NOTE: This guide specification covers the requirements for constructing a permeable interlocking concrete pavement for pedestrian and vehicular uses such as parking lots, alleys and low volume roads. This section includes construction of the paving surface which consists of solid concrete units with joints filled with permeable aggregate installed over a permeable aggregate bedding course. This section includes subbase and base reservoir materials and construction specific to permeable interlocking concrete pavement.
Edit this guide specification for project specific requirements by adding, deleting, or revising text. For bracketed items, choose applicable items(s) or insert appropriate information.
Remove information and requirements not required in respective project, whether or not brackets are present.
Comments and suggestions on this guide specification are welcome and should be directed to the technical proponent of the specification. A listing of technical proponents, including their organization designation and telephone number, is on the Internet.
Recommended changes to a UFGS should be submitted as a Criteria Change Request (CCR).
NOTE: This guide specification covers the requirements for constructing a concrete block pavement.
Adhere to UFC 1-300-02 Unified Facilities Guide Specifications (UFGS) Format Standard when editing this guide specification or preparing new project specification sections. Edit this guide specification for project specific requirements by adding, deleting, or revising text. For bracketed items, choose applicable items(s) or insert appropriate information.
Remove information and requirements not required in respective project, whether or not brackets are present.
Comments, suggestions and recommended changes for this guide specification are welcome and should be submitted as a Criteria Change Request (CCR).
Note: This guide specification for the U.S. is for concrete pavers for airfields. Concrete pavers are approved for FAA- funded projects on a case-by-case basis. This guide specification is not published by FAA in their Advisory Circulars. However, it follows FAA specification format and structure as well as for quality control and quality assurance. The specification accompanies the CMHA manual, Airfield Pavement Design with Concrete Pavers. The text must be edited by a qualified, licensed design professional to suit specific project requirements. CMHA makes no representations or warranties of any kind, expressed or implied, and disclaims any liability for damages resulting in the use of this guide construction specification.
Note: This guide specification for Canada is for Canadian airports with concrete pavers. The text must be edited by a qualified, licensed design professional to suit specific project requirements. CMHA makes no representations or warranties of any kind, expressed or implied, and disclaims any liability for damages resulting in the use of this guide construction specification.
Foam plastic insulation is often used in exterior concrete masonry construction to improve steady state thermal performance (R-values), and in some cases to improve air and moisture infiltration properties as well. Because of their potential flammability and smoke generation in case of fire, the International Building Code (IBC) (ref. 1) imposes additional requirements on these materials when they are used in exterior walls. These requirements are covered in IBC section 2603.
Foam plastic insulations include both rigid board (expanded polystyrene, extruded polystyrene, polyisocyanurate) as well as open cell and closed-cell spray-applied or foamed-in-place insulations. They may be used on the interior, exterior or in the cores (as either inserts or foamed-in-place) of single wythe masonry walls, and in the cavities of masonry cavity walls.
Because these plastics are flammable, the IBC mandates that they be protected by fire-resistance-rated materials or assemblies in wall and roof assemblies, to prevent the plastic insulation from contributing to the spread of fire in a building.
This TEK describes the IBC requirements for assemblies containing foam plastic insulation and presents details of concrete masonry walls that comply with those requirements. Note that this TEK focuses on the requirements for masonry wall assemblies: there may be additional requirements for the insulation, such as flame spread index and labeling.
IBC REQUIREMENTS
IBC Section 2603 regulates the use of foam plastic insulation in all types of construction, both combustible and noncombustible, with the intent of limiting the spread of fire via these materials. For exterior walls, Section 2603 requires:
a thermal barrier between foam plastic insulation and the building interior, which can be satisfied with a 1 in. (25 mm) minimum thickness of concrete or masonry,
ignition testing for foam plastic insulations applied to wall exteriors, although assemblies protected with at least 1 in. (25 mm) of concrete or masonry on the exterior are exempt from testing, and
successful testing in accordance with NFPA 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components (ref. 2).
Note that there are two important exceptions to the requirement for NFPA 285 testing:
Wall assemblies where the foam plastic insulation is covered on each face by a minimum 1 in. (25 mm) thickness of masonry or concrete and meeting one of the following: a) there is no air space between the insulation and the concrete or masonry (as occurs with foamed-in-place insulation); or b) the insulation has a flame spread index of 25 or less as determined by ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials, or UL 723, Standard for Test for Surface Burning Characteristics of Building Materials, (refs. 3, 4) and the air space between the insulation and the concrete or masonry does not exceed 1 in. (25 mm).
One-story buildings meeting the following conditions: foam plastic with a flame spread index of 25 or less and a smoke-developed index of 450 max can be placed in exterior walls without a thermal barrier where it is covered with aluminum (at least 0.032 in. (0.813 mm) thick) or corrosion-resistant steel (at least 0.0160 in. (0.406 mm) thick), provided that the insulation is not thicker than 4 in. (102 mm), and that the building is equipped with an automatic sprinkler system.
Wall assemblies meeting the requirements listed under number 1 above and buildings meeting the requirements listed under number 2 are deemed to comply with the Section 2603 requirements. Note that in cases where there is less than 1 in. (25 mm) of masonry over the insulation, there are insulations available that will meet the NFPA 285 requirements.
NFPA 285 REQUIREMENTS
NFPA 285 addresses the possibility of fire entering wall cavities through door or window openings, igniting foam plastic insulation and spreading vertically to upper stories.
The test evaluates exterior wall assemblies for buildings required to have exterior walls of noncombustible construction. The test provides a method of determining the flammability characteristics of exterior nonloadbearing wall assemblies. It is intended to evaluate combustible components included within wall assemblies required to be noncombustible, under conditions of a fire originating in the building interior.
NFPA 285 evaluates four conditions:
flame propagation over the exterior face;
flame propagation within combustible components from one story to the next;
vertical flame propagation on the interior wall surface from one story to the next; and
lateral flame propagation from one compartment to the next.
To evaluate these conditions, a two-story wall assembly with a window opening on the first floor is constructed in the test assembly. After a 30-minute fire exposure with the burner in the window opening, recorded temperatures are compared to the Standard’s conditions of acceptance to determine compliance. Note that the test evaluates wall assemblies, not specific materials.
SINGLE WYTHE CONCRETE MASONRY WALLS
Single wythe walls may incorporate foam insulation in the cores of the masonry units as either rigid foam inserts or foamed in-place insulation. As discussed above, IBC Chapter 26 essentially requires a minimum of 1 in. (25 mm) of concrete or masonry on the interior and exterior of the foam insulation, as well as protection at headers to prevent ignition of the insulation above door and window openings.
When placed in concrete masonry cores, the foam plastic insulation is protected on the interior and exterior by the concrete face shells. Minimum face shell thickness for concrete masonry units is governed by ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units, (ref. 5) as listed in Table 1. Table 1 shows that concrete masonry units of 6-in. (152 mm) thickness or greater provide the IBC-required 1 in. (25 mm) interior and exterior protection. Because of the small core size of 4-in. (102-mm) units, the cores of these units are rarely insulated. When insulation is placed in the cells of concrete masonry units and bond beams are provided at each story and lintels over each opening, the insulation is fully encapsulated. This meets the intent of the code to prevent the propagation of fire within wall cavities and no further isolation is necessary in this case.
In single wythe construction, door and window headers are typically constructed using either a reinforced precast lintel or a reinforced concrete masonry lintel (shown in Figure 1). This detail provides concrete cover well over the 1 in. (25 mm) minimum required by Section 2603. The detail and level of protection would be similar with a precast concrete lintel. Refer to TEK 19-02B, Design for Dry Single Wythe Concrete Masonry Walls (ref. 6), for additional details on flashing single wythe walls.
MULTI-WYTHE WALLS
Multi-wythe concrete masonry construction is most commonly masonry cavity walls, which often incorporate foam plastic insulation in the cavity formed by the two masonry wythes. In this case, there is more than 1 in. (25 mm) of masonry on both the interior and exterior, so the focus for protecting the insulation is on the headers and jambs of window and door openings.
Per Building Code Requirements for Masonry Structures (ref. 8) concrete masonry veneer walls are to have a minimum specified 1 in. (25 mm) air space with special precautions to limit mortar overhangs inside the cavity to allow adequate drainage between the wythes. Exception b to NFPA 285 testing (see page 1) limits the air space between the insulation and the masonry to 1 in. (25 mm) maximum. Therefore, when exception b is being used, the designer should specify a 1 in. (25 mm) air space to meet both requirements.
Figure 3 shows a window top of opening detail in a concrete masonry cavity wall. In this case, 1 in. (25 mm) of mortar is slushed into the cavity below the insulation to provide the required level of protection. In addition, testing (refs. 7, 10) has shown that mineral wool fire safing covering insulation board exposed at openings in a masonry cavity wall is sufficient to pass NFPA 285 requirements. Note that mineral wool insulation cannot be exposed to the moisture in the drainage cavity. If used, it must be behind flashing or similarly protected.
The jambs of metal doors (see Figure 4) are typically filled with mortar as the wall is constructed, again providing adequate protection for the insulation.
For wood door jambs, several options are shown in Figures 5 and 6. Figure 5 shows a detail where the insulation is held 1 in. (25 mm) back from the jamb. An additional piece of insulation bridges the cavity and acts as a backer for a 1 in (25 mm) layer of mortar. Another option is shown in Figure 6, where the unit adjacent to the jamb is turned 90o, and the unit is cut so that part of the face shell extends across the cavity, between the jamb and the insulation. On the alternate courses, a piece of the cut face shell can be mortared across the cavity to provide the protection. Wood window jamb details are very similar, as shown in Figures 7 and 8.
