Page 190 - CW E-Magazine (27-2-2024)

Special Report

stage by carrying out periodic corrosion Corrosion monitoring of reinforced dragging needs training. The practice
surveys and maintaining a record of concrete structures is difficult when vehicles are mov-
data. For measuring the corrosion rate A proper test plan should take into ing over the deck, as distinguishing
of reinforced steel in concrete, many account the following: the hollow sound becomes difficult.
electrochemical and non-destructive Exposure conditions (access to

tests (NDTs) are available. moisture, oxygen, de-icing salts, The main disadvantage of the method
chemicals, carbon dioxide, etc.); is that it can only provide results
Corrosion of reinforcement has Geometry of the structures and if the defect and deterioration are

been established as the predominant components; well advanced. Early diagnosis is not
factor causing premature deterioration Access to structural and non-struc- possible using this technique.

of concrete construction, especially tural components;
of structures located in coastal marine Dimension and scale of the area Chloride content (profile)

environment(1). The most important under investigation; Measuring the chloride content in
cause is the ingress of chloride ions Importance of the element, etc. concrete cover (and at the rebar surface)

and carbon dioxide to the steel surface. is a classic method in corrosion inves-
After initiation of corrosion, corrosion The following inspection proce- tigation. Powder samples are obtained
products (iron oxides and hydroxides) dures are widely used during a routine from different depths (usually five,
are usually deposited in the restricted corrosion monitoring programme. from exposed surface to rebar level),
space in the concrete around the steel. and the chloride profile is developed.
Their formation sets up expansive Chain drag delamination survey Diffusion coefficient can be determined
stresses, which crack and spall the con- Chain dragging is widely used to in this method. The main advantage is
crete cover. This, in turn, results in pro- detect de-lamination in concrete bridge to understand if the concentration of
gressive deterioration of the concrete. decks. The concept behind this simple chloride ion is higher than the thresh-
As a result, repair costs constitute a method is the unique hollow sound old value (the amount required for de-
major part of the current spending on made by dragging a chain across a passivating the protective film over rebar).
infrastructure. Quality control, mainte- de-laminated surface.
nance and planning for the restoration Electrical resistivity measurement
of these structures need NDTs that The main advantage of the method The use of electrical resistivity for
detect corrosion at an early stage. More- is that it is simple, and no special quality control and evaluation of con-
over, repair operations are complex equipment is required. However, chain crete durability is becoming popular, as
and require special treatments of the
cracked zone, and in most instances the (I) Current applied
life expectancy of the repair is limited.
Corrosion monitoring can give more + Potential measured
(V)
complete information of changing
conditions of a structure in time(2,3).
Concrete steel reinforcement corrosion
of a critical factory roof is depicted in
Figure-2.

Equipotential lines Lines of current flow Concrete specimen
under test
Fig. 2: Concrete slab rebar (steel reinforcement)
corrosion of a critical factory roof Fig. 3: Set-up for measurement of electrical resistivity in concrete

190 Chemical Weekly February 27, 2024

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