Page 68 - Design of Reinforced Masonry Structures

MASONRY UNITS: APPLICATIONS, TYPES, SIZES, AND CLASSIFICATION 2.21

Specification for Structural Clay Tile [2.37] places requirements on size and number of
cells (different from ASTM C34) as well as web and shell thicknesses (e.g., one cell for
4-in.-thick, two for 6 and 8-in.-thickness, and three for 10 and 12-in. units). Other uses
include nonload-bearing partitions, facings over other supports, and components of com-
posite walls. A discussion on production, usage, and application of glazed ceramic tiles can
be found in several references [2.7, 2.13, 2.38].

2.5.8 Architectural Terra-Cotta
Terra-cotta is a fired clay product used for ornamental work. The term “terra-cotta,” which
means “baked earth,” has been applied for centuries to describe the molded and fired clay
objects whose properties are similar to those of brick. Architectural terra-cotta was origi-
nally used as a load-bearing element in multiwythe walls. In the late nineteenth and early
twentieth century, it gained popularity as a cladding material, particularly for structural
frame buildings. Today, terra-cotta is used essentially as a ceramic veneer or ornamental
facing tile for both exterior and interior walls [2.7].
Terra-cotta can be either hand molded or extruded. Hand-molded slabs are produced in
the traditional manner with either plain or sculptured surfaces. Extruded units are mechani-
cally fabricated with smooth-ground, beveled, scored, scratched, or fluted surfaces. Both
may be glazed in clear monochrome, or polychrome colors and in matte (i.e., dull or luster-
less), satin, or gloss finishes. Individual pieces are usually larger in face dimensions than
brick, and are usually produced to order.
Terra-cotta also falls into the ceramic glazed classification, although it has only non-
structural uses. There are no governing ASTM Specifications for terra-cotta, but the units
should meet the minimum requirements of the Standard Specifications for Ceramic Veneer
and Standards for Sampling and Testing Ceramic Veneer [2.39].

2.5.9 Second-Hand Clay Masonry Units
Second-hand (also referred to as reclaimed, used, or salvaged) bricks are occasionally used
in construction due to their “rugged appearance” and/or low initial cost. Architects may
specify their use because of their weathered appearance, and broad color range that varies
from dark-red to the whites and grays of units still partially covered with mortar. Most
salvaged bricks are obtained from demolished buildings that may be 40 or 50 years old, or
even older. Generally speaking, walls using salvaged bricks are weaker and less durable
than those built from new brick units.
Several arguments are advanced in favor of using the salvaged bricks [2.40]:

1. Because bricks are extremely durable, they can be salvaged and used again.
2. If the bricks were satisfactory at the time they were first used, they are satisfactory at
present.
However, both arguments are weak. This is because bricks, when initially placed in contact
with mortar, absorb some particles of cementitious material. These absorbed particles can-
not be cleaned completely from the surfaces of the brick units, resulting in a weakened bond
between brick and mortar when reused. Therefore, salvaged units require attention to their
condition at the time of use. Building code requirements vary regarding the use of salvaged
bricks, and should be consulted prior to their selection and specification. There may be seri-
ous ramifications for using the salvaged bricks. 2009 IBC [2.5] which states: “Second-hand
units shall not be reused unless they conform to the requirements of new units. The Units