REFERENCES
International Building Code. International Code Council, 2015.
Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components, NFPA 285. National Fire Protection Association, 2012.
Standard Test Method for Surface Burning Characteristics of Building Materials, ASTM E84-13a. ASTM International, 2013.
Standard for Test for Surface Burning Characteristics of Building Materials, UL 723. Underwriter’s Laboratories, 2008.
Standard Specification for Loadbearing Concrete Masonry Units, ASTM C90-13. ASTM International, 2013.
Design for Dry Single-Wythe Concrete Masonry Walls, TEK 19 02B. Concrete Masonry & Hardscapes Association, 2012.
NFPA 285-[06] Approved Wall Assemblies Using Foam Plastic Insulation From Dow, Tech Solutions 514.0. Dow Chemical Company, 2009.
Building Code Requirements for Masonry Structures, TMS 402 11/ACI 530-11/ASCE 5-11. Reported by the Masonry Standards Joint Committee, 2011.
Standard Test Method for Determining Ignitability of Exterior Wall Assemblies Using a Radiant Heat Energy Source, NFPA 268. National Fire Protection Association, 2012.
A wall constructed with two or more wythes of masonry can technically be classified in one of three ways, depending on how each individual wythe is designed and detailed. These three wall systems are composite, noncomposite or veneer walls. A true veneer is nonstructural—any contribution of the veneer to the wall’s out-of plane load resistance is neglected.
Building Code Requirements for Masonry Structures (ref. 1) defines veneer as a masonry wythe which provides the exterior finish of a wall system and transfers out-of-plane loads directly to the backing, but is not considered to add load resisting capacity to the wall system.
Noncomposite walls, on the other hand, are designed such that each wythe individually resists the loads imposed on it. Bending moments (flexure) due to wind or gravity loads are distributed to each wythe in proportion to its relative stiffness.
Composite walls are designed so that the wythes act together as a single member to resist structural loads. This requires that the two masonry wythes be connected by masonry headers or by a mortar or grout filled collar joint and wall ties to help ensure adequate load transfer between the two wythes.
The primary function of anchored veneers is to provide an architectural facade and to prevent water penetration into the building. As such, the structural properties of veneers are neglected in veneer design. The veneer is assumed to transfer out-of-plane loads through the anchors to the backup system. Building Code Requirements for Masonry Structures Chapter 6 (ref. 1) includes requirements for design and detailing anchored masonry veneer.
A masonry veneer with masonry backup and an air space between the masonry wythes is commonly referred to as a cavity wall. The continuous air space, or cavity, provides the wall with excellent resistance to moisture penetration and wind driven rain as well as a convenient location for insulation. This TEK addresses concrete masonry veneer with concrete masonry backup.
DESIGN CONSIDERATIONS
Masonry veneers are typically composed of architectural units such as: concrete or clay facing brick; split, fluted, glazed, ground face or scored block; or stone veneer. Most commonly, anchored masonry veneers have a nominal thickness of 4 in. (102 mm), although 3 in. (76 mm) veneer units may be available as well.
Although structural requirements for veneers are minimal, the following design considerations should be accounted for: crack control in the veneer, including deflection of the backup and any horizontal supports; adequate anchor strength to transfer applied loads; differential movement between the veneer and backup; and water penetration resistance.
The continuous airspace behind the veneer, along with flashing and weeps, must be detailed to collect any moisture that may penetrate the veneer and direct it to the outside. A minimum 1 in. (25 mm) air space between wythes is required (ref. 1), and is considered appropriate if special precautions are taken to keep the air space clean (such as by beveling the mortar bed away from the cavity or by placing a board in the cavity to catch and remove mortar droppings and fins while they are still plastic). Otherwise, a 2 in. (51 mm) air space is preferred. As an alternative, proprietary insulating drainage products can be used.
Although veneer crack control measures are similar to those for other concrete masonry wall constructions, specific crack control recommendations have been developed for concrete masonry veneers. These include: locating control joints to achieve a maximum panel length to height ratio of 11/2 and a maximum spacing of 20 ft (6,100 mm), as well as where stress concentrations occur; incorporating joint reinforcement at 16 in. (406 mm) on center; and using Type N mortar for maximum flexibility. See CMU-TEC-009-23, Crack Control Strategies for Concrete Masonry Construction (ref. 2) for more detailed information.
Because the two wythes in a veneer wall are designed to be relatively independent, crack control measures should be employed as required for each wythe. It is generally not necessary for the vertical movement joints in the veneer wythe to exactly align with those in the backup wythe, provided that the ties allow differential in-plane lateral movement.
Wall ties may be joint reinforcement or wire wall ties. Wall ties for veneers transfer lateral loads to the structural wythe and also allow differential inplane movement between wythes. This second feature is particularly important when the two wythes are of materials with different thermal and moisture expansion characteristics (such as concrete masonry and clay brick), or in an insulated cavity wall which tends to have differential thermal movement between the wythes. When horizontal joint reinforcement is used to tie the two wythes together, hot-dipped ladder type reinforcement is preferred over truss type, because the ladder shape accommodates differential in-plane movement and facilitates placing vertical reinforcement, grout and loose fill insulation. Because veneers rely on the backup for support, wall ties must be placed within 12 in. (305 mm) of control joints and wall openings to ensure the free ends of the veneer are adequately supported. More information on ties for veneers can be found in TEK 03-06C, Concrete Masonry Veneers (ref. 4).
The distance between the inside face of the veneer and the outside face of the masonry backup must be a minimum of 1 in. (25 mm) and a maximum of 4 1/2 in. (114 mm). For glazed masonry veneer, because of their impermeable nature, a 2 in. (51 mm) wide airspace is recommended with air vents at the top and bottom of the wall to enhance drainage and help equalize air pressure between the cavity and the exterior of the wall. Vents can also be installed at the top of other masonry veneer walls to provide natural convective air flow within the cavity to facilitate drying. For vented cavities, it is prudent to create baffles in the cavity at the building corners to isolate the cavities from each other. This helps prevent suction being formed in the leeward cavities.
REFERENCES
Building Code Requirements for Masonry Structures, ACI 530-02/ASCE 5-02/TMS 402-02. Reported by the Masonry Standards Joint Committee, 2002.
CMU-TEC-009-23, Crack Control Strategies for Concrete Masonry Construction, Concrete Masonry and Hardscapes Association, 2023.
TEK 03-06C, Concrete Masonry Veneers, Concrete Masonry and Hardscapes Association, 2012.
The current trend of urban renewal and infill has sparked a high volume of new low-rise masonry residences. These structures come in many forms, but quite often they employ the use of load-bearing concrete masonry walls supporting a wood floor system. These new buildings are largely derivative of the historic load bearing masonry “brownstone” or “three flat” structures of old. This guide is intended to assist contractors and architects to give this building type a modern approach to detailing.
FLOOR SYSTEM CONNECTIONS
When designing low-rise loadbearing structures, the connection detail between the floor system and the wall system is critical for achieving a watertight structure. Much of this TEK will deal with which strategy should be utilized in connecting a wood floor system to a masonry load-bearing wall. Connection methods covered are joist hangers, beam pockets and ledger beam details. Other floor systems are used in low-rise construction that are not addressed here – see 05-07A for further information (ref. 2).
BRICK AND BLOCK COMPOSITE WALL DETAILS
Quite often, the front facade of these structures is composed of brick to give the building a more residential, more human scale. One way to construct a brick and block wall is to separate the two wythes with an airspace, creating a cavity wall. Another is to use a composite wall design. The composite wall consists of an exterior wythe of brick directly mortared or grouted and tied to an inner wythe of CMU. The collar joint between the two wythes should be 100% solid as it is the only defense against water penetration. Minimum tie requirements are one tie per 22/3ft2 of wall area for W1.7 (MW11)(9 gauge) wire or one tie per 41/2ft2 of wall area using W2.8 (MW19)(3/16 in.)wire (ref. 2). A W1.7 (MW11)(9 gauge) joint reinforcement @16 in. (406 mm) on center would meet this requirement and is often used. Details covered for this system are base flashing, window head and window sill details.
EXTERIOR CONCRETE MASONRY
The use of water repellent admixtures in concrete masonry and mortars can greatly reduce the amount of water entering the masonry. In addition, they inhibit any water that penetrates the face from wicking to the back of the wall.
Proper selection and application of integral water repellents and surface treatments can greatly enhance the water resistive properties of masonry, but they should not be considered as substitutes for good fundamental design including flashing details and crack control measures. See TEKs 19-01, 19-02A, and 19-04A (refs. 6, 3, & 5) for more information on water resistant concrete masonry construction.
Because a 4 in. (102 mm) concrete masonry veneer will shrink over time, a 4 in. (102 mm) hot-dipped galvanized ladder type joint reinforcement should be placed in bed joints spaced 16 in. (406 mm) vertically.
Compared to type N or O, type S mortar tends to be less workable in the field and should only be specified when dictated by structural requirements. Sills, copings and chimney caps of solid masonry units, reinforced concrete, stone, or corrosion resistant metal should be used. Copings, sills and chimney caps should project beyond the face of the wall at least 1 in. (25 mm) and should have functional flashing and weep holes.
In addition, all sills, copings and chimney caps should have a minimum slope of 1:4, be mechanically anchored to the wall, and should have properly sized, sealed, and located movement joints when necessary.
Flashing should be installed at locations shown on the plans and in strict accordance with the details and industry standard flashing procedures. Functional, unpunctured flashing and weep holes are to be used at the base of wall above grade, above openings, at shelf angles, lintels, wall-roofing intersections, chimneys, bay windows, and below sills and copings. The flashing should be extended past the face of the wall. The flashing should have end dams at discontinuous ends, and properly sealed splices at laps.
