Testing - Concrete Mix Design, Quality Control and Specification - page 186

We feel that corrosion inhibitors can play a significant role in durability
enhancement. Until widely accepted practical test procedures are available
for confirming the increase in chloride threshold level, the full potential of
this group of admixtures may not be achieved.
7.6.10 Assurance of long-term performance
Obviously the only true test for durability is the test of time exposed to a
severe environment. Many products and technologies may have had prom-
ising performance in the laboratory but poor long-term field performance.
Epoxy-coated rebar, which, based on laboratory data, was once thought to
be the final solution to problems of reinforcement corrosion. Yet, Sagues
et al. (2001) state that “damage from corrosion of ECR (epoxy-coated
rebar) has continued to develop steadily in the substructure of five major
Florida Keys bridges. Since the first indications of corrosion ~6 years after
construction, damage increased at a rate of ~0.1 spall per bent per year
until the present ~20 years age of the structures, with no indication of
slowdown”. Certain hydrophobic ingredients proposed for damp-proofing
concrete were found to have reduced effectiveness or even to be leached
from concrete over time (Aldred, 1989).
In the light of lessons from the past, it would be wise to insist that a
certain performance requirement has been achieved over a period of not less
than l5 years in an environment similar to that anticipated in the new struc-
ture or repair. This is a most demanding requirement in a rapidly changing
world. On the other hand, the number of materials proposed as solutions
to deterioration that have either not persisted over time or even given
inferior performance, suggests such a bold step is necessary until a far better
understanding of the processes of deterioration of both reinforced concrete
and the proposed protective measure is achieved. It is clear that a material
with a long history of proven success would justifiably inspire confidence.
Measuring resistivity/chloride migration from 7 days (or even 3 days) to
say 90 days would help establish the expected time-dependent improve-
ment in chloride resistance.
7.7 NONDESTRUCTIVE TESTING
With nondestructive testing (NDT) it is necessary to be particularly careful
to clarify the objectives of the testing and the assessment of the results.
Clearly the strength of the concrete in the structure is not necessarily the
same thing as the potential strength (according to a standard compression
test) of the concrete as it leaves the mixer or delivery truck. If it is not
clear which of these is being sought, it is unlikely that the relative merits of
different testing procedures will be correctly assessed.