Page 56 - Masonry and Concrete

Concrete Construction Techniques
55
CONCRETE CONSTRUCTION TECHNIQUES

1
mum of 1 ⁄2 inches between the wire and
the soil, and supported on small stones or
pieces of concrete block. At splices, rein-
forcing mesh must be lapped one full row
of squares and tied with soft steel tie wire
(Figure 3-21).

3.5 Mixing Concrete on Site

If you’re mixing concrete on site, the mix-
ing area should be close to the pour area if
possible, and your ingredients stockpiled
nearby. Store bags of cement off the ground
and cover them with plastic to keep them
dry. Small quantities of sand can usually
be purchased in bags at building supply
yards. Larger quantities of both sand and
gravel are sold by the ton or half-ton by
aggregate suppliers and delivered to the
site in dump trucks. Spread tarps on the FIGURE 3-15
ground before the sand is dumped so that Permanent forms (Photo courtesy PCA).
the moisture content of the sand is not
affected by the moisture content of the
soil, and so that rocks or soil are not acci-
dentally shoveled up with the sand. QUICK>>>TIP
One of the most important things in ■ Damp sand falls apart when you
mixing concrete is consistency from batch try to squeeze it into a ball in your
to batch. The ingredient weights and pro- hand.
portions in the tables in Figure 3-3 are
■ Wet sand forms a ball when
based on “wet” sand. Most sand that is sold
squeezed in your hand, but leaves
for construction uses is “wet” sand, and
no noticeable moisture on the
the moisture that it contains has been
palm.
accounted for in the recommended
amounts of mixing water. If the sand you ■ Very wet sand, such as sand
are using is “damp” rather than “wet,” and exposed to a recent rain, forms a
you are mixing ingredients by weight, ball if squeezed in your hand, and
reduce the quantity of sand in Table A by leaves moisture on the palm.
one pound, and increase the quantity of

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