Building Design and Construction Handbook - Merritt - Ventech!

BUILDING MATERIALS 4.9
Gypsum plasters, in general, have a strong set, gain their full strength when dry,
do not have abnormal volume changes, and have excellent fire-resistance characteristics.
They are not well adapted, however, for use under continued damp conditions
or intermittent wet conditions. See also Arts. 4.26 to 4.30.
4.7 OXYCHLORIDE CEMENTS
Lightly calcined magnesium oxide mixed with a solution of magnesium chloride
forms a cement known as magnesium oxychloride cement, or Sorel cement. It is
particularly useful in making flooring compositions in which it is mixed with colored
aggregates. Floors made of oxychloride cement are sparkproof and are more
resilient than floors of concrete.
Oxychloride cement has very strong bonding power and, because of its higher
bonding power, may be used with greater quantities of aggregate than are possible
with portland cement. Oxychloride cement also bonds well with wood and is used
in making partition block or tile with wood shavings or sawdust as aggregate. It is
moderately resistant to water but should not be used under continually wet conditions.
4.8 MASONRY CEMENTS
Masonry cements, or—as they are sometimes called—mortar cements, are intended
to be mixed with sand and used for setting unit masonry, such as brick, tile, and
stone. They may be any one of the hydraulic cements already discussed or mixtures
of them in any proportion.
Many commercial masonry cements are mixtures of portland cement and pulverized
limestone, often containing as much as 50 or 60% limestone. They are sold
in bags containing from 70 to 80 lb, each bag nominally containing a cubic foot.
Price per bag is commonly less than of portland cement, but because of the use of
the lighter bag, cost per ton is higher than that of portland cement.
Since there are no limits on chemical content and physical requirements, masonry
cement specifications are quite liberal. Some manufacturers vary the composition
widely, depending on competition, weather conditions, or availability of
materials. Resulting mortars may vary widely in properties.
4.9 FLY ASHES
Fly ash meeting the requirements of ASTM C618, ‘‘Specification for Fly Ash and
Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland
Cement Concrete,’’ is generally used as a cementitious material as well as an admixture.
Natural pozzolans are derived from some diatomaceous earths, opaline cherts
and shales, and other materials. While part of a common ASTM designation with
fly ash, they are not as readily available as fly ashes and thus do not generate the
same level of interest or research.