JOIST HANGER DETAILS
The use of a joist hanger system can greatly simplify the bearing detail. The floor system does not interrupt the continuity of the bearing wall. Installation is quicker and easier resulting in a more economical installation.
BEAM POCKET DETAILS
The traditional beam pocket detail still can be effective. Stepped flashing above the bearing line is critical to the performance of this system. Without the flashing, any water present in the wall has an unobstructed path inside the building and has the potential to deteriorate the floor structure.
LEDGER BEAM DETAILS
The use of a ledger beam which is bolted to a bond beam is also a good option for this bearing condition. Through wall flashing is still required to maintain a watertight wall. Any water that penetrates the block with run down the inner cores of the block until it hits the flashing. The flashing and weep holes will allow the water to exit without damaging the structure.
PARAPETS AND WINDOW SILLS
Below are details for a parapet condition and a window sill condition. The parapet is reinforced with No. 4 bars at 48 in. (No.13M @1219 mm) on center or as required for wind resistance. If a metal cap is used, it should extend down the face of the wall at least 3 in. (76 mm) with continuous sealant at the joint on both sides of the wall. The sill detail shows the arrangement of flashing, end dam, weep holes and drip edge and how they all form a watertight
WINDOW HEAD DETAILS
These two window head details show the relationship between the steel lintel, drip edge, flashing, end dams, and weep holes. The first option shows the use of a concrete masonry lintel which is grouted solid and reinforced. The second detail shows two steel lintels used for spanning the opening.
CONTROL JOINT DETAILS
Control joints simply are weakened planes placed at approximately 20 ft. (6 m) on center in concrete masonry walls and at changes in wall elevation/thickness. Notice that the joint reinforcement is discontinuous at the joint. Cores are shown grouted adjacent to the joints as well to ensure structural stability in taller walls and/or high load situations.
COMPOSITE WALL BASE FLASHING DETAILS
Figure 14 shows a stair-stepped flashing detail with the exposed drip edge and weep holes. Figure 15 shows a straight through wall flashing detail. The flashing must be set in mastic on top of the concrete foundation, or the flashing must be self adhesive. The flashing should be turned up on the inner side of the wall to direct water to the outside of the wall.
COMPOSITE WALL WINDOW DETAILS
Here steel lintels back-to-back create the above window span. Stepped flashing turned up on the inside, and folded to form an end dam protects the head condition from moisture. The sill detail also uses flashing, end dams and weep holes to keep moisture out of the wall. The use of a precast concrete or stone sill is highly suggested over using brick rowlock sills.
CONCRETE MASONRY VENEER DETAILING
Figure 18 shows the detailing of a 4 in. (102 mm) concrete masonry veneer used in conjunction with a 8 in. (205 mm) CMU backup wall.
Three types of joint reinforcement are shown including tri-rod, tab and adjustable types. It is imperative that the veneer have a continuous wire embedded in every other course to control movement. With the tri-rod system, the joint reinforcement satisfies this requirement. With the other two systems, an additional ladder type joint reinforcement is used to provide this movement control for the veneer.
REFERENCES
Building Code Requirements for Masonry Structures, ACI 530-05/ASCE 6-05/TMS-402-05. Reported by the Masonry Standards Joint Committee, 2005.
Floor and Roof Connections to Concrete Masonry Walls, TEK 05-07A, Concrete Masonry & Hardscapes Association, 2001.
Design for Dry Single-Wythe Concrete Masonry Walls, TEK 19-02B, Concrete Masonry & Hardscapes Association, 2004.
Flashing Details for Concrete Masonry Walls, TEK 19-05A, Concrete Masonry & Hardscapes Association, 2004.
Flashing Strategies for Concrete Masonry Walls, TEK 19- 04A, Concrete Masonry & Hardscapes Association, 2003.
Water Repellents for Concrete Masonry Walls, TEK 19-01, Concrete Masonry & Hardscapes Association, 2002.
Basements allow a building owner to significantly increase usable living, working, or storage space at a relatively low cost. Old perceptions of basements have proven outdated by stateofthe-art waterproofing, improved drainage systems, and natural lighting features such as window wells. Other potential benefits of basements include room for expansion of usable space, increased resale value, and safe haven during storms.
Historically, plain (unreinforced) concrete masonry walls have been used to effectively resist soil loads. Currently, however, reinforced walls are becoming more popular as a way to use thinner walls to resist large backfill pressures. Regardless of whether the wall is plain or reinforced, successful performance of a basement wall relies on quality construction in accordance with the structural design and the project specifications.
Materials
Concrete Masonry Units: Concrete masonry units should comply with Standard Specification for Loadbearing Concrete Masonry Units, ASTM C 90 (ref. 8). Specific colors and textures may be specified to provide a finished interior to the basement. Drywall can also be installed on furring strips, if desired. A rule of thumb for estimating the number of concrete masonry units to order is 113 units for every 100 ft2 (9.3 m2) of wall area. This estimate assumes the use of 3/8 in. (9.5 mm) mortar joints.
Mortar: Mortar serves several important functions in a concrete masonry wall; it bonds the units together, seals joints against air and moisture penetration, and bonds to joint reinforcement, ties, and anchors so that all components perform as a structural element.
Mortar should comply with Standard Specification for Mortar for Unit Masonry, ASTM C 270 (ref. 9). In addition, most building codes require the use of Type M or S mortar for construction of basement walls (refs. 2, 4, 5, 9, 13), because Type M and S mortars provide higher compressive strengths. Table 1 lists mortar proportions.
Typical concrete masonry construction uses about 8.5 ft3 (0.24 m3) of mortar for every 100 ft2 (9.3 m2) of masonry wall area. This figure assumes 3/8 in. (9.5 mm) thick mortar joints, face shell mortar bedding, and a 10% allowance for waste.
Grout: In reinforced concrete masonry construction, grout is used to bond the reinforcement and the masonry together. Grout should conform to Standard Specification for Grout for Masonry, ASTM C 476 (ref. 10), with the proportions listed in Table 2. As an alternative to complying with the proportion requirements in Table 2, grout can be specified to have a minimum compressive strength of 2000 psi (13.8 MPa) at 28 days. Enough water should be added to the grout so that it will have a slump of 8 to 11 in. (203 to 279 mm). The high slump allows the grout to be fluid enough to flow around reinforcing bars and into small voids. This initially high water-to-cement ratio is reduced significantly as the masonry units absorb excess mix water. Thus, grout gains high strengths despite the initially high waterto-cement ratio.
Construction
Prior to laying the first course of masonry, the top of the footing must be cleaned of mud, dirt, ice or other materials which reduce the bond between the mortar and the footing. This can usually be accomplished using brushes or brooms, although excessive oil or dirt may require sand blasting.
Masons typically lay the corners of a basement first so that alignment is easily maintained. This also allows the mason to plan where cuts are necessary for window openings or to fit the building’s plan.
To make up for surface irregularities in the footing, the first course of masonry is set on a mortar bed joint which can range from 1/4 to 3/4 in. (6.4 to 19 mm) in thickness. This initial bed joint should fully bed the first course of masonry units, although mortar should not excessively protrude into cells that will be grouted.
All other mortar joints should be approximately 3/8 in. (9.5 mm) thick and, except for partially grouted masonry, need only provide face shell bedding for the masonry units. In partially grouted construction, webs adjacent to the grouted cells are mortared to restrict grout from flowing into ungrouted cores. Head joints must be filled solidly for a thickness equal to a face shell thickness of the units.
Tooled concave joints provide the greatest resistance to water penetration. On the exterior face of the wall, mortar joints may be cut flush if parging coats are to be applied.
When joint reinforcement is used, it should be placed directly on the block with mortar placed over the reinforcement in the usual method. A mortar cover of at least 5/8 in. (15.9 mm) should be provided between the exterior face of the wall and the joint reinforcement. A mortar cover of 1/2 in. (12.7 mm) is needed on the interior face of the wall. For added safety against corrosion, hot dipped galvanized joint reinforcement is recommended.
See Figures 1-4 for construction details.
Reinforced Masonry: For reinforced masonry construction, the reinforcing bars must be properly located to be fully functional. In most cases, vertical bars are positioned towards the interior face of basement walls to provide the greatest resistance to soil pressures. Bar positioners at the top and bottom of the wall prevent the bars from moving out of position during grouting. A space of at least 1/2 in. (12.7 mm) for coarse grout and 1/4 in. (6.4 mm) for fine grout should be maintained between the bar and the face shell of the block so that grout can flow completely around the reinforcing bars.
As mix water is absorbed by the units, voids can form in the grout. Accordingly, grout must be puddled or consolidated after placement to eliminate these voids and to increase the bond between the grout and the masonry units. Most codes permit puddling of grout when it is placed in lifts less than about 12 in. (305 mm). Lifts over 12 inches (305 mm) should be mechanically consolidated and then reconsolidated after about 3 to 10 minutes.
Surface Bonding: Another method of constructing concrete masonry walls is to dry stack units (without mortar) and then apply surface bonding mortar to both faces of the wall. The surface bonding mortar contains thousands of small glass fibers. When the mortar is applied properly to the required thickness, these fibers, along with the strength of the mortar itself, help produce walls of comparable strength to conventionally laid plain masonry walls. Surface bonded walls offer the benefits of excellent dampproof coatings on each face of the wall and ease of construction.
Dry-stacked walls should be laid in an initial full mortar bed to level the first course. Level coursing is maintained by using a rubbing stone to smooth small protrusions on the block surfaces and by inserting shims every two to four courses.
