There are other operations where work is best
internal temperature of concrete, not just the am-
done during the winter when more workers are
bient temperature.
available and construction is less disruptive.
Caution must be used when comparing this
temperature limit with the limits presented in the
promotional literature of some commercial ad-
mixtures that present low-temperature limits of
CONCLUSIONS
the ambient instead of the internal concrete tem-
The experimental results of this project show
perature. In many cases, the ambient temperature
may be below 0C, but the internal concrete tem-
that it is possible to place concrete at tempera-
perature may be above 0C because of the heat of
tures significantly below the freezing point of
water and obtain acceptable structural strength.
hydration and the presence of insulation. With
The test results also show that accelerating ad-
those admixtures, the key to success is to keep the
mixtures, such as Daraset, do not provide accept-
internal concrete temperature above freezing. With
able strengths in freezing temperatures. PolarSet,
DP, the ambient temperature can be lower than
5C, as long as the internal concrete temperature
an accelerating admixture designed for cool tem-
remains at about 5C or higher. Neither Daraset
peratures, was developed and tested during this
nor PolarSet met the 5C strength requirement
project. It performed very well at temperatures
below 5C, the current low-temperature limit for
that was preset at the beginning of this project.
admixture-free concrete, provided the concrete
DP did. Daraset and PolarSet are excellent prod-
ucts for concrete temperatures above 0C.*
was prevented from freezing. It was unable to
provide protection down to the 5C goal of this
Knowledge of the processes of ice formation in
project. That required that a new admixture be
fresh and hardened concrete was advanced. Cur-
developed.
rent winter practice assumes that concrete is auto-
A new prototype admixture code-named DP
matically damaged if frozen before developing a
was developed in this project. DP was tested in
compressive strength of 3.4 MPa. Experiments
the laboratory for compressive strength at vari-
with antifreeze concrete showed that some ice in
ous curing temperatures, and for several other
concrete does not necessarily cause damage, as
relevant concrete properties. The laboratory tests
long as certain minimum unfrozen water content
indicate that this admixture met the pre-set re-
is maintained. This added knowledge will be use-
quirement of causing concrete to gain strength at
ful for future research in the areas of low tem-
5C equal or higher than its equivalent, admix-
perature concrete and masonry. In the past, the
ture-free concrete cured at 5C. The tests also in-
temperature frontier for placing and curing con-
crete was at 5C.
dicate that this admixture has no known detri-
mental side effects for concrete. It does not contain
There are obstacles when introducing a new
chlorides or alkalis, and therefore it does not in-
admixture to the market. The existing standards
duce corrosion or cause alkali-silica reaction. DP
for concrete admixtures are not applicable to low-
did not interfere with the function of an air-
temperature admixtures because they evaluate the
entraining agent known by the trade name
admixtures at higher temperatures. Not having
Daravair.
industry standards discourages concrete practi-
Although DP needs to be tested prior to its use
tioners from using a product because doing so
with other admixtures to ensure compatibility, so
would increase liability.
far there is no indication of compatibility prob-
Admixture manufacturers must find a large-
lems. The strength of concrete containing DP and
enough market to dilute the cost of promotion,
cured at 20C was slightly enhanced compared to
storage, transportation, and distribution of a new
that of equivalent admixture-free concrete. DP was
admixture. Current winter concrete operations are
successfully applied to a winter field construction
relatively small because of the added cost of build-
as described earlier. This field application indi-
cated that concrete containing DP displayed ad-
equate workability, adequate set regime, and ad-
*The manufacturer (Jeknavorian et al. 1994) has published
equate strength. The field application indicates
information showing that concrete mixed with PolarSet at
22C may not gain appreciable strength when cured at 5C,
that DP can be successfully applied without spe-
but is able to regain strength when the concrete is warmed to
cial equipment or specialized labor. The labora-
22C. The 28-day strength for concrete cylinders treated in
tory tests show that DP can be safely used with
this manner is comparable to a control concrete cured at 22C
concrete cured at 5C. This temperature is the
for 28 days.
19
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