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Estimating Concrete Masonry Materials

  • August 2018

INTRODUCTION

Estimating the quantity or volume of materials used in a typical masonry project can range from the relatively simple task associated with an unreinforced single wythe garden wall, to the comparatively difficult undertaking of a partially grouted multi-wythe wall coliseum constructed of varying unit sizes, shapes, and configurations.

Large projects, due to their complexity in layout and detailing, often require detailed computer estimating programs or an intimate knowledge of the project to achieve a reasonable estimate of the materials required for construction. However, for smaller projects, or as a general means of obtaining ballpark estimates, the rule of thumb methods described in this TEK provide a practical means of determining the quantity of materials required for a specific masonry construction project.

It should be stressed that the information for estimating materials quantities in this section should be used with caution and checked against rational judgment. Design issues such as non-modular layouts or numerous returns and corners can significantly increase the number of units and the volume of mortar or grout required. Often, material estimating is best left to an experienced professional who has developed a second hand disposition for estimating masonry material requirements.

ESTIMATING CONCRETE MASONRY UNITS

Probably the most straightforward material to estimate for most masonry construction projects is the units themselves. The most direct means of determining the number of concrete masonry units needed for any project is to simply determine the total square footage of each wall and divide by the surface area provided by a single unit specified for the project.

For conventional units having nominal heights of 8 in. (203 mm) and nominal lengths of 16 in. (406 mm), the exposed surface area of a single unit in the wall is 8/9 ft2 (0.083 m 2). Including a 5 percent allowance for waste and breakage, this translates to 119 units per 100 ft2 (9.29 m2) of wall area. (See Table 1 for these and other values.) Because this method of determining the necessary number of concrete masonry units for a given project is independent of the unit width, it can be applied to estimating the number of units required regardless of their width.

When using this estimating method, the area of windows, doors and other wall openings needs to be subtracted from the total wall area to yield the net masonry surface. Similarly, if varying unit configurations, such as pilaster units, corner units or bond beam units are to be incorporated into the project, the number of units used in these applications need to be calculated separately and subtracted from the total number of units required.

ESTIMATING MORTAR MATERIALS

Next to grout, mortar is probably the most commonly misestimated masonry construction material. Variables such as site batching versus pre-bagged mortar, mortar proportions, construction conditions, unit tolerances and work stoppages, combined with numerous other variables can lead to large deviations in the quantity of mortar required for comparable jobs.

As such, masons have developed general rules of thumb for estimating the quantity of mortar required to lay concrete masonry units. These general guidelines are as follows for various mortar types. Note that the following estimates assume the concrete masonry units are laid with face shell mortar bedding; hence, the estimates are independent of the concrete masonry unit width.

Masonry cement mortar
Masonry cement is typically available in bag weights of 70, 75 or 80 lb (31.8, 34.0 and 36.3 kg), although other weights may be available as well. One 70 lb (31.8 kg) bag of masonry cement will generally lay approximately 30 hollow units if face shell bedding is used. For common batching proportions, 1 ton (2,000 lb, 907 kg) of masonry sand is required for every 8 bags of masonry cement. If more than 3 tons (2,721 kg) of sand is used, add 1/2 ton (454 kg) to account for waste. For smaller sand amounts, simply round up to account for waste. This equates to about 240 concrete masonry units per ton of sand.

Preblended mortar
Preblended mortar mixes may contain portland cement and lime, masonry cement or mortar cement, and will always include dried masonry sand. Packaged dry, the mortars typically are available in 60 to 80 lb (27.2 to 36.3 kg) bags or in bulk volumes of 2,000 and 3,000 lb (907 and 1,361 kg).

Portland cement lime mortar
One 94 lb (42.6 kg) bag of portland cement, mixed in proportion with sand and lime to yield a lean Type S or rich Type N mortar, will lay approximately 62 hollow units if face shell bedding is used. This assumes a proportion of one 94 lb (42.6 kg) bag of portland cement to approximately one-half of a 50 lb (22.7 kg) bag hydrated lime to 4 1/4 ft3 (0.12 m3) of sand. For ease of measuring in the field, sand volumes are often correlated to an equivalent number of shovels using a cubic foot (0.03 m3) box, as shown in Figure 1.

ESTIMATING GROUT

The quantity of grout required on a specific job can vary greatly depending upon the specific circumstances of the project. The properties and configuration of the units used in construction can have a huge impact alone. For example, units of low density concrete tend to absorb more water from the mix than comparable units of higher density. Further, the method of delivering grout to a masonry wall (pumping versus bucketing) can introduce different amounts of waste. Although the absolute volume of grout waste seen on a large project may be larger than a comparable small project, smaller projects may experience a larger percentage of grout waste.

Table 3 provides guidance for the required volume of grout necessary to fill the vertical cells of walls of varying thickness. Additional grout may be necessary for horizontally grouting discrete courses of masonry. Note that walls constructed of 4-in. (102-mm) masonry units are not included in Table 3. Due to the small cell size and difficulty inadequately placing and consolidating the grout, it is not recommended to grout conventional 4-in. (102-mm) units.

