused by corrosion damage cannot be assessed to a satisfactory degree, mainly due to the lack of relevant experimental studies. Similarly, the physical mechanisms which contribute to the degradation have not been totally resolved. In the framework of the current PhD thesis, a systematic study of the mechanical behaviour of concrete reinforcing steel bars, corroded both in their natural environment (embedded in concrete) and by means of laboratory accelerated corrosion, was performed. By comparing the mass loss as a function of time recorded during the laboratory corrosion tests with the respective mass loss recorded from naturally corroded samples, an empirical acceleration factor was derived for laboratory corrosion damage compared to natural corrosion damage. Reinforcing steel grades S400* and S500s*, which have been used in the recent past for the reinforcement of concrete structures in Greece, as well as steel grade B500c**, which from the end of 2006 is used almost exclusively, were tested. To obtain a sufficient experimental database more than 500 tensile tests on corroded and non-corroded samples were performed. The tensile tests performed have shown only a slight degradation of the strength properties of the corroded steel bars. However, the reduction of the cross sectional area of the corroded bars lead to an increase of the applied stress, as the loads applied to which steel bars in structures are constant over time. This leads to a significant reduction of the safety factors applied during design. On the contrary, a significant reduction of the material’s ductility properties was recorded. Elongation to failure and strain energy density are crucial properties in the case of alternating loading during earthquakes. In order to understand the physical mechanisms which contribute to the recorded degradation of the mechanical properties, an extensive metallographic investigation as well as an investigation of the fracture surfaces of corroded material was performed. From this investigation it was concluded that corrosion damage is uniform without pitting, while along the bars’ length areas more severe corrosion damage was noted. Furthermore, the investigation of the fracture surfaces showed ductile fracture characteristics even of the most severely corroded specimens. It can therefore be concluded that the degradation of the tensile properties of corroded material is caused mainly by the non-uniformity of the corrosion damage and therefore of the cross sectional area along the longitudinal axis of the bars. This leads to a local stress concentration as well as to the depression of the uniform elongation during the tensile testing of the material. Finally, in the current PhD thesis a method by which corrosion damage can be simulated by a fictitious notch is suggested. This method is based on the assumptions that the ductility of the material remains unaffected by corrosion and the recorded reduction of the ductility properties is attributed to the depression of the uniform elongation caused by notches which are formed on the bars due to corrosion exposure and facilitate necking. In addition, the recorded reduction of the strength properties is attributed to the stress concentration caused by these notches. Tensile tests performed on specimens with artificial notches of known geometry have shown that the suggested method can be used to assess to a satisfactory degree the tensile properties of steel reinforcing bars without the need to perform tensile tests. * Names according to the Hellenic regulations. These steel grades are similar to the StIIIs and StIVs steel grades of the DIN regulations respectively. ** Name according to the Hellenic regulations. It is similar to StIV steel grade but with higher ductility requirements compared to S500s.

The following thesis presents the results of six full scale beams tests as part of a research program conducted at McGill University on the effect of steel fibres on the shear capacity of a beam with an aid ratio greater than 2.5. The test specimens had the following dimensions: 4400 mm long, 300 mm wide and 500 mm long. The beams had 4-25M bottom reinforcing bars and 2-20M top reinforcing bars. Two series were designed with different reinforcing details: the "BA" series contained transverse reinforcement spaced at 275 mm center to center while the "BB" series had no transverse reinforcement. The specimens were cast in three batches of two specimens from each series, with each batch containing concrete with respectively 0%, 0.5% and 1% fibres content by volume. The beams were simply supported and were tested with two equal point loads located at 500 mm from the centre of the beam. / This research project demonstrated a clear improvement of the shear capacity resulting from the use of steel fibres for the beams without transverse reinforcement. For the beams with transverse reinforcement, displacement ductility was highly increased. This suggests that fibres have the potential to reduce the congestion of the reinforcement if fibres are designed to replace partially closely spaced transverse reinforcement. Also, it was noted that a redistribution of stresses occurred resulting in the formation of more well-controlled cracks. Finally, the strength predictions using the method developed by Aoude (Aoude, 2007) agree very well with the experimental results.