Water Penetration Resistance: Protecting below grade walls from water entry involves installation of a barrier to water and water vapor. An impervious barrier on the exterior wall surface can prevent moisture entry.
The barrier is part of a comprehensive system to prevent water penetration, which includes proper wall construction and the installation of drains, gutters, and proper grading.
Building codes (refs. 2, 4 , 5, 9, 13) typically require that basement walls be dampproofed for conditions where hydrostatic pressure will not occur, and waterproofed where hydrostatic pressures may exist. Dampproofing is appropriate where groundwater drainage is good, for example where granular backfill and a subsoil drainage system are present. Hydrostatic pressure may exist due to a high water table, or due to poorly draining backfill, such as heavy clay soils. Materials used for waterproofing are generally elastic, allowing them to span small cracks and accommodate minor movements.
When choosing a waterproof or dampproof system, consideration should be given to the degree of resistance to hydrostatic head of water, absorption characteristics, elasticity, stability in moist soil, resistance to mildew and algae, impact or puncture resistance, and abrasion resistance. A complete discussion of waterproofing, dampproofing, and drainage systems is included in TEK 19-03A (ref. 6).
All dampproofing and waterproofing systems should be applied to walls that are clean and free from dirt, mud and other materials which may reduce bond between the coating and the concrete masonry wall.
Draining water away from basement walls significantly reduces the pressure the walls must resist and reduces the possibility of water infiltration into the basement if the waterproofing (or dampproofing) system fails. Perforated pipe has historically proven satisfactory when properly installed. When placed on the exterior side of basement walls, perforated pipes are usually laid in crushed stone to facilitate drainage. To prevent migration of fine soil into the drains, filter fabrics are often placed over the gravel.
Drainage pipes can also be placed beneath the slab and connected into a sump. Pipes through the footing or the wall drain water from the exterior side of the basement wall.
The drainage and waterproofing systems should always be inspected prior to backfilling to ensure they are adequately placed. Any questionable workmanship or materials should be repaired at this stage since repairs are difficult and expensive after backfilling.
Backfilling: One of the most crucial aspects of basement construction is how and when to properly backfill. Walls should be properly braced or have the first floor in place prior to backfilling. Otherwise, a wall which is designed to be supported at the top may crack or even fail from the large soil pressures. Figure 5 shows one bracing scheme which has been widely used for residential basement walls. More substantial bracing may be required for high walls or large backfill pressures.
The backfill material should be free-draining soil without large stones, construction debris, organic materials, and frozen earth. Saturated soils, especially saturated clays, should generally not be used as backfill materials since wet materials significantly increase the hydrostatic pressure on the walls.
Backfill materials should be placed in several lifts and each layer should be compacted with small mechanical tampers. Care should be taken when placing the backfill materials to avoid damaging the drainage, waterproofing or exterior insulation systems. Sliding boulders and soil down steep slopes should thus be avoided since the high impact loads generated can damage not only the drainage and waterproofing systems but the wall as well. Likewise, heavy equipment should not be operated within about 3 feet (0.9 m) of any basement wall system.
The top 4 to 8 in. (102 to 203 mm) of backfill materials should be low permeability soil so rain water is absorbed into the backfill slowly. Grade should be sloped away from the basement at least 6 in. (152 mm) within 10 feet (3.1 m) of the building. If the ground naturally slopes toward the building, a shallow swale can be installed to redirect runoff.
Construction Tolerances
Specifications for Masonry Structures (ref. 8) specifies tolerances for concrete masonry construction. These tolerances were developed to avoid structurally impairing a wall because of improper placement.
Dimension of elements in cross section or elevation …………………………………….¼ in. (6.4 mm), +½ in. (12.7 mm)
Mortar joint thickness: bed………………………..+⅛ in. (3.2 mm) head………………………………..-¼ in (6.4 mm), +⅜ in. (9.5 mm)
Elements
Variation from level: bed joints………………………………………. ±¼ in. (6.4 mm) in 10 ft (3.1 m), ±½ in. (12.7 mm) max top surface of bearing walls…………………………………………….. ±¼ in.(6.4 mm), +⅜ in.(9.5 mm), ±½ in.(12.7mm) max
Variation from plumb………….±¼ in. (6.4 mm) 10 ft (3.1 m) ………………………………………±⅜ in. (9.5 mm) in 20 ft (6.1 m) ……………………………………………±½ in. (12.7 mm) maximum
True to a line…………………..±¼ in. (6.4 mm) in 10 ft (3.1 m) ………………………………………±⅜ in. (9.5 mm) in 20 ft (6.1 m) ……………………………………………±½ in. (12.7 mm) maximum
Alignment of columns and bearing walls (bottom versus top) ……………………………………………………………..±½ in (12.7 mm)
Location of elements
Indicated in plan……………..±½ in (12.7 mm) in 20 ft (6.1 m) …………………………………………….±¾ in. (19.1 mm) maximum
Indicated in elevation ……………………………………….±¼ in. (6.4 mm) in story height …………………………………………….±¾ in. (19.1 mm) maximum
Insulation: The thermal performance of a masonry wall depends on its R-value as well as the thermal mass of the wall. Rvalue describes the ability to resist heat flow; higher R-values give better insulating performance. The R-value is determined by the size and type of masonry unit, type and amount of insulation, and finish materials. Depending on the particular site conditions and owner’s preference, insulation may be placed on the outside of block walls, in the cores of hollow units, or on the interior of the walls.
Thermal mass describes the ability of materials like concrete masonry to store heat. Masonry walls remain warm or cool long after the heat or air-conditioning has shut off, keeping the interior comfortable. Thermal mass is most effective when insulation is placed on the exterior or in the cores of the block, where the masonry is in direct contact with the interior conditioned air.
Exterior insulated masonry walls typically use rigid board insulation adhered to the soil side of the wall. The insulation requires a protective finish where it is exposed above grade to maintain durability, integrity, and effectiveness.
Concrete masonry cores may be insulated with molded polystyrene inserts, expanded perlite or vermiculite granular fills, or foamed-in-place insulation. Inserts may be placed in the cores of conventional masonry units, or they may be used in block specifically designed to provide higher R-values.
Interior insulation typically consists of insulation installed between furring strips, finished with gypsum wall board or panelling. The insulation may be fibrous batt, rigid board, or fibrous blown-in insulation.
Design Features
Interior Finishes: Split faced, scored, burnished, and fluted block give owners and designers added options to standard block surfaces. Colored units can be used in the entire wall or in sections to achieve specific patterns.
Although construction with staggered vertical mortar joints (running bond) is standard for basement construction, the appearance of continuous vertical mortar joints (stacked bond pattern) can be achieved by using of scored units or reinforced masonry construction.
Natural Lighting: Because of the modular nature of concrete masonry, windows and window wells of a variety of shapes and sizes can be easily accommodated, giving basements warm, natural lighting. For additional protection and privacy, glass blocks can be incorporated in lieu of traditional glass windows.
References
Basement Manual-Design and Construction Using Concrete Masonry, CMU-MAN-002-01, Concrete Masonry & Hardscapes Association, 2001.
BOCA National Building Code. Country Club Hills, IL: Building Officials and Code Administrators International, Inc. (BOCA), 1999.
Building Code Requirements for Masonry Structures, ACI 530-02/ASCE 5-02/TMS 402-02. Reported by the Masonry Standards Joint Committee, 2002.
International Residential Code. Falls Church, VA: International Code Council, 2000.
International Building Code. Falls Church, VA: International Code Council, 2000.
Preventing Water Penetration in Below-Grade Concrete Masonry Walls, TEK 19-03A. Concrete Masonry & Hardscapes Association, 2001.
Seismic Design Provisions for Masonry Structures, TEK 14-18B, Concrete Masonry & Hardscapes Association, 2009.
Specifications for Masonry Structures, ACI 530.1-02/ASCE 6-99/TMS 602-02. Reported by the Masonry Standards Joint Committee, 2002.
Standard Building Code. Birmingham, AL: Southern Building Code Congress International, Inc. (SBCCI), 1999.
Standard Specification for Grout for Masonry, ASTM C 476-01. American Society for Testing and Materials, 2001.
Standard Specification for Load-Bearing Concrete Masonry Units, ASTM C 90-01. American Society for Testing and Materials, 2001.
Standard Specification for Mortar for Unit Masonry, ASTM C 270-00. American Society for Testing and Materials, 2000.
Uniform Building Code. Whittier, CA: International Conference of Building Officials (ICBO), 1997.
At critical locations throughout a building, moisture that manages to penetrate a wall is collected and diverted to the outside by means of flashing. The type of flashing and its installation may vary depending upon exposure conditions, opening types, locations and wall types. This TEK includes typical flashing details that have proven effective over a wide geographical range. The reader is also encouraged to review the companion TEK 19-04A Flashing Strategies for Concrete Masonry Walls (ref. 1) which addresses the effect of moisture on masonry, design considerations, flashing materials, construction practices, and maintenance of flashing.
CAVITY WALLS
For cavity walls, as illustrated in Figure 1, the cavity typically ranges from a minimum of 2 in. to a maximum of 4 ½ in. (25 to 114 mm) wide, with a minimum of a 1 in. (25 mm) clear airspace if rigid insulation is placed in the cavity. Cavities wider than 4 ½ in. (114 mm) are permitted only if a detailed analysis is performed on the wall ties per the International Building Code and Building Code Requirements of Masonry Structures (refs. 2, 3) The 1 in. (25 mm) clear airspace works only if the mason takes precautions to insure that mortar will not bridge the airspace. Such precautions would include beveling the mortar bed away from the cavity or drawing a piece of wood up the cavity to collect mortar droppings. If precautions are not taken, it is suggested that a wider airspace be utilized, i.e. 1½ to 2 in (38 to 51 mm). Also when using glazed masonry veneer, a 2 in. (51 mm) minimum airspace is recommended with air vents provided at the top and bottom of the wall because of the impermeable nature of the unit. Proprietary insulated drainage boards or mats are available that provide an unobstructed drainage path that eliminate the need for a clear airspace (ref. 4).
