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From The Inspectors Blog

Cement Substitutes

7/4/2016

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by Nick Gromicko
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Cement substitutes are materials that may be substituted, to some degree, for cement in order to improve different properties, such as strength and longevity. The use of cement substitutes is generally encouraged because of the environmental advantages gained from their diversion from the waste stream, the reduction of the energy required in their re-purposing (as compared to the manufacture of cement), and the conservation of raw materials, such as silica, alumina and iron oxide. In fact, as much greenhouse gas is created during the production of cement used in the U.S. as the operation of 22 million cars. In addition, the U.S. imports about 20% of its cement, which adds to its cost and wastes a great deal of energy, according to Environmental Building News.  

 
Inspectors are more likely to encounter cement substitutes in heavy construction as opposed to residential construction, where contractors are less familiar with their use. Cement substitutes are distinguished from aggregate substitutes, such as ground scrap rubber and ground glass, and concrete additives, such as air-entrapment agents and plasticizers.  Inspectors will not be able to visually identify concrete that has had substitutes for concrete incorporated into the mix.

 
The most common cement substitutes include the following:
  • Silica fume, also known as microsilica, is a byproduct of the combustion of quartz, coal and wood chips during the production of silicon metals. silica improves compressive strength, bond strength, and the abrasion resistance of concrete.  Prior to the 1970s, its release into the atmosphere was permitted, but environmental concerns eventually forced its collection and deposition into landfills. It then became economical for silica fume to be used in various applications, chiefly in high-performance concrete. Consisting of fine silicon dioxide particles that are approximately one-hundredth the size of the average cement particle, silica fume is the cement substitute of choice where high strength is critical, such as in high-rise buildings. Cement that contains silica fume looks darker than ordinary cement. Although a respirator should be worn while handling pure silica fume, a cement-silica fume mix is not considered dangerous to humans.
  • Fly ash is a fine, light, glassy residue generated during ground- or powdered-coal combustion. Contractors find that fly ash enables cement to flow better in pump hoses and makes it more workable under hand-finishing.  It includes substantial amounts of silicon dioxide and calcium oxide, both of which are natural ingredients in coal-bearing rock. Mixed with cement during the construction of the Hoover Dam during the 1930s, it wasn’t until the 1980s when its use in construction became commonplace. There are two types of fly ash:
    • Class C fly ash is produced from the burning of younger lignite or sub-bituminous coal, and it contains considerably more lime and is stronger than its alternative, Class F fly ash. It is preferable for green building projects and is the standard type of fly ash found in residential applications. Inspectors can identify this type of cement substitute by its buff, tan, or occasionally orange coloring. 
    • Class F fly ash results from the burning of harder, older anthracite and bituminous coal. Excessive carbon, which may be indicated by a dark colored cement mix, means that the coal was not burned thoroughly, which may reduce the concrete’s freeze-thaw resistance. 
Fly ash contains a number of hazardous minerals, such as mercury, cadmium, arsenic, lead and selenium. There is little evidence that these substances can leach out of the concrete, although disposal and re-use of cement containing fly ash has raised health concerns. 
  • Slag is a byproduct of the production of iron and steel in blast furnaces. The benefits of the partial substitution of slag for cement are improved durability, reduction of life-cycle costs, lower maintenance costs, and greater concrete sustainability.  The molten slag is cooled in water and then ground into a fine powder. Slag is used in very high concentrations, often occupying more than half of the total composition of cement. The energy required to grind and ship slag makes it less energy-efficient than fly ash but better than Portland cement. Slag concrete is reflective and lighter in color than fly ash and silica fume, and it may initially have a blue-green coloring that typically disappears within a week. Known as “greening,” this discoloration will not disappear if the slag is used in swimming pools or other wet locations.
Cement substitutes can alleviate the following types of concrete weathering:
  • alkali-silica reaction, in which crazing and the expansion of concrete results from the interaction between high-alkali cement and high-silica aggregates. Much of the alkalinity can be removed through the action of slag, while Class F fly ash is also effective;
  • corrosion, in which de-icing salts migrate through pores in the concrete to corrode the reinforcement steel and rebar. Cement substitutes mitigate this corrosion by removing the calcium hydroxide that makes the concrete permeable; and
  • sulfate attack, in which concrete is attacked by sulfates that are found in some arid soils, seawater and wastewater. Concrete that incorporates fly ash or are composed of more than 60% slag are effective in limiting attack by sulfates.
In summary, cement substitutes are used to enhance certain qualities of cement and reduce the environmental and financial costs of cement creation.


Craftsman Home Inspections llc is a home inspection and Radon Testing company proudly serving the Aurora CO and Denver CO Metro Areas. If you are looking for a Home Inspector in Aurora or Denver, please give us a call at 720-593-0383 or check us out online at CraftsmanColorado.com or simply schedule your home inspection below.

