had a positive effect on when concrete

can first be frozen. For both of the Type

I cement mixtures (Fig. 5a and b),

Pozzutec 20 produced a 28-day strength

that exceeded that of the admixture-

free control, regardless of the strength

2,1

2 (37)

1.0 (5.7)

47 (1.8)

2,2

1 (34)

1.1 (6.3)

52 (2.0)

at which the concrete was frozen. The

2,3

0 (32)

1.2 (6.9)

56 (2.2)

exception to this was for the Type III

*2,0

2 (28)

1.4 (8.1)

66 (2.6)

cement mixture (Fig. 5c), where Pozzu-

*2,2

4 (25)

1.6 (9.2)

75 (3.0)

tec 20 caused a 5% decrease in the 28-

* Denotes Type III cement.

50

Room

3.4 MPa

1.7 MPa

5.2 MPa

Table 9 shows the amount of insulation that

40

the various mixtures tested can replace. The table

is based on ACI requirements to maintain a 150-

30

mm- (6 in.) thick wall of concrete made with Type

I cement at a cement factor of 365 kg/m3 (611 lb/

20

yd3) at 10C (50F) for seven days. For instance,

according to ACI, an ambient air temperature of

10

0C (32F) requires insulation to have a thermal

0

2, 0

2, 1

2, 2

2, 3

which is equivalent to 56 mm (2.2 in.) of fibrous

60

glass insulation. Pozzutec 20 dosed at 100 mL/kg

(150 fl oz/cwt) is equivalent to that amount of

insulation (Table 9).

40

The objective of this task was to determine if

20

Pozzutec 20 affected the minimum strength at

which concrete can be frozen without being frost-

damaged. The critical freezing strength of normal

air-entrained concrete, according to ACI 1988, is

0

3, 0

3, 1

3, 2

3, 3

3.5 MPa (500 psi). A complete list of strength

50

results at all test ages is provided in Appendix B.

Figure 5 highlights this data by showing the 28-

40

day strengths for the 365-kg/m3 (611 lb/yd3) ce-

ment factor of Type I and III cement. These data

30

provide evidence of the effect of Pozzutec 20 on

the critical freezing strength of concrete.

20

Before discussing the effects of Pozzutec 20, it

is worth noting in Figure 5 that the three admix-

10

ture-free concretes, i.e., (2,0), (3,0), and (*2,0), were

unaffected by one cycle of freezing and thawing

0

*2, 0

*2, 2

once they had attained a compressive strength of

3.4 MPa (500 psi). The freezing actually produced

a slightly stronger concrete for the Type I cement

and showed no ill effect for the Type III cement. It

is interesting to note that the 3.5 MPa (500 psi)

critical strength value is for air-entrained con-

crete. The concretes in this study were non-air-

entrained. Thus, the real critical strength is prob-

ably less than that given by ACI.

The addition of Pozzutec 20 to the concrete

10