George Sergi - Academia.edu (original) (raw)

Papers by George Sergi

"SP-114: Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete: Proceedings of the Third International Conference"

This paper will discuss how zinc coatings, applied mainly by galvanizing, have been widely used t... more This paper will discuss how zinc coatings, applied mainly by galvanizing, have been widely used to provide supplementary corrosion protection to reinforcing steel in concrete exposed to aggressive media. Their performance, particularly in concretes contaminated with chloride salts, has been variable; this is believed to be due, at least in part, to the effects of differences in cement alkalinity on the rate of zinc dissolution. To investigate this, specimens were made in which well characterized zinc coated steel electrodes were embedded in cement pastes containing various proportions of silica fume and sodium chloride. They were exposed to moist air for several months, during which time the pore electrolyte compositions were analyzed and the corrosion rates of the embedded electrodes were monitored by linear polarization. It was found that the major influence on the corrosion rate of the zinc coatings was the pH of the pore electrolyte phase, so that quite modest levels of silica fume were capable of reducing corrosion rates by orders of magnitude when compared with those sustained in the unblended pastes. The implications regarding the effective service lives of the coatings are believed to be considerable. Analysis of the relationship between corrosion potential and corrosion rate for the embedded electrodes revealed that the rates of corrosion were generally subject to anodic control, except at very high values when oxygen diffusion became the rate-limiting process.

Concrete specimens containing steel electrodes were made from a mix that contained a reactive agg... more Concrete specimens containing steel electrodes were made from a mix that contained a reactive aggregate but insufficient alkali concentration to cause expansion due to alkali-silica reaction (ASR). Cathodic protection was applied to the steel at various levels of potentiostatic or galvanostatic polarisation and the strains in the concrete were monitored over gauge lengths close to and remote from the steel. Expansions in the vicinity of the steel were found to be dependent on the level of applied polarisation and were associated with local development of ASR in a zone of enhanced alkalinity formed around the cathode. Practical implications with regard to cathodic protection of reinforced concrete are considered. (A) For the covering abstract see IRRD 871351.

The research reported in this paper forms part of a collaborative project involving Aston Univers... more The research reported in this paper forms part of a collaborative project involving Aston University and a number of industrial and science-based partners, supported by the LINK Construction Maintenance and Refurbishment Programme. The aims of the project are to assess whether or not four commercially-available surface treatment systems are likely to be useful in extending the service-lives of concrete structures in which reinforcement corrosion has been initiated as a consequence of carbonation or chloride contamination and to determine whether their performance is affected by exposure to natural weathering. (A) For the covering abstract, see IRRD 892188.

Corrosion of steel reinforcement and the alkali silica reaction (ASR) are well documented problem... more Corrosion of steel reinforcement and the alkali silica reaction (ASR) are well documented problems. Many reinforced concrete highway structures are deteriorating as a result of corrosion induced by de-icing salts. Cathodic protection (CP) is one of a variety of techniques available for dealing with this. In principle, CP is likely to cause an increase in the alkalinity of the concrete around the cathodically polarised reinforcing steel with the consequential risk that ASR will be induced in concretes containing reactive aggregates. This report describes research aimed at investigating the possibility of a link between CP and ASR.

Construction and Building Materials, 2021

Ceramic tubular electrodes have been in use successfully as discrete anodes in impressed cathodic... more Ceramic tubular electrodes have been in use successfully as discrete anodes in impressed cathodic protection (CP) applications for several years tolerating current densities several times higher than most commercially available anodes. They owe their success to the stable highly conductive nature of the particular titanium suboxide used. Although stable, the titanium sub-oxide ceramic is known to slowly polarise when subjected to extreme cathodic current densities so it was important to determine their longevity under such strong polarising conditions. A long term programme was, therefore, initiated in 1994 with the objective of monitoring the performance of anodes embedded in steel reinforced concrete blocks over a period of between 7 and 12 years under a range of polarising levels. The work was supplemented by subjecting tubular anodes to the NACE Standard Test Method (NACE Standard TM0294-2001) at normal and four times normal current densities by surface area of the anode at equivalent charge levels of up to 100 years at 110mA/m 2 and 900mA/m 2 . Electrochemical results indicated a very good performance of the anodes over the test period and showed clearly that any polarisation of the anodes was acceptably low.