Tables 4 and 5 contain estimated yields for bagged preblended grouts for vertical and horizontal grouting, respectively.

REFERENCES

  1. Kreh, D. Building With Masonry, Brick, Block and Concrete. The Taunton Press, 1998.
  2. Annotated Design and Construction Details for Concrete Masonry, CMU-MAN-001-03, Concrete Masonry & Hardscapes Association, 2003.

Construction of Reinforced Concrete Masonry Diaphragm Walls

  • August 2018

INTRODUCTION

Diaphragm walls are composed of two wythes of masonry with a large cavity or void. The wythes are bonded together with masonry ribs or crosswalls in such a way that, structurally, the wythes function compositely—as though the entire thickness is effectively solid.

Figure 1 shows a stone-clad university building with reinforced concrete masonry diaphragm walls, used to recreate the campus’ Gothic architecture. The use of reinforced diaphragm walls allowed support of the tall sidewalls and gable ends.

Figure 2 shows a cross-section of a typical diaphragm wall. The reinforced wythes can be fully or partially grouted. The exterior face can be constructed with a weathering face, like a conventional single wythe wall, or finished with a veneer. The voids can be used for placement of utilities and/or insulation.

This TEK discusses construction considerations for diaphragm walls: TEK 14-24, Design of Reinforced Concrete Masonry Diaphragm Walls, (ref. 1) covers the structural design.

CONSTRUCTION ADVANTAGES

Reinforced diaphragm walls present several construction benefits. These include:

  1. As shown in Figure 1, thick walls can be created efficiently using standard units bonded together. Thicker walls can be used to create taller walls.
  2. The wall can have exposed finished surfaces both inside and out. In addition, those finishes can be different because they are created by two different masonry wythes and can, therefore, feature different unit types/sizes/colors.
  3. The wall construction proceeds very much as conventional single wythe or cavity wall construction.
  4. The exterior wythe can be constructed with a veneer.
  5. The large interior voids allow for easy placement of utilities and/or insulation.

KEY CONSTRUCTION FEATURES

Construction Sequence

The construction sequence for diaphragm walls can vary based upon how the ribs are interconnected with the two wythes. Building Code Requirements for Masonry Structures (ref. 2), referred to as TMS 402, Section 5.1.1.2.5 provides three methods for connecting intersecting walls to allow shear transfer:

  1. At least fifty percent of the masonry units at the interface must interlock. This means the ribs could be constructed in running bond with every other course interlocking with the wythes. Thus, the wythes and the ribs would be constructed concurrently.
  2. Walls must be anchored by steel connectors grouted into the wall and meeting the following requirements: (a) Minimum size: 1/4 in. x 1-1/2 in. x 28 in. (6.4 x 38.1 x 711 mm) including 2-in. (50.8-mm) long, 90-degree bend at each end to form a U or Z-shape. (b) Maximum spacing: 48 in. (1,219 mm). Thus, it is possible to build the ribs separately from the wythes, which provides significant flexibility in construction.
  3. Intersecting reinforced bond beams must be provided at a maximum spacing of 48 in. (1,219 mm) on center. The area of reinforcement in each bond beam must be not less than 0.1 in.2 per ft (211 mm2/m) multiplied by the vertical spacing of the bond beams in feet (meters). Reinforcement must be developed on each side of the intersection.

Again, this provides flexibility in sequencing the wall construction. However, the grouting must be done simultaneously with the wythe construction.

Masonry Bond

TMS 402 Section 5.1.1.2.1 requires that the masonry at intersecting walls be laid in running bond for composite action between wythes to be effective. This requirement controls the entire construction of a diaphragm wall and mandates running bond for both the wythes and the ribs.

Reinforcement

Vertical reinforcement is typically placed in the cells of the wythes as is done in single-wythe construction. Posttensioning can be placed either in the cells of the wythes or within the void itself. If placed within the void and laterally restrained tendons are specified, tendon restraints must be fabricated. TEK 03-14, Post-Tensioned Concrete Masonry Wall Construction (ref. 3) provides a more detailed overview. Depending on the project’s seismic and/or loading requirements, horizontal reinforcement can be placed in either grouted bond beams or in the bed joints of the wythes and ribs. Horizontal bond beams are beneficial in that they can also serve as the interlock between the ribs and wythes, as well as shear reinforcement for the ribs.

Ribs (Crosswalls)

The structural design will determine whether or not the ribs require vertical reinforcement. The interlock with the wythes transfers shear forces across the intersections, and the vertical reinforcement in the wythes acts as the total wall reinforcement.

Wall Grouting

The requirement for full or partial wall grouting is a design decision. Any cells or bond beams with reinforcement must be grouted. The need for additional grouting is determined based on the design requirements. Both low-lift and high-lift grouting techniques are suitable to diaphragm walls. See TEK 03-02A, Grouting Concrete Masonry Walls, (ref. 4) for more detailed information.

