locations: on grade next to the slabs, and overhead
Cost comparison
in the heated enclosure. A concrete testing labora-
Freeze protection is the primary cost-multiplier
tory (Coleman Engineering Co., Iron Mountain,
of a concrete job done during the winter. Based on
Michigan) periodically tested the cylinders' com-
the field tests, the main differences between nor-
mal winter concreting practice at the Soo and con-
pressive strength.
creting done with antifreeze admixtures are the
Their compressive strengths cannot be used as
heat, shelter, and labor needed to protect the nor-
an indicator of the in-place strength of the anti-
mal concrete, and the chemicals in the antifreeze
freeze concrete because, as Figure 4f shows, the
concrete. Table 5 shows an estimate of the relative
cylinders probably froze. At CRREL, subsequent
surcharge, per slab, of each winter concreting
petrographic analysis of the suspected frozen
method. It is useful to know that the cost of ready-
cylinders revealed typical ice lens patterns.
mix concrete at the Soo was .50/m3 the sum-
Strengths reported by the testing laboratory indi-
mer before this project and that placement would
cate that the cylinders developed only about half
double this cost.
of their potential strength, which is indicative of
concrete that has frozen while curing.
Table 5. Winter surcharge estimate per slab.
Likewise, the strengths of the cylinders stored
overhead in the heated shelter were not consid-
Shelter
Antifreeze
ered useful information, other than to confirm
5.1 m3
that the admixtures promoted strength in concrete
Erect
2
Concrete
Materials
8
Dosage
97.1mL/kg cement
cured at above-freezing temperatures. They shed
391 kg/m3
Heat
6
Cement
little light on the in-place strength of the concrete
Dismantle
6
Admixture
||content||
.80.10/Lslabs.
Total
82
Total
57
The most interesting and useful results came
from cores drilled from each slab in the summer.
DISCUSSION
The cores showed that the antifreeze concrete was
Normal unprotected concrete would have fro-
at least as good as the control concrete in compres-
zen during this test. The freezing-point-depres-
sive strength and appearance. None of the slabs
sion and accelerated cure properties of the anti-
showed signs of frost damage and all of the con-
freeze concretes enabled them to resist freezing.
crete exceeded minimum design strengths (Table
The best evidence that the concrete did not
4). In fact, when it is considered that entrained
freeze was obtained by examining drilled cores.
Table 4. Test results from 9.2- 13.3-cm
The core samples, taken from each slab 4 months
core samples drilled in July 1994.
after construction and examined under a micro-
scope, showed no signs of frost damage.
Compressive
Bulk
density†
strength*
Evidence of
The drilled cores were also tested for compres-
(g/cm3)
past ice?
Mix
(Mpa)
sive strength, which provided additional infor-
mation that the admixtures produced a concrete
Control
46.7
2.31
No
DP
46.0
2.21
No
that was unaffected by the outdoor winter condi-
EY11L
50.6
2.32
No
tions.
EY11H
55.5
2.29
No
Other than the cold weather, the major concern
* Minimum design strength was 32 Mpa.
during the test was that concrete was placed on a
† Densities based on cylinder dimensions and
subgrade that was significantly below the 5C
mass.
protection capability of the admixtures at their
highest dosage, let alone at the low dosage. This
air can reduce compressive strength 3% for each
could mean that the bottom of the concrete would
1% of entrained air (U.S. Department of the Interi-
be damaged by frost. Gavrish et al. (1974) report-
or, Water and Power Resources Service 1981; Kos-
ed that up to 16 times more heat is lost from a con-
matka and Panarese 1988), and that the air con-
crete slab to frozen ground than is lost to the air
tents were generally higher in the admixtured
during initial curing. From our data, however, it
concretes than in the control concrete (Table 3), the
was clear that the bottom of the concrete was free
strength of the admixtured concretes exceeded the
from frost damage. The lowest slab-bottom tem-
strength of the control concrete. Though air con-
perature of the low dosage EY11 concrete was
tents can change when a concrete hardens, the
about 1.2C, 21 hours after placement, and for
core densities (Table 4) suggest that the concretes
the high dosage EY11 concrete it was 2.6C, 4
retained their relative proportions of air.
8
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