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Evaluating Fire-Exposed Concrete Masonry Walls After a Fire

  • August 2018

INTRODUCTION

Fire safety requires that a wall not only halt the spread of fire from one area to another, but also retain its structural integrity throughout the fire and fire-fighting operations. If occupants, firefighters and building contents are to be fully protected, the structure must not collapse, add fuel to the fire nor emit toxic gases during the fire.

Concrete masonry fire walls provide maximum safety during and after severe fire exposure. Because concrete masonry is a noncombustible structural material which neither adds fuel to a fire nor emits toxic gases, it is widely used to provide compartmentation—containing a fire until it can be brought under control by fire fighters. In addition, even after severe fires, concrete masonry walls can typically be repaired by simply patching cracks and tuckpointing mortar joints, rather than requiring demolition and replacement. Experience with building fires has shown that the most damage to concrete masonry walls during a fire often occurs due to lost support rather than as a direct result of fire on the masonry.

This TEK provides general information on assessment methods and repair techniques and discusses what can be expected after concrete masonry walls have been subjected to fire.

EVALUATING FIRE-EXPOSED WALLS

Preliminary Inspection

After a fire occurs, a preliminary inspection should be conducted as soon as possible to assess: the condition of the structure, the type and severity of problems observed in the affected area(s), the feasibility of rehabilitation and the need for conducting a detailed investigation. After collecting data on the building structure and the fire event, the preliminary investigation should take place as soon as safe entry into the building can be arranged.

The first step in the preliminary investigation is a visual inspection of structural members in the fire-affected areas. Indications of cracking, spalling, deflections, distortions, misalignment of elements and/or exposure of steel reinforcement should be documented. Measurements of deflections, deformations and geometry can be taken of any suspect members for comparison to unexposed members in the same structure. These observations should be recorded, documenting the type of damage and its severity for each affected member. This summary helps identify damaged members in need of more detailed investigation, as well as the extent and nature of any necessary repairs.

As an adjunct to visually assessing the structural members in fire affected areas, the building contents in these areas should be observed. The melting points of various materials (see Table 1) indicate the temperature ranges that have occurred in localized areas, providing an estimate of the maximum temperatures achieved during the fire. These estimated maximum temperatures help establish the severity of the fire relative to the Standard Test Methods for Fire Tests of Building Construction and Materials, ASTM E 119 (ref. 2) fire test, or to another recognized baseline. If the maximum temperatures during the fire are similar to those of the E 119 test, the potential damage to the concrete masonry is somewhat predictable, based on the history of E 119 testing on concrete masonry.

The ASTM E 119 fire test time/temperature protocol is shown in Figure 1.

There is a large body of data on concrete masonry walls tested according to the ASTM E 119 protocol. This test method evaluates walls subjected to the standard test fire. Performance criteria include: resistance to temperature rise on the unexposed side of the wall; resistance to the passage of hot gases or flames through the wall; structural stability during the test; and resistance of the masonry to deterioration under direct exposure to a fire hose stream immediately following the fire test. Research has shown that the fire resistance ratings of concrete masonry walls are invariably determined by the temperature rise on the cold (unexposed) side of the wall.

Field Testing Procedures

Part of the preliminary inspection is determining the need for further testing and evaluation. Nondestructive field tests, such as the use of an impact rebound hammer, are typically not used with concrete masonry, as the hollow cells interfere with obtaining meaningful results in many cases. In addition, extensive field testing is not always prudent, as removal and replacement of the fire-damaged element can sometimes be more economical than extensive testing. A solid understanding of both structural engineering and the effects of fire on building materials is invaluable to this decision-making process. When necessary, destructive test methods can be used to assess the strength of the in-situ concrete masonry (see reference 3). However, nonuniform fire damage on opposite sides of the wall and corresponding strength differences can lead to unreliable results. In most cases, strength testing is unnecessary.

ASSESSING THE CONCRETE MASONRY

In general, structural concrete masonry without excessive deformations, deflections, misalignments or large extensive cracks can typically be repaired rather than replaced. When these types of conditions are present, it indicates that the member’s load-carrying capacity may be impaired, which would require removal and replacement of the suspect members.

