Page 117 - Design of Reinforced Masonry Structures

MATERIALS OF MASONRY CONSTRUCTION 3.11

FIGURE 3.3 Relationship between grout mix and compressive strength. (Courtesy: National Concrete
Masonry Association.)

3.4 DIFFERENCES BETWEEN MORTAR, GROUT,
AND CONCRETE

To a casual observer, the only difference between mortar, grout, and concrete might be their
fluidity. Although the three materials have the same principal constituents (cement mix,
sand, gravel, water), there are many important differences between the three materials. They
have different mix proportions, properties, and functions, and are governed by different
ASTM Standards. Concrete is not used in masonry except for foundations. Concrete itself
is a structural material just as masonry is; both are designed and used to support loads. The
two can be used independently in the same structure at designer’s discretion, for example, a
reinforced concrete lintel or slab can be used in a building of masonry walls, columns, and
pilasters. Mortar and grout are two different kinds of materials. Mortar is commonly used
to bind masonry units into a single structural material (applied by hand by a mason using a

trowel), whereas grout is poured into cells of masonry units to encapsulate reinforcement
and provide a core. Mortar differs from concrete in working consistency, in method of
placement, and in the curing environment.
Grout is neither concrete nor mortar. Both mortar and grout have their own specifica-
tions with regard to proportioning, testing, and strength. The strength of these two materials
is correlated to specified compressive strength of masonry.
There are marked differences in water content and material composition of these mate-
rials. Concrete differs from grout in two distinct ways. Concrete contains much coarser
aggregate, significantly lower water-cement ratio, and typically has a slump of 3 to 4 in.
for typical construction; it can have even zero slump when used for specific purposes. It is
poured with a minimum water concentration into nonporous forms, whereas grout is poured