Masonry Magazine February 2012 Page. 36
SUSTAINABILITY
Fired, the individual clay particles are fused together through vitrification.
Since this process cannot be compromised, fly ash is limited to about 15 percent by weight, while the maximum for waste glass is about 2 percent. Some manufacturers have used clay or soil that otherwise would have been considered waste, such as mine overburden and tailings, clay from gravel and sand washing operations, fire clay overburden from coal mining; and excavated soil from swimming pool and road construction. Such materials may be included up to 100 percent of the weight. Mortar can comprise up to 20 percent of brick masonry. A portion of the cement in mortar can be substituted with fly as a pre-consumer waste product.
Reused
Shown is the Great Lakes Cancer Institute at Clarkson McLaren Health Care, which won a Silver Award in the BIA Brick in Architecture Awards Competition. The architect was RTKL Associates Inc.; landscape architect was Professional Engineering Associates; bullder was Canningham-Limp Inc; brick manufacturer was Glen-Gery Brick and brick distributor was West Friendship Materials.
THE DEMAND for reused/reclaimed bricks is high. The fact that bricks, which, in many cases, were made more than a century ago, can be used again is a testimony to the superior durability. Now, most reclaimed bricks are salvaged from buildings constructed more than 60 years ago. These bricks typically were laid with a mortar made of lime and sand with minimal-if any-portland cement content. This type of mortar was not as strong as contemporary mortars made with portland cement. As a result, when older bricks surrounded with this mortar are extracted from an existing wall, most of the mortar residue can be removed easily during cleaning.
However, mortar that has penetrated the surface of the bricks into the pore structures below is difficult to remove. Consequently, when reclaimed bricks are re-laid, the bond between the mortar and the reclaimed bricks is less than that of bricks that have not been laid in mortar previously.
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Photo by Feinknopf Photography
When using reclaimed bricks, be aware of the different types of bricks available in the early-1900s and the practices common to brick masonry construction at that time. Bricks from this era were made primarily in periodic and scove kilns. Unlike contemporary tunnel kilns in use today, greater temperature variations were present in the kiln when the bricks were fired, resulting in bricks with a wide range of properties - from over-burned bricks ("clinkers") and hard-burned bricks, to under-burned bricks (known as "salmons" due to their usual pinkish-orange color).
The prevalent method of construction, at the time, made use of all these bricks, consisting of load-bearing brick walls at least 12 inches thick. The hardest, most durable units were placed in the exterior wythes, the salmons (and others) were used for wythes inside the wall and were not exposed to the weather. As a result, when bricks are salvaged from buildings of this era, it is important to separate bricks taken from interior wythes from others. Salmon bricks should not be exposed to weather.
Made of natural, renewable resources
OXYGEN, SILICA, ALUMINA, AND IRON-the clements that make up the clay and shale used to make bricks are the four most abundant elements in the Earth's crust. Soils made of these elements are not viable