30
gardless of which construction method is em-
ployed. The primary difference between the two
methods is that with the antifreeze method the
shelter would not have to be heated after the
25
work stopped. In this case, the weather was mild
enough that the antifreeze side of the shelter did
not have to be heated for the comfort of the masons.
The workers were able to stay warm just by wear-
20
ing jackets but no gloves. There was no signifi-
cant difference in the production rate between the
two walls. Other labor and materials are consid-
ered common to both construction methods.
15
A heater produced 34,000 Btu/hr for each day
it was in operation. Two heaters were used. A
commonly used heat source on construction sites
is liquid propane. At
||content||
.94/gal and 91,000 Btu/5
gal, the cost to keep the conventional mortar
above freezing was about /day. On the other
hand, based on costs for other admixtures sold on
the market today, the antifreeze admixture is esti-
0
Control Site
mated to cost about .00 for the total amount of
KC1 Site
admixture used on this project. Since the mortar
Figure 22. Strength of mortar cylinders
only had to be heated for 1 day, the antifreeze ad-
cast during construction.
mixture produced no cost saving--it cost as
much as the heat. Keep in mind that the average
daily outdoor temperature was roughly 3C
antifreeze mortar, cured in the unheated side of
(37F). Colder temperatures would increase heat-
the shelter for 7 days, is as strong as the conven-
ing demand. The saving in this case, however, is
tional mortar.
that no fuel had to be burned to protect the anti-
freeze mortar.
Efflorescence
Although the cost comparison and productiv-
Efflorescence is of concern whenever anything
ity of the two walls in this demonstration did not
is added to the mortar, and it appears to occur
yield significant differences, antifreeze admix-
with greater frequency in cold-weather construc-
tures may cause significant savings for masonry
tion projects. It was reported that the wall exhibit-
built with large, prefabricated units. In this type
ed some white discoloring at the joints on the half
of construction, cranes are used to lift and place
of the wall containing the KC1 admixture during
the heavy units into the assembly, and the ability
the spring time. However, after the first rain the
to do this work in the open, without a shelter,
white coloring had disappeared. During a sum-
opens new opportunities for cost-effective winter
mertime inspection, both halves of the wall
masonry construction.
appeared identical.
Cost comparison
CONCLUSIONS
The primary difference between conventional
1. The frost susceptibility of newly placed mor-
winter masonry construction and masonry con-
tar is directly related to its moisture content.
struction done with antifreeze admixtures is with
Fresh mortar is frost-susceptible because it is
the type of freeze protection provided in each
water-saturated. Dry mortar is frost-immune.
case. The conventional practice is to provide heat
After mortar is placed, its moisture content
to keep the masonry above freezing until it gains
decreases. There is a critical moisture con-
sufficient strength. With antifreeze admixtures,
tent at which the mortar becomes frost-resis-
the mortar is placed and cured in the cold with-
tant. The experiments in this project showed
out heaters or insulation. However, since the
that the moisture content of the masonry
work environment must not be too cold for the
units at the time of assembly and the absorp-
workers, most winter masonry construction
tive characteristics of the unit are the pre-
projects would require a temporary shelter re-
26
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