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CONTROL JOINTS FOR CONCRETE MASONRY

WALLS - ALTERNATIVE ENGINEERED METHOD

TEK 10-3
Movement Control (2003)

Keywords: bond beams, construction details, control

joints, crack control, engineered method, joint reinforcement, reinforcing bars, reinforced concrete masonry,
shrinkage, wall movement
INTRODUCTION
This TEK supplements TEK 10-2B Control Joints for
Concrete Masonry Walls - Empirical Method (ref. 3). The reader
is encouraged to refer to that TEK for other pertinent information
such as construction details and location of control joints.
Controlling shrinkage cracking historically has been addressed by limiting the moisture content of units at the time of
placement in the wall and indirectly incorporated the effects of
variations in temperature and cement carbonation as well as
drying shrinkage. In 2000 however, due to problems associated
with maintaining moisture controlled units (Type I) in that state
until placement in the wall, moisture controlled units (and Type
designations) were removed from ASTM C 90 (ref. 4).
In view of this, the concrete masonry industry has developed
an engineered approach to controlling cracking which examines
each of these three parameters separately, and then incorporates
them into a single Crack Control Coefficient. In general, this
engineered approach is more complicated and requires more
detailed knowledge of the masonry characteristics than the
empirical approach of TEK 10-2B (ref. 3), which is based on
historical solutions that have proven successful over many years
of experience for a broad geographic distribution. The empirical
method is the most commonly used method and is applicable to
most conventional building types. The engineered method is
generally used only when unusual conditions are encountered
such as dark colored units in climates with large temperature
swings.
ENGINEERED CRACK CONTROL CRITERIA
The engineered criteria was developed to produce a more
rational approach to crack control in concrete masonry - particularly in areas of high seismicity where relatively large amounts of
continuous reinforcing steel are used. Also addressed is additional reinforcement around openings to provide strengthening
and allow placement of the control joints at locations other than
at the openings. The effectiveness of this method depends on
TEK 10-3 2003 National Concrete Masonry Association

reliable criteria being correctly incorporated into the project

design, the materials meeting the requirements of the project
specifications, and the masonry being constructed in accordance
with the project drawings.
The engineered criteria is based on a Crack Control Coefficient to accommodate internal volume changes. Once the internal
movement due to volume change has been estimated, the designer can control crack width to a maximum value by 1) limiting
the distance between control joints when used in combination
with a minimum amount of horizontal reinforcement or 2) incorporating a predetermined, higher amount of horizontal reinforcement (when needed for structural purposes) to limit crack width
without the use of control joints.
Crack Control Coefficient
The Crack Control Coefficient (CCC) is an indicator of
anticipated wall movement. Concrete masonry unit shortening
per unit length is estimated by including the possible combined
effects of movement due to drying shrinkage, carbonation shrinkage and contraction due to temperature reduction. The Crack
Control Coefficient value itself is determined by summing the
coefficients of these three properties for a specific concrete
masonry unit. It is a function of unit mix design and production/
curing methods.
The total linear drying shrinkage is determined in accordance with Standard Test Method for Linear Drying Shrinkage of Concrete Masonry Units and Related Units, ASTM C
426 (ref. 5). ASTM C 90 (ref. 4) limits total linear drying
shrinkage of concrete masonry units to 0.00065 in./in. (mm/
mm). Note that this is based a saturated condition (immersed
in water for 48 hours). In the field, units will probably be no
higher than 70% of saturation. Therefore, the highest realistic
drying shrinkage potential realized in the field will be around
0.00045 in./in. (mm/mm) or 0.54 in. in 100 ft (13.7 mm in 30.48 m).
It for this reason that the Building Code Requirements for
Masonry Structures (ref. 1) stipulates the use of only 50% of
the total linear drying shrinkage determined in accordance with
ASTM C 426 (ref. 5) for design.

