Properties of the steel-mortar interface derived by impedance spectroscopy in different environment and curing conditions

In practice, reinforced concrete structures may encounter different kinds of curing conditions
due to the weather (sun radiation, air moisture and wind), nearby external environment
(seawater, attack of stray current arising from nearby railways), or human factors (insufficient
curing period). In some extreme conditions, the corrosion of embedded steel will occur at early
age, and the pore structure of cementitious material matrix can also be influenced. One of the
significant consequences is the premature failure of steel- matrix interface, which plays
important role for the integrity of a structure during the subsequent service life. This
phenomenon leads frequently to early deterioration and eventually to risky situations for the
stability of structures. In any case, the economic costs inherent to reparation works are
considerable.
Therefore, the state and properties of the steel/cement-based material interface is to
be monitored from early ages, especially under extreme operating conditions. As one of the
nondestructive testing methods, electrochemical impedance spectroscopy (EIS) can be
employed to account for properties at the steel/cement paste interface. EIS measurements are
very useful since they provide the possibility of correlating the dielectric properties and the
microstructure of a cementitious material (derived from the high frequency region), with the
corrosion behavior of the embedded steel (derived from the low frequency region).
In this work, to simulate different curing conditions, standard curing for 28d and “on-air” curing
after 24h were employed. Different groups of reinforced mortar specimens of the same mixture
were designed according to the existence or coexistence of chloride, stray current, and anodic
polarization. The steel-mortar interface properties with age and under different curing conditions
was monitored by EIS measurement. The paper presents the evolution of the fitting parameters,
corresponding to the cementitious material matrix, embedded steel and interaction between
them are explained and compared in terms of different curing conditions. This research is
expected to clarify that the, curing conditions in unusual work environment (as for example stray
current conditions) must be taken into account regarding the behavior of steel-matrix interface at
early age, and some curing methods must be put into practice in order to obtain satisfactory
performance of the reinforced structure before the structure is used at full operational capacity.