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masonry systems are familiar to most people because they have been
used for such a long time. All types of low-rise buildings are made
with these materials, from residential to educational to commercial
and industrial. The tough exterior of exposed units provides a durable
finish in demanding environments. And architects often prefer the
aesthetic appeal of masonry to many other finishes.
Overview and History
 During
the past 100 years, manufacture of concrete masonry units (CMU)
transitioned from a hand cast process to a highly automated one.
Single molds compacted by hand gave way to ganged molds that travel
on assembly lines in high-tech manufacturing facilities. These changes
have also led to excellent quality control and uniformity of units.
CMU are manufactured from very dry, stiff concrete mixtures. The
“no-slump” or “low-slump” material is placed
into molds, vibrated and compacted, and demolded quickly. Units
are stiff enough to hold their shape as they enter the curing chamber.
Afterwards, they are palletized and readied for shipping. They are
manufactured throughout the country, adding to local economies and
meeting sustainable criteria for availability.
Advantages
It’s hard to determine which attribute of CMU is its best.
It may vary from one project to another. Certainly, the fact that
these are non-combustible is very important. They are durable and
long lasting, can provide an attractive finish, can be reinforced
as needed to meet demanding structural applications, can contain
recycled materials, do not require painting or other treatment,
contain no VOCs or other potentially harmful offgassing materials,
and provide thermal mass to maintain uniform temperatures.
From a construction perspective, a nice feature of masonry is that
it can be built without much space for staging the construction.
On constricted sites or between buildings, this is helpful. It may
be more labor intensive than some other concrete construction, but
materials are literally available off the shelf and this is advantageous
because there is less chance for time delays waiting for special
orders.
Sizes, Components, Configurations,
Systems
 CMU
are modular. The most common size is a nominal 8 x 8 x 16 in. Door
and window openings are positioned to minimize cutting of units.
Walls that contain one vertical layer of units are called single
wythe and two layers are double wythe. It is most common to build
single- or double-wythe walls. When wythes are separated by a continuous
vertical space, the assembly is known as a cavity wall. Units are
held together by mortar.
Reinforcement is placed into horizontal and vertical cavities as
needed, with grout placed around it. This helps walls to carry loads
and resist other forces acting on them.
Insulation may be added to interior or exterior faces, between wythes,
or inside special unit cavities. The benefit of keeping the insulation
inside the wall is that the masonry faces are quite durable. Other
accessories may be needed to promote proper drainage, attach finishes,
and otherwise complete the wall.
Installation, Connections,
Finishes
 Masonry
is laid by skilled masons. They place mortar between units to tie
them together. Masonry requires little machinery for placement:
a mason and a trowel are the two main things necessary.
Walls, within and between them, are tied together with reinforcement.
Joint reinforcement may be used along mortar joints to help control
cracking in the wall. Anchors, plates, and other items that are
common with other construction are used in masonry, too.
Finishes are often simplified when using masonry. It can be sealed
or painted. It can be plastered for aesthetics and improved moisture
resistance [link]. But in many cases, it is left exposed. This can
be done with plain or architectural units. Some finishes are made
specifically for durability in moist exposures, like locker rooms,
pools, or kitchen or laundry facilities. These masonry surfaces
are often brightly colored to provide a hard, attractive finish.
Sustainability and Energy
Concrete masonry is sustainable for a number of reasons. It can
contain recycled materials. It is made from local materials and
usually shipped short distances to a project. These aspects often
contribute toward credits in green rating systems like LEED.
Masonry construction is energy efficient, providing thermal mass
to help moderate temperature in buildings. Lighter weight units
are made with lightweight aggregate to help provide added thermal
resistance. In addition, masonry walls can be insulated in a wide
variety of ways.
Building Codes
Masonry has its own code requirements. A Code and Specification
jointly published by The Masonry Society, American Concrete Institute,
and the Structural Engineering Institute of the American Society
of Civil Engineers are written as legal documents so that they may
be adopted by reference in general building codes. They address
materials, labor, design, and construction.
Resources
There are many helpful tools for designing and building with masonry.
The National
Concrete Masonry Association has online technical publications
known as TEK
sheets and details for concrete masonry. The Brick
Industry Association also publishes technical notes for clay
masonry (brick). A number of other groups such as The
Masonry Society publish guides and other documents used for
the design and construction of masonry.
PCA’s masonry Web pages are filled
with information on mortar, grout, and many other related topics.
Concrete Masonry Projects:
Concrete Masonry Affords Opportunities for Building Green
on Infill Sites
 Infill
sites are neglected public spaces and clusters of vacant or nearly-empty
buildings and land in either urban or suburban communities. Concrete
masonry units (CMU) are an ideal building material for infill projects
because there is often no adjacent space available for large equipment
or staging areas. And because these projects tend to be tall, thin,
and closely situated to property lines, the inherent strength, fire
resistance, and noise abatement of CMUs provide an economical solution.
One recent infill project is an eco-friendly residence in southern
California. It has a small carbon footprint in balance with lifestyle
common in the area, but functions as a high-performance building.
More on concrete masonry
residential project.
Twenhofel Middle School: Benefits Add Up in Classroom Settings
 Located
near Cincinnati, Twenhofel Middle School was one of Kentucky’s
first schools to incorporate sustainable building principles and
energy conservation measures. In 2004, these ideas were not necessarily
revolutionary, but neither had they been the focus of school administrators
prior to that time. The excellent results achieved with Twenhofel
have only increased the district’s efforts to do more of the
same.
The backbone of this school is concrete masonry. Generally, one
reason concrete masonry has been so popular in schools is its durability.
More on Twenhofel
Middle School
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