Materials and Corrosion, 2012

ABSTRACT For reinforced concrete structures a localisation of all significant critical areas can ... more ABSTRACT For reinforced concrete structures a localisation of all significant critical areas can only be done by a full surface inspection. The economic advantages are obvious: uncritical areas have not to be repaired expensively [1].The first step of the assessment should always be a visual inspection [2]. The range of deterioration causes can be limited and the degree of deterioration may be estimated roughly.The inspection program can be adjusted to the requirements. By means of a full surface potential mapping areas with a high risk for chloride induced reinforcement corrosion can be localised, although no deteriorations are visually detectable at the concrete surface. In combination with concrete cover depth and resistivity measurements areas with corrosion promoting exposure conditions can be localised even if the reinforcement is not yet depassivated. The following publication gives an overview about the essential full surface investigation methods to localise critical areas regarding corrosion of steel in concrete. The selection of methods is based on the inspection procedure given in [2].

Materials and Structures, 1991

Materials and Corrosion, 2010

Magazine of Concrete Research, 1992

One end surface of a cylindrical specimen of hardened OPC paste of water/cement ratio (w/c) 0·5 w... more One end surface of a cylindrical specimen of hardened OPC paste of water/cement ratio (w/c) 0·5 was exposed to 1 mol/l NaCl solution saturated with Ca(OH)2. The free hydroxyl, free chloride and total chloride concentration profiles were determined after 100 days of exposure by analysis of the paste at various depths from the exposed surface. Attempts were made to characterize these concentration profiles by Fick's laws. It was found that the total and free chloride profiles could be interpolated by Fick's second law to a fairly good approximation, but the hydroxyl concentration profile near the exposed surface deviated from such an interpolation. It was also confirmed that the relationship between free and bound chloride could be approximately represented by the Langmuir adsorption isotherm. The effect of chloride binding on chloride diffusion was determined by consideration of mass conservation, and this yielded a good characterisation of the free chloride profile. It is su...

Magazine of Concrete Research, 1993

One end surface of a cylindrical specimen of hardened OPC paste of water/cement ratio 0·5 was cem... more One end surface of a cylindrical specimen of hardened OPC paste of water/cement ratio 0·5 was cemented to that of a similar specimen which contained 2% chloride ion by weight of cement, added as sodium chloride. The total chloride contents, as well as the concentration profiles across the interface of potassium, sodium, chloride and hydroxyl ions in the pore solution phase, were determined. It was found that the sodium concentration profile could be interpolated by Fick's Second Law to a good approximation. By assuming a Lungmuir-type relationship between the free and bound chloride, the effect of chloride binding on diffusion was incorporated into diffusion equations derived from Fick's First Law and mass conservation. This also yielded a good characterization of the free chloride profile. The concentration profile of hydroxylions in the pore solution was more complex than those for sodium and chlorideions, but it could be modelled by assuming that hydroxyl ions move simply...

Steel reinforced concrete blocks were subjected to chloride extraction after they were dosed with... more Steel reinforced concrete blocks were subjected to chloride extraction after they were dosed with either NaCl or CaCl2. All the blocks were then exposed to the elements at the BRE exposure site for a total period of about 6 years. The steel reinforcement was regularly monitored electrochemically to determine its level of corrosion. Core samples were also analysed before and after treatment to determine the chloride concentration profiles. A selection of blocks were cut into smaller steel-containing prisms after 4 ½ years of exposure and were exposed to controlled laboratory conditions for 6 months while determining the level of corrosion electrochemically. At termination, each steel bar was removed and examined visually. The total weight loss was assessed gravimetrically. The final chloride concentration profile of each prism was also determined. Results suggested that corrosion was reduced significantly following chloride extraction but that the primary long-term controlling factor, both for the desalinated and control specimens, appeared to be the level of chloride present at the depth of the steel reinforcement. As, under normal procedures, a proportion of chloride remains after chloride extraction, a significant level of corrosion of the reinforcement, although greatly reduced, is still likely.