Fire distress such as soot and smoke deposits, pitting of aggregates, hairline cracks, shallow spalling and other surface damage generally require only cosmetic repairs. The following sections provide some more detailed guidance on assessing various concrete masonry characteristics after a fire.

Cracks

Cracks wider than about 1/16 in. (1.6 mm) should be further investigated to determine the potential structural impact. When the reinforcing steel in conventionally-reinforced masonry has not been exposed, the load-carrying capacity of the wall can typically be assumed to be relatively unaffected (see also Exposed Reinforcement, below).

Mortar Joint Damage

Mortar joints often appear to be more affected by fire exposure than the adjacent surface of the masonry units. When concrete masonry walls are subjected to a fire hose immediately after fire exposure in ASTM E 119 testing, mortar in the dehydrated state is sometimes flushed out, typically to a depth of about 1/4 in. (6.7 mm). In actual fires, mortar joints subjected to the most severe fire exposures can become softened or chalky, although this damage is typically not deeper than about 3/4 in. (19 mm). However, this loss of mortar does not affect the load-carrying ability of the concrete masonry wall (ref. 4), so can most often be adequately repaired by tuckpointing.

Exposed Reinforcement

Reinforcement exposed during or after a fire must be evaluated for quenching, buckling and/or loss of prestress. The investigator must consider that any exposed steel may have been quenched during fire fighting operations. This rapid cooling causes a loss of ductility in the steel that can reduce the load-carrying capacity of the member. A visual inspection of any exposed structural reinforcement can help asses the potential structural damage. This assessment must be tied to the element under consideration: either a conventionally-reinforced wall or prestressed wall, as follows. In a conventionally-reinforced wall, local buckling of exposed reinforcing bars usually indicates that the steel has been directly exposed to fire. When steel is exposed to temperatures of 1,100 o F (593 o C) or higher, the bars lose about half of their yield strength and buckling occurs. If the bars are exposed but not buckled or otherwise deformed, spalling may have occurred after the fire exposure. In general, flexural reinforcement that is not visibly deformed is unlikely to have suffered significant permanent damage. Similarly, if the spalling does not expose the reinforcement, i.e. the cover protection remains intact, the wall strength is unlikely to be compromised.

In prestressed concrete masonry walls, on the other hand, significant loss of prestress can occur without any visible distress to exposed tendons. Therefore, for prestressed masonry, any exposed prestressing tendons should indicate the need for a more in-depth structural evaluation. Tendon buckling is rarely observed, as the tendon typically remains in tension, even with significant loss of prestress.

EFFECT OF FIRE EXPOSURE ON WALL STRENGTH—EXPERIMENTAL RESULTS

One effect of fire exposure, as determined by testing (ref. 4), was reduced wall compressive strength due to the gradual dehydration of the cement and, depending on the aggregate type, to the expansion and changes in the physical properties of the aggregate used in the concrete masonry units. Reductions in compressive strength for 8-in. (203-mm) units exposed to 3 to 3 1/2 hours of fire varied widely, resulting in maximum reductions of 50 percent for some types of concrete masonry units. Lightweight aggregates, manufactured by expanding certain minerals in a kiln, are stable under fire exposure, so minimize loss of strength. During testing, limestone aggregate concrete masonry units also showed substantial stability and minimized loss of strength after fire exposure (ref. 4). For the wide range of masonry units tested, the wall strength after fire exposure remained directly proportional to the concrete masonry unit compressive strength before fire exposure.

A number of 8-in. (203-mm) walls underwent 2 1/2 to 3 1/2 hours of fire exposure, were cooled, then subjected to another 2 1/2 hour fire before being tested for compressive strength. These results showed that these walls were able to carry the same, or slightly higher, loads as similar walls exposed once for three to four hours, as well as serving as an effective fire barrier during the second fire.

PREPAIRING FIRE-EXPOSED CONCRETE MASONRY

For fire-exposed concrete masonry free from large cracks or deflections, repairs should be minimal. Crack repair and mortar joint tuckpointing procedures and recommendations are covered in detail in Maintenance of Concrete Masonry Walls, TEK 08-01A (ref. 5). Recommended cleaning procedures are covered in Cleaning Concrete Masonry, TEK 08-04A (ref. 6).

