Page 19 - Masonry and Concrete

Understanding Concrete
18 CHAPTER TWO

FIGURE 2-6
Aggregate gradation.

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large as 1- ⁄2 in. Coarse aggregate with the largest allowable maximum
size produces the most economical concrete mix. However, it is not
necessary on any single project to use concrete with different maxi-
mum aggregate sizes for slabs, beams, piers, and so on. For conve-
nience, the smallest recommended allowable aggregate size may be
used throughout the project. In practice, aggregate of /4-in. or 1-in.
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maximum size is most commonly available and therefore most com-
monly used in all structural concrete. Figure 2-8 shows the American
Concrete Institute (ACI) recommendations for maximum aggregate
size for various types of construction.
The fine aggregate in concrete is sand. By definition, sand parti-
3
cles are /16-in. diameter and smaller. The sand fills in the voids
between coarse aggregate particles. Like coarse aggregate, sand for
use in concrete should include a well-graded mix of large and small
sizes. Sharp, angular sand manufactured by crushing rock produces
harsher concrete mixes with poor workability. Natural sand from
river banks or pits has rounded particles, which increase workabil-

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