Page 393 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

ROADWAYS 8.55

FIGURE 8.40 Cement requirements for soils. (Courtesy of Portland Cement
Association.)

In the freeze-thaw tests, 7-day specimens are placed on moist blotters, refrigerated at 10°F
( 23°C) for 24 hours. They are then thawed in a moist atmosphere at 70°F (21°C) for 23 hours.
They are brushed, and half-loose scales are pried off with an ice pick. After 12 cycles, the speci-
mens are oven-dried and weighed. Permissible, or perhaps desirable, loss is the same as in the
wet-dry test.
Compressive strength, in spite of its great importance in the pavement, is not necessarily tested
directly, but is assumed from these two. The 7-day strength ranges from 300 to 800 pounds per
square inch. After long curing, it may be 1,200 to 3,000 psi.
Water. Water requirement is figured out very carefully for optimum compaction, without regard
to the quantity needed for hydration of the cement. Air-dry, pulverized soil is weighed in a labo-
ratory, then blended with the proper amount of cement. Water is mixed in, in small measured