CHAPTER 7
CONCRETE AND MASONRY
This chapter provides information and
guidance for the Engineering Aid engaged in or
responsible for drawing structural and architec-
tural layouts from existing plans, engineering
sketches, or specifications, It includes informa-
tion on basic materials commonly used in
concrete and masonry construction.
Basic principles and procedures associated
with the construction of reinforced, precast, and
prestressed concrete and tilt-up construction are
also discussed in this chapter. Terminology as it
applies to masonry units is used to acquaint the
Engineering Aid with the various terms used in
this type of construction.
CONCRETE
CONCRETE is a synthetic construction
material made by mixing CEMENT, FINE
AGGREGATE (usually sand), COARSE AG-
GREGATE (usually gravel or crushed stone), and
WATER together in proper proportions; the
product is not concrete unless all four of these
ingredients are present. A mixture of cement,
sand, lime, and water, without coarse aggregate,
is NOT concrete, but MORTAR or GROUT.
Mortar is used mainly for bonding masonry
units together. The term grout refers to a water-
cement mixture (called neat-cement grout) or
water-sand-cement mixture (called sand-cement
grout) used to plug holes or cracks in concrete,
to seal joints, and for similar plugging or sealing
purposes.
The fine and coarse aggregates in a concrete
mix are called the INERT ingredients; the cement
and water are the ACTIVE ingredients. The
inert ingredients and the cement are thoroughly
mixed together first. As soon as the water is
added, a chemical reaction between the water and
the cement begins, and it is this reaction (which
is called HYDRATION) that causes the concrete
to harden.
Always remember that the hardening process
is caused by hydration of the cement by the water,
not by a DRYING OUT of the mix. Instead of
being dried out, the concrete must be kept as moist
as possible during the initial hydration process.
Drying out would cause a drop in water content
below the amount required for satisfactory
hydration of the cement.
The fact that the hardening process has
nothing whatever to do with a drying out of the
concrete is clearly shown by the fact that concrete
will harden just as well under water as it will in
the air.
Concrete may be cast into bricks, blocks, and
other relatively small building units that are used
in concrete MASONRY construction.
The proportion of concrete to other materials
used in building construction has greatly increased
in recent years to the point where large, multistory
modern building are constructed entirely of
concrete, with concrete footings, foundations,
columns, walls, girders, beams, joists, floors, and
roofs.
REQUIREMENTS FOR
GOOD CONCRETE
The first requirement for good concrete is a
supply of good cement of a type suitable for the
work at hand. Next is a supply of satisfactory
sand, coarse aggregate, and water; all of which
must be carefully weighed and measured.
Everything else being equal, the mix with the best
graded, strongest, best shaped, and cleanest
aggregate will make the strongest and most
durable concrete.
The best designed, best graded, and highest
quality mix in the world will NOT make good
concrete if it is not WORKABLE enough to fill
the form spaces thoroughly. On the other hand,
too much fluidity will result in certain defects.
Improper handling during the whole concrete-
making process (from the initial aggregate
handling to the final placement of the mix) will
7-1