E-glass has been widely used as a reinforcing material for years, especially as a plastic reinforcer in the production of GRP (Glass Reinforced Plastic). Failure of GRP materials under stress came in to the picture quite recently. Since then studies have been conducted in an attempt to understand the causes and the underlying behaviour. / Except for the last section of the research (analysis using a kinetic approach) where glass fibre was cut out to weigh approximately 1.0g, standard sized specimens were soaked in the required acid solutions of desired concentrations for varying temperatures and time frames. Wherever tensile strength retention was measured, LLOYD instrument was employed. Leaching of the cations were analysed using Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES and also know and ICP-AES). / The scope of this project can be divided in to four sections; first section involved investigating the effects of malonic acid. The study of malonic acid was narrowed to investigating the trend in strength retention. A rapid strength loss was observed initially followed by a much steady decline in the strength. However the continuation of the loss of strength was unmistakable throughout the time period of exposure. Furthermore, temperature can be observed as a facilitating factor in this degradation reaction. / Secondly the corrosive effect of glyoxylic acid on E-glass fibre was studied. This was explored at two different temperatures for two specific time frames using various concentrations of the acid of interest. The influence of this acid on the glass fibre was found out in terms of strength retention and loss of cations from the glass matrix. The mildness of this acid was accentuated by the fact that 70% or more of the strength was retained at all the conditions employed. A minima in strength retention was observed at 2M acid concentration similar to the trends observed in the past (Betz and Jones 2003 and Jones and Chandler 1986). Leaching of cations reflected this trend. The large strength retention could be related to the fewer amounts of Ca and K leached from the glass matrix (Kumosa and Qui, 1997). Similar to malonic acid, an unusually large amount of B was leached out that could be due to the favourable orientation of the anion with the trivalent ions during the complex formation. Yet again temperature was found to enhance the degradation process. / Next the extent of passivation (if any) showed by malonic acid was investigated using E-glass fibre pre-treated in 5M malonic acid and post treated in known corrosive acids hydrochloric acid and oxalic acid. Passivation of malonic acid was put to test through examination of strength retention of the fibres under these conditions. This segment was carried out as an extension of a finding (a behaviour synonymous to passivation) shown by malonic that surfaced the previous year by the present researcher. Increasing the pre-treatment time showed a great improvement in the retained strength for all the post-treatment acid mediums. Furthermore, while Jones and Betz (2004) featured 20-40% strength retention within a short time frame in 3M HCl, the immense amount of strength retention (60-70%) preceding pre-treatment should definitely be noted. Similarly strength retention of about 80% was observed when post-treated with the severely corrosive oxalic acid. Hence its is clear that passivation can be induced through prolonged pre-treatment in 5M malonic acid that could inhibit the attack of corrosive acid at least for a period of time. / The last fragment of the study focussed on understanding and working out the mechanism behind the reactions between the E-glass fibre and acid medium in terms of kinetics. The acids utilized were 1.5M malonic acid and 3M glyoxylic acid and the assessments were made through the analysis of the weight changes brought about by the acid medium at various temperatures and time frames. In addition leaching patterns of cations were evaluated as this could contribute in achieving the objective. Maximum weight loss reached 4% in glyoxylic acid while that for malonic acid exceeded 20%. The general trend was that the glass fibres lost weight in both acids for a period of time followed by an evident weight gain. Furthermore the weight loss results fit the first order rate law. While the leaching of cations reflects the weight loss for the shorter time frames, steady loss of ions was visible even for the longer time frames where the weight has increased. The weight gain could be explained in terms of binding of anions to certain cations on the glass surface, accounting for the hindrance in the loss of cations at the longer time frames as well. About 50% of weight loss was associated to Ca while 20% was to Al, leaving 6% to B where as the rest of the ions had shown almost insignificant contribution to the weight loss.

Thesis (Ph.D.)--University of Adelaide, Dept. of Civil and Environmental Engineering, 2002. / Includes corrigenda (inserted at front) and list of publications published as a result of this research. Includes bibliographical references (leaves 192-199).

The main purpose of this study was to investigate and implement a repair design for corrosion damaged bridge bents in order to resist lateral loading, such as wind loads or ship impact. Using the results from a one-third scale bridge bent constructed and tested for a previous study, non-linear modeling was used to simulate the same corrosion damage and load response. The principle variable considered was damage, represented as a percent of effective area loss of prestressing steel within a designated damage zone along the length of piles. Other influencing variables included: prestress transfer length, localized loss in prestress due to corrosion damage, prestress force, and concrete modulus of elasticity. Upon successful convergence of measured and modeled results, carbon fiber repair schemes were then modeled to restore bents to their full capacity. Suitable repairs were judged on the basis of restoration of capacity of the entire pile bent and the interaction diagrams of the individual piles. Results of the modeled repairs suggested that a single layer of a commercially available unidirectional carbon fiber would be sufficient when aligned longitudinally. No benefit from accompanying transverse fibers were considered although such a repair was suggested by the study findings. Analysis indicated that longitudinally bonded carbon fiber reinforced polymer (CFRP) to bridge piles increases a bent’s ability to resist bending moment due to lateral loading at the cap. However, additional capacity to plastic region of the response curve indicated larger capacity gains than by gains to elastic regions.