Table 1Criteria for Controlling Cracking in

Reinforced Concrete Masonry Walls a

Maximum length, ft (m)

wall panel
2
dimensions length/height ratio
Minimum horizontal
reinforcement ratio As/A n

Crack Control Coefficient

in./in. (mm/mm)
0.0010
0.0015
25 (7.62) 20 (6.10)
2
0.0007

2
0.0007

Notes:
1. As = cross-sectional area of steel, in.2 /ft (mm2 /m).
An = net cross-sectional area of masonry, in.2 /ft (mm2 /m).
2. Maximum wall panel dimension criteria need not apply for walls
with a minimum horizontal reinforcement area, As of 0.002 times
the net cross sectional area of the masonry, An see Table 3.
3. See Table 2 for maximum spacings of reinforcement to meet
0.0007 minimum horizontal reinforcement ratio As/An.
4. The minimum horizontal reinforcement ratio criteria need not
apply for walls with a length not exceeding one half the maximum
length values shown above.
5. CCC's less than 0.0010 may be available in some areas and
spacing could be adjusted accordingly for this as well.
6. This criteria is based on an analytical study over a wide geographical area with wide temperature and and material property
variations. Control joint spacing may be adjusted up or down
based on local experience.
7. As shrinkage is related to moisture content, consider using the
higher crack control coefficient for masonry units that are wet
from lack of protection while stored on the jobsite.

Carbonation shrinkage is an irreversible reaction between

cementitious materials and carbon dioxide in the atmosphere. It
occurs over a long period of time and there currently is no
standard test method to determine it. Therefore, it is recommended that 0.00025 in./in. (mm/mm) be used for the carbonation
shrinkage coefficient 0.3 in. in 100 ft (7.6 mm in 30.48 m).
Thermal coefficients for concrete masonry units typically
range from 0.0000025 to 0.0000055 in./in./F (0.0000045 to
0.0000099 mm/mm/C) (refs. 4 and 5). For design purposes, the
value of 0.000004 in./in./F (0.0000081 mm/mm/C) be used as
outlined in the Building Code Requirements for Masonry
Structures (ref. 1). Based on a temperature change of 70 F
(38.9 C), this would translate to a thermal contraction value
of 0.00028 in./in. (mm/mm) or 0.34 in. in 100 ft (8.5 mm in 30.48 m).
The CCC is the sum of the potential length change due to
each of these three parameters and for typical concrete masonry units varies from 0.00063 to 0.00108 in./in. (mm/mm).
This range corresponds to a 100 ft (30.48 m) long wall shortening 0.76 to 1.30 in. (19.3 to 33.0 mm).
Control Joints with Horizontal Reinforcement
The most common (and usually most cost effective) method
of controlling cracks in concrete masonry is to use control joints
in conjunction with a minimum amount of horizontal reinforcement between the joints. Reinforcement is often required for wind
or seismic resistance and it is prudent to utilize it for assisting in