As shown in Figure 1, the flashing in a cavity wall at the intersection of the foundation should be sealed to the exterior faceshell of the backup wythe, project downward to the foundation surface, outward to the exterior face of the wall, and terminate with a sloped drip. Weep holes or open head joints should be located a maximum of 32 in. (813 mm) apart. Flashing at lintels and sills (shown in Figures 2 and 3, respectively) is very similar. Although not shown, vents can be installed in the vertical head joints at the top of masonry walls to provide natural convective air flow within the cavity to facilitate drying. Prefabricated flashing boots available for both single and multiwythe walls are shown in Figure 7.
Figure 1—Flashing Cavity Walls at Foundations
Figure 2—Flashing Cavity Walls at Bond Beam Locations
Figure 3—Flashing Cavity Walls at Sills
SINGLE WYTHE WALLS
Flashings in single wythe walls, like cavity walls should be positioned to direct water to the exterior. This is normally accomplished using two narrower units to make up the thickness of the wall and placing flashing between them as shown in Figures 4 and 8. Care should be exercised to insure that surfaces supporting the flashing are flat or are sloping to the exterior. This can be accomplished by using solid units, lintel or closed bottom bond beam units turned upside down similar to Figure 3, or by filling cells of hollow units with mortar or grout.
Flashing of single wythe walls at lintels, foundations, and bond beams is accomplished in the same manner as shown in Figure 4 while sills are shown in Figure 6. Through-wall flashing is used in many areas of the country as shown in Figure 9. However, the bondbreaking effects of this type of detail need to be evaluated in regard to the structural performance of the wall. Additional information for flashing single-wythe walls, particularly architectural concrete masonry walls, and means for providing a higher level of structural continuity at flashings is contained in TEK 19-02B (ref. 5). Flashing single wythe walls at the ends of bar joists which utilize wall pockets for bearing is shown in Figures 8 and 8a.
Figure 4—Flashing Single Wythe Walls
Figure 5—Two-Piece Flashing Detail
Figure 6—Flashing Single Wythe Walls at Sills
Figure 7—Prefabricated Flashing Boots
FLASHINGS AT COPINGS AND CAPS
The type of flashing detail to use on low-sloped roofs will in part depend on the type of roofing membrane being used. As with any flashing detail, the materials used should result in a uniform and compatible design. For example, joining two materials with significantly different coefficients of thermal expansion (such as metal flashing and bitumen roofing membrane) can cause tearing and failure of the joint. Many roofing membranes also shrink as they age. As a result, roofing membranes extending over the top of a parapet may pull the parapet off the wall as the roofing membrane shrinks. Counter flashing provides a solution to these problems as shown in Figure 8. Counter flashing also facilitates the reroofing process by allowing easy removal and access to the flashing membrane fasteners.
During placement of the final courses of masonry in parapets, and commencing with the second course below the coping/cap location, a grout stop should be placed over cores so that grout can be placed for the positioning of anchor bolts (Figure 8).
In coping installations it is imperative that penetrations of through-wall flashing be tightly sealed to prevent water infiltration. A full mortar bed is required to be placed on the through-wall flashing to allow proper positioning of coping units. Full head joints are placed between the coping units as well as properly spaced control joints. The joints between the coping units should then be raked and a joint sealant applied.
Coping units should be sized such that overhangs and a drip reveal are provided on both sides of the wall. Metal caps require wood plates for anchorage, which in turn are usually attached to the wall with anchor bolts. The cap should be sloped to prevent water from draining onto the exposed surface of the masonry and should extend at least 4 in. (102 mm) over the face of the masonry and sealed on both sides. Smooth face or uniform split face CMU should be considered for use under the cap to ensure a relatively tight fit between the masonry and cap that might be hindered by uneven concrete masonry units such as split-face or fluted units.
Figure 8a—Isometric of Flashing Around End of Joist (ref. 6)
Figure 8—Flashing Single Wythe Walls at Roof/Parapet Intersection (ref. 6)
INTERIOR WALL TREATMENTS
Concrete masonry walls with an interior treatment may also utilize a through-wall flashing installation of flashings as shown in Figure 9. However, as noted in the figure, through-wall flashings generally create a bond-breaker, which reduces the structural capacity of a masonry wall. This effect should be carefully evaluated before implementing this type of detail particularly in high-wind and seismic areas.
As shown in Figure 9, the flashing should project through the wall and be carried up on the interior concrete masonry surface. Furring strips installed to receive the plastic vapor retarder and the interior gypsum board will hold the flashing in position. This procedure permits any water that may penetrate to the interior surface of the concrete masonry wall to drain out at the base of the wall. Weep holes should project completely through the wall thickness. Vents, if used, should project into the core areas only.
Figure 9—Through-Wall Flashing
SPLICING FLASHING
When it is necessary to splice the flashing, extra precautions are required to ensure that these discreet locations do not become sources of water penetration. Flashing should be longitudinally continuous or terminated with an end dam as shown in Figure 7. The splicing of flashing materials consisting of plastic and rubber compounds is acheived by overlapping the joint a minimum distance of 4 in. (102 mm). The lapped area is then bonded together with adhesive if the flashing material is not self-adhering.
Lap splicing of metal flashing is not recommended as it has a different coefficient of thermal expansion than that of concrete masonry. As the temperature fluctuates, the flashing material will expand and contract differently than the masonry material, which can result in sealant failure and a potential point of entry for moisture. A typical flashing splice is detailed in Figure 10. Here, two sections of sheet metal type flashing that are to be spliced are first installed with a ¼-in. (6.4 mm) gap between them to allow for expansion of the flashing. Next, a section of pliable self-adhering membrane (such as rubberized-asphalt) or other pliable membrane set in mastic is fully bonded to the flashing at the location of the gap.
Figure 10—Splicing Metal Flashing
REFERENCES
Flashing Strategies for Concrete Masonry Walls, TEK 1904A, Concrete Masonry & Hardscapes Association, 2008.
International Building Code. International Code Council, 2003 and 2006.
Building Code Requirements for Masonry Structures, ACI 530/ASCE 5/TMS 402, reported by the Masonry Standards Joint Committee, 2002 and 2005.
Flashing…Tying the Loose Ends, Masonry Advisory Council, Chicago, IL, 1998.
Design for Dry Single-Wythe Concrete Masonry Walls, TEK 19-02B, Concrete Masonry & Hardscapes Association, 2012.
Generic Wall Design, Masonry Institute of Michigan, 1998.
Single-wythe concrete masonry walls are cost competitive because they provide structural form as well as an attractive and durable architectural facade. However, because they do not have a continuous drainage cavity (as do cavity and veneered walls), they require special attention to moisture penetration.
The major objective in designing dry concrete masonry walls is to keep water from entering or penetrating the wall. In addition to precipitation, moisture can find its way into masonry walls from a number of different sources (see Figure 1). Dry concrete masonry walls are obtained when the design and construction addresses the movement of water into, through, and out of the wall. This includes detailing and protecting building elements including parapets, roofs, all wall penetrations (utility and fire protective openings, fenestration, doors, etc.), movement joints, sills and other features to resist water penetration at these locations. Annotated Design and Construction Details for Concrete Masonry (ref. 1) contains comprehensive details for reinforced and unreinforced concrete masonry walls. Further, condensation and air leakage must be controlled. See the Condensation Control section on page 7.
The primary components of moisture mitigation in concrete masonry walls are flashing and counter flashing, weeps, vents, water repellent admixtures, sealants (including movement joints), post-applied surface treatments, vapor retarders and appropriate crack control measures. For successful mitigation, all of these components should be considered to be used redundantly, however not all will be applicable to all wall systems. For example, flashing and weeps are not necessary in solidly grouted construction, and may not be appropriate in areas of high wind or seismic loading where compromise of masonry shear resistance may occur (see the Wall Drainage section on page 3 for more information). The determination on structural effect must be made by the structural engineer. As another example, the use of integral water repellents for surfaces to receive a stucco finish may not be appropriate. Successful design for moisture mitigation considers each of these components, and provides for redundancy of protection, also known as a “belt and suspenders” approach.
This TEK provides a brief overview of the issues to consider when designing single wythe walls for water penetration resistance. The information presented is not meant to be comprehensive. Where appropriate, references to more detailed sources are provided.
Figure 1—Moisture Sources
SOURCES OF WATER IN WALLS
Driving Rain
Although concrete masonry units and mortar generally do not allow water to pass through quickly, rain can pass through if driven by a significant force. Cracks caused by building movements, or gaps between masonry and adjoining building elements are common points of water entry. If rain enters wall other than by way of the roof or at element interfaces (such as penetrations and window openings), it often can be traced to the masonry unit-mortar interface.
Capillary Action
Untreated masonry materials (without a compatible integral water repellent and/or post-applied surface treatment) typically take on water through absorption, adsorption and/or capillary forces. The amount of water depends on the characteristics of the masonry and mortar. Integral water repellents greatly reduce the absorption and adsorption characteristics of the units and mortar, but may not be able to prevent all moisture migration if there is a significant head pressure of approximately 2 in. water (51 mm) or more. Post-applied surface treatments reduce moisture penetration of masonry at the treated surface as well, but have little effect on the interior of the units.
