As a Steelworker, you must be able to cut, bend,
place, and tie reinforcing steel. This chapter describes
the purpose of reinforcing steel in concrete
construction, the types and shapes of reinforcing steel
commonly used, and the techniques and tools used by
Steelworkers in rebar (reinforcing steel) work. This
chapter begins with a presentation of fundamental
information about concrete to help you understand
rebar work fully.
As a Steelworker you will be primarily concerned
with reinforcing steel placement but you should to
some extent, be concerned with concrete as well.
Concrete with reinforcing steel added becomes
reinforced concrete. Structures built of reinforced
concrete, such as retaining walls, buildings, bridges,
highway surfaces, and numerous other structures, are
referred to as reinforced concrete structures or
reinforced concrete construction.
Concrete is a synthetic construction material made
by mixing cement, fine aggregate (usually sand),
coarse aggregate (usually gravel or crushed stone),
and water in proper proportions. This mixture hardens
into a rocklike mass as the result of a chemical reaction
between the cement and water. Concrete will continue
to harden and gain strength as long as it is kept moist
and warm. This condition allows the chemical reaction
to continue and the process is known as curing.
Durable, strong concrete is made by the correct
proportioning and mixing of the various materials and
by proper curing after the concrete is placed.
The correct proportioning of the concrete
ingredients is often referred to as the mix. The quality
of the concrete is largely determined by the quality of
the cement-water paste that bonds the aggregates
together. The strength of concrete will be reduced if
this paste has water added to it. The proportion of
water to cement is referred as the water-cement ratio.
The water-cement ratio is the number of gallons of
water per pounds of cement. High-quality concrete is
produced by using the lowest water-cement mixture
possible without sacrificing workability.
Because concrete is plastic when it is placed
forms are built to contain and form the concrete until
it has hardened In short forms and formwork are
described as molds that hold freshly placed concrete
in the desired shape until it hardens. All the ingredients
of the mix are placed in a concrete mixer, and after a
thorough mixing, the concrete is transferred by
numerous methods, such as by bucket, by
wheelbarrow, and so forth, into the formwork in which
the reinforcing steel has already been placed.
Concrete reaches its initial set in approximately 1
hour under normal conditions and hardens to its final
set in approximately 6 to 12 hours. Before the initial
set, concrete must be placed in the forms and vibrated
to consolidate it into the formwork and ensure
complete coverage of all reinforcing bars. Finish
operations, such as smooth troweled finishes, must be
performed between initial and final set. After the final
set, concrete must be protected from shock, extreme
temperature changes, and premature drying until it
cures to sufficient hardness. Concrete will be
self-supportive in a few days and attain most of its
potential strength in 28 days of moist curing. For
further information on concrete, refer to Builder 3 &
2, Volume 1, NAVEDTRA 12520.
As stated previously, the strength of concrete is
determined by the water-cement ratio. The strength of
ready-mixed concrete ranges from 1,500 to about
5,000 pounds per square inch (psi); and, with further
attention paid to proportioning, it can go even higher.
Under usual construction processes, lower strength
concrete will be used in footers and walls and higher
strength in beams, columns, and floors. The required
strength of concrete on a given project can be found
in the project plans and specifications for a specific
NOTE: Quality control is important to ensure
specific design requirements are met. If the design
specifications do not meet minimum standards,
structural integrity is compromised and the structure