Figure 2. Effect of temperature on strength gain of concrete

sive than the small samples tested in this task and

in the three colder rooms cooled to below freez-

would likely produce higher concrete tempera-

ing within five hours, showing that essentially all

tures. However, the referenced curves clearly dem-

strength gained by the samples in the cold rooms

onstrate the accelerating effect of Pozzutec 20. In

occurred at the temperature of the particular cur-

all three figures, increased dosages of this admix-

ing room. Therefore, the cold room temperature

ture caused the temperature of the concrete to

can be thought of as the temperature of the con-

rise more quickly and attain higher temperatures

crete.

than did lower dosages. For example, Figure 1a

Figure 2 shows the two most important find-

ings from this task. A complete list of strength

shows that mixture 2,3 produced a concrete tem-

perature that was about 2C (3.6F) higher than

results is provided in Appendix A. As was done

mixture 2,0 and about 1C (1.8F) higher than

with the temperature measurements, the strength

results for the 308-kg/m3 (517 lb/yd3) mixes are

mixtures 2,1 and 2,2. Comparing Figure 1a to 1b

shows that increasing the cement content has the

not provided due to segregation of this mixture.

same accelerating effect as does adding Pozzutec

The first finding of this task was that Pozzutec

20 to the mix. The 3,0 mixture, containing the

20 not only accelerated early strength gain in con-

high cement factor (420 kg/m3) and no admix-

crete but that it also enhanced ultimate strength.

ture, produced a concrete temperature that was

This result can be seen in Figure 2 by comparing

nearly identical to the 2,3 mixture, containing the

the room-temperature strength of the control con-

middle cement factor (365 kg/m3) and Pozzutec

crete (2,0,20) to those of the three concretes made

20. Comparing Figures 1b to 1c shows that the

with Pozzutec 20, cured at room temperature.

high early strength cement produced the same

The low, medium, and high dosages of Pozzutec

temperature that was produced by a higher

20 increased the seven-day strength of concrete

amount of normal cement.

by 5, 16, and 17 percent, respectively, and that of

Figure 1d shows a typical temperature history

the 56-day strengths by 8, 18, and 30 percent,

of samples cured in each of the five curing rooms.

respectively. The second finding was that none of

Samples stored at room temperature briefly rise

the Pozzutec 20 dosages produced acceptable

strengths when cured at 5, 10, or 20C (23, 14,

in temperature before cooling to room tempera-

4F); it is probable that mass concrete produced

ture at about 30 hours. The heat loss for the

in the field with higher dosages (90 fl oz) of

samples in the other rooms was rapid enough to

Pozzutec 20 and curing temperatures above 14F

preclude any rise in temperature. The samples

quickly cooled from about 20C (70F) to ambient

would have acceptable compressive strengths. The

initial goal of this project was to produce an ad-

temperature. Within eight hours the sample in

the 5C (40F) room cooled to ambient while those

mixture that would promote strength in concrete

Room Temperature

2, 0, 20

2, 1, 20

2, 2, 20

2, 3, 20

ACI @ 5 C

2, 3, 5 C

2, 3, 10 C

2, 3, 20 C

Age (days)

Figure 2. Effect of temperature on strength gain of concrete. The dotted

lines show the strength gain of control concrete at 20C (70F) and 5C

(40F). The 5C (40F) line is based on guidance from ACI (1988). All

results are for concrete made with a 365-kg/m3 (611 lb/yd3) cement factor

cured at a given temperature for 28 days, followed by 28 days of curing at

room temperature.