Water Vapor
Water as vapor moves through a wall either via air leakage or by diffusion (from higher to lower: relative humidity, pressure and/or temperature). As air cools, it becomes more saturated, and when it reaches the dew point temperature the water vapor will condense into liquid form. See the Condensation Control section on page 7 for more information.
Ground Water
Protecting below-grade walls from water entry involves installing a barrier to water and water vapor. Below grade moisture tends to migrate from the damp soil to the drier area inside the basement. An impervious barrier on the exterior wall surface can prevent moisture entry. The barrier is part of a comprehensive system to prevent water penetration, which includes proper wall construction and the installation of drains, gutters, and proper grading (location of finished grade as well as grade sloping away from the building). Landscaping can also contribute to water ponding adjacent to the foundation wall and/or to insufficient drainage. IBC Section 1805 contains requirements for dampproofing and water proofing foundations. More detailed information for concrete masonry foundation walls can be found in Preventing Water Penetration in Below Grade CM Walls, TEK 19-03B (ref. 2).
DESIGN CONSIDERATIONS
When designing for moisture mitigation in walls, three levels of defense should be considered: surface protection (properly constructed mortar joints, surface water repellents, surface coatings), internal protection (integral water repellents), and drainage/drying (flashing, weeps, vents). The most successful designs often provide redundancy among these three levels. This redundant design approach helps ensure that the wall remains free of moisture problems even if one of the defense mechanisms is breached. Flashing and weeps, for example, provide a backup in case surface coatings are not reapplied as needed or leaks develop around windows or other openings. The following sections discuss the individual mechanisms in more detail.
Physical Characteristics of the Units
Open-textured concrete masonry units possessing large voids tend to be more permeable than closed-textured units. The texture can be affected by aggregate gradation, water content of the concrete mix, amount of cement in the mix, other materials in the mix such as admixtures, and the degree of compaction achieved during molding. These factors can also affect capillary action and vapor diffusion characteristics. Units should be aged at least 21 days if possible before installation to reduce the chance of shrinkage cracks at the mortar-unit interface.
Smooth-faced units facilitate mortar joint tooling, so will generally result in a more water resistant wall, as opposed to fluted units which are more difficult to tool and therefore the most susceptible to leakage. Horizontal effects such as corbels and ledges that may hold water are more prone to water penetration.
Integral Water Repellents
The use of integral water repellents in the manufacture of concrete masonry units can greatly reduce the wall’s absorption characteristics. When using units with an integral water repellent, the same manufacturer’s water repellent for mortar must be incorporated in the field for compatibility and similar reduced capillary action characteristics.
Integral water repellents make masonry materials hydrophobic, significantly decreasing their water absorption and wicking characteristics. While these admixtures can limit the amount of water that can pass through units and mortar, they have little impact on moisture entering through cracks and voids in the wall. In addition, when using an integral water repellent, any water that does penetrate can not exit as easily. Therefore, even with the incorporation of integral water repellents, flashing and weeps, as well as proper detailing of control joints and quality workmanship are still essential. See Water Repellents for Concrete Masonry Walls, TEK 19-01 (ref. 3), and Characteristics of CMU with Integral Water Repellent, TEK 19-07 (ref. 4), for more complete information on integral water repellents for concrete masonry walls.
Post-Applied Surface Treatments
For integrally colored architectural masonry, a clear surface treatment should be post-applied whether or not integral water repellent admixtures are used. Most post-applied coatings and surface treatments are compatible with integral water repellents although this should be verified with the product manufacturers before applying. When using standard units for single-wythe walls, application of a clear treatment, portland cement plaster (stucco), paint, or opaque elastomeric coating improves the water resistance of the wall. Coatings containing elastomerics have the advantage of being able to bridge small gaps and TEK 19-02B 3 CONCRETE MASONRY & HARDSCAPES ASSOCIATION masonryandhardscapes.org cracks. See Water Repellents for Concrete Masonry Walls, TEK 19-01 (ref. 3) for more detailed information.
Wall Drainage
In areas with high seismic loads, masonry walls tend to be heavily reinforced and it is often more economical to fully grout the masonry. In fully grouted masonry, flashing is not necessary. In these cases, the wall is designed as a barrier wall, rather than as a drainage wall.
When flashing is used, the importance of proper detailing cannot be over-emphasized. Traditionally, through-wall flashing has been used to direct water away from the inside wall face and toward weep holes for drainage. Figure 2 shows one example of flashing that spans completely across the width of the wall. In this example, the termination angle prevents any water that collects on the flashing from penetrating to the interior, and the weeps and drip edge drain water to the exterior.
Where it is necessary to retain some shear and flexural resistance capabilities, there are several options. One is to terminate the flashing within the inside face shell of the wall, as shown in Figure 3. In reinforced walls, some shear is provided through doweling action of the reinforcement, and by design the reinforcement takes all tension (refs. 5, 6). Proper grouting effectively seals around where the vertical reinforcement penetrates the flashing. The absence of reinforcement to provide doweling in plain masonry may be more of a concern, but loads tend to be relatively low in these applications. If structural adequacy is in doubt, a short reinforcing bar through the flashing with cells grouted directly above and below can be provided as shown in Figure 3c.
A better option to maintain shear at the level of the flashing is to use a product that maintains some bond in both face shells, such as that shown in Figure 4.
Ensuring that a buildup of mortar droppings does not clog the cells or weep holes is critical. Traditionally, a cavity filter consisting of washed pea stone or filter paper immediately above the flashing was provided to facilitate drainage, as shown in Figure 3. This should be accompanied by a means of intercepting or dispersing mortar droppings, as an accumulation can be sufficient to completely fill and block a cell at the bottom. As an alternative, mortar interception or isolation devices that provide pathways for the water to migrate through the layer of mortar droppings, or filling the cells with loose fill insulation a few courses at a time as the wall is laid up, can disperse the droppings enough to prevent clogging. Examples of polyester mesh drainage mats are shown in Figures 4 and 5. Another alternative is to leave out facing block at regular intervals just above the flashing until the wall is built to serve as cleanouts. The units left out can be mortared in later. See Flashing Strategies for Concrete Masonry Walls, TEK 19-04A and Flashing Details for Concrete Masonry Walls, TEK 19-05A, (refs. 7, 8) for an in-depth discussion and additional details regarding flashing.
In addition to conventional flashing systems, proprietary flashing systems are available that direct the water away from the inside face of the wall to weep holes without compromising the bond at mortar joints in the face shells. See Figure 4 for one example. These are not intended to be comprehensive, but rather to provide examples of some types of available systems. Specialty units that facilitate drainage are also available from some manufacturers.
Solid grouted single-wythe walls do not require flashing because they are not as susceptible to moisture penetration, since voids and cavities where moisture can collect are absent. However, fully cured units and adequate crack control measures are especially important to minimize cracks. In some regions of the country, the bottom of the wall is recessed about 1 in. (25 mm) below the floor level to ensure drainage to the exterior.
Figure 2—Three-Piece Through-Wall Flashing
Figure 3—Flashing Details to Maintain Structural Continuity
Figure 4—Pan Flashing with Integral Weeps
Figure 5—Stainless Steel Strip with Integral Weeps
Crack Control
Because cracks provide an entry point for rainwater and moist air, crack control provisions are very important in producing dry walls. There are various sources of potential wall cracking. A detailed list, as well as an overview of crack control strategies, can be found in Crack Control Strategies for Concrete Masonry Construction, CMU-TEC-009-23 (ref. 9).
Control joints and/or horizontal reinforcement should be located and detailed on the plans to alleviate cracking due to thermal and shrinkage movements of the building. Specifying a quality sealant for the control joints and proper installation is a must to maintain the weather-tightness of the joint. Joint Sealants for Concrete Masonry Walls, TEK 19-06A (ref. 10) contains more comprehensive information on this topic. See Crack Control Strategies for Concrete Masonry Construction, CMU-TEC-009-23 (ref. 11) for detailed information on control joint placement and construction.
Mortar and Mortar Joints
The type of mortar and type of mortar joint can also impact a wall’s watertightness. A good rule of thumb is to select the lowest strength mortar required for structural and durability considerations. Lower strength mortars exhibit better workability and can yield a better weather-resistant seal at the mortar/unit interface. See Mortars for Concrete Masonry, TEK 09-01A (ref. 12), for a more complete discussion.
Unless otherwise specified, mortar joints should be tooled to a concave profile when the mortar is thumbprint hard (refs. 5, 13), as shown in Figure 6. For walls exposed to weather, concave joints improve water penetration resistance by directing water away from the wall surface. In addition, because of the shape of the tool, the mortar is compacted against the concrete masonry unit to seal the joint. V-shaped joints result in sharper shadow lines than concave joints. Raked, flush, struck, beaded, grapevine, squeezed or extruded joints are not recommended in exposed exterior walls as they do not compact the mortar and/or they create ledges that intercept water running down the face of the wall.
Head and bed joints should be the full thickness of the face shells for optimum water resistance. Head joints are particularly vulnerable to inadequate thickness (see Figure 7).
Figure 6—Mortar Joint Profiles
Figure 7—Mortar Joints Should Be the Full Thickness of the Face Shells
Condensation Control
Condensation is a potential moisture source in building assemblies. Because condensation potential varies with environmental conditions, seasonal climate changes, the construction assembly, building type and building usage, condensation control strategies vary as well. For a full discussion, see Condensation Control in Concrete Masonry Walls, TEK 06-17B, and Control of Air Leakage in Concrete Masonry Walls, TEK 06-14A (refs. 14, 15).
