Table 14 shows the approximate time each con-
Observations and results
crete was placed. The air temperature during trans-
Workability
portation of the concrete on the 17th began at
16C, rose to a high of 4.5C at 2:00 p.m., and
The concrete water content was reduced at the
ready-mix plant to account for the water to be
then dropped off to well below freezing that night.
added with the admixtures to the concrete truck
The slab concrete temperature at placement was
10C. It rose to 12C by noon and then dropped
at the construction site. Accordingly, the water/
off to 0.4C by 4:00 a.m. Though the air tempera-
cement ratio at the plant was 0.34 and became
0.43 after the respective admixture solution was
ture during the next three nights got quite cold
(15C at 6:30 a.m. on the 18th, 10.3C at 6 a.m.
added. The negative effect of holding back water
on the 19th, and 5.4C at 2 a.m. on the 20th), the
during initial mixing was that the concrete air
contents were very low (i.e., 3% instead of the
concrete did not freeze. It dipped to a low of
1.2C, which is not a freezing temperature for
desired 6%). The impact of such a low air content
is that the concrete may not be as durable as it
these mixes, at 6:30 a.m. on the 19th. The slab
finally cooled to below 5C at 8:00 p.m. on the
would have been had the concrete contained 6%
air. It was also noticed that adding the admixture
26th, and remained below that temperature for
at the mix plant, though producing a concrete of
five days, until 5 a.m. on 3 March. It then rose
slowly for the next seven days to near 0C on 10
correct air content, had the tendency to result in
stiffer mixes at the job site. The DPTC mixture lost
March. These low temperatures, though harmful
slump relatively fast, perhaps because the con-
to fresh concrete, were not harmful to the nine-
crete and the air temperatures were higher than
day-old concrete.
anticipated, and because it did not have a plasti-
The low ground temperature, which acted as a
cizer. The slump was 5 cm during placing.
heat sink, caused concern that the bottom of the
concrete would not be able to warm the ground
above 5C , and that the concrete would freeze
Finishability
Finishing antifreeze concrete was the same as
from the bottom up. The temperature data show
finishing normal concrete. The trowel did not
that freezing did not happen. For several days the
bottom of the concrete slab remained near 0C. It
freeze to the surface of the concrete and the result-
ing finish looked good. The main complaint from
remained slightly warmer than the top surface of
the finishers was that some of the mixes arrived
the slab, even after a week of curing. This result
very stiff. This may be corrected by adding a plas-
has implications for normal winter concreting, in
ticizer.
which placing fresh concrete on frozen ground is
prohibited because of the danger of freezing.
Thermal record
The wall was placed on 18 February. The
Five thermocouples were equally positioned
wooden forms were erected and the rebar was set
through the thickness of the slab and six through
during the morning. Concrete placement began at
the wall beginning at the outside surface. An ad-
11:35 a.m. Figure 3b gives the wall surface tem-
ditional thermocouple was positioned slightly
perature history. The air temperature at 11:35 was
away from the concrete, out of direct sunlight, to
1.8C, rose to 2.5C at 3 p.m., and fell to below
record air temperature. The complete thermal
freezing that night. The concrete arrived some-
records can be found in Appendix B. A 21-day
what warmer than the prior day's concrete. It be-
temperature history for the most relevant loca-
gan at 13C, rose to 19.7C at 3:30 p.m. and (unlike
tions is presented in Figures 3ac. The outside
the slab) its coldest portion, the surface, did not
surface was the coolest portion of the slab and
cool off appreciably over the next several days.
wall. It cooled more quickly and experienced
The combination of the insulation effect provided
wider temperature excursions than the interior
by the wooden forms and the fact that there was
concrete.
no cold substrate to place concrete against helped
the concrete to remain warmer longer. The forms
Table 14. Concrete placement
were removed at 9:30 a.m. on the 19th, allowing
time.
the concrete to cool somewhat but to remain sig-
Mix
Date
Start
nificantly above ambient temperature until the
22nd, three days after being cast. From that point
PolarSet
17 Feb
9 a.m.
on, the wall temperature tracked air temperature,
DP
18 Feb
11:35 a.m.
DPTC
18 Feb
11:55 a.m.
which indicates that much of the chemical reac-
13
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