Page 85 - ICJ Jan 2023

POINT OF VIEW COLLECTOR’S EDITION

In the past, it was generally found that neither and durability. To pursue the goal of building
structural design nor materials were responsible environmentally sustainable concrete structures, a
for the lack of durability. In most cases, it was paradigm shift in certain beliefs and construction
the construction practice that turned out to practices is needed.
be the culprit. Inadequate consolidation or
curing of concrete, insufficient cover for the BEFORE 1930
reinforcement, and leaking joints are examples of According to Burrows, photographs of two
poor construction practice. A serious issue now is independent surveys on the condition of
the growing evidence of premature deterioration portland cement concrete structures built before
7
in recent structures that were built in conformity 1930 were shown at the 1931 ACI convention .
with the state-of-the-art construction practice. This Deterioration of concrete had occurred either
means that the premature deterioration of concrete due to crumbling (possibly from exposure to
structures will continue to occur at unacceptably freezing and thawing) or due to leaching from
high rates unless we take a closer look at the leaking joints or poorly consolidated concrete.
current construction practice to understand and No cases of cracking-related deterioration were
reported. It is known that concrete with pre-1930
control the primary causes that adversely affect portland cements developed strengths at a very
the durability of concrete. Deterioration, such as slow rate because they were coarsely ground
corrosion of reinforcing steel and sulfate attack, (~ 1100 cm /g, Wagner specific surface) and
2
occurs when water and ions are able to penetrate contained a relatively small amount (less than
into the interior of concrete. This penetration 30 percent) of tricalcium silicate C S. Burrows
3
happens when interconnections between isolated believes that the transition from a concrete that
6
microcracks, visible cracks, and pores develop . deteriorated by crumbling or leaching to one that
Therefore, deterioration is closely associated deteriorates by cracking occurred when cement
with cracking. The causes of cracking are many; manufacturers started making faster-hydrating
however, there is one cause that has emerged portland cements by raising the fineness and the
as the most predominant factor in the cracking C S content. His observation is confirmed by the
3
of concrete structures at early ages, namely, the results of a 1944 survey, as discussed next.
use of high early strength cements and concrete
mixtures to support the high speed of modern THE CONCRETE INDUSTRY IN THE
construction. 20TH CENTURY, WHILE RESPONDING
TO CALLS FOR HIGHER AND HIGHER
In this article, the authors have presented a STRENGTH, INADVERTENTLY VIOLATED
historical review to show how the concrete industry A FUNDAMENTAL RULE IN MATERIALS
in the 20th century, while responding to calls for
higher and higher strength, inadvertently violated SCIENCE THAT THERE EXISTS A CLOSE
a fundamental rule in materials science that CONNECTION BETWEEN CRACKING
there exists a close connection between cracking AND DURABILITY

*Reprinted with permission of the American Concrete Institute, P.O. Box 9094, Farmington Hills, MI 48333, USA. This
Point of View feature was first published in the Concrete International, March 2001, Vol. 23, No. 3, pp. 57-63.

86 The Indian Concrete Journal | November 2018