Abstract
In general, corrosion of steel bars is the predominant cause of failure in reinforced concrete structures. The alkalinity of bulk concrete is protecting the steel surface by passivation. Slow ingress of aggressive ions from the atmosphere is degrading the bulk matrix by decreasing of pH and subsequently destroying the passivation layer. Moreover, the volume increase through corrosion products initiated by chloride ions penetrated into the porous bulk matrix is leading to crack formation and loss of mechanical properties. Especially reinforced concrete structures in harsh environmental conditions like offshore platforms or windmill towers consequently suffer from limited service life.
Novel inhibition concepts are aiming on immobilizing of corrosion inhibitors on smart nanostructures that provides triggered release by external stimuli like presence of aggressive species or pH changes. The control over release during service life is depending on different encapsulation technologies in use.
Functionalized derivatives based on polyhedral oligomeric silsesquioxanes (POSS) are hyper-branched hybrid nanostructures ([O3/2 Si(CH2)3NX2]n, n=8,10,12 deriving from a cost-efficient two-step production (www.funzionano.com), including a sol-gel process followed by functionalization. This synthesis route has the strategic advantage to yield in a variety of chemical surface functionalities appropriate to tune response efficiency to prevent corrosion.
Different structural features of POSS derivatives as host for corrosion inhibitors (salicylate and mercaptobenzothiazole) have been synthesized at SINTEF Industry and their ability on corrosion protection screened. The release of active compounds from POSS complexes by environmental stimuli (e.g. artificial seawater) has been investigated in the laboratory. Two artificial environments were applied:
1. Ca(OH)2 sat + 0.05 M NaCl (pH=12.6), to simulate concrete pore solution contaminated with Cl-,
2. 0.05 M NaCl (pH~6), which is a common corrosion testing medium.
The resistance to corrosion of carbon steel in these media with different amounts of POSS was investigated by visual inspection, open circuit potential monitoring, polarization curves (potential-current curves) and electrochemical impedance spectroscopy (EIS). No signs of steel corrosion were observed in the environments containing POSS in a concentration of 0.01 M and the impedance was at least one order of magnitude higher compared to samples in the same medium without inhibitor.
Further tests including the incorporation of POSS in reinforced concrete samples will be reported.
Acknowledgements: This work is supported by the HORIZON 2020 Collaborative project “LORCENIS” (Long Lasting Reinforced Concrete for Energy Infrastructure under Severe Operating Conditions, Grant agreement no.: 685445).
Novel inhibition concepts are aiming on immobilizing of corrosion inhibitors on smart nanostructures that provides triggered release by external stimuli like presence of aggressive species or pH changes. The control over release during service life is depending on different encapsulation technologies in use.
Functionalized derivatives based on polyhedral oligomeric silsesquioxanes (POSS) are hyper-branched hybrid nanostructures ([O3/2 Si(CH2)3NX2]n, n=8,10,12 deriving from a cost-efficient two-step production (www.funzionano.com), including a sol-gel process followed by functionalization. This synthesis route has the strategic advantage to yield in a variety of chemical surface functionalities appropriate to tune response efficiency to prevent corrosion.
Different structural features of POSS derivatives as host for corrosion inhibitors (salicylate and mercaptobenzothiazole) have been synthesized at SINTEF Industry and their ability on corrosion protection screened. The release of active compounds from POSS complexes by environmental stimuli (e.g. artificial seawater) has been investigated in the laboratory. Two artificial environments were applied:
1. Ca(OH)2 sat + 0.05 M NaCl (pH=12.6), to simulate concrete pore solution contaminated with Cl-,
2. 0.05 M NaCl (pH~6), which is a common corrosion testing medium.
The resistance to corrosion of carbon steel in these media with different amounts of POSS was investigated by visual inspection, open circuit potential monitoring, polarization curves (potential-current curves) and electrochemical impedance spectroscopy (EIS). No signs of steel corrosion were observed in the environments containing POSS in a concentration of 0.01 M and the impedance was at least one order of magnitude higher compared to samples in the same medium without inhibitor.
Further tests including the incorporation of POSS in reinforced concrete samples will be reported.
Acknowledgements: This work is supported by the HORIZON 2020 Collaborative project “LORCENIS” (Long Lasting Reinforced Concrete for Energy Infrastructure under Severe Operating Conditions, Grant agreement no.: 685445).