Building Design and Construction Handbook - Merritt - Ventech!

BUILDING MATERIALS 4.21
C780, and C476). The strength of mortar is affected primarily by the amount of
cement in the matrix. Other factors of importance are the ratio of sand to cementing
material, curing conditions, and age when tested.
Volume change of mortars constitutes another important property. Normal volume
change (as distinguished from unsoundness) may be considered as the shrinkage
during early hardening, shrinkage on drying, expansion on wetting, and changes
due to temperature.
After drying, mortars expand again when wetted. Alternate wetting and drying
produces alternate expansion and contraction, which apparently continues indefinitely
with portland-cement mortars.
Coefficients of thermal expansion of several mortars, reported in ‘‘Volume
Changes in Brick Masonry Materials,’’ Journal of Research of the National Bureau
of Standards, Vol. 6, p. 1003, ranged from 0.38 � 10 �5 to 0.60 � 10 �5 for masonrycement
mortars; from 0.41 � 10 �5 to 0.53 � 10 �5 for lime mortars, and from
0.42 � 10 �5 to 0.61 � 10 �5 for cement mortars. Composition of the cementitious
material apparently has little effect on the coefficient of thermal expansion of a
mortar.
4.16.3 High-Bond Mortars
When polymeric materials, such as styrene-butadiene and polyvinylidene chloride,
are added to mortar, greatly increased bonding, compressive, and shear strengths
result. To obtain high strength, the other materials, including sand, water, Type I
or III portland cement, and a workability additive, such as pulverized ground limestone
or marble dust, must be of quality equal to that of the ingredients of standard
mortar. The high strength of the mortar enables masonry to withstand appreciable
bending and tensile stresses. This makes possible thinner walls and prelaying of
single-wythe panels that can be hoisted into place.
4.17 PORTLAND-CEMENT CONCRETE
Portland-cement concrete is a mixture of portland cement, water, coarse and fine
aggregates, and admixtures proportioned to form a plastic mass capable of being
cast, placed, or molded into forms that will harden to a solid mass. The desirable
properties of plastic concrete are that it be workable, placeable and nonsegregating,
and that it set in the desired time. The hardened concrete should provide the desired
service properties:
1. Strength (compressive and flexural)
2. Durability (lack of cracks, resistance to freezing and thawing and to chemical
attacks, abrasion resistance, and air content)
3. Appearance (color, lack of surface imperfections)
Each of these properties affects the final cost of the mix design and the cost of
the in-place concrete. These properties are available from normal-weight, lightweight,
and heavyweight concretes.