Steel reinforced concrete blocks were subjected to electrochemical chloride extraction after they... more Steel reinforced concrete blocks were subjected to electrochemical chloride extraction after they were dosed with chlorides. Following treatment, the blocks were exposed to the elements at the BRE exposure site for a period of up to 6 years. A selection of blocks were cut into smaller steel-containing prisms after 4 ½ years of exposure and were exposed to controlled laboratory conditions for 6 months while determining the level of corrosion by linear polarisation. At termination, each steel bar was removed and examined visually. The level of corrosion of each bar was also assessed gravimetrically. The final chloride concentration profile of each prism to a depth beyond the steel bars was also determined. Results suggested that corrosion was reduced significantly following chloride extraction but that the primary controlling factor, both for the desalinated and control specimens, was the level of chloride present at the depth of the steel reinforcement. Coating the concrete after treatment resulted in an overall increase in corrosion level, possibly because the coatings were not coherent and allowed moisture to penetrate the concrete through cracks and defects which could not subsequently escape owing to the coating.

Corrosion, 1985

Well-characterized zinc coatings on steel have been prepared so that either the eta or zeta phase... more Well-characterized zinc coatings on steel have been prepared so that either the eta or zeta phase was present as the outermost layer. Their electrochemical behavior was studied in a range of solutions by galvanostatic anodic polarization and potentiodynamic anodic polarization scans. The corrosion products were identified using scanning electron microscopy (SEM) and x-ray analysis. Results show that the solution pH has the most marked effect on electrochemical behavior and the nature of the corrosion product formed. At a given solution pH, the behavior and products formed are modified according to the concentration of chloride in the solution and the type of iron-zinc alloy layer investigated. The results are discussed in relation to the practical use of galvanized reinforcement in concrete.

Materials and Corrosion, 2013

MATEC Web of Conferences

It has been shown experimentally that corrosion of steel reinforcement can be arrested if suffici... more It has been shown experimentally that corrosion of steel reinforcement can be arrested if sufficient cathodic charge at a current density higher than 20 mA/m2 is applied over a period of weeks. Once corrosion is arrested, a cathodic prevention current density, which requires a current density an order of magnitude lower than for conventional cathodic protection, can be applied for long-term prevention of re-initiation of corrosion. Self-contained products were developed in the laboratory according to the Two-Stage principle, each single product containing a battery-operated ICCP element which produces a high initial current output of between 20 mA/m2 and 50 mA/m2 of steel area during an initial polarisation corrosion arrest phase and a galvanic anode component which delivers the lower cathodic prevention current long-term. Diodes ensure that the current from the battery is delivered to the steel reinforcement and not dumped onto the galvanic anode and allow the galvanic current to f...

Journal of Materials in Civil Engineering, 2001

Impressed current cathodic protection (CP) has been shown to provide an effective means of restra... more Impressed current cathodic protection (CP) has been shown to provide an effective means of restraining corrosion associated with the presence of chloride ions in reinforced concrete structures. Advances in extended anode systems and monitoring methods, together with ...

Cathodic protection (CP) of steel reinforced concrete is a well-established technique for control... more Cathodic protection (CP) of steel reinforced concrete is a well-established technique for controlling reinforcement corrosion of structural elements. Long-term maintenance of the system, however, is seen as a burden to most structure owners and managers as it involves additional and continual costs. There is, therefore, a requirement for simpler CP systems to be made available which will involve less maintenance and monitoring requirements. This paper demonstrates a methodology, backed by laboratory experiments, that has enabled such a userfriendly system to be developed and applied. The paper presents results that demonstrate corrosion arrest of steel samples, corroded by embedding in a range of chloride-containing mortars and delay in the onset of corrosion in chloride-free mortars subsequently exposed to external chlorides. This process is suggested as Stage-1 of a two-stage process for long-term protection of steel reinforcement, Stage-2 being corrosion or cathodic prevention, a...