and as a check to determine if sufficient materials are
available to constructor complete a project. In general,
the term bulk material refers to concrete, bituminous
paving materials, and mineral products, such as sand,
gravel, or rock. A few examples of estimating these
materials are described below.
Concrete
Estimating the amount of concrete required for a
project consists of determining the volume (in cubic
yards or, in many locations outside the United States, in
cubic meters) of the spaces that will be occupied by the
concrete. As an example, let’s look at figure 5-2. This
figure shows the foundation plan and a typical
foundation detail for a small 20 foot by 32 foot building.
As shown in the detail, the foundation is continuous and
the floor is a 4-inch-thick concrete slab. Our task is to
determine the amount of concrete that will be required
for the foundation and slab. Since in any concrete job a
certain amount of concrete will be unavoidably lost
during placement, we will include a 10-percent waste
factor. You can find this waste factor listed in the P-405.
Although we could proceed in various ways to
estimate the amount of concrete that is required, an easy
method is tabulated as follows:
Foundation wall:
(32.00 ft x .67 ft x 2 fi) x 2 = 85.76 cu ft
(18.67 ft x .67 ft x 2 ft) x 2 = 50.04 cu ft
Footing:
(33.33 ft x 2 ft x 1 ft) x 2 = 133.032 cu ft
(17.33 ft x 2 ft x 1 ft) x 2 = 69.32 cu ft
Slab:
18.67 ft x 30.67 ft x .33 ft = 188.96 cu ft
527.40 cu ft
x 1.10 (10% waste)
580.14 cu ft
= 21 cu yd
From the above tabulation, you can see that separate
estimates were prepared for the foundation wall,
footing, and slab. You can also see that both the
foundation wall and the footing were further subdivided
based on the length and width of the building; for
example, the foundation wall consists of two walls
measuring 32 feet long and two measuring 18 feet 8
inches long (allowing for overlap at the foundation
corners). Then, the separate estimates were added
together, the waste factor was applied, and the final
cubic feet of concrete was converted to cubic yards.
Now let’s see how much compacted fill will be
required for this job. For this example, we will assume
that the project specifications call for sand to be used as
the fill material.
Figure 5-2 shows that the fill material is to be 8
inches thick after compaction. Therefore, the volume of
the compacted fill is 383.65 cubic feet. However, from
your knowledge of soils, you know that compacted sand
occupies less volume than loose sand. Since the sand for
this project will be delivered to the jobsite in a loose
condition, a compaction factor must be applied.
NAVFAC P-405 lists compaction factors for various
materials. For sand, the compaction factor listed is 1.17.
So, the total amount of sand required for this project is
383.65 x 1.17=448.87 cubic feet, or 16.6 cubic yards.
Again, however, we know that a certain amount of sand
will be wasted. So, let’s increase the total by 10 percent.
Now we need approximately 18 cubic yards of sand for
the job.
Bituminous Paving
Although not always, most bituminous paving
projects that are accomplished by the Seabees use
hot-mixed bituminous concrete that is purchased from
a central plant. In this case, the job of estimating consists
of determining the compacted volume, in cubic feet, of
the pavement. This volume is then multiplied by the unit
weight of the mix, in pounds per cubic foot (pcf), and
the final result is converted to tons of mix required. An
equation for determining the required tons of mix can
be expressed as follows:
Tons of mix =
L x W x T x U W
12 x 2000
Where:
L =
W =
T =
UW =
Length of paved area in feet
Width of paved area in feet
Compacted thickness of the pavement in
inches
Unit weight of the mix in pounds per
cubic foot
To illustrate the use of this formula, let’s assume
that we are estimating a 2-inch-thick hot-mix
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