The Thermal Characteristics of a Brick Breeze Block
Breeze blocks, usually called cinder or clinker blocks in the United States, are light building materials where ashes from coal, coke or volcanic, are major components. The term “breeze” derives from the French “braise” meaning hot coals. The original blocks were made with cement and locally available aggregates, often waste products such as coal-fired steam boiler ash and blast furnace slag. The construction industry has developed this product since the 1950s and calls it “concrete block” though the term “breeze block” survives as a popular name. Varieties of breeze blocks are used for insulation, partition walls and sometimes, load-bearing walls.
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Thermal Conductivity
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Thermal conductivity is the ability of a material to conduct heat. The units for this measure are expressed in the metric system as watts per meter Kelvin (W/mK). A breeze block’s insulation value rises as its thermal conductivity decreases.
Thermal Mass
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Thermal mass, or thermal inertia, is the ability of building material to store heat during periods of high temperature and to release the heat when the temperature falls. This way, the material evens out temperature fluctuations within the building. Heavy building materials usually have a high thermal mass while lightweight materials have a low thermal mass.
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Dense Aggregate Block
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Dense aggregate blocks are the most common form of breeze block. They are manufactured from crushed limestone and pulverized fuel ash with a concrete binding. They can be for both load-bearing and non load-bearing purposes. Their thermal conductivity is typically 0.7 to 1.28 W/mK. This is a high conductivity measure. Although they have a high thermal mass, they have poor insulating properties.
Lightweight Aggregate Block
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These blocks have higher insulating properties and a lighter weight than the dense variety. They are manufactured from cement with a variety of natural and man-made aggregates such as blast furnace slag, furnace bottom ash, pulverized fuel ash and pumice and vermiculite, a volcanic material that is mainly mica. Their thermal conductivity is 0.11 to 0.20 W/mK and is lower than that for dense blocks. Lightweight aggregates have a moderate thermal mass.
Aircrete
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Aircrete is a term for aerated concrete. First produced in Sweden in 1923, it came into general use in the 1960s. These are the lightest of the concrete blocks. They are both structural and insulating bricks. Made from cement, lime, sand, pulverized fuel ash (PFA) and water. The PFA is mixed with water to form slurry which is heated with some aluminum sulfate. The sulfate compound reacts with lime to form bubbles of hydrogen. The brick rises like a cake in an oven as air displaces the hydrogen. The thermal conductivity is the same as aircrete at 0.11 to 0.20 W/mK. The brick has a moderate thermal mass but is a superior insulator. These bricks are able to reduce heat loss from a dwelling by 25 percent compared with other building materials.
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References
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