Title:
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The effect of cement type on the potential and corrosion behaviour of steel reinforcement
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The corrosion of reinforcing steel has emerged as the most prevalent factor causing
deterioration of reinforced concrete structures in aggressive exposures, such as the
Middle East and Arabian Gulf States. Recently, the effect of using embedded steel
bars passing through different types of concrete has been found to exacerbate the
corrosion activity. This may occur with a steel bar passing from a foundation
manufactured with sulphate resistance Portland cement (SRPC) into a beam or
column manufactured with ordinary Portland cement (OPC).
This thesis aims at elucidating the behaviour of reinforcing steel (RC) embedded in
concrete mixes of different types by incorporating both OPC and SRPC and blends
with ground granulated blast furnace slag and pulverised fuel ash. Two different types
of RC specimens were used: Single bars in a single mix and electrically connected
bars in same or different mix types sharing a common electrolyte in the absence and
presence of a specific interface. The RC specimens were exposed to wet-dry cycles of
chloride and sulfate solutions.
The results of steel bars that were electrically connected, and were embedded in
concrete cubes manufactured with different cement types and without a direct
interface exhibited reduced times to onset of corrosion when subjected to chloride ion
ingress. In the worst case, the connection of the a bar in OPC (0.45) concrete and one
in SRPC (0.45) concrete caused the bar in the SRPC (0.45) mix to start corroding after
only 3 cycles (6 weeks) compared to 15 cycles (30 weeks) for a single unconnected
bar in the same SRPC (0.45) concrete. Moreover, measurements of the half-cell
potential, polarisation resistance and corrosion current, all confirm that a single bar
passing the interface between two different concretes manufactured with different
cement types can suffer the formation of anode and cathode regions that depend on
the local environment. For example, a steel bar passing from an OPC (0.45) concrete
to a SRPC (0.45) concrete will preferentially form an active anode within the SRPC
concrete. This has implications for concrete structures manufactured using SRPC
foundations and OPC superstructure, as often used in the Arabian Gulf States
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