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Characterization of Bricks and Their Resistance to Deterioration Mechanisms
Pages 145-162

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From page 145...
... The rate of deterioration is a function of composition, pore structure, manufacturing procedure, structural design, and cleaning procedure. Deterioration of masonry results from several mechanisms, including freezing and thawing, salt crystallization, chemical attack by water and other substances, moisture expansion, other internal expansive reactions, and mismatch in dimensional characteristics of wall components.
From page 146...
... The properties of brick are determined by manufacturing procedures, and these have changed over time. It is important to consider this influence when contemplating restoration procedures or the likelihood of success in restoration.
From page 147...
... The tunnel kiln produced exceptionally uniform properties and allowed much shorter firing cycles perhaps 30 hours, compared with 5 days in the periodic kiln. Coloration During the early period of production, the fired color of brick was determined by the clay raw matenal.
From page 148...
... PAVING BRICK X X X — FA I L E D PAV I N G B R I C K ......................... / ~ I I I 5 ~ 1 0.6 0.4 0.2 0.1 0.06 0.04 0.02 PORE SIZE, MICRONS FIGURE 1 The pore-size distribution of a soft molded brick of good durability compared to two extruded bricks that failed in service and two durable paving bricks.
From page 149...
... An oxygen-deficient kiln atmosphere produces equivalent properties at Tower temperature than does a kiln with an oxidizing atmosphere. The pattern of properties at various firing temperatures is distinctive for each raw matenal.
From page 150...
... Lime sand mortars have been used since early times and once were the predominant bonding medium. Later, Portland cement was added to lime mortars; today, prepared proprietary mixtures called masonry cements are commonplace.
From page 151...
... Cut surfaces on extruded brick can produce shaggy overhang projections that assist adhesion. DiesTickened surfaces are less conducive to bond development.
From page 152...
... Early attempts to evaluate pore structure used saturation coefficient as a measure of the proportions of large pores and small pores. Present efforts are directed toward determining pore-size distribution, but the saturation coefficient remains a useful if imperfect index of the durability of brick.6 7
From page 153...
... Bricks and Resistance to Deterioration Mechanisms 153 FIGURE 3 The appearance of brick disintegrated (upperJ and cracked in lamination planes {lower) by exposure to freezing and thawing.
From page 155...
... Nevertheless, attempts to correlate compressive strengths with durability have been unsuccessful. Figure 4 shows freeze-thaw resistance versus strength for commercially manufactured units.
From page 156...
... There are other sources of salts within masonry structures. Brickwork around flower beds or gardens may collect soluble salts from FIGURE 5 Salt disintegration of solar screen tile in Miami Beach, Florida.
From page 157...
... Cleaning agents dissolve cement and other substances to produce soluble salts; injudicious use of these agents can contribute to increased salts within the masonry structure. Chemical Attack Properly fired bricks have unusual resistance to attack by chemical agents.
From page 158...
... Structural Design A common source of damage to masonry walls' in those few instances where damage occurs, is inadequate design of the structure. Inadequate
From page 159...
... . any exlstmg mismate nest Cleaning Procedures Cleaning brick masonry walls generally can be accomplished with the use of water alone or in combination with chemical reagents or sometimes by sandblasting.
From page 160...
... Furthermore, chemical cleaners produce soluble salts that may penetrate the masonry and cause development of new discoloration or contribute to new deterioration. The injudicious selection and/or mung of various cleaning reagents can cause worse staining than that originally present.
From page 161...
... Drisko discusses different waterproofing materials and gives recommended coatings for different situations. Cleaning procedures should be selected to suit the stains and materials involved.
From page 162...
... 8. Cleaning Clay Products Masonry, Technical Notes on Brick and Tile Construction, 20.


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