CONCLUSIONS - SR96

temperatures and by these times, even ad-

400

mixture-free concrete may have been able

to set and become resistant to freezing.

300

The test showed that a plastic sheet was

capable of providing more than just protec-

tion against moisture loss. Figures 13 and

200

14 show that the concrete under the plastic

sheet was actually warmer than the con-

100

crete inside the unheated shelter, at least on

sunny days. The sheet-covered concrete was

5 to 10C warmer during the day on all

days but 21 March, which was cloudy. On

Lowest Working Temperature (C)

that day, the two concrete temperatures

were nearly identical. During nighttime, the

Figure 16. Possible extension of construction season with vari-

opposite occurred: the concrete inside the

ous low-temperature limits (Horrigan 1995, unpublished).

unheated shelter was up to 1.5C warmer.

These observations can be explained by the

effect of the large volume of air within the shelter.

peratures can cause significant strength loss.

The plastic sheet, having essentially no air to heat

The potential effect on the length of the con-

up and cool off, allowed the concrete to heat and

struction season of being able to place and keep

concrete at 5C (23F) instead of at the current

cool faster than could the concrete inside the shel-

limit of 5C (41F) can be determined by looking

ter. The six-day temperature of the concrete un-

der the plastic sheet averaged 2.4C (36.3F) com-

at weather records. The number of days that the

pared to only 0.9C (33F) for the concrete in the

maximum air temperature in northern Michigan

unheated shelter. A blanket of insulation would

(at the Soo Locks) exceeded various low tempera-

undoubtedly have performed even more effec-

tures is shown in Figure 16. As can be seen, push-

ing the temperature envelope to 5C (23F) in-

tively.

Of special interest in these tests was how the

creases the length of the construction season by

work would progress in cold weather. The work-

nearly 80 days. More working days become avail-

ers at the Soo Locks stated that working outdoors

able at lower temperatures, to the point that con-

was much preferred to working in a confining,

creting is a year-round proposition without the

though heated, enclosure. It was much easier to

need for heat. The climate at the Soo is similar to

place and finish the concrete where there was

that of the coldest areas in the contiguous United

freedom of movement. The consensus was that

States.

outdoor concreting was practical down to 20C

(4F), possibly lower, provided a heated shelter

was available to warm up in periodically. At the

CONCLUSIONS

Soo, the workers worked outdoors in windy

10C (14F) weather for two-hour intervals. The

The results from investigating Pozzutec 20 and

finishing operation required no special tools, skills,

developing a new prototype admixture indicate

or precautions. The antifreeze concrete finished

the following:

in the same manner as normal concrete. Ice did

1. Pozzutec 20 accelerates and enhances the

not build up on the cold metal tools as suspected.

strength gain of concrete. When cured at room

Concreting in winter costs more than during

temperature, Pozzutec 20, used at its maximum

the rest of the year. The extra costs in this test

permissible dosage of 60 mL/kg (90 fl oz/cwt),

were 113 percent for the enclosure, and up to 43

improved the seven-day strength of concrete by

percent for the admixture. Costs associated with

nearly 20%. A similar result was produced when

antifreeze admixtures were more than offset by

the concrete was tested after 56 days of room-

savings on protection requirements.

temperature curing.

From a strength development standpoint, the

2. Compared to the more-than 35 trial admix-

antifreeze concrete was equal to or better than the

tures tested, Pozzutec 20 provided the fastest set-

concrete placed inside a heated enclosure. Dry

ting concrete. In one test conducted in mortar,

heat can create problems. In fact, if the tempera-

Pozzutec 20 shortened the initial set time of con-

ture of concrete is not closely regulated, high tem-

crete from 4 1/6 hours to 2 5/6 hours. The best