Searched for: author%3A%22Koleva%2C+D.A.%22
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Chen, Zhipei (author), Koleva, D.A. (author)
Different concrete structures (viaducts, bridges, or tunnels) in the neighborhoods of railways may be subject to the stray current leaking from the rails. In these cases, the reinforcing rebars embedded in concrete act as conductors, “pick up” the stray current, and can corrode. For simulating the stray current-induced corrosion of metals, most...
journal article 2021
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Chen, Zhipei (author), Koleva, D.A. (author), Schlangen, E. (author)
The focus of this work is to present test results on the bond of steel-mortar interface undergoing stray current. The bond strength, derived by pull-out tests, is correlated to the electrochemical response of the steel rebar and the properties of the mortar bulk matrix. The effects of curing regimes (in terms of duration of curing) and...
journal article 2021
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Pargar, F. (author), Koleva, D.A. (author), van Breugel, K. (author)
In this paper the potentiometric response of a Ag/AgCl electrode as a chloride sensor in cementitious materials of different mix design was studied. The chloride sensor’s response was discussed with respect to the presence of hydration products around the sensor. The free chloride content inferred from the sensor’s response was compared to the...
journal article 2019
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Pargar, F. (author), Kolev, H (author), Koleva, D.A. (author), van Breugel, K. (author)
The stability and reproducibility of an Ag/AgCl sensors’ response in an alkaline medium are important for the application of these sensors in cementitious materials. The sensors’ response, or their open circuit potential (OCP), reflects a dynamic equilibrium at the sensor/environment interface. The OCP response in an alkaline medium is affected...
journal article 2018
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Pargar, F. (author), Koleva, D.A. (author), van Breugel, K. (author)
Determination of the free chloride content in a concrete structure is important for evaluation of the risk of corrosion of reinforcing steel. The Ag/AgCl sensor is sensitive to chloride ions and exhibits an open circuit potential (OCP) that depends on the chloride ions activity in the environment. The interference of hydroxide and sulfide ions...
conference paper 2018
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Pargar, F. (author), Kolev, H (author), Koleva, D.A. (author), van Breugel, K. (author)
Characterization of the Ag/AgCl electrode is a necessary step toward its<br/>application as a chloride sensor in a highly alkaline medium, such as concrete.<br/>The nucleation and growth of AgCl on Ag in 0.1 M HCl was verified through<br/>cyclic voltammetry. Ag anodization was performed at current densities, determined<br/>by potentiodynamic...
journal article 2018
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Koleva, D.A. (author)
The corrosion of reinforced steel, and subsequent reinforced concrete degradation, is a major concern for infrastructure durability. New materials with specific, tailor-made properties or the establishment of optimum construction regimes are among the many approaches to improving civil structure performance. Ideally, novel materials would...
journal article 2018
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Chen, Zhipei (author), Koleva, D.A. (author), van Breugel, K. (author)
Metallic corrosion can cause substantial damage at various levels and in almost all types of infrastructure. For metallic corrosion to occur, a certain external environment and the presence of corrodents are the prerequisites. Stray current-induced corrosion, however, is a rather underestimated issue in the field of corrosion and civil...
journal article 2017
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Ouyang, X. (author), Koleva, D.A. (author), Ye, G. (author), van Breugel, K. (author)
A complete understanding of the mechanisms upon which a filler acts in a cement-based material, e.g. as a C–S–H nucleation and/or growth-inducing factor, is of high importance. Although various studies report on accelerated cement hydration in the presence of fillers, the reason behind these observations is not completely understood yet. This...
journal article 2017
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Susanto, A. (author), Koleva, D.A. (author), van Breugel, K. (author), van Beek, C. (author)
This work reports on the development of microstructural and mechanical properties of mortar cubes under the synergetic action of stray current and various environmental/curing conditions. The study refers to specimens cured for 24h only, followed by a 112 days period of partial or full submersion in water or alkaline medium. Additionally,...
journal article 2017
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Susanto, A. (author), Peng, G (author), Koleva, D.A. (author), van Breugel, K. (author)
Stray current is an electrical current “leakage” from metal conductors and electrical installations. When it flows through cement-based materials, electrical energy is converted to thermal energy that causes increasing temperature due to Joule heating phenomena. The aim of this paper is to shed light on the influence of electrical current flow...
journal article 2017
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Pargar, F. (author), Koleva, D.A. (author)
When studying chloride-induced corrosion in reinforced concrete structures, essential information of interest is the concentration of chloride ions in the system. The absence of a reliable method for monitoring the free chloride ions justifies the attempts towards establishing a feasible practice in the application of the already known Ag/AgCl...
journal article 2017
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Pargar, F. (author), Koleva, D.A. (author), van Breugel, K. (author)
This paper reports on the advantages and drawbacks of available test methods for the determination of chloride content in cementitious materials in general, and the application of Ag/AgCl chloride sensors in particular. The main factors that affect the reliability of a chloride sensor are presented. The thermodynamic behaviour of silver in the...
journal article 2017
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Chen, Zhipei (author), Koleva, D.A. (author)
Stray current circulating in reinforced concrete structures may initiate corrosion or accelerate existing corrosion processes on embedded reinforcement. In some cases, the range of dangerous or unwanted interactions of stray currents under favorable conditions (environment), is much broader than is generally recognized. All these show that...
journal article 2016
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Chen, Zhipei (author), Koleva, D.A. (author), van Breugel, K. (author)
Stray current arising from direct current electrified traction systems and then circulat-ing in reinforced concrete structures may initiate corrosion or even accelerate existing corrosion processes on embedded reinforcement. Therefore, stray-current induced corrosion of nearby reinforced concrete structures deserves more attention in view of...
conference paper 2015
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Susanto, A. (author), Koleva, D.A. (author), Van Breugel, K. (author)
This work reports on the influence of stray current flow on temperature rise in hardening cement-based materials and consequently altered cement hydration. To simulate stray current, different levels of electrical current were applied to cement paste and mortar specimens immediately after casting. Isothermal calorimetry tests were carried out to...
conference paper 2015
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Chen, Z. (author), Koleva, D.A. (author), van Breugel, K. (author)
In practice, reinforced concrete structures may encounter different kinds of curing conditions<br/>due to the weather (sun radiation, air moisture and wind), nearby external environment<br/>(seawater, attack of stray current arising from nearby railways), or human factors (insufficient<br/>curing period). In some extreme conditions, the...
abstract 2015
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Pargar, F. (author), Koleva, D.A. (author), van Breugel, K. (author)
Free chloride ions are the main cause of steel corrosion in reinforced concrete structures. Ag/AgCl electrodes, as chloride sensors, are predominantly sensitive to chloride ions and respond electrochemically to the chloride ion activity in the environment. This is reflected by changes of the open circuit potential (OCP) of the sensors. To...
conference paper 2015
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Susanto, A. (author), Koleva, D.A. (author), Van Breugel, K. (author)
This paper reports on the influence of stray current flow on microstructural prop-erties, i.e. pore connectivity and permeability of mortar specimens, and link these to the observed alterations in mechanical properties and cement hydration. Mortar specimens were partly submerged in water and calcium hydroxide (Ca(OH)2) as an external environment...
conference paper 2014
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Blagojevic, A. (author), Koleva, D.A. (author), Walraven, J.C. (author)
This work reports on the investigation of steel corrosion behavior in 1000 mm in length reinforced concrete beams under sustained load, aiming to define a feasible experimental protocol for corrosion monitoring. The beams were subjected to wetting (5% NaCl for corroding cases and tap water for control ones) and drying cycles. Generally applied...
conference paper 2014
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