Corrosion monitoring of steel in concrete by means of electrochemical impedance spectroscopy (EIS)

Korozija jeklene armature v betonu je prevladujoč razlog za skrajšano življenjsko dobo armiranobetonskih objektov. Predstavlja velik javnovarstveni, ekonomski in naravovarstveni izziv, spremljanje in preprečevanje le-te pa nujno dejavnost moderne družbe. Uporaba karakterizacijskih metod z namenom spremljanja stanja armature je zato aktualna tema mnogih znanstvenih raziskav. V sklopu magistrskega dela sem z metodo elektrokemijske impedančne spektroskopije (EIS) eno leto spremljal skupno 12 vzorcev armiranega betona. Vsak vzorec sestavlja par palic ogljičnega jekla, zalitih v beton, pri čemer ima ena od palic na površini medfazne meje umetno vdelano špranjo, ki posnema naravno napako ob vgradnji. Del vzorcev je bil pred pričetkom eksperimenta izpostavljen pogojem za pospešeno karbonatizacijo betona. Vzorci so bili v času eksperimenta tedensko omočeni z elektrolitom, pri čemer je polovica vzorcev kot elektrolit uporabljala vodovodno vodo, druga polovica pa raztopino NaCl. Po končanem obdobju merjenja je bila magnituda korozijskih poškodb ocenjena iz rentgenskih slik jeklene armature. Namen magistrskega dela je evalvacija metode EIS za spremljanje korozijskih procesov jeklene armature znotraj betona ter ovrednotenje vpliva različnih parametrov na korozijsko hitrost. Rezultati eksperimenta kažejo izjemno učinkovitost metode pri spremljanju korozije ter očiten vpliv merjenih parametrov na potek korozije. Za razliko od večine drugih metod EIS nudi vpogled v mehanistične procese korozije ter omogoča določitev različnih doprinosov k celokupni korozijski hitrosti. Eksperiment je pokazal tudi vrsto slabosti metode. Meritev je relativno dolgotrajna, analiza in interpretacija rezultatov pa zelo zahtevna. Poleg tega betonski vzorci izražajo visoko stopnjo neidealnosti in v nekaterih primerih nizko časovno stabilnost, kar dodatno oteži proces.Corrosion of steel reinforcement in concrete is the predominant reason for the shortened lifespan of reinforced concrete structures. It poses significant challenges in terms of public safety, economics, and environmental impact, making its monitoring and prevention an essential endeavour of modern society. The utilization of characterization methods for the purpose of monitoring the condition of steel reinforcement is therefore a subject of many scientific investigations. As part of this master\u27s thesis, the technique of electrochemical impedance spectroscopy (EIS) was employed to monitor 12 reinforced concrete samples over the course of a year. Each sample consists of a pair of carbon steel bars embedded in concrete, with one of the bars artificially embedded with a crevice at the interfacial boundary, simulating a natural installation flaw. Prior to the beginning of the experiment, a subset of the samples was subjected to accelerated carbonation of concrete. During the experiment, all the samples were immersed weekly into an electrolyte solution, with half of the samples using tap water and the other half using a NaCl solution. After the conclusion of the measurement period, the magnitude of corrosion damage was assessed through X-ray imaging of the steel reinforcement. The objective of this thesis is to evaluate the applicability of the EIS technique for monitoring the corrosion processes of concrete reinforcement, along with assessing the influence of various parameters on the corrosion rate. The results of the experiment demonstrate a great effectiveness of the method in monitoring corrosion, as well as a large impact of the measured parameters on the corrosion progression. Unlike many other techniques, EIS provides insights into the mechanistic processes of corrosion and enables the determination of different contributions to the overall corrosion rate. The experiment also revealed several limitations of the method. The measurement process is relatively time-consuming, and the analysis and interpretation of results are highly demanding. Furthermore, the concrete samples exhibit a high degree of non-ideal behaviour and, in certain cases, low temporal stability, further complicating the process