Note that the location and vapor permeability of insulation can influence the condensation potential of a wall. The following references provide more detailed information. Insulating Concrete Masonry Walls, TEK 06-11A (ref. 16), discusses various insulation strategies and the advantages and disadvantages of each. R-Values and U-Values for Single Wythe Concrete Masonry Walls, TEK 06-02C, and Thermal Catalog of Concrete Masonry Assemblies (refs. 17, 18) provide calculated thermal values of various walls and insulation types. Details for Half-High Concrete Masonry Units, TEK 05-15 (ref. 19), contains comprehensive details of various single wythe walls.
Cleaning
Concrete masonry cleaning methods can generally be divided into four categories: hand cleaning, water cleaning, abrasive cleaning and chemical cleaning. In general, the least aggressive method that will adequately clean the wall should be used, as overzealous cleaning can damage the water repellent characteristics of the wall. Keeping the masonry wall clean as the construction progresses using a brush and water minimizes cleaning efforts after the mortar has hardened. See Cleaning Concrete Masonry, TEK 08-04A (ref. 20) for more detailed information.
SPECIFICATIONS
Well-worded specifications are essential to ensure the design details are properly constructed. Items to address in the contract documents in addition to those previously mentioned include:
All work to be in accordance with the International Building Code and Specification for Masonry Structures (refs. 5, 13).
Require a qualified mason by documentation of experience with similar type projects.
Require sample panels to assure an understanding of the level of workmanship expected and to be used as a standard of reference until the project is completed.
Proper storage of all masonry materials (including sand) at the job site to protect from contaminants such as dirt, rain and snow.
The tops of unfinished walls shall be covered at the end of each work day. The cover should extend 2 ft (610 mm) down each side of the masonry and be held securely in place.
REFERENCES
Annotated Design and Construction Details for Concrete Masonry, TR 90. National Concrete Masonry Association, 2002.
Preventing Water Penetration in Below-Grade CM Walls, TEK 19-03B, Concrete Masonry & Hardscapes Association, 2012.
Water Repellents for Concrete Masonry Walls, TEK 19-01, Concrete Masonry & Hardscapes Association, 2006.
Characteristics of CMU with Integral Water Repellent, TEK 19-07, Concrete Masonry & Hardscapes Association, 2008.
International Building Code. International Code Council, 2012.
Building Code Requirements for Masonry Structures, TMS 402-11/ACI 530-11/ASCE 5-11, reported by the Masonry Standards Joint Committee, 2011.
Flashing Strategies for Concrete Masonry Walls, TEK 1904A, Concrete Masonry & Hardscapes Association, 2008.
Flashing Details for Concrete Masonry Walls, TEK 19-05A, Concrete Masonry & Hardscapes Association, 2008.
Crack Control Strategies for Concrete Masonry Construction, CMU-TEC-009-23, Concrete Masonry & Hardscapes Association, 2023.
Joint Sealants for Concrete Masonry Walls, TEK 19-06A, Concrete Masonry & Hardscapes Association, 2014.
Crack Control Strategies for Concrete Masonry Construction, CMU-TEC-009-23, Concrete Masonry & Hardscapes Association, 2023.
Mortars for Concrete Masonry, TEK 09-01A, Concrete Masonry & Hardscapes Association, 2004.
Specification for Masonry Structures, TMS 602-11/ACI 530.1-11/ASCE 6-11, reported by the Masonry Standards Joint Committee, 2011.
Condensation Control in Concrete Masonry Walls, TEK 06-17B, Concrete Masonry & Hardscapes Association, 2011.
Control of Air Leakage in Concrete Masonry Walls, TEK 06-14A, Concrete Masonry & Hardscapes Association, 2011.
Construction of masonry wall systems is possible without the use of mortar. The use of standard CMU units laid dry and subsequently surface bonded with fiber reinforced surfaced bonding cement has been well documented in the past. (ref. 16) With the use of specially fabricated concrete masonry units known as “dry-stack units,” construction of these mortarless systems is simple, easy and cost effective. This TEK describes the construction and engineering design of such mortarless wall systems.
The provisions of this TEK apply to both specialty units manufactured specifically for dry-stack construction and conventional concrete masonry units with the following system types:
Grouted, partially grouted or surface bonded
Unreinforced, reinforced, or prestressed
Note that dry-stacked prestressed systems are available that do not contain grout or surface bonding. The provisions of this TEK do not apply to such systems due to a difference in design section properties (ref 8).
Specially designed units for dry-stack construction are available in many different configurations as shown in Figure 1. The latest and most sophisticated designs incorporate face shell alignment features that make units easier and faster to stack plumb and level. Other units are fabricated with a combination of keys, tabs or slots along both horizontal and vertical faces as shown in Figure 1 so that they may interlock easily when placed. Physical tolerances of dry-stack concrete units are limited to ±1/16 in. (1.58 mm.) which precludes the need for mortaring, grinding of face shell surfaces or shimming to even out courses during construction. Interlocking units placed in running bond resist flexural and shear stresses resulting from out-of-plane loads as a result of the keying action: (a) at the top of a web with the recess in the web of the unit above, (b) at two levels of bearing surface along each face shell at the bed joint, and (c) between adjacent blocks along the head joint. The first of these two interlocking mechanisms also ensures vertical alignment of blocks.
The interlocking features of dry-stack units improve alignment and leveling, reduce the need for skilled labor and reduce construction time. Floor and roof systems can be supported by mortarless walls with a bond beam at the top of the wall which expedites the construction process.
Wall strength and stability are greatly enhanced with grouting which provides the necessary integrity to resist forces applied parallel, and transverse to, the wall plane. Vertical alignment of webs ensures a continuous grout column even when the adjacent cell is left ungrouted. Grouting is necessary to develop flexural tensile stress normal to the bed joints, which is resisted through unit-mortar bond for traditional masonry construction. Strength of grouted dry-stack walls may also be enhanced by traditional reinforcement, prestressing, post-tensioning or with external fiber-reinforced surface coatings (surface bonding) as described in the next section.
Typical applications for mortarless concrete masonry include basement walls, foundation walls, retaining walls, exterior above-grade walls, internal bearing walls and partitions. Dry-stack masonry construction can prove to be a cost-effective solution for residential and low-rise commercial applications because of it’s speed and ease of construction, strength and stability even in zones of moderate and high seismicity. More information on design and construction of dry-stack masonry can be found in Reference 5.
Figure 1–– Dry-Stack Masonry Units
CONSTRUCTION
Dry-stack concrete masonry units can be used to construct walls that are grouted or partially grouted; unreinforced, reinforced or prestressed; or surface bonded. With each construction type, walls are built by first stacking concrete masonry units.
For unreinforced construction as shown in Figure 2a, grouting provides flexural and shear strength to a wall system. Flexural tensile stresses due to out-of-plane bending are resisted by the grout cores. Grout cores also interlace units placed in running bond and thus provide resistance to in-plane shear forces beyond that provided by friction developed along horizontal joints. Grout cores can also be reinforced to increase flexural strength.
Reinforcement can be placed vertically, in which case only those cells containing reinforcement may be grouted as shown in Figure 2b, as well as horizontally, in which case the masonry must be fully grouted. Another version is to place vertical prestressing tendons in place of reinforcement. Vertical axial compressive stress, applied via the tendons, increases flexural and shear capacity. Tendons may be bonded to grout, or unbonded, based upon the design. Placement of grout may be optional. Horizontally reinforced bond beam lintels can be created using a grout stop beneath the unit to contain grout.
As an alternative to reinforcing or prestressing, wall surfaces may be parged (coated) with a fiber-reinforced surface bonding cement/stucco per ASTM C887(ref. 14) as illustrated in Figure 2c. This surface treatment, applied to both faces of a wall, bonds concrete units together without the need for grout or internal reinforcement. The parging material bridges the units and fills the joints between units to provide additional bonding of the coating to the units through keying action. The compressive strength of the parging material should be equal to or greater than that of the masonry units.
Figure 2–– Basic Dry-Stack Masonry Wall Types
Laying of Units
The first course of dry-stack block should be placed on a smooth, level bearing surface of proper size and strength to ensure a plumb and stable wall. Minor roughness and variations in level can be corrected by setting the first course in mortar. Blocks should be laid in running bond such that cells will be aligned vertically.
Grout and Reinforcement
Grout and grouting procedures should be the same as used in conventional masonry construction (ref. 1, 10) except that the grout must have a compressive strength of at least 2600 psi (190 MPa) at 28 days when tested in accordance with ASTM C 1019 (ref.12). Placement of grout can be accomplished in one lift for single-story height walls less than 8 ft (2.43 m). Grout lifts must be consolidated with an internal vibrator with a head size less than 1 in. (25 mm).
Vertical Reinforcing
As for conventional reinforced masonry construction, good construction practice should include placement of reinforcing bars around door and window openings, at the ends, top and bottom of a wall, and between intersecting walls. Well detailed reinforcement such as this can help enhance nonlinear deformation capacity, or ductility, of masonry walls in building systems subjected to earthquake loadings – even for walls designed as unreinforced elements. Additional information on conventional grouting and reinforced masonry wall can be found in TEK 09-04A and TEK 03-03B (refs. 9 & 6).
Pre-stressed Walls
Mortarless walls can also be prestressed by placing vertical tendons through the cores. Tendons can be anchored within the concrete foundation at the base of a wall or in a bottom bond beam and are tensioned from the top of a wall.
Surface Bonded Walls
For walls strengthened with a surface bonding, a thin layer of portland cement surface bonding material should be troweled or sprayed on to a wall surface. The thickness of the surface coating should be at least ⅛ in. (3.2 mm.) or as required by the material supplier.
