Page 86 - ICJ Jan 2023

POINT OF VIEW COLLECTOR’S EDITION

1930-1950 Brewer and Burrows in 1951 and by Backstrom and
Burrows in 1955, are discussed in Reference 7.
In 1944, the U.S. Public Roads Administration
undertook an extensive survey of concrete bridges 1950-1980
in California, Oregon, Washington, and Wyoming. Since 1950, several important changes have
According to Jackson, the purpose of the survey taken place in the concrete construction practice.
was to investigate the causes of an alarmingly Changes such as rapid development of the ready-
rapid rate of disintegration of concrete in these and mixed concrete industry, placement of concrete
8
other western states . In all, some 200 structures by pumping, and consolidation by immersion
from small, singlespan bridges to large multispan vibrators triggered the need for high-consistency
bridges, 3 to 30 years old, were inspected. Jackson concrete mixtures which, before the advent of
high-range water-reducing admixtures in 1970,
observed that there was sufficient evidence to were made by increasing the water content of fresh
show that concrete structures built after 1930 concrete. Consequently, to achieve sufficiently
were not proving as durable in service as earlier high strength levels at early ages for the purpose
structures. For example, 67 percent of the pre- of maintaining fast construction schedules, further
1930 bridges were found to be in good condition increases were made in the fineness and the C S
3
as compared to only 27 percent of the post-1930 content of the general-purpose portland cement.
bridges. Because the construction technology had By 1970, according to Price, the C S content of
3
remained essentially the same, Jackson concluded the ASTM Type I portland cements in the U.S. had
that the change in the cement fineness was the risen up to 50 percent and the Blaine fineness
9
2
to 300 m /kg .
probable cause of the problem. He reported
that, in 1930, as a result of users’ demand for
higher early strength, the ASTM specification was The impact of this drastic change in the composition
and hydration characteristics of general-purpose
changed to permit more finely ground portland portland cement on durability of concrete can be
cement. Jackson theorised that “modern cements, judged from the fact that with the 1945 cements,
ground to a Wagner fineness of 1800 cm /g do not a 0.47 water-cement ratio (w-c) concrete typically
2
2
make as durable a concrete as the more coarsely gave 4500 lb/in (31 MPa) strength at 28 days.
ground cements in use 25 years ago.” Note that With the ASTM Type I portland cements available
2
a Wagner fineness of 1800 cm /g corresponds in 1980, it was possible to achieve the same
to a Blaine fineness of about 300 m /kg. The U.S. strength with a lower cement content and a much
2
Bureau of Reclamation conducted a series of field higher w-c of 0.72. Being more permeable, this
and laboratory studies that confirmed Jackson’s concrete naturally proved less durable in corrosive
environments.
theory. The results from two of these, reported by

*High-Performance Concrete (HPC) is concrete that meets special combinations of performance and uniformity
requirements that cannot always be achieved routinely using conventional constituents and normal mixing, placing,
and curing practices. Thus, a high-performance concrete is a concrete in which certain characteristics are developed for
a particular application and environment. Examples of characteristics that may be considered critical in an application
are: ease of placement, compaction without segregation, early age strength, long- term mechanical properties,
permeability, density, heat of hydration, toughness, volume stability, and long life in severe environments.

The Indian Concrete Journal | November 2018 87