day strength when the concrete was frozen at the
and 28 days. This was later changed to three,
1.7-MPa (250 psi) strength. The strength of the
seven, and 28 days because the one-day strengths
Pozzutec 20 concrete when frozen after it had
were too low to be of value in this screening pro-
attained the 3.4-MPa (500 psi) strength exceeded
cess.
that of the control by 1% (Fig. 5c).
Three series of trial admixtures were created,
Based on the data in Table B1 and in Figure 5, it
coded EX, EY, and EZ, along with two others
is clear that concrete made with Pozzutec 20 can
modeled after Pozzutec 20, for a total of 35 solu-
safely be frozen after it has achieved a compres-
tions.
sive strength of 3.5 MPa (500 psi).
Task 2: Concrete testing
The best trial admixtures from Task 1 were
PHASE II: DEVELOPMENT
tested in concrete. Mixing took place at room tem-
perature in a 0.17-m3 (6 ft3) drum mixer rotating
OF IMPROVED ADMIXTURE
at 18 rpm for five minutes. The test specimens,
100- 200-mm (4 8 in.) cylinders, were cast and
Procedure
The objective of this phase was to develop a
divided into two groups. One group was cured at
room temperature and one at 10C (14F) for
new admixture that would outperform Pozzutec
20 in early strength gain at lower temperatures.
one, seven, and 28 days. All specimens from the
This work consisted of creating trial admixtures
cold room were thawed at room temperature for
composed of chemicals in aqueous solution. The
four to six hours (the amount of time necessary to
raw materials are proprietary information and
are not disclosed. Although no listing of indi-
Table 10. Phase II tasks.
vidual chemicals is provided, the general catego-
ries of chemicals used are given: 1) inorganic salts,
Task
Description
2) organic chemicals containing hydroxy or
1
Mortar screening
carboxy groups, and 3) organic surfactants (plas-
2
Concrete testing
ticizer). Phase II was divided into the three tasks
3
Follow-up testing
indicated in Table 10.
Task 1: Mortar screening
Table 11. Phase II, Task 1; mortar mixture proportions.
Task 1 used mortar as a rapid way to
Ingredient
Amount
screen the various chemicals. Using
mortar instead of concrete simplified Type I cement, Blue Circle
500550 gm (1.11.2 lb)
mixing operations by reducing mate-
Concrete sand
13751513 gm (3.03.3 lb)
rial handling and permitting smaller
test specimens to be used. The perfor- Tap water--16C (60F)
195213 mL (6.67.2 fl oz) (admixture mortar)
225242 mL (7.68.2 fl oz) (plain mortar)
mance of each trial admixture was
judged against two references: mortar Trial admixture
60 mL/kg (90 fl oz/cwt)
produced with 60 mL/kg (90 fl oz/
100 mL/kg (150 fl oz/cwt)
160 to 176 mL/kg (245 to 270 fl oz/cwt)
cwt) of Pozzutec 20, and plain mortar.
The mortars were cured at 10C (50F).
This temperature was used in the hope that it
allow for elevating the concrete specimen tem-
perature to 50F) before being tested for compres-
would yield a reasonable indication of relative
admixture efficacy for lower temperatures. The
sive strength. Set time was determined according
mix proportions are given in Table 11.
to ASTM C 403, air content according to ASTM C
The mortar was prepared according to ASTM
231 (pressure method [Type B]), and slump ac-
cording to ASTM C 143 (penetrometer). The trial
C 109 in a Hobart mixer. Set times were obtained
with Gillmore needles at 10C (50F) ambient tem-
admixtures were added to the mix water before
mixing started. Table 12 provides the mixture pro-
perature. The mortars were tested at a 0.50 w/c
portions used in this task.
ratio so as to provide near-equal flow, or work-
ability, for each mix. The water contents of the
Task 3: Follow-up testing
mixtures were adjusted for water content of each
Task 3 consisted of follow-up work using the
admixture. Compressive strengths were obtained
better trial admixture systems found in Task 2.
from 2-in. cubes cast after curing for one, three,
11
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