Building Materials, Third Edition

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and thawing, and the requirements they place on the concrete. Further, potential chemical
attack must also be considered for those structures in contact with the ground, exposed to
chemicals in the air or exposed to chemicals because of the end use. In short, the concrete must
be resistant to the environment in which it is placed. As with the structural requirements, the
environmental requirements can vary widely: a concrete pavement built on a sulphate rich
subgrade and subject to deicing chemicals in a freeze/thaw climatic zone will certainly have
different requirements to achieve long term durability than a second story interior floor slab in
a climatically controlled high rise building.

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Depending on the breadth of the definitions, either structural or environmental considerations
could easily include the loads to which a structure will be subjected. For buildings the engineer
must consider loads, including those from wind or earthquakes. Marine structures present
another set of conditions and requirements. The loads may be compressive, flexural or tensile,
or include multiple types. In short, the type, magnitude and number of expected loads must be
carefully considered.

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Beyond the three basic influences discussed above, additional factors must also be considered.
First, no matter how good the potential of our mix design is for meeting the three influences,
in order to be practical the concrete must be constructable. That is, while in the plastic state the
concrete must be workable, pumpable (as required) and easily consolidated within the confines
of any form-work or reinforcement. It must maintain this plasticity for the time period necessary
to transport, place and consolidate the concrete. Any desired concrete properties, such as the
entrained air void system, must not be adversely affected during transportation, placement or
consolidation. A wide range of specific materials requirements may be placed on the mix
components, depending on the environmental exposure and type of structure in which the
concrete is placed, and the concrete must meet these requirements while still remaining
construction-friendly.
Secondly, good practices must be followed during construction. The base or form-work
must be well prepared: adequate coverage must be provided for reinforcement: placement
techniques must be such as to avoid segregation of the concrete components; consolidation
techniques must be adequate to attain target densities, but not so great as to adversely affect the
air void system or produce segregation; and finishing and curing techniques must be properly
timed and adequate for environmental conditions.
Thirdly, the interaction of the concrete at an early age with the environment and any loads
must be considered. Heat generated during hydration must be estimated and combined with
the effects of expected environmental conditions. Hot weather concreting requires special
considerations, and changes in mix proportions may become necessary to prevent excessive
internal temperatures, thermal gradients and thermal stresses. Similar concerns must be
addressed for cold weather, or where large swings in ambient temperature are expected in
short periods of time. These factors, and others which may influence the maturity of the
concrete, must be considered when determining the allowable load for the concrete at any
given age. The load may be (for instance) construction traffic, for pavements, or the mass of