Arizona Contractor & Community Fall 2015 V4 I3 | Page 24

Luke M. Snell, P.E.
Senior Materials Engineer at Western Technologies in
Phoenix, Arizona and Emeritus Professor of Construction
at Southern Illinois University Edwardsville.

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utumn weather in Arizona presents
challenges to concrete construction.
Desert areas are still experiencing tripledigit days while freezing may occur at
higher elevations.
Since most
specifications require that concrete
temperatures must be between 40-95
degrees Fahrenheit (F), the contractor will
need to monitor this factor using an
infrared (IR) thermometer.
The IR thermometer is a simple point
and shoot, instantaneously providing the
temperature of the object. Most IR
thermometers use a laser to pinpoint the
desired object. The user must understand
a few basic principles about the IR
thermometer:
● The laser must not be pointed at any
person’s
eyes.
Although
thermometers use a Class II laser that
is not considered harmful, eye contact
should still be avoided. The user
should also use care so that the laser
light doesn’t reflect off shiny objects
and indirectly hit a person’s eye.
● The user must be relatively close,
preferably within two-to-four feet, to
the object they are measuring.
● You must have a clear unobstructed
path to the object to obtain an

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accurate reading. Avoid shooting
through closed windows, during rain,
and in dusty or smoky weather.
● The IR thermometer provides an
approximate temperature with the
normal accuracy of +/- 3 degrees F.
When higher accuracy is needed, a
calibrated American Society for
Testing and Materials (ASTM)
thermometer must be used.
● The IR thermometer will only measure
the surface temperature of the object.
Thus, if I measure the temperature on
my arm, I may get a reading of 90
degrees, depending on the air
temperature and the relative
humidity.
My body or core
temperature would be close to 98.6
degrees.
Concrete Temperature
Since the material must be kept in a
narrow temperature range, the user can
determine the concrete temperature of
each load of concrete as the truck starts to
discharge the contents. In a research
project, I observed that an accurate
concrete temperature could be obtained
just as the material enters the chute
without interrupting the work. Thus, the
contractor can provide immediate

feedback to the batch plant when
temperature adjustments must be made.
Subgrade/Forms Temperature
Requirements – Cold Weather
American Concrete Institute (ACI) 301
“Specifications for Structural Concrete,”
states that the material should not come
in contact with surfaces that are less than
35 degrees. The IR thermometer can easily
allow the user to determine if the subgrade
and form surfaces meet these
requirements. If the surfaces need to be
heated, the T