SUMMARY

  • In conventionally-reinforced concrete masonry, if reinforcing steel is not exposed, there is little likelihood of structural damage.
  • Lintels and beams free from excessive deflections are unlikely to be structurally impaired.
  • Softening of the top surface of mortar results in little loss of load carrying capacity and can be easily repaired by tuckpointing.
  • Walls subjected to fire one time without structural damage can be expected to perform just as well in a second fire.
  • Field tests are typically not conducted to assess fire damaged concrete masonry walls. Post-fire investigation typically consists only of visual inspection.
  • If no severe distortion, cracking or displacement of concrete masonry walls is present, complete reinstatement of the wall can usually be accomplished by patching cracks and tuckpointing mortar joints.

REFERENCES

  1. Assessing the Condition and Repair Alternatives of Fire-Exposed Concrete and Masonry Members. National Codes and Standards Council of the Concrete and Masonry Industries, August, 1994.
  2. Standard Test Methods for Fire Tests of Building Construction and Materials, ASTM E 119-05. ASTM International, 2005.
  3. Evaluating Existing Concrete Masonry Construction, TEK 18-09A. Concrete Masonry & Hardscapes Association, 2003.
  4. Menzel, Carl A. Tests of the Fire Resistance and Strength of Walls of Concrete Masonry Units. Portland Cement Association, January, 1934.
  5. Maintenance of Concrete Masonry Walls, TEK 08-01A. Concrete Masonry & Hardscapes Association, 2004.
  6. Cleaning Concrete Masonry, TEK 08-04A. Concrete Masonry & Hardscapes Association, 2005.

Rolling Door Details for Concrete Masonry Construction

  • August 2018

INTRODUCTION

Openings in concrete masonry walls utilize lintels and beams to carry loads above the openings. When openings incorporate rolling doors (also referred to as overhead coiling doors or coiling doors), wind loads on the door are transferred to the surrounding masonry through the door guides and fasteners.

In some instances, the rolling doors have been designed for specific wind load applications, and are heavily dependent on the structural integrity of the door jamb members as they are attached to building walls at jamb locations. This TEK discusses the forces imposed on a surrounding concrete masonry wall by rolling doors, and includes recommended details for jamb construction. Lintel design, to carry the loads imposed on the top of the opening, are covered in Allowable Stress Design of Concrete Masonry Lintels and Precast Concrete Lintels for Concrete Masonry Construction (refs. 1, 2).

LOADS EXERTED BY ROLLING DOORS

Architects and building designers should determine the loads that rolling doors exert on the wall around the opening. Dead loads include the weight of the door curtain, counterbalance, hood, operator, etc., that is supported by the wall above the opening. Live loads result from wind that acts on the door curtain. Rolling doors are available with windlocks, which prevent the door curtain from leaving the guides due to wind loading. On doors without windlocks, the only wind load force that the curtain exerts on the guides is normal to the opening. For doors with windlocks, there is an additional load parallel to the opening (see Figures 1 and 2 for face-mounted and jambmounted doors, respectively). This load is the catenary tension that results when the curtain deflects sufficiently to allow the windlocks to engage the windbar in the guide. This force acts to pull the guides toward the center of the opening. The door is exposed to a additive wind loads, from both inside and outside the building.

Calculating the parallel force involves several variables, the most prominent of which are the width of the opening and the design wind load. It is also important to note that the door must withstand both positive and negative wind loads. Including these forces in the design of the jamb and its supporting structure can help prevent a jamb failure and allow the building to fully withstand its specified wind load requirements. The rolling door manufacturer can provide a guide data sheet for quantifying the loads imposed by the overhead coiling doors due to the design wind load.

The following conditions need to be considered:

  • The wall above the door opening must be designed to support the total hanging dead load. The face of wallmounted doors may extend above the opening for 12 to 30 in. (305-762 mm). The door guide wall angles must be mounted to the wall above the opening to support the door. When the door has a hood to cover the coiled door and counter-balance, some provision must be made to fasten the top of the hood and hood supports to the masonry wall. See also Fasteners for Concrete Masonry (ref.3).
  • Reinforcement in jambs is recommended to adequately distribute the forces imposed by the door.
  • Reinforcement locations should be planned such that the reinforcement does not interfere with expansion anchor placement.