crack control as well. The amount of horizontal reinforcement

needed is based on limiting cracks to a width of 0.02 in. (0.51 mm)
since water repellent coatings can effectively resist water penetration for cracks of this size. Based on this premise and the CCC
criteria discussed earlier, control joint spacing criteria are presented in Table 1 utilizing a minimum horizontal reinforcement
ratio of As/An > 0.0007. An is the net area of the vertical crosssection of the wall. For hollow unit masonry and partially grouted
masonry it essentially is the total thickness of the face shells times
the height of the wall plus the additional area provided by any
grouted bond beams. Table 2 presents the maximum spacing of
the various sizes of typical horizontal reinforcement to meet the
0.0007 criteria. The wall panel length to height ratio and the
maximum length of wall panel criteria in combination with horizontal reinforcement in Table 1 are based on historical field experience
and analytical studies.
Horizontal Reinforcement Only
In some regions of the country, significant amounts of
horizontal reinforcement are required for structural purposes, i.e.
Seismic Performance Categories D and E. Studies have shown
that horizontal reinforcement of sufficient quantity can effectively limit crack width in concrete masonry walls. For standard
reinforcing bar sizes, horizontal reinforcement spacings up to 48
in. (1219 mm) o.c. have been shown to effectively control cracking
without the use of control joints. It has also been shown that
horizontal reinforcement provides internal restraint, which results in transfer of tension from the masonry to the reinforcement,
resulting in more frequent but much smaller cracks. As the level
of horizontal reinforcement increases, cracking becomes more
uniformly distributed and crack width decreases.
When a crack is formed, tension in the masonry is released.
This masonry tension is transferred to the reinforcement at the
time of crack formation. Therefore, reinforcement should be sized
such that the resulting tensile force in the reinforcement does not
exceed the yield strength of the steel. This keeps the steel within
the elastic range and minimizes the crack width to a point where
control joints are not necessary in the design.
To ensure the steel is within the elastic range, the width of
a crack at the horizontal reinforcement location would be limited
to the yield strain of the steel multiplied by the length of
reinforcing bar being strained:
crack width = ?s l
where: ?s = yield strain of steel, fy /Es
= 60,000 psi / 29,000,000 psi (413 MPa/
199,810 MPa)
= 0.002 in./in. (mm/mm)
l = length of reinforcing bar being strained
For example, a bar being strained at its yield strain over a length
of 10 in. (254 mm) would limit crack width to 0.02 in. (0.51 mm).
In order to meet this criteria of limiting the steel to the
elastic range, the tension in the masonry (Tm = Ft An) just prior
to crack formation must be less than the yield strength of the
steel (Ts = fy As):
Ft An < fy As, or
As > Ft An /fy ,
where:
Ft = average tensile strength of masonry. A vertical

Table 2Maximum Spacing of Horizontal Reinforcement to Meet the Criteria As > 0.0007An1
Wall
thickness,
in. (mm)

No. 5
(M 16)

Maximum spacing of horizontal reinforcement, in. (mm)

Reinforcement size
No. 4
No. 3 4 x3/16 in. 4 x 8 gage 4 x 9 gage 2 x3/16 in. 2 x 8 gage 2 x 9 gage
(M 13)

(M 10)

(MW 18)

(MW 13)

(MW 11)

6 (152)
8 (203)
10 (254)

Ungrouted or partially grouted

144 (3658) 128 (3251) 64 (1626) 72 (1829) 56 (1422)
144 (3658) 96 (2438) 40 (1016) 64 (1626) 48 (1219)
136 (3458) 80 (2032) 32 (1219) 56 (1422) 40 (1016)

12 (305)

120 (3048) 72 (1829) 24 (610) 48 (1219) 40 (1016)

32 (813)

6 (152)
8 (203)
10 (254)
12 (305)

Fully grouted walls

24 (610) 16 (406)
16 (406)
8 (203)
16 (406)
8 (203)
8 (203)
8 (203)

16 (406)
8 (203)
8 (203)
8 (203)

72 (1829)
56 (1422)
40 (1016)
32 (813)

48 (1219) 24 (610)
32 (813) 16 (406)
24 (610) 16 (406)
24 (610) 8 (203)

(MW 18)

walls
48 (1219) 40 (1016)
40 (1016) 32 (813)
32 (813) 16 (406)

(MW 13 ) (MW 11)

24 (610)
24 (610)
16 (406)

24 (610)
16 (406)
16 (406)

16 (406)

16 (406)

16 (406)

8 (203)
8 (203)
8 (203)

8 (203)
8 (203)

8 (203)