Water Management

Strategies for water penetration resistance of conventional masonry walls depend on whether the wall is singlewythe or a cavity wall. Water penetration resistance for the exterior wythe of a diaphragm wall follows the strategies employed for single wythe construction. If the exterior wythe has a veneer and cavity, it is flashed and weeped the same way as a single wythe masonry cavity wall. With no veneer and cavity, the exterior wythe of a diaphragm wall is flashed and weeped the same way as a similarly constructed partially grouted single wythe wall. Flashing and weeps are not necessary if the exterior wythe is solid grouted.

Figure 3 shows a typical wall base detail for a diaphragm wall with an exterior veneer and cavity. The cavity between the exterior diaphragm wythe may contain insulation and an air/moisture barrier, as required. The veneer is anchored to the exterior wythe of the diaphragm wall and is weeped and flashed. TEK 19-05A, Flashing Details for Concrete Masonry Walls, (ref. 6) provides additional details applicable to this construction.

Figure 4 shows a wall base detail applicable to an exterior diaphragm wythe without a cavity and veneer. TEK 19-02B, Design for Dry Single Wythe Concrete Masonry Walls, (ref. 7) provides additional details for single wythe construction.

Openings through diaphragm walls, roof/floor intersections, etc. are also flashed and weeped similar to conventional concrete masonry walls.

Top of the Wall

Diaphragm walls require closure at the top to transfer vertical loads and close off the void. Figure 5 shows one common detail for capping the walls. The cast-in-place capping slab at the top takes the place of what would normally be bond beams in single-wythe walls. For post tensioned walls, the top slab provides a convenient anchorage point for the tendons.

Utilities and Insulation

The voids offer several opportunities not common in masonry walls. They provide chases for duct work and utilities with minimal cutting of the units and allow for additional insulation if desired. Diaphragm walls can be insulated on the exterior, by using a veneer and insulated cavity, or by using an exterior insulation system. They can also be insulated on the interior, using furring, insulation and gypsum wallboard. When insulation is placed in the voids, however, the ribs produce a large thermal bridge, reducing the effectiveness of the insulation. 06-11A, Insulating Concrete Masonry Walls, (ref. 5) provides more detailed information.

Openings

Constructing openings in diaphragm walls is also very similar to single-wythe walls (see Figure 6). The entire void should be spanned/filled at the opening and the exterior wythe flashed above (as appropriate), as shown in Figure 4. Figure 6 Option 1 shows a reinforced concrete slab that has been designed as a header for the opening. Figure 6 Option 2 has lintels to support the wythes over the opening. The void at the headers and sills is infilled with a nonmasonry material, such as exterior gypsum sheathing. The jambs should be infilled with masonry wherever they don’t already align with the ribs. Note that Figure 6 does not show flashing that may be necessary.

Control Joints

Control joints are provided in concrete masonry walls to control cracking primarily from movement due to shrinkage and thermal effects. In diaphragm walls, the ribs will tend to restrict some of that movement, however, because there is currently no research to quantify these effects, current practice is to place control joints at intervals based upon CMU-TEC-009-23, Crack Control Strategies for Concrete Masonry Construction, (ref. 8). TEK 14-24 discusses these criteria and provides an example for determining control joint spacing for a diaphragm wall.

Although the inner wythe will generally be exposed principally to shrinkage with only minor thermal effects, it is common to place control joints in the same locations and to provide similar shrinkage reinforcement in both wythes.

Figure 7 shows two methods of creating control joints in a diaphragm wall. Option 1, with ribs on both sides of the control joint, does a better job keeping water out of the void than Option 2 because a failure of the sealant would allow water to penetrate between the ribs, rather than into the void itself. The control joints in both wythes should be sealed for water protection.

CMU-TEC-009-23 contains additional control joint constructions/details that can also be used on diaphragm walls, including fire-rated joints and control joints that allow shear transfer.

SUMMARY

Diaphragm walls provide several beneficial features and are applicable to a wide variety of projects. Constructing reinforced concrete masonry diaphragm walls uses methods and techniques commonly known to most masons. The added thickness of the wall provides some variations in the overall reinforcement and layout concepts but the techniques are typical for masonry.

REFERENCES

  1. Design of Reinforced Concrete Masonry Diaphragm Walls, TEK 14-24. Concrete Masonry & Hardscapes Association, 2014.
  2. Building Code Requirements for Masonry Structures, TMS 402-16, Reported by The Masonry Society 2016.
  3. Post-Tensioned Concrete Masonry Wall Construction, TEK 03-14. Concrete Masonry & Hardscapes Association, 2002.
  4. Grouting Concrete Masonry Walls, TEK 03-2A. Concrete Masonry & Hardscapes Association, 2005.
  5. Insulating Concrete Masonry Walls, TEK 06-11A. Concrete Masonry & Hardscapes Association, 2010.
  6. Flashing Details for Concrete Masonry Walls, TEK 19-05A.
    Concrete Masonry & Hardscapes Association, 2008.
  7. Design for Dry Single Wythe Concrete Masonry Walls, TEK 19-02B. Concrete Masonry & Hardscapes Association, 2012.
  8. Crack Control Strategies for Concrete Masonry Construction, CMU-TEC-009-23, Concrete Masonry & Hardscapes Association, 2023.