ACCOMODATING MASONRY REINFORCEMENT AND DOOR FASTENERS

Rolling door contractors and installers sometimes encounter reinforcement in walls at locations where door jamb fasteners have been specified. Arbitrarily changing either the reinforcement location or the fastener location is not recommended, as either can negatively impact performance. Changing the door manufacturer’s recommended jamb fastener locations may reduce the structural performance of the rolling door or possibly void the fire rating.

The typical masonry jamb detail shown in Figure 3 indicates recommended vertical reinforcement locations for concrete masonry jambs to provide an area for the door fasteners. The detail shows a “reinforcement-free zone” to allow for fasteners of either face mounted or jamb-mounted rolling doors. The Door and Access Systems Manufacturers Association International (DASMA) recommends that vertical reinforcement should be within 2 in. (51 mm) of either corner of the wall at the jamb (ref. 4).

EXISTING CONSTRUCTION

Before installing fasteners in existing masonry construction, the following steps should be followed to locate the reinforcement, to avoid interference:

  • If structural drawings are available, the project engineer should review the drawings to determine whether or not the jamb reinforcement locations conflict with the specified door jamb fastener locations.
  • If the building’s structural plans are not available, either drill
    representative “pilot holes” or use a device similar to an electronic stud locator to determine the steel reinforcement locations.

Once the steel reinforcement has been located, if it is concluded that the reinforcement will interfere with installing jamb fasteners, DASMA recommends that one of the following courses of action be taken:

  1. Consider an alternate door jamb mounting or door size to assure that the reinforcement will not interfere with jamb fasteners.
  2. If an alternate door jamb mounting or alternate door size cannot be accomplished, consult a structural engineer to determine a workable solution. One possible solution is to contact the door manufacturer to obtain an alternate conforming hole pattern for the mounting, which would not interfere with the existing reinforcement. Another solution may be to bolt a steel angle to the concrete masonry jambs, which allows the door guides to then be welded or bolted to the steel angle.

FIRE-RATED ROLLING DOOR CONNECTIONS

When installed in a fire-rated concrete masonry wall, rolling steel fire doors must meet the code-required fire rating corresponding to the fire rating of the surrounding wall. For fire testing, the doors are mounted on the jambs of a concrete masonry wall intended to replicate field construction. The fire door guides must remain securely fastened to the jambs and no “through gaps” may occur in the door assembly during the test. Figure 4 shows a representative jamb construction and guide attachment details for a four-hour fire rated assembly. Note that guide configurations and approved jamb construction will vary with individual fire door manufacturer’s listings. Consult with individual manufacturers for specific guide details and approved jamb constructions.

REFERENCES

  1. Allowable Stress Design of Concrete Masonry Lintels
    Based on 2012 IBC/2011 MSJC, TEK 17-01D, Concrete
    Masonry & Hardscapes Association, 2011.
  2. Precast Concrete Lintels for Concrete Masonry
    Construction, TEK 17-02A, Concrete Masonry &
    Hardscapes Association, 2000.
  3. Fasteners for Concrete Masonry, TEK 12-05, Concrete
    Masonry & Hardscapes Association, 2005.
  4. Metal Coiling Type Door Jamb Construction: Steel
    Reinforcement In Masonry Walls, TDS-259. Door and
    Access Systems Manufacturers Association International,
    2005.
  5. Architects and Designers Should Understand Loads
    Exerted By Overhead Coiling Doors, TDS-251. Door and
    Access Systems Manufacturers Association International,
    2005.
  6. International Building Code 2003. International Code
    Council, 2003.
  7. International Building Code 2006. International Code
    Council, 2006.
  8. Common Jamb Construction for Rolling Steel Fire Doors:
    Masonry Construction—Bolted and Welded Guides, TDS-
  9. Door and Access Systems Manufacturers Association
    International, 2005.
  10. Steel Reinforcement for Concrete Masonry, TEK 12-04D,
    Concrete Masonry & Hardscapes Association, 2006.