1. A n includes cross-sectional area of grout in bond beams

crack would pass through a head joint and then

a block in alternate fashion. The tensile strength
of typical masonry units is 200 psi (1.38 MPa) and
the tensile strength of a typical head joint is 25 psi
(0.172 MPa). Average tensile strength is, therefore, 225 psi / 2 or 112 psi (0.772 MPa).
fy = yield strength of steel reinforcement
= 60,000 psi (413 MPa)
Substituting these values, the criteria becomes:
As > 0.0019 An
When this condition is met, there is sufficient horizontal
steel to limit masonry cracking to widths of 0.02 in. and control
joints may be eliminated as stated in footnote 2 of Table 1.
Table 3 indicates the amount of reinforcement that will meet
this criteria for various concrete masonry walls.
Control Joints in Vertically Reinforced Walls
In plain masonry walls, control joints are typically placed at an
opening as it is a weak point subject to cracking due to the reduced
masonry cross section. This requires the control joint above the
opening to be aligned with the end of the lintel, cross under the
lintel via a slip plane, and then proceed through the opening (ref.
3). In walls containing vertical reinforcement, however, the cell
adjacent to the opening usually is grouted and reinforced. Using
the same type of detail would require the control joint to cross the
vertical reinforcement thereby preventing movement and defeating the purpose of the control joint. However, if the opening is
completely surrounded by reinforcement as detailed in Figures 1
and 2, the area through the opening is strengthened and control
joints can be placed outside the opening. For best performance
the vertical reinforcement should be placed in the cell immediately
adjacent to the opening. However, due to congestion in the cell
at this location, vertical reinforcement is often placed in the
second cell from the opening. On large openings, it is recommended to grout the cell next to the opening as well as the cell

Table 3Maximum Spacing of Horizontal

Reinforcement to Meet the Criteria As > 0.002An1
Wall
thickness,
in. (mm)

Maximum spacing of horizontal

reinforcement, in. (mm)
Reinforcement size
No. 6 (M19) No. 5 (M16) No.4 (M13)

Ungrouted or partially grouted walls

6 (152)
48 (1219)
48 (1219)
8 (203)
48 (1219)
40 (1016)
10 (254)
48 (1219)
32 (813)
12 (305)
48 (1219)
24 (610)
Fully grouted walls
6 (152)
32 (813)
24 (610)
8 (203)
24 (610)
16 (406)
10 (254)
16 (406)
16 (406)
12 (305)
16 (406)
8 (203)

32 (813)
24 (610)
16 (406)
8 (203)
16 (406)
8 (203)
8 (203)
8 (203)

1. A n includes cross-sectional area of grout in bond beams

containing the reinforcement to provide additional resistance for

attaching the door or window frame. These details may also be
used in unreinforced walls and walls utilizing steel lintels since the
area through the opening is strengthened by the additional
reinforcement.
When utilizing these details and the wall segments on either
side of openings are designed to resist the lateral loads applied
directly to them plus those transferred from the opening enclosure, shear transfer devices such as preformed gaskets (see TEK
10-2B, ref. 3) are not necessary. However, some designers still
incorporate them to limit the relative movement between the two
panels on either side of a control joint thereby reducing the stress
on the joint sealant and providing longer life.

Masonry lintel or
precast lintel
(notched if vertical
reinforcement in
cell next to opening

Maximum control joint

spacing per Table 1
12 in. (305 mm) min. typ.

Maximum control joint

spacing per Table 1
Ladder joint
reinforcement in
first two joints
above opening
from control joint
to control joint
(min.)

12 in. (305 mm) max. typ.

Vertical
reinforcement in
grouted cell each
side of opening (typ.)
(alternate-place in
second cell from
opening)
Lintel reinforcement
Sill

Control joint
(typ.)

Ladder joint reinforcement

in mortar joint below sill
from control joint to
control joint (min.)

By Extending Lintel Reinforcement (Preferred)

Sill

By Adding Joint Reinforcement (Alternate)

Figure 1Reinforcement Around Openings Option

REFERENCES
1. Building Code Requirements for Masonry Structures, ACI 530-02/ASCE 5-02/TMS 402-02, reported by the Masonry
Standards Joint Committee, 2002.
2. Selden, J. K. Shrinkage Characteristics of Concrete Masonry Walls, Housing and Home Finance Agency Paper 34, pages
1-60, 1954.
3. Control Joints for Concrete Masonry Walls Empirical Method, TEK 10-2B. National Concrete Masonry Association, 2003.
4. Standard Specification for Loadbearing Concrete Masonry Units, ASTM C 90-02. American Society for Testing and
Materials, 2002.
5. Standard Test Method for Linear Drying Shrinkage of Concrete Block , ASTM C 426-99. American Society for Testing
and Materials, 1999.
6. Toennies, H. T. Concrete Masonry Shrinkage. National Concrete Masonry Association, 1961.

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