What are Masonry units?

Concrete masonry is among the most surplus building materials present since a wide range of aspects can be accomplished using Concrete Masonry Units (CMU) as they have more benefits than stone or brick masonry. CMU are manufactured in a variety of shapes, colors, sizes, and patterns for various functions and finishing. Due to their modular properties, different CMU can be mixed in the same wall for various textures, colors, and so on. For the formation of the concrete blocks, cement, aggregate, and water are required.

The compressive strength of concrete masonry block and masonry walls alters from 6.9 MPa to 34.5 MPa roughly. ASTM C-90-91 contains the requirements for the compressive strength of concrete masonry blocks. The cement-aggregate ratio is 1:6 with 60% fine aggregate and 40% coarse aggregate. Definite concrete masonry sizes and shapes are Standard CMU, while others are famous only in selected areas. Local manufacturers can produce detailed information on custom products and units.

Unit sizes

Typically, CMU have face dimensions of 8 inches by 16 inches and are available in thicknesses of 4, 6, 8, 10, 12, 14, and 16 inches. Certain actual dimensions of CMU are usually 3/8 inch lesser than the nominal dimensions for maintaining enough space for mortar joints. Along with these standard sizes, other-dimensional properties and characteristics of CMUs are readily accessible from local concrete masonry generators and distributors.

Standard specifications for loadbearing CMU, ASTM C90 is often constantly referred to as a standard for CMU. ASTM C90 contains minimum face shell and web thicknesses for the various sizes of CMU.  ASTM C90 also projects the contrast between hollow and solid CMU. The net cross-sectional area of a solid unit is at least 75% of the gross cross-sectional area.

Unit shapes

Concrete masonry unit shapes have been produced for different applications. Normally, the face shells and webs are tapered on CMU. Open-ended units permit to be tied around reinforcing bars which eliminate the requirement to lift heavy units above the reinforcing bar or to tie the reinforcing bars through the masonry cores after building the wall. Bond beams in concrete masonry walls can be lodged either by cutting a portion of the webs out of a standard unit by a saw or by utilizing bond beam units. Horizontal bond beam reinforcement is simply fixed in these units. Applications of CMUs include exterior fences, interior partitions, and openings within interior concrete masonry walls. Different CMU are constructed to gain energy effectively. Insulating inserts can also be installed into standard CMU to increase energy efficiency.

A building constructed with concrete masonry blocks
CC BY-SA 4.0 | Image Credits: https://en.wikipedia.org | Salil Kumar Mukherjee

Surface finishes

The finished impression of a concrete masonry wall can be altered with the shape and size of units, bond texture, and surface finish.

Types of concrete blocks

Solid concrete blocks

They are heavy and produced from a dense aggregate for giving better stability and strength. They are preferred huge masonry walls with almost negligible water penetration on the load-bearing wall system due to their high compressive strength. Due to the availability of bigger sizes than bricks, masonry construction time is reduced in concrete masonry than brick masonry.

Hollow concrete blocks

The gaps in the hollow blocks are 25% of the total area, the filled area of hollow bricks is not more than 50% and are produced for lightweight concrete.

Types of hollow concrete blocks

Stretcher concrete blocks: The concrete stretcher blocks are utilized widely for combining the corner joints and placed parallel to the wall’s face.

Corner concrete blocks

They are useful at the edges of any structure such as windows, door entries, and so on.

Pillar concrete blocks

Also called double corner concrete blocks, normally they are used when both the ends of a corner are seen. Applications include piers and pillar construction.

Jamb concrete blocks

Useful for a massive window opening, connected to corner and stretcher blocks. For space provision of casing in windows, jamb blocks can be placed.

Partition concrete blocks

They are placed on partition walls with unequal dimensions having greater height than their width. The hollow section is divided into two or three parts.

Lintel concrete blocks

They are utilized in beams and lintel beams. The lintel beam is usually given at the upper space of the doors and windows to sustain the load coming from above. The deep grove inside the lintel blocks is filled with concrete and reinforcement at the later stages.

Frogged brick blocks

The frogged brick blocks comprise of a header and a stretcher such as frogged brick which help the block to retain mortar and make a tight bond with the upper placed block.

Bullnose concrete blocks

They are almost the same as the corner blocks with similar functions but the edges are kept rounded for the need of corner bullnose bricks.

Split face blocks

The split face masonry units are hand chiseled and useful for exterior wall claddings.

Context and Applications

  • Bachelors in Technology (Civil Engineering)
  • Masters in Technology (Pavement and brick design)
  • Masters in Science (Building Construction Materials)

Practice problems

1. The cement-aggregate ratio of CMU is-

  1. 1:3
  2. 1:4
  3. 1:5
  4. 1:6

Correct option- d

Explanation: The cement-aggregate ratio of CMU is 1:6.

2. How much percentage of fine and coarse aggregate is used in the preparation of concrete blocks?

  1. 60% fine aggregate and 40% coarse aggregate
  2. 70% fine aggregate and 30% coarse aggregate
  3. 80% fine aggregate and 20% coarse aggregate
  4. 90% fine aggregate and 10% coarse aggregate

Correct option- a

Explanation: 60% fine aggregate and 40% coarse aggregate are used in the preparation of concrete blocks.

3. Identify the type of concrete block used for huge window openings.

  1. Non-load-bearing blocks
  2. Jamb blocks
  3. Lintel blocks
  4. Pillar blocks

Correct option- b

Explanation: The type of concrete block used for huge window openings is jamb blocks.

4. What is the full form of NCMA?

  1. National Concrete Masonry Association
  2. National Construction Masonry Association
  3. National Concrete Manufacture Association
  4. None of these

Correct option- a

Explanation: The full form of NCMA is National Concrete Masonry Association.

5. The nominal face dimensions of CMU is-

  1. 8 in. by 8 in.
  2. 16 in. by 16 in.
  3. 8 in. by 16 in.
  4. 16 in. by 16 in.

Correct option- c

Explanation: The nominal face dimensions of CMU is 8 in. by 16 in.

  • NCMA (National Concrete Masonry Association)
  • Non-loadbearing concrete blocks
  • Recycled materials

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