Grouting Concrete Masonry Walls

  • August 2018

INTRODUCTION

Grouted concrete masonry construction offers design flexibility through the use of partially or fully grouted walls, whether plain or reinforced. The industry is experiencing fast-paced advances in grouting procedures and materials as building codes allow new opportunities to explore means and methods for constructing grouted masonry walls.

Grout is a mixture of: cementitious material (usually portland cement); aggregate; enough water to cause the mixture to flow readily and without segregation into cores or cavities in the masonry; and sometimes admixtures. Grout is used to give added strength to both reinforced and unreinforced concrete masonry walls by grouting either some or all of the cores. It is also used to fill bond beams and occasionally to fill the collar joint of a multi-wythe wall. Grout may also be added to increase the wall’s fire rating, acoustic effectiveness termite resistance, blast resistance, heat capacity or anchorage capabilities. Grout may also be used to stabilize screen walls and other landscape elements.

In reinforced masonry, grout bonds the masonry units and reinforcing steel so that they act together to resist imposed loads. In partially grouted walls, grout is placed only in wall spaces containing steel reinforcement. When all cores, with or without reinforcement, are grouted, the wall is considered solidly grouted. If vertical reinforcement is spaced close together and/or there are a significant number of bond beams within the wall, it may be faster and more economical to solidly grout the wall.

Specifications for grout, sampling and testing procedures, and information on admixtures are covered in CMHA TEK 09-04A, Grout for Concrete Masonry (ref. 1). This TEK covers methods for laying the units, placing steel reinforcement and grouting.

WALL CONSTRUCTION

Figure 1 shows the basic components of a typical reinforced concrete masonry wall. When walls will be grouted, concrete masonry units must be laid up so that vertical cores are aligned to form an unobstructed, continuous series of vertical spaces within the wall.

Head and bed joints must be filled with mortar for the full thickness of the face shell. If the wall will be partially grouted, those webs adjacent to the cores to be grouted are mortared to confine the grout flow. If the wall will be solidly grouted, the cross webs need not be mortared since the grout flows laterally, filling all spaces. In certain instances, full head joint mortaring should also be considered when solid grouting since it is unlikely that grout will fill the space between head joints that are only mortared the width of the face shell, i.e., when penetration resistance is a concern such as storm shelters and prison walls. In cases such as those, open end or open core units (see Figure 3) should be considered as there is no space between end webs with these types of units.

Care should be taken to prevent excess mortar from extruding into the grout space. Mortar that projects more than ½ in. (13 mm) into the grout space must be removed (ref. 3). This is because large protrusions can restrict the flow of grout, which will tend to bridge at these locations potentially causing incomplete filling of the grout space. To prevent bridging, grout slump is required to be between 8 and 11 in. (203 to 279 mm) (refs. 2, 3) at the time of placement. This slump may be adjusted under certain conditions such as hot or cold weather installation, low absorption units or other project specific conditions. Approval should be obtained before adjusting the slump outside the requirements. Using the grout demonstration panel option in Specification for Masonry Structures (ref. 3) is an excellent way to demonstrate the acceptability of an alternate grout slump. See the Grout Demonstration Panel section of this TEK for further information.

At the footing, mortar bedding under the first course of block to be grouted should permit grout to come into direct contact with the foundation or bearing surface. If foundation dowels are present, they should align with the cores of the masonry units. If a dowel interferes with the placement of the units, it may be bent a maximum of 1 in. (25 mm) horizontally for every 6 in. (152 mm) vertically (see Figure 2). When walls will be solidly grouted, saw cutting or chipping away a portion of the web to better accommodate the dowel may also be acceptable. If there is a substantial dowel alignment problem, the project engineer must be notified.

Vertical reinforcing steel may be placed before the blocks are laid, or after laying is completed. If reinforcement is placed prior to laying block, the use of open-end A or H- shaped units will allow the units to be easily placed around the reinforcing steel (see Figure 3). When reinforcement is placed after wall erection, reinforcing steel positioners or other adequate devices to hold the reinforcement in place are commonly used, but not required. However, it is required that both horizontal and vertical reinforcement be located within tolerances and secured to prevent displacement during grouting (ref. 3). Laps are made at the end of grout pours and any time the bar has to be spliced. The length of lap splices should be shown on the project drawings. On occasion there may be locations in the structure where splices are prohibited. Those locations are to be clearly marked on the drawing.

