Page 21 - Masonry and Concrete

Understanding Concrete
20 CHAPTER TWO

Max. Size of Aggregate, in.
Minimum Reinforced walls, Heavily Lightly
dimension of beams, and reinforced reinforced
section, in. columns slabs slabs
1
1
3
2 /2–5 1 /2– /4 3 /4–1 3 /4–1 /2
1
1
1
6–11 3 /4–1 /2 1- /2 1 /2–3
1
1
12–29 1 /2–3 1 /2–3 3
1
1
30 or more 1 /2–3 1 /2–3 3–6
FIGURE 2-8
Maximum sizes of aggregate recommended for various types of construc-
tion. (from American Concrete Institute, Concrete Primer, Detroit).

2.2.3 Water
As a rule of thumb, water used for mixing concrete should be drink-
able. Any water that is drinkable is generally free of harmful impuri-
ties. In urban areas where municipal water supplies are available,
contaminated water is usually not a problem. The same is true in most
rural areas where well water is usually tested by local health officials
to assure that it is fit for human consumption. In general, if water is
reasonably clear and does not have a foul odor, or a brackish or salty
taste, it is acceptable for mixing concrete.

2.2.4 Admixtures
Admixtures are substances other than cement, water, or aggregates
which are added to concrete mixes for the purpose of altering proper-
ties of the fresh or hardened concrete. Admixtures are not generally
required to produce high-quality, low-cost concrete, but they may
sometimes be necessary or desirable to alter specific properties of the
concrete for specific conditions or circumstances. They must be care-
fully controlled, however, to avoid adversely affecting the concrete, so
it is best to use admixtures only in concrete supplied by an experi-
enced and reputable ready-mix producer. Accurate job-site mixing can
be difficult to achieve, and the ready-mix producer has the advantage

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