Page 39 - Masonry and Concrete

Concrete Construction Techniques
38 CHAPTER THREE

3.1.1 Estimating Total Concrete Volume
To estimate the cubic yardage of concrete needed, first calculate the
area in square feet, then use the graph in Figure 3-1 to find the volume
of concrete needed. Locate the calculated square footage along the top
of the graph. Then follow the vertical line down until it intersects the
diagonal line for the required concrete thickness. Read horizontally to
the right to find the volume in cubic yards and to the left to find the
volume in cubic feet. If the area is larger than 300 sq. ft., first find the
volume for 300 sq. ft., then find the volume for the remainder of the
square footage, and add the two together. To allow for slight irregular-
ities in concrete thickness and for some spillage and waste, round up
at least to the next whole or half-cubic yard measure, allowing a mini-
mum of 5–10% extra.
Ready-mix suppliers will need to know minimum compressive
strength and maximum aggregate size for the concrete mix, and any spe-
cial requirements such as air entrainment for added freeze-thaw dura-
bility. As a general guideline for ordering ready-mix concrete, Figure 3-2
shows recommended requirements. The weathering regions indicated
on the map are intended as a general guideline. Local conditions can
change within a very short distance, particularly in mountainous
regions, and may be more or less severe than indicated by the regional
classification. Severe exposures are those in which deicing salts are
used because of significant snowfall combined with extended periods
in which natural thawing does not occur. If you are in doubt about
which classification applies, always use the more severe exposure.
3.1.2 Estimating Individual Ingredients

The actual ingredient proportions in concrete can be measured either
by volume or by weight. To estimate the volume of concrete and the
volume of the various ingredients needed for the mix, first calculate
the total area in square feet as above, and use the graph in Figure 3-1 to
find the volume of concrete needed. From the intersection of the verti-
cal line for area and the diagonal line for thickness, read horizontally
to the left to find the volume in cubic feet. Then use Figure 3-3 to
determine the proportions of cement, sand, gravel, and water required.
Table A in Figure 3-3 shows the required weight of each ingredient

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