Reinforcement can be spliced by either contact or noncontact splices. Noncontact lap splices may be spaced as far apart as one-fifth the required length of the lap but not more than 8 in. (203 mm) per Building Code Requirements for Masonry Structures (ref. 4). This provision accommodates construction interference during installation as well as misplaced dowels. Splices are not required to be tied, however tying is often used as a means to hold bars in place.

As the wall is constructed, horizontal reinforcement can be placed in bond beam or lintel units. If the wall will not be solidly grouted, the grout may be confined within the desired grout area either by using solid bottom masonry bond beam units or by placing plastic or metal screening, expanded metal lath or other approved material in the horizontal bed joint before laying the mortar and units being used to construct the bond beam. Roofing felt or materials that break the bond between the masonry units and mortar should not be used for grout stops.

Figure 1—Typical Reinforced Concrete Masonry Wall Section
Figure 2—Foundation Dowel Clearance
Figure 3—Concrete Masonry Units for Reinforced Construction

CONCRETE MASONRY UNITS AND REINFORCING BARS

Standard two-core concrete masonry units can be effectively reinforced when lap splices are not long, since the mason must lift the units over any vertical reinforcing bars that extend above the previously installed masonry. The concrete masonry units illustrated in Figure 3 are examples of shapes that have been developed specifically to accommodate reinforcement. Open-ended units allow the units to be placed around reinforcing bars. This eliminates the need to thread units over the top of the reinforcing bar. Horizontal reinforcement in concrete masonry walls can be accommodated either by saw-cutting webs out of a standard unit or by using bond beam units. Bond beam units are manufactured with either reduced webs or with “knock-out” webs, which are removed prior to placement in the wall. Pilaster and column units are used to accommodate a wall- column or wall-pilaster interface, allowing space for vertical reinforcement and ties, if necessary, in the hollow center.

Concrete masonry units should meet applicable ASTM standards and should typically be stored on pallets to prevent excessive dirt and water from contaminating the units. The units may also need to be covered to protect them from rain and snow.

The primary structural reinforcement used in concrete masonry is deformed steel bars. Reinforcing bars must be of the specified diameter, type and grade to assure compliance with the contract documents. See Steel Reinforcement for Concrete Masonry, TEK 12-04D for more information (ref. 6). Shop drawings may be required before installation can begin.

Light rust, mill scale or a combination of both need not be removed from the reinforcement. Mud, oil, heavy rust and other materials which adversely affect bond must be removed however. The dimensions and weights (including heights of deformations) of a cleaned bar cannot be less than those required by the ASTM specification.

GROUT PLACEMENT

To understand grout placement, the difference between a grout lift and a grout pour needs to be understood. A lift is the amount of grout placed in a single continuous operation. A pour is the entire height of masonry to be grouted prior to the construction of additional masonry. A pour may be composed of one lift or a number of successively placed grout lifts, as illustrated in Figure 4.

Historically, only two grout placement procedures have been in general use: (l) where the wall is constructed to pour heights up to 5 ft (1,520 mm) without cleanouts—generally termed “low lift grouting;” and (2) where the wall is constructed to a maximum pour height of 24 ft (7,320 mm) with required cleanouts and lifts are placed in increments of 5 ft (1,520 mm)—generally termed “high lift grouting.” With the advent of the 2002 Specification for Masonry Structures (ref. 5), a third option became available – grout demonstration panels. The 2005 Specification for Masonry Structures (ref. 3) offers an additional option: to increase the grout lift height to 12 ft-8 in. (3,860 mm) under the following conditions:

  1. the masonry has cured for at least 4 hours,
  2. grout slump is maintained between 10 and 11 in. (245 and 279 mm), and
  3. no intermediate reinforced bond beams are placed between the top and the bottom of the pour height.

Through the use of a grout demonstration panel, lift heights in excess of the 12 ft-8 in. (3,860 mm) limitation may be permitted if the results of the demonstration show that the completed grout installation is not adversely affected. Written approval is also required.

These advances permit more efficient installation and construction options for grouted concrete masonry walls (see Figure 4).