ENGINEERING PROPERTIES
Walls constructed with mortarless masonry can be engineered using conventional engineering principles. Existing building code recommendations such as that produced by the building code (ref. 1) can serve as reference documents, but at the time of this printing it does not address mortarless masonry directly. It is thus considered an alternate engineered construction type. The International Building Code (ref. 7) does list allowable stresses based on gross-cross-sectional area for dry-stacked, surface-bonded concrete masonry walls. These values are the same as presented in TEK 03-05A (ref. 16). Suggested limits on wall or building height are given in Table 1.
Test data (refs. 2, 3 and 4) have shown that the strength of drystack walls exceeds the strength requirements of conventional masonry, and thus the recommended allowable stress design practices of the code can be used in most cases. When designing unreinforced, grouted masonry wall sections, it is important to deduct the thickness of the tension side face shell when determining the section properties for flexural resistance.
Table 1 –– Summary of Wall Heights for 8” (203 mm) Dry-stacked Units (ref. 5)
* Laterally supported at each floor
Unit and Masonry Compressive Strength
Units used for mortarless masonry construction are made of the same concrete mixes as used for conventional masonry units. Thus, compressive strength of typical units could vary between 2000 psi (13.79MPa) and 4000 psi. (27.58 MPa) Standard Methods of Sampling and Testing Concrete Masonry Units (ref. 11) can be referred to for determining strength of dry-stack units.
Masonry compressive strength f’m can conservatively be based on the unit-strength method of the building code (ref . 15), or be determined by testing prisms in accordance with ASTM C1314 (ref. 4). Test prisms can be either grouted or ungrouted depending on the type of wall construction specified.
Because no mortar is used to resist flexural tension as for conventional masonry construction, flexural strength of mortarless masonry is developed through the grout, reinforcement or surface coating. For out-of-plane bending of solid grouted walls allowable flexural strength can be estimated based on flexural tensile strength of the grout per Equation 1.
Consideration should be given to the reduction in wall thickness at the bed joints when estimating geometrical properties of the net effective section.
Correspondingly, flexural strength based on masonry compressive stress should be checked, particularly for walls resisting significant gravity loads, using the unity equation as given below.
Buckling should also be checked. (Ref. 8)
In-Plane Shear Strength
Shear strength for out-of-plane bending is usually not a concern since flexural strength governs design for this case. For resistance to horizontal forces applied parallel to the plane of a wall, Equation 3 may be used to estimate allowable shear strength.
Fv is the allowable shear strength by the lesser of the three values given in Equation 4.
Grouted, Reinforced Construction
Mortarless masonry that is grouted and reinforced behaves much the same as for conventional reinforced and mortared construction. Because masonry tensile strength is neglected for mortared, reinforced construction, flexural mechanisms are essentially the same with or without the bed joints being mortared provided that the units subjected to compressive stress are in good contact. Thus, allowable stress design values can be determined using the same assumptions and requirements of the MSJC code. (ref.1)
Axial and flexural tensile stresses are assumed to be resisted entirely by the reinforcement. Strains in reinforcement and masonry compressive strains are assumed to vary linearly with their distance from the neutral axis. Stresses in reinforcement and masonry compressive stresses are assumed to vary linearly with strains. For purposes of estimating allowable flexural strengths, full bonding of reinforcement to grout are assumed such that strains in reinforcement are identical to those in the adjacent grout.
For out-of-plane loading where a single layer of vertical reinforcement is placed, allowable flexural strength can be estimated using the equations for conventional reinforcement with the lower value given by Equations 5 or 6.
In-Plane Shear Strength
Though the MSJC code recognizes reinforced masonry shear walls with no shear, or horizontal reinforcement, it is recommended that mortarless walls be rein- forced with both vertical and horizontal bars. In such case, allowable shear strength can be determined based on shear reinforcement provisions (ref. 1) with Equations 7, 8 and 9.
Where Fv is the masonry allowable shear stress per Equations 8 or 9.
Solid Grouted, Prestressed Construction
Mortarless masonry walls that are grouted and pre- stressed can be designed as unreinforced walls with the prestressing force acting to increase the vertical compres- sive stress. Grout can be used to increase the effective area of the wall. Flexural strength will be increased because of the increase in the fa term in Equation 1. Shear strength will be increased by the Nv term in Equation 4.
Because the prestressing force is a sustained force, creep effects must be considered in the masonry. Research on the long-term behavior of dry-stacked masonry by Marzahn and Konig (ref. 8) has shown that creep effects may be accentuated for mortarless masonry as a result of stress concentrations at the contact points of adjacent courses. Due to the roughness of the unit surfaces, high stress concentrations can result which can lead to higher non-proportional creep deformations. Thus, the creep coefficient was found to be dependent on the degree of roughness along bed-joint surfaces and the level of applied stress. As a result, larger losses in prestressing force is probable for dry-stack masonry.
Surface-Bonded Construction
Dry-stack walls with surface bonding develop their strength through the tensile strength of small fiberglass fibers in the 1/8” (3.8mm) thick troweled or surface bonded cement-plaster coating ASTM C-887(Ref. 14). Because no grouting is necessary, flexural tension and shear strength are developed through tensile resistance of fiberglass fibers applied to both surfaces of a wall. Test data has shown that surface bonding can result in a net flexural tension strength on the order of 300 psi.(2.07 MPa) Flexural capacity, based on this value, exceeds that for conventional, unreinforced mortared masonry construction, therefore it is considered conservative to apply the desired values of the code (ref. 1) for allowable flexural capacity for portland cement / lime type M for the full thickness of the face shell.
Out-of-Plane and In-Plane Flexural Strength
Surface-bonded walls can be considered as unreinforced and ungrouted walls with a net allowable flexural tensile strength based on the strength of the fiber-reinforcement. Flexural strength is developed by the face shells bonded by the mesh. Allowable flexural strength can be determined using Equation 1 with an Ft value determined on the basis of tests provided by the surface bonding cement supplier. Axial and flexural compressive stresses must also be checked per Equation 2 considering again only the face shells to resist stress.
Surface Bonded In-Plane Shear Strength
In-plane shear strength of surface-bonded walls is attributable to friction developed along the bed joints resulting from vertical compressive stress in addition to the diagonal tension strength of the fiber coating. If the enhancement in shear strength given by the fiber reinforced surface parging is equal to or greater than that provided by the mortar-unit bond in conventional masonry construction, then allowable shear strength values per the MSJC code (ref. 1) may be used. In such case, section properties used in Equation 3 should be based on the cross-section of the face shells.
Figure 3 – A Mortarless Garden Wall Application
Figure 4 – A Residential, Mortarless, Single-Family Basement – Part of a 520 Home Development
REFERENCES
Building Code Requirements for Masonry Structures), ACI 530-02/ ASCE 5-02/TMS 402-02. Reported by the Masonry Standards Joint Committee (MSJC), 2002.
Drysdale, R.G., Properties of Dry-Stack Block, Windsor, Ontario, July 1999.
Drysdale, R.G., Properties of Surface-Bonded Dry-Stack Block Construction, Windsor, Ontario, January 2000.
Drysdale, R.G., Racking Tests of Dry-Stack Block, Windsor, Ontario, October 2000.
Drysdale, R.G., Design and Construction Guide for Azar Dry-Stack Block Construction, JNE Consulting, Ltd., February 2001.
Grout for Concrete Masonry, TEK 09-04A, Concrete Masonry & Hardscapes Association, 2002.
2000 International Building Code, Falls Church, VA. International Code Council, 2000.
Marzahn, G. and G. Konig, Experimental Investigation of Long-Term Behavior of Dry-Stacked Masonry, Journal of The Masonry Society, December 2002, pp. 9-21.
Hybrid Concrete Masonry Construction Details, TEK 0303B. Concrete Masonry & Hardscapes Association, 2009.
Specification for Masonry Structures, ACI 530.1-02/ASCE 6-02/ TMS 602-02. Reported by the Masonry Standards Joint Committee (MSJC), 2002.
Standard Methods of Sampling and Testing Concrete Masonry Units, ASTM C140-02a, ASTM International, Inc. , Philadelphia, 2002.
Standard Method of Sampling and Testing Grout, ASTM C1019-02, ASTM International, Inc., Philadelphia, 2002.
Standard Specification for Grout for Masonry, ASTM C 476-02. ASTM International, Inc., 2002
Standard Specification for Packaged, Dry, Combined Materials for Surface Bonding Mortar, ASTM C 887-79a (2001). ASTM International, Inc., 2001.
Standard Test Method for Compressive Strength of Masonry Assem blages, ASTM C1314-02a, ASTM International, Inc., Philadelphia, 2002.
An net cross-sectional area of masonry, in² (mm²) As effective cross-sectional area of reinforcement, in2 (mm2) b width of section, in. (mm) d distance from extreme compression fiber centroid of tension reinforcement, in. (mm) Fa allowable compressive stress due to axial load only, psi (MPa) Fb allowable compressive stress due to ß exure only, psi (MPa) Fs allowable tensile or compressive stress in reinforcement, psi (MPa) Ft flexural tensile strength of the grout, psi(MPa) Fv allowable shear stress in masonry psi (MPa) fa calculated vertical compressive stress due to axial load, psi (MPa) fb calculated compressive stress in masonry due to ß exure only, psi (MPa) f’ specified compressive strength of masonry, psi (MPa) I moment of inertia in.4 (mm4) j ratio of distance between centroid of flexural compressive forces and centroid of tensile forces to depth, d k ratio of the distance between compression face of the wall and neu tral axis to the effective depth d M maximum moment at the section under consideration, in.-lb (N-mm) Nv compressive force acting normal to the shear surface, lb (N) Q first moment about the neutral axis of a section of that portion of the cross section lying between the neutral axis and extreme fiber in.³ (mm³) Sg section modulus of uncracked net section in.³ (mm³) V shear force, lb (N)