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Ceiling Fan Inspection

7/4/2016

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by Nick Gromicko
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A fan attached to a room’s ceiling is known as a ceiling fan. Like other fans, it is used to provide comfort for building occupants by circulating air within a room. 
 Fun Facts About Ceiling Fans
  • An adult human cannot be decapitated by a ceiling fan, according to the TV show "MythBusters."  A powerful, industrial-strength fan might be able to damage a skull or slice a person’s neck, however. 
  • Ceiling fans were first used in the United States in the 1860s. They were powered by a system of belts driven by a stream of running water. 
  • Unlike air conditioners, fans do not actually cool the air, which is why they merely waste electricity when they circulate air in an unoccupied room.
Ceiling Fan Components
A ceiling fan is comprised of the following parts:
  • electric motor:  varies with the size of the fan and its application; 
  • blades:  typically, two to six spinning, precision-weighted blades made from metal, wood or plastic; industrial fans typically have three blades, while residential models have four or five; 
  • blade irons:  connect the blades to the motor; 
  • safety cable: on heavy fans, these are required to hold the fan in place in case the support housing fails; 
  • flywheel:  connects the blade irons to the motor; 
  • ceiling mount:  designs include ball-in-socket and J-hook; 
  • downrod:  used where ceiling fans are suspended from high ceilings; 
  • motor housing:  protects the fan motor from dust and its surroundings; may also be decorative; and 
  • lamps: may be installed above, below or inside the motor housing.
Common Fan Defects
  • The fan falls. A ceiling fan that breaks free from its ceiling mount can be deadly. Fans must be supported by an electrical junction box listed for that use, according to the National Electric Code, and a fan brace box will need to be installed. While a particular junction box might support a fully assembled fan, during operation, it will exert additional forces (notably, torsion) that can cause the support to fail. Homeowners often overlook this distinction by carelessly replacing light fixtures with ceiling fans without upgrading the junction box, which should clearly state whether it’s rated to hold a ceiling fan. 
  • The fan wobbles. This is a common and distracting defect that is usually caused when fan blades are misaligned from one another. Specific problems stem from minute differences in the size or weight of individual blades, warping, bent blade irons, or blades or blade irons that are not screwed in tightly enough. The ceiling mount may also be loose. Wobbling is not caused by the ceiling or the particular way that the fan was mounted. Wobbling will not cause the fan to fall, and there have been no such reports. Wobbling can, however, cause light fixture covers or shades to loosen and potentially fall. These items should be securely attached, with all screws tightly set in place. An easy way to tell if the blades are not on the same plane is to hold a yardstick or ruler against the ceiling and measure the distance that the tip of each blade is from the ceiling by manually pushing the blades. A homeowner can carefully bend the misaligned blade back into place. Blades can also be corrected in this way if measurement reveals that they are not equidistant from one another.  
  • There is inadequate floor-to-ceiling blade clearance. No part of the fan blades of a residential ceiling fan (usually having four or more blades) should be closer than 7 feet from the floor in order to prevent inadvertent contact with the blades. Downward air movement is maximized when the fan blades are around 8 or 9 feet from the floor. For high ceilings, the fan may be hung to a desired height. Low-profile fan models are available for ceilings that are lower than 8 feet from the floor. Also, fan blades should be at least 18 inches from walls. For commercial ceiling fans (usually having three blades), no part of the fan blades should be closer than 10 feet from the floor in order to prevent inadvertent contact with the blades.  Underwriters Laboratories UL 507 Section 70.2.1 says: 

    "The blades of a ceiling-suspended fan shall be located at least 3.05 m (10 feet) above the floor when the fan is installed as intended."
Underwriters Laboratories makes exceptions if the fan blade edges are thick and the fan is turning slowly.
  • Blades are turning in the wrong direction. In the winter months, the leading edge of the fan's blades should be lower than the trailing edge in order to produce a gentle updraft, which forces warm air near the ceiling down into the occupied space below. In the summer, the leading edge of the fan's blades should be higher as the fan spins counter-clockwise to cool occupants with a wind-chill effect. On most models, the fan direction can be reversed with an electric switch located on the outside of the metal housing, but the same effect can be achieved on other models by unscrewing and remounting the fan blades. 
  • An indoor fan is not designed for exterior use. Ordinary indoor ceiling fans are unsafe to use outdoors or in humid environments, such as bathrooms.  They will wear out quickly. Fans that are rated “damp” are safe for humid environments, but they, too, should never be used where they might come into contact with liquid water. Only fans that are rated “wet” are safe for such use, as they incorporate features such as all-weather, UV-resistant blades, sealed motors, rust-resistant housing, and stainless steel hardware.
In summary, properly installed and maintained ceiling fans can inexpensively cool or warm building occupants.


Craftsman Home Inspections llc is a home inspection and Radon Testing company proudly serving the Aurora CO and Denver CO Metro Areas. If you are looking for a Home Inspector in Aurora or Denver, please give us a call at 720-593-0383 or check us out online at CraftsmanColorado.com or simply schedule your home inspection below.

SCHEDULE INSPECTION
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