Figure 4—Comparison of Grouting Methods for a 12 ft-8 in. (3,860 mm) High Concrete Masonry Wall
Grouting Without Cleanouts—”Low-Lift Grouting”

Grout installation without cleanouts is sometimes called low-lift grouting. While the term is not found in codes or standards, it is common industry language to describe the process of constructing walls in shorter segments, without the requirements for cleanout openings, special concrete block shapes or equipment. The wall is built to scaffold height or to a bond beam course, to a maximum of 5 ft (1,520 mm). Steel reinforcing bars and other embedded items are then placed in the designated locations and the cells are grouted. Although not a code requirement, it is considered good practice (for all lifts except the final) to stop the level of the grout being placed approximately 1 in. (25 mm) below the top bed joint to help provide some mechanical keying action and water penetration resistance. Further, this is needed only when a cold joint is formed between the lifts and only in areas that will be receiving additional grout. Steel reinforcement should project above the top of the pour for sufficient height to provide for the minimum required lap splice, except at the top of the finished wall.

Grout is to be placed within 1 ½ hours from the initial introduction of water and prior to initial set (ref. 3). Care should be taken to minimize grout splatter on reinforcement, on finished masonry unit faces or into cores not immediately being grouted. Small amounts of grout can be placed by hand with buckets. Larger quantities should be placed by grout pumps, grout buckets equipped with chutes or other mechanical means designed to move large volumes of grout without segregation.

Grout must be consolidated either by vibration or puddling immediately after placement to help ensure complete filling of the grout space. Puddling is allowed for grout pours of 12 in. (305 mm) or less. For higher pour heights, mechanical vibration is required and reconsolidation is also required. See the section titled Consolidation and Reconsolidation in this TEK.

Grouting With Cleanouts—”High-Lift Grouting”

Many times it is advantageous to build the masonry wall to full height before grouting rather than building it in 5 ft (1,520 mm) increments as described above. With the installation of cleanouts this can be done. Typically called high-lift grouting within the industry, grouting with cleanouts permits the wall to be laid up to story height or to the maximum pour height shown in Table 1 prior to the installation of reinforcement and grout. (Note that in Table 1, the maximum area of vertical reinforcement does not include the area at lap splices.) High lift grouting offers certain advantages, especially on larger projects. One advantage is that a larger volume of grout can be placed at one time, thereby increasing the overall speed of construction. A second advantage is that high-lift grouting can permit constructing masonry to the full story height before placing vertical reinforcement and grout. Less reinforcement is used for splices and the location of the reinforcement can be easily checked by the inspector prior to grouting. Bracing may be required during construction. See Bracing Concrete Masonry Walls During Construction, TEK 03-04C (ref. 7) for further information.

Cleanout openings must be made in the face shells of the bottom course of units at the location of the grout pour. The openings must be large enough to allow debris to be removed from the space to be grouted. For example, Specification for Masonry Structures (ref. 3) requires a minimum opening dimension of 3 in. (76 mm).

Cleanouts must be located at the bottom of all cores containing dowels or vertical reinforcement and at a maximum of 32 in. (813 mm) on center (horizontal measurement) for solidly grouted walls. Face shells are removed either by cutting or use of special scored units which permit easy removal of part of the face shell for cleanout openings (see Figure 5). When the cleanout opening is to be exposed in the finished wall, it may be desirable to remove the entire face shell of the unit, so that it may be replaced in whole to better conceal the opening. At flashing where reduced thickness units are used as shown in Figure 1, the exterior unit can be left out until after the masonry wall is laid up. Then after cleaning the cell, the unit is mortared in which allowed enough time to gain enough strength to prevent blowout prior to placing the grout.

Proper preparation of the grout space before grouting is very important. After laying masonry units, mortar droppings and projections larger than ½ in. (13 mm) must be removed from the masonry walls, reinforcement and foundation or bearing surface. Debris may be removed using an air hose or by sweeping out through the cleanouts.

The grout spaces should be checked by the inspector for cleanliness and reinforcement position before the cleanouts are closed. Cleanout openings may be sealed by mortaring the original face shell or section of face shell, or by blocking the openings to allow grouting to the finish plane of the wall. Face shell plugs should be adequately braced to resist fluid grout pressure.

