TM 5-852-4/AFM 88-19, Chap. 4
b. Air entraining agents. An approved air
materials to inordinately high temperatures before mixing
or over-zealous use of hot air blowers to protect against
entraining agent should be used to produce a proper
freezing are, therefore, not proper solutions to cold
number, size and spacing of air bubbles in concrete
weather concreting. Rather the materials should be
which will be exposed to weathering. Concrete must
heated to maintain a concrete placing temperature not
have a satisfactory entrained air-void system in order to
less than shown in table 6-1, but not over 70F after
resist freezing and thawing if the concrete is in an
placing. The air, water, and forms in contact with the
environment where critical saturation with water may
concrete surfaces should be maintained at not less than
exist at the time freezing may occur. If the environment
50 F throughout the curing period specified for the type
is quite severe, the concrete should be protected from
of cement used in the concrete. Accurate periodic
freezing until it has matured sufficiently to have
concrete temperature readings should be taken during
developed a compressive strength such as would be
setting and curing to obtain a quantitative measure of the
indicated by test of 6-inch by 12-inch cylinders of 4000 to
actual degree of protection afforded. Ice or snow on
4500 psi. If the air-entraining agent is either an approved
reinforcing steel and within forms must be removed
air-entraining addition to the cement or an air-entraining
before placing concrete. Hot air heaters of various types
admixture incorporated into the concrete mixture at the
or live steam may be employed to warm reinforcement,
time of batching, it may be assumed with normal
forms or ground just before concrete is placed.
concrete mixtures that the air-void system will be
adequate, provided the
Table 6-1. Effect of Temperature of Materials on Temperature of Various Freshly Mixed Concrete203
Subject to controlling criterion that the thickness of section shall not be less than 5 times the maximum size of rock.
(Courtesy of Bureau of Reclamation, U.S. Dept of Interior)
6-5
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