Accelerated AC impedance testing for prequalification of marine construction materials

The AC impedance technique was used in this study for the evaluation and prequalification of concrete materials prepared with chemical corrosion inhibitors and pozolanic admixtures of GGBS slag. In the Arabian Gulf region, marine seawater corrosion has caused severe concrete deterioration over the past decades. Major industrial buildings such as power generation plants, desalination plants and off-shore structures, and oil or water piers deteriorate severely in the marine industrial seawater environment due to the deleterious effect of chloride ions and CO2 gas. It has only recently been appreciated in this difficult region that concrete with supplementary cementing materials exhibit a very significant reduction in permeability and corrosion effects. Assessment of the corrosion condition of steel rebar in concrete for newly proposed projects can be carried out with different techniques. Most of the testing methods suggested are based on the ASTM standards G-109, ASTM C876, and ASTM C1202. The duration for ASTM testing requires at least a minimum of 1 to 3 years of exposure in simulated weathering conditions before any reliable conclusion can be drawn. In the present study, accelerated AC impedance measurements were carried out over a wide frequency range on reinforced Lollipop specimens of GGBS slag with different degrees of compaction of the concrete mix. The AC impedance technique allows detection of the breakdown of passivity and performance of the steel reinforcement in concrete within a much shorter time than with other tests. The correlation between the AC impedance technique and traditional ASTM standards indicated concurring results of the benefit of the application of multicomponent corrosion protection systems under the prevailing conditions of the marine environment in the Arabian Gulf region.

Slag concrete with 50% cement replacement can provide the requirements for a high level of corrosion protection in coastal areas and marine facilities in Kuwait; however, poorly prepared, uncompacted and inadequately cured slag concrete will be as poor as any ordinary prepared concrete. The corrosion evaluation of reinforced concrete with supplementary cementing materials by means of sophisticated methods of accelerated EIS measurement and analysis is conceptually possible. Evidence of accelerated results for optimum material selection of concrete mix design for the Kuwaiti marine environment was established using the EIS technique. Equivalent circuit analysis of the impedance spectra showed the presence of a constant phase element that was found in some cases to be approximately equal to the Warburg diffusion impedance. In other spectra, it indicated a depressed semi-circle. The laboratory slag concrete (GGBS) exhibited very high impedance and capacitance values that exceeded the performance of other concrete samples, which is in agreement with ASTM C876 and G109. The degree of protection for concrete with supplementary cementing materials can be arranged under the prevailing condition in the following order: from highest to lowest protective properties SLG > SIT > PC > CNI. Acknowledgments The authors are grateful for the financial support provided by the Kuwait Foundation for the Advancement of Sciences (KFAS) and the Kuwait Institute for Scientific Research (KISR).