The addition of calcium chloride will accelerate the curing process to counteract the effect of
the low temperature of the surroundings. You may have also noticed as you walk by newly
poured concrete for a driveway or sidewalk that water is sprayed onto the concrete for some time
after it is poured. This is to control the rate of contraction of the concrete as it sets.
Concrete is a brittle material that can support compressive loads much better than it does
tensile loads. Because of this fact, concrete is commonlyreinforcedwith steel bars or steel mesh
that consists of thin metal rods to increase its load-bearing capacity, especially in the sections
where tensile stress is expected. Concrete is poured into forms that contain the metal mesh or
steel bars. Reinforced concrete is used in foundations, floors, walls, and columns. Another com-
mon construction practice is the use ofprecast concrete. Precast concrete slabs, blocks, and struc-
tural members are fabricated in less time with less cost in factory settings where surrounding
conditions are controlled. The precast concrete parts are then moved to the construction site
where they are erected. This practice saves time and money. As we mentioned, concrete has a
higher compressive strength than tensile strength. Because of this fact, concrete is alsoprestressed
in the following manner. Before concrete is poured into forms that have the steel rods or wires,17.3 Some Common Solid Engineering Materials 565
Examples of concrete used in construction.
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