and repair of the locks themselves is normally

The concrete was placed and finished in the

done during the winter months, January through

normal fashion. Except for the heated control sec-

March, when shipping is stopped. Other repair

tion, the concrete remained thermally unprotected.

work, such as the replacement of the slabs de-

A plastic sheet was placed over the two exposed

scribed here, is also most conveniently done dur-

concrete sections for seven days to minimize wa-

ing the winter nonshipping season, making this

ter loss. The concrete in the two shelters was left

test particularly relevant.

uncovered. Thermocouples connected to data log-

For this test, four reinforced slabs on grade

gers monitored concrete and air temperatures.

Numerous 75- 150-mm (3 6 in.) cylindrical

were selected for testing two admixtures. Each

slab measured 5.5 m wide by 6.1 m long by 150

samples were cast from each concrete section and

mm thick (18 20 ft 6 in.). The two admixtures

stored in two locations next to the slabs on grade

tested were EY-11 and Pozzutec 20. The EY-11

and overhead in the heated enclosure. A concrete

admixture was used in two dosages: low and high,

testing laboratory in northern Michigan tested the

designated EY11L and EY11H. The Pozzutec 20

cylinders for compressive strength at regular in-

admixture was used in a single dosage. The four

tervals.

test slabs were cast between 15 and 16 March.

The concrete was transported by rotary-drum

Site preparation consisted of jackhammering

truck from a ready-mix plant 8 km (5 mi) from the

out alternate sections of concrete, replacing 150

job site. The concrete was mixed with unheated

mm (6 in.) of base material with an equal amount

aggregate and heated water. The ingredients, in-

of coarse crushed stone, and setting forms and

cluding all admixtures, were mixed before being

reinforcing steel. The slabs that remained between