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Large scale reinforced concrete test specimen for potential mapping under practical conditions
(2017)
Electrochemical potential mapping according to guideline B3 of DGZfP (German Society for Non-Destructive Testing) is a recognized technique for the localization of corroding reinforcing steels. In reinforced concrete structures the measured potentials are not necessarily directly linked to the corrosion likelihood of the reinforcing steel. The measured values may be significantly affected, different from e.g. stress measurement, by different influences on the potential formation at the phase boundary metal/concrete itself as well as the acquisition procedure. Due to the complexity of influencing factors there is a risk that the results are misinterpreted. To investigate these influencing factors under practical conditions it requires a specimen with similar damage patterns, dimensions and more factors e.g. metallic mounting parts. Recently the BAM realized such a large scale test specimen for this purpose.
Corrosion of galvanized steel in chloride containing mortar is different from the corrosion of reinforcement made of carbon steel. This is based on the corrosion behavior of galvanized steel in chloride containing mortar. To describe the influence of a chloride containing zinc-hydroxide layer at the phase boundary against a zinc-hydroxide layer in chloride free mortar, different electrochemical measurements were made. The anodic and cathodic partial reaction were investigated by galvanostatic pulse measurements and potentiodynamic measurements. Especially the galvanostatic pulse measurements can describe the influence of the chloride content by the polarization resistance with pt = 20 sec. (polarization time). Additionally, corrosion current measurements were performed, coupled with potential measurements, between galvanized steel in chloride containing and chloride free concrete. Normally, the potential measurements are an indicator to localize the anodic and cathodic parts of a macro system. In this case the results show that there is no formation of a significant macro element cell between chloride containing and chloride free mortar. After 1500 h of potential and current measurement the results show a more positive corrosion potential with increasing chloride content. The results of the potential/current curves show a significant different free corrosion current depending on the chloride content, the free corrosion current increase with increasing chloride contents; reasons for this behavior are discussed.
Concrete is the most produced material in the world. Every year approx. 6.000.000.000 m³ are produced worldwide and it is expected that the production volume will continue to increase because of the economic growth of many countries around the world. This development will also result in an increase of manufacturing CO₂ emissions if nothing changes. The cement production is already responsible for 5-10 % of the worldwide anthropogenic CO₂ emissions. An immense decrease of the CO₂ emissions (approx. 45-65 %) can be achieved by the use of geopolymers as binder instead of ordinary Portland cement. However, so far only limited data exists regarding the corrosion behavior of reinforcements in geopolymer concretes.
The poster shows by means of different electrochemical investigations the formation of a protective layer on the surface of carbon steel reinforcement and galvanized steel reinforcement in fresh geopolymer mortars and in a fresh mortar with Portland cement as reference. The free corrosion potential in combination with current density potential curves as well as polarization resistances show the development of a protective layer on the reinforcement. The monitoring of the free corrosion potential starts with the first contact of the rebar with fresh mortar and ends after a passive condition was reached. The further electrochemical investigations are done during the potential monitoring under active conditions, semi active conditions and passive conditions.
The results show that the formation of the protective layer in geopolymer mortars is significant slower than in mortar with Portland cement. The two investigated geopolymer mortars also show a significant difference in formation of the protective layer. This can depend on the different solidification time of the geopolymer mortar.