Cathodic Protection Criteria for Two-Layered Reinforced Concrete Sections

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Title: Cathodic Protection Criteria for Two-Layered Reinforced Concrete Sections

Author(s): Mohammad G. Ali, A. S. Al-Gahtani and R. Sri Ravindrarajah

Publication: Special Publication

Volume: 170

Issue:

Appears on pages(s): 1097-1118

Keywords: Cathodic protection; corrosion; reinforcement of concrete.

Date: 7/1/1997

Abstract:
The results on the relatively high level of protection provided to the top steel in a reinforced concrete slab when the bottom steel is just adequately protected are presented in this paper. The steel reinforcement corrosion was accelerated with the use of chloride contaminated concrete. The chloride gradient within the specimen was created by inserting a relatively higher chloride bearing macrocell. Current reversal technique was used to monitor the corrosion protection level. The results showed that the presence of a higher chloride gradient requires a higher protection current density and potential. An instant-off potential of 632 mV CSE and a 4-hour decay potential of 100 mV were sufficient to protect steel reinforcement against corrosion in chloride rich concrete (19 kg/m3). The protection level at the top steel is significantly high when the bottom steel is just adequately protected from the anode source located above the top steel. In a chloride bearing concrete with the chloride gradients of 3.0 and 1.5, the top steel received 103 and 59 mA/m2 cathodic protection current densities compared to the current densities of 42 and 31 mA/m2, respectively required to protect the bottom steel. The instant-off potential of 730 mV CSE and the decay potential of 128 mV for the top steel also indicate a relatively high level of protection of the top steel. In a two-layer steel reinforced concrete slabs, it is necessary to develop a mechanism, specially in new construction, to facilitate the flow of current to the bottom steel. The current reversal technique used in the test was effective in determining the protection level against corrosion.