Page 113 - Design of Reinforced Masonry Structures

MATERIALS OF MASONRY CONSTRUCTION 3.7

completely fill openings (or cells) in masonry units and to encapsulate steel reinforcement,
the latter being necessary for reinforcement to participate in load sharing in the structure.
The high initial water content of grout compensates for absorption of water by concrete
masonry units after placement. Thus, grouts gain high strength despite the high initial water
to cement ratios [3.14].
The fluid consistency of grout is described with slump requirements specified in
building codes. Specification for Masonry Structures [3.4] requires a slump between 8
and 11 in. Lower slump-grout can be more difficult to place and ensure that the grout
space has been completely filled. This high slump requirement for grout is in marked
contrast with concrete for which 3 to 4 in. slump is commonly used in construction.
The proper grout slump for a specific application would depend on how much water
would be absorbed by the masonry. The more water the masonry units absorb, the more
water the grout should contain to maintain fluidity. Grout slump requirement (between
8 and 11 in. slump) would depend on several factors as follows, and should be adjusted
accordingly:
1. Initial rate of absorption (IRA) of masonry units. Masonry units with high IRA would
absorb more water than units with low IRA.
2. Weather conditions: masonry constructed in hot and arid conditions would absorb water
more rapidly than masonry constructed in cold or humid conditions.
3. Size of grout space: Amount of absorbed water depends on the masonry surface exposed
to grout. Small, narrow grout spaces have a larger surface to volume ratio than wider
grout spaces, and would absorb water at a greater rate.
Slump test of grout is performed in the same manner as for concrete (Fig. 3.1). First, the
cone is dampened and placed on a flat, moist, nonabsorbent surface, and filled with grout in
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three layers. Each layer is rodded 25 times with a round steel rod (usually a / 8-in. nominal
diameter and 12 in. long, with rounded ends) to consolidate the grout. The second and third
layers are rodded through the depth of the layer and penetrating the layer below. After the
top layer is rodded, excess grout is struck off flush with the top of the cone. The mold (i.e.,
the cone) is immediately lifted, and the slump is measured by the distance between the top
of the cone and the displaced original surface of the specimen.

3.3.3 Strength of Grout
When grout strength is specified, the minimum grout strength should equal or exceed the
specified compressive strength of masonry (f ′ ) but should not be less than 2000 psi, or
m
greater than 5000 psi for concrete masonry and 6000 psi for clay masonry [3.2 (Section
3.1.8)]. Note that the upper limits on maximum compressive strength of masonry for design

are 4000 and 6000 psi for concrete and clay masonry, respectively. When grout strength
is specified, the grout must be sampled and tested in accordance with ASTM C1019-05:
Standard Test Method for Sampling and Testing Grout [3.15].

3.3.4 Methods of Specifying Grout
ASTM C476-02: Specification for Grout for Masonry [3.16] contains standards for all
materials used to make grout. This standard defines two types of grouts: fine grout and
coarse grout. Fine grout contains only sand as its aggregate, whereas the coarse grout con-
tains pea gravel or other acceptable aggregate (maximum aggregate size to pass through