chapter 3 rigid pavement - DOT On-Line Publications - Department ...

FHWA TECHNICAL ADVISORY T 5080.17
July 14, 1994
Thin sections are defined as those less than
300 mm.
(2) Concrete should never be placed on a frozen
subgrade. Care should be taken to assure
that the subqrade is free from frost.
(3) Hot weather conditions can be defined as a
condition of high temperature, low humidity,
and high winds. The existence of these
conditions can be determined by finding the
evaporation rate described in AC1 305 and
included in Attachment 5. An evaporation
rate exceeding 1 kg/m'/hr has the potential
of causing plastic shrinkage cracks. The
evaporation rate is a function of concrete
temperature, ambient temperature, relative
humidity, and wind velocity. This chart
has been incorporated into several State
specifications. It may not completely apply
in all cases, especially in mixes containing
admixtures which reduce the amount of
bleeding.
(4) In addition to the plastic shrinkage cracking
problem, ultimate strength will decrease with
higher temperatures. The AC1 has not
recommended a maximum concrete temperature
since strength loss can be compensated for by
other means.
-- 1
However, significant strength loss occurs
above 32'OC. Due to the strength loss and
increase in potential for plastic shrinkage
cracking, many States have set a maximum
ambient placement temperature of 32OC. In
all cases, trial batches should be performed
at the highest expected temperature to ensure
that the concrete will have the desired
properties.
9. CONCRRTE DISTRESS CONDITIONS
a. Alkali aggregate reactivity can be one of two
types, alkali-silica and alkali-carbonate. The
most prominent problem is cracking of the concrete
due to the alkali-silica reaction (ASR).
3.10.18