(66.2F), and following that would have 1.2 hours to

peratures below freezing. The mortar, mixed at room

temperature, was cast into 50.8- ↔ 101.6-mm plastic

be completely finished. Cold weather would increase

these times: each 10C drop in temperature would

cylindrical molds and placed into 20, 5, 10, and

20C (68, 23, 14, and 2F) rooms within 30 minutes

double them. Thus, anything that can accelerate setting

of the mix water being added to the cement. Three

often translates into big savings in time, labor, and money

samples from each mix from each temperature were

at the construction site, particularly during the winter.

tested in uniaxial compression according to ASTM C

None of the commercial admixtures appeared to

39 (ASTM 1997b) at 7 and 14 days. Prior to testing,

accelerate setting. This was not unexpected for the Type

the cylinders were stripped from their molds, warmed

A, D, and F admixtures, as they can retard setting (Table

to 5C (41F), and capped with unbonded neoprene held

1). However, the Type C and E admixtures, being ac-

within a steel-retaining cup conforming to ASTM C

celerators, should have reduced the initial and final set

1231 (ASTM 1997d). At 14 days, the remaining three

times by about one hour (Table 1), but they did not.

cylinders from each mix in each coldroom were moved

Instead, both of these admixtures appeared to increase

to the 20C (68F) room for an additional 18 days be-

the initial set by more than one hour. Final set was simi-

fore testing.

larly affected. As a possible explanation for the slow

setting times, past studies have found that accelerators,

when used at higher doses, can prolong setting times

RESULTS AND DISCUSSION

(Korhonen et al. 1997a). Another possible explanation

for these poor showings could be that the room in which

Individual admixtures

the setting times were done was cooler on the days that

Table 3 shows the effect of each admixture on the

the accelerators were tested. Measurements taken later

showed that the room did vary by as much as 5C daily.

properties of fresh mortar. The admixtures' effect on

Since the testing was done over a several-week period,

stiffening is given in terms of setting time. Initial set

between-test temperature differences are likely. Thus,