Reinforced concrete--Deterioration.

The durability of Reinforced Concrete (RC) structures in the Marine environment is
causing serious concern in the structural infrastructure. Reinforced concrete structures,
exposed to aggressive environments, are expected to last with little or no maintenance for
long periods of time. However, one of the most serious environmental exposures that
causes degradation is Chloride Diffusion, due to shrinkage, atmospheric corrosion, and
tide-induced wet and dry conditions at the air-water interfaces of coastal structures.
Therefore, chloride diffusivity, which correlates with the electrical resistivity, has a
significant impact on the durability of concrete. Concrete chloride diffusivity has been
experimented by multiple agencies and researchers on sound concrete, but there is a
considerable need for investigation of the durability of cracked concrete in the marine
environment. The two test methods carried out are presented: Standardized American Society for Testing
and Materials (ASTM) C1202 for Rapid Chloride Permeability (RCP) and ASTM D257
for Surface Resistivity (SR), and Nordtest (NT) Build 492 for Rapid Chloride Migration
(RCM) and Bulk Resistivity (BR) for both sound (uncracked) and cracked (micro and
macro) concrete. The limitations of the ASTM method, due to measurements before the
steady-state migration is reached, does not account for leakage in cracked concrete, and the
heating of the specimen due to higher current that increase the conductivity are indicated.
The Rapid Chloride Migration test provides for the non-steady state of diffusion. Again,
Bulk Resistivity, in contradistinction to Surface Resistivity is more accurate for cracked
concrete. The correlation betweeen RCM-BR are plotted. Chloride Permeability/Migration
is an important parameter that governs the Durability of Concrete.
The principal contribution is the highlighting of the inadequacy of the current widely used
standard ASTM C1202 for diffusivity testing, and the need for revision with further
investigation.

The FDOT has been using supplementary cementitious materials while constructing steel reinforced concrete marine bridge structures for over 3 decades. Previous findings indicated that such additions in concrete mix makes the concrete more durable. To better understand corrosion propagation of rebar in high performance concrete: mature concrete samples that were made (2008/2009) with Portland cement, a binary mix, a ternary mix and recently prepared (April 2016 with 50% OPC + 50% slag and 80% OPC + 20% Fly ash) concrete samples were considered. None of these concretes had any admixed chloride to start with. An accelerated chloride transport process was used to drive chloride ions into the concrete so that chlorides reach and exceed thechloride threshold at the rebar surface and initiate corrosion. Electrochemical measurements were taken at regular intervals (during and after the electro-migration process) to observe the corrosion propagation in each sample.