It may be advisable to delay grouting until the mortar has been allowed to cure, in order to prevent horizontal movement (blowout) of the wall during grouting. When using the increased grout lift height provided for in Article 3.5 D of Specification for Masonry Structures (ref 3), the masonry is required to cure for a minimum of 4 hours prior to grouting for this reason.

Table 1—Grout Space Requirements (ref. 3)
Figure 5—Unit Scored to Permit Removal of Part of Face Shell for Cleanout
Consolidation and Reconsolidation

An important factor mentioned in both grouting procedures is consolidation. Consolidation eliminates voids, helping to ensure complete grout fill and good bond in the masonry system.

As the water from the grout mixture is absorbed into the masonry, small voids may form and the grout column may settle. Reconsolidation acts to remove these small voids and should generally be done between 3 and 10 minutes after grout placement. The timing depends on the water absorption rate, which varies with such factors as temperature, absorptive properties of the masonry units and the presence of water repellent admixtures in the units. It is important to reconsolidate after the initial absorption has taken place and before the grout loses its plasticity. If conditions permit and grout pours are so timed, consolidation of a lift and reconsolidation of the lift below may be done at the same time by extending the vibrator through the top lift and into the one below. The top lift is reconsolidated after the required waiting period and then filled with grout to replace any void left by settlement.

A mechanical vibrator is normally used for consolidation and reconsolidation—generally low velocity with a ¾ in. to 1 in. (19 to 25 mm) head. This “pencil head” vibrator is activated for a few seconds in each grouted cell. Although not addressed by the code, recent research (ref. 8) has demonstrated adequate consolidation by vibrating the top 8 ft (2,440 mm) of a grout lift, relying on head pressure to consolidate the grout below. The vibrator should be withdrawn slowly enough while on to allow the grout to close up the space that was occupied by the vibrator. When double open- end units are used, one cell is considered to be formed by the two open ends placed together. When grouting between wythes, the vibrator is placed at points spaced 12 to 16 in. (305 to 406 mm) apart. Excess vibration may blow out the face shells or may separate wythes when grouting between wythes and can also cause grout segregation.

GROUT DEMONSTRATION PANEL

Specification for Masonry Structures (ref. 3) contains a provision for “alternate grout placement” procedures when means and methods other than those prescribed in the document are proposed. The most common of these include increases in lift height, reduced or increased grout slumps, minimization of reconsolidation, puddling and innovative consolidation techniques. Grout demonstration panels have been used to allow placement of a significant amount of a relatively new product called self-consolidating grout to be used in many parts of the country with outstanding results. 

Research has demonstrated comparable or superior performance when compared with consolidated and reconsolidated conventional grout in regard to reduction of voids, compressive strength and bond to masonry face shells. Construction and approval of a grout demonstration panel using the proposed grouting procedures, construction techniques and grout space geometry is required. With the advent of self-consolidating grouts and other innovative consolidation techniques, this provision of the Specification has been very useful in demonstrating the effectiveness of alternate grouting procedures to the architect/engineer and building official.

COLD WEATHER PROTECTION

Protection is required when the minimum daily temperature during construction of grouted masonry is o o expected to fall below 40 F (4.4 C). Grouted masonry requires special consideration because of the higher water content and potential disruptive expansion that can occur if that water freezes. Therefore, grouted masonry requires protection for longer periods than ungrouted masonry to allow the water to dissipate. For more detailed information on cold, hot, and wet weather protection, see All-Weather Concrete Masonry Construction, TEK 03-01C (ref. 9).

REFERENCES

  1. Grout for Concrete Masonry, TEK 09-04A. Concrete Masonry & Hardscapes Association, 2005.
  2. Standard Specification for Grout for Masonry, ASTM C 476-02, ASTM International, 2005.
  3. Specification for Masonry Structures, ACI 530.1-05/ ASCE 6-05/TMS 602-05. Reported by the Masonry Standards Joint Committee, 2005.
  4. Building Code Requirements for Masonry Structures, ACI 530-05/ASCE 5-05/TMS 402-05. Reported by the Masonry Standards Joint Committee, 2005.
  5. Specification for Masonry Structures, ACI 530.1-02/ ASCE 6-02/TMS 602-02. Reported by the Masonry Standards Joint Committee, 2002.