well as expected. See Table A4 for their perfor-
Other ways to view antifreeze admixtures
mance.) Calcium nitrite initially caused the early
If early age strength is not critical, another way
age strengths to be somewhat delayed, but they
to judge the usefulness of antifreeze admixtures
were still well above the benchmark level. The
is by whether they ultimately allow mortar to
strengths beyond 14 days became significantly
gain full strength even though freezing takes
greater than those of the 20C mortar, and greater
place during curing. The practicality of this is that
than those of the single component sodium nitrite
a concrete structure could be cast during cold
for that matter. This combination appears to be a
weather and then later returned to when the
long-term strength enhancer. The potassium car-
weather turns warm. In this light, we see in Table
bonate, on the other hand, caused the mortar, at
3 that, even though none of the chemical dosages
10C, to act as if it was at 20C at all ages. This
promoted strengths acceptable to the previous
criteria while being cured at 20C, 12 of them
admixture effectively canceled the effect of cold
weather. However, sodium is an alkali that can
allowed essentially full recovery of strength
cause certain siliceous aggregates to swell
when thawed. Thus, antifreeze admixtures can
destructively within concrete. More work should
protect concrete against frost damage down to
20C, perhaps lower, even though strength devel-
be done to find alternative freezing point chemi-
cals that are benign to aggregate in the long-term
ops very slowly at that temperature.
or to find ways to mitigate the negative effect of
Another viewpoint is to consider that we can
added alkalis. For the short-term, these chemicals
expect normal concreting practices during the
are fine as expedient admixtures.
summer to result in more than a 25% loss of ulti-
Sodium sulfate, when combined with sodium
mate strength (Table 1). If one were to hold winter
nitrite, forms the basis of the antifreeze admixture
concrete to that same expectation, then many of
patented by the U.S. Army in 1993. As Figure 2
the chemicals tested in this study would qualify
shows, it produces excellent strengths up to 14
as acceptable antifreeze admixtures.
days when cured at 10C but seems to provide
little benefit thereafter (it exceeds benchmark
CONCLUSIONS AND
strengths at all ages when cured at 5C). For ex-
RECOMMENDATIONS
pedient purposes, this combination of chemicals
is still viable, as most severely cold weather does
Until now, insulation, supplemental heating,
not last more than a few days in most parts of the
and tenting have been the only ways to protect
world. The chemicals are readily available most
fresh concrete from freezing during cold weather.
anywhere, and destructive alkali reactions take
Though effective, they are costly in labor, mater-
10 or more years before they become a problem.
ials, and money--and sometimes they are not
Table 3. Mortars that recovered more than 95% strength after
being cured at 20C for 28 days and then at 20C for an addi-
tional 28 days.
Percent strength
Percent
Freezing
of control mortar
by weight
point
cured for 28 days
(C)
at 20C
Chemical
of cement
Calcium bromide
4
2.9
105.7
6
4.0
127.8
Calcium nitrite
6
5.7
118.8
Calcium chloride (deicer)
6
2.25
110.3
9
4.0
110.5
Calcium magnesium acetate
8
8.2
96.4
Magnesium chloride
6
11.5
96.9
Car antifreeze--ethylene glycol
6
6.6
101.0
Calcium chloride deicer/sodium
3/3
5.1
98.5
nitrate fertilizer
4.5/1.5
na*
99.5
Calcium chloride deicer/potash
fertilizer
4.5/1.5
6.6
98.2
Fertilizer (calcium nitrate)/car
antifreeze (ethylene glycol)
1.5/4.5
5.2
96.5
* Tests were not conducted, or information was not available.
6
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