Expedient Low-Temperature Concrete Admixtures
for the Army
CHARLES J. KORHONEN
INTRODUCTION
on early age strength gain. It did not consider
their effect on paste shrinkage, aggregate degra-
Currently, portland cement concrete cannot be
dation, reinforcing steel corrosion, or concrete
placed at below-freezing temperatures without
durability. (These studies should be conducted if
some form of thermal protection. Therefore, Field
the concrete is intended for long-term use.) The
Manual, FM 5-428, Concrete and Masonry (U.S.
objective of this study was to develop guidance to
Army 1998), directs that freshly placed concrete
enable military engineers to design expedient
must be protected from freezing by keeping it
above 5C with insulation or heated enclosures
cold weather concrete admixtures, from chemi-
cals that are readily available but not marketed
for a minimum of 3 days or until it has sufficiently
expressly as concrete admixtures, for field expe-
cured to gain strength and serve its intended pur-
dient use. Expedient concrete is defined as con-
pose. On the battlefield or in an emergency, when
crete that is intended to have service life up to 5
concrete must be placed regardless of the temper-
years.
ature, engineers may not have access to insula-
tion, let alone heated enclosures. If concrete must
be placed in the cold, it may freeze and the results
EFFECT OF TEMPERATURE ON STRENGTH
can be disastrous.
Portland cement concrete, in its simplest form, is
An alternate approach to winter concreting,
composed of cement, aggregate, and water. A
and one not yet recognized by standard practice,
chemical reaction between the cement and water
is to use antifreeze admixtures. These are chemi-
forms a gel that binds the aggregate together and
cals that depress the freezing point of water and
gives concrete its strength. As long as the cement
accelerate the hydration rate of cement when the
internal temperature of the concrete is below 0C.
is wet, the concrete continues to gain strength at a
rate that is strongly influenced by temperature.
Commercial standards do not permit the use of
Common belief is that hot weather is the best
antifreeze admixtures because their long-term
time to cast concrete because concrete sets up
effect on concrete is unknown. However, two
faster when it is hot than when it is cold. Table 1
recently completed studies (Korhonen and Brook
supports this belief by showing that mortar gains
1996, Korhonen et al. 1997b) concluded that cer-
77% more strength in 1 day when cured at 50C
tain chemicals could protect concrete from freez-
than it does when cured at 20C. Getting this
ing without causing detrimental side effects. But,
much extra strength in 1 day can save an engineer
partly out of resistance to change and partly for
several days of extra expense in labor and in wait-
other reasons, antifreeze admixtures have not
ing time to reuse the forms. However, the
been commercialized and are not in general use.
strength benefits are only temporary. As can be
This report details a laboratory investigation
seen, the early age strength increase caused by
in search of chemicals to allow portland cement
high temperatures virtually disappears by day 7.
concrete to resist freezing during initial curing.
Moreover, the mortar ultimately becomes 28%
This search targeted chemicals, other than those
weaker when cured at 50C than when cured at
specifically marketed for concrete, for their effect
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