Epoxy Coatings On Metallic Substrates - Quantitative Assessment Of The Water Absorption By Use Of Single-Sided NMR

摘要

About 40 years ago epoxy-coated reinforcement (ECR) for concrete structures has been developed and since then more and more applied particularly in North America. Nevertheless, early corrosion damages e.g. in Florida soon became well known. In general latest products available on the market are powder coated. Up-to-date the technologies of resins and application appear to be significantly improved. Therefore, this kind of protection against corrosion should be reconsidered. Higher initial investments due to the application of ECR should yield measurably increased protection against corrosion of the reinforcement, especially under aggressive environmental conditions (e.g. chlorides due to de-icing salts or seawater). One key parameter in the mechanisms of failure of the rebar-coating-system is the impermeability (barrier effect) of the coating against water or the electrolyte. Due to the coating process, the transportation or even the handling on site a defect-free product cannot be guaranteed. In practice building the concrete pore solution provides for the electrolytic connection between possibly anodic and cathodic areas (interaction of defects) for both regular reinforced concrete structures and ECR concrete structures. In relevant international standards mostly qualitative test proceduresare processed. However, in order to judge the performance of epoxy-coated reinforcements, it is not sufficient to enforce a qualitative comparison of good or poor systems - a quantitative assessment of the corrosion protection is needed. The combination of different test procedures (gravimetry, electro-chemical analysis) and the application of the Single-sided Nuclear Magnetic Resonance spectroscopy (NMR) offer new quantitative test results to assess or monitor the barrier properties of organic coatings on non-magnetic metallic substrates. First experimental results of the quantification of the water absorption of an organic coating (in solution and embedded in concrete) on different metallic substrates by means of the Single-sided NMR-Technology will be presented. This non-destructive testing might offer chances for applications in R&D and quality management of coating manufactures.