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10–1 Concrete Work
The concrete for a project may be either ready mixed or
mixed on the job. Most of the concrete used on commercial
and residential work is ready mixed and delivered to the job
by the ready-mix company. Quality control, proper grada-
tion, water, and design mixes are easily obtained by the
ready-mix producers. When ready-mix is used, the estimator
must determine the amount of concrete required and the
type and amount of cement, aggregates, and admixtures.
These are discussed with the supplier, who then gives a pro-
posal for supplying the specific concrete.
Concrete for large projects or those in remote loca-
tions will typically be mixed at the job site and will require
a field batch plant. To successfully estimate a project of
this magnitude, the estimator must have a thorough
understanding of the design of concrete mixes. The basic
materials required for concrete are cement, aggregates
(fine and coarse), and water. Various admixtures, which
modify the properties of the concrete, may also be
required. If field batching is desired, the estimator will
have to compute the amounts of each material required,
evaluate the local availability, and determine if these
ingredients will be used or if materials will be shipped to
the site from somewhere else. If the materials are shipped
in, they are bulky, heavy, and typically transported by rail.
If the site is not adjacent to a rail line, provisions will need
to be made to move the materials from the rail siding to
the project batch plant. No attempt will be made here to
show the design of concrete mixes. It is suggested that the
estimator who is unfamiliar with mix design and control
consult with a professional civil engineer.
10–2 Estimating Concrete
Concrete is estimated by the cubic yard (cy) or by the cubic
foot (cf ) and then converted into cubic yards. Concrete
quantities are measured in cubic yards as it is the pricing
unit of the ready-mix companies, and most tables and charts
available relate to the cubic yard.
Roof and floor slabs, slabs on grade, pavements, and
sidewalks are most commonly measured and taken off in
length, width, and thickness and converted to cubic feet and
cubic yards (27 cf1 cy). Often, irregularly shaped projects
are broken down into smaller areas for more accurate and
convenient manipulation.
When estimating footings, columns, beams, and girders,
their volume is determined by taking the linear footage of each
item times its cross-sectional area. The cubic footage of the var-
ious items may then be tabulated and converted to cubic yards.
When estimating footings for buildings with irregular
shapes and jogs, the estimator must be careful to include the
corners only once. It is a good practice for the estimator to
highlight on the plans which portions of the footings have
been figured. When taking measurements, keep in mind that
the footings extend out from the foundation wall; therefore,
the footing length is greater than the wall length.
In estimating quantities, the estimator makes no deduc-
tions for holes smaller than 2 sf or for the space that rein-
forcing bars or other miscellaneous accessories take up.
Waste ranges from 5 percent for footings, columns, and
beams to 8 percent for slabs.
The procedure that should be used to estimate the con-
crete on a project is as follows:- Review the specifications to determine the requirements
for each area in which concrete is used separately (such as
footings, floor slabs, and walkways) and list the following:
(a) Type of concrete
(b) Strength of concrete
(c) Color of concrete
(d) Any special curing or testing - Review the drawings to be certain that all concrete items
shown on the drawings are covered in the specifications.
If not, a call will have to be made to the architect-engineer
so that an addendum can be issued.
CONCRETE
CHAPTER TEN