days after placement. At these temperatures and
workers at the Soo said that working outdoors
by these times, even admixture-free concrete may
was much preferred to working in a confining,
have been able to set and become resistant to
though heated, enclosure. It was much easier to
freezing.
place and finish the concrete where there was free-
The fact that the antifreeze concrete placed on
dom of movement. The consensus was that out-
door concreting was practical down to 20C, pos-
frozen ground didn't suffer frost damage has im-
plications for normal winter concreting, when
sibly lower, provided a heated shelter was avail-
placing fresh concrete on frozen ground is prohib-
able to warm up in periodically. At the Soo, the
personnel worked outdoors in windy 10C
ited because of the danger of freezing. In this
study, when the top surface temperature of the 15-
weather for 2-hour intervals. The finishing opera-
cm slab was above freezing, the bottom surface of
tion required no special tools, skills or precau-
the slab did not develop ice. Recall that the con-
tions. The antifreeze concrete finished in the same
crete was placed on a gravel pad, free of ice. If the
manner as normal concrete. Ice did not build up
concrete had been placed directly on the ground,
on the cold metal tools as expected.
which contained ice, the situation may have
Concreting in winter costs more than during
changed because ice can significantly increase
the rest of the year. The extra costs in this test were
heat loss rates. In this case, air spaces among the
113% for the enclosure, and up to 43% for the ad-
pieces of gravel probably slowed the heat loss
mixture. Costs associated with antifreeze admix-
from the slab enough to prevent freezing. Also,
tures were more than offset by savings on protec-
the accelerators in the admixture probably pro-
tion requirements.
vided increased protection through increased heat
From a strength development standpoint, the
release during early hydration. More study is
antifreeze concrete was equal to or better than the
needed to test the practice of placing admixture-
concrete placed inside a heated enclosure. Dry
free concrete on frozen ground.
heat can create problems. In fact, if the tempera-
The test showed that, at times, a plastic sheet
ture of concrete is not closely regulated, high tem-
provided more than just protection against mois-
peratures can cause significant strength loss, as
shown in Figure 1 for the 40C concrete.
ture loss. Figures 4b and c show that the concrete
under the plastic sheet was actually warmer than
The potential effect on the length of the con-
the concrete inside the unheated shelter, at least
struction season of being able to place and keep
concrete at 5C, instead of at the current limit of
on sunny days. The sheet-covered concrete was 5
to 10C warmer during the day on all but 21
5C, can be determined by looking at weather
March, which was a cloudy day. On that day, the
records. The number of days that the maximum
two concrete temperatures were nearly identical.
air temperature at the Soo exceeded various low
At night, the opposite occurred: the concrete in-
temperatures are shown in Figure 5. As can be
side the unheated shelter was
400
up to 1.5C warmer. These ob-
servations can be explained by
the effect of the large volume of
air in the shelter. The plastic
300
sheet, having essentially no air
to heat up and cool off, allowed
the concrete to heat and cool
faster than could the concrete in-
200
side the shelter. The 6-day tem-
perature of the concrete under
the plastic sheet averaged 2.4C,
vs. 0.9C for the concrete in the
100
unheated shelter. A blanket of
insulation would undoubtedly
have performed even more ef-
0
fectively.
5
0
5
10
-20
Lowest Working Temperature (C)
Of special interest in these
tests was how the work would Figure 5. Extension of construction season possible with various low temper-
progress in cold weather. The ature limits (unpublished chart from Horrigan, 1995).
9
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