Page 87 - ICJ Jan 2023

POINT OF VIEW COLLECTOR’S EDITION

The performance of concrete in bridge decks
serves as an accelerated field test for durability,
because bridge decks are generally exposed to
deicer chemicals and frequent cycles of wetting-
drying, heating-cooling, and freezing-thawing. A
1987 report of the U.S. National Materials Advisory
Board made a startling observation that concrete
bridge decks, mostly built after the 1940s, were
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suffering from an epidemic of durability problems .
It was estimated that 253,000 bridge decks, some of
them less than 20 years old, were in varying states
of deterioration and that the number was growing
at the rate of about 35,000 bridge decks every year.

There are reasons to believe that the acceleration Fig 1 Increase in the 7-day strength of ASTM Type I
of bridge deck durability problems since 1974 is portland cement, produced in the USA during the last
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70 year
directly attributable to the use of cements and
concrete mixtures possessing relatively high
strength at early ages. Neville has also stated that
the deterioration of concrete increased because
cement specifications did not have limits on
fineness, C S, and early strength . Today, ASTM
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3
Type I and II cements can be found with more than
60 percent C S and higher than 400 m /kg fineness.
2
3
Gebhardt has compiled a comprehensive survey of
North American cements produced in 1994 . His
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analysis of the data for 71 ASTM Type I cements
and 153 Type II cements showed that, except for Fig 2 Distribution of ASTM type II portland cements
a lower C A content in Type II cement, there is produced in the USA, according to the 7-day strength 11
3
essentially no difference in the composition and
physical properties of the two cement types. The THE FAST SCHEDULES OF THE
average C S content and fineness for both cement CONSTRUCTION INDUSTRY HAVE
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2
types is approximately 56 percent and 375 m /kg, VIRTUALLY DRIVEN THE SLOWER-
Blaine, respectively. In both cases, the compressive
strength of ASTM C 109 mortar cubes at the ages HARDENING AND MORE DURABLE
1, 3, 7, and 28 days is approximately 2000, 3600, PORTLAND CEMENTS OF THE PAST
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4500, and 6000 lb/in (14, 25, 31, and 41 MPa), OUT OF THE MARKET PLACE
respectively. The author concluded: “It appears
that the general property of moderate heat of Fig 1 shows that the 7-day compressive strength
hydration as a defining characteristic of Type II of ASTM Type I portland cement has doubled,
cement has been lost over the years, except when a from about 2500 to 4500 lb/in (17 to 31 MPa)
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moderate heat cement was specifically designated during the last 70 years. In regard to ASTM
and produced.”

88 The Indian Concrete Journal | November 2018