Masonry Construction: Concrete Masonry

Question 1

What are some advantages of using Concrete Masonry Units (CMU)? (4)

Answer 1

• very versatile building material
• more economical than brick or stone
• hollow cores allow for easy installation of rebar
• available in a variety of textures and colors

Question 2

Describe the CMU manufacturing process. (4)

Answer 2

• stiff concrete mix vibrated into metal molds
• wet blocks immediately turned out onto a rack
• steam curing pressure vessels accelerate the curing process
• also made with cinders, pumice, or blast furnace slag

Question 3

Describe the dimensions of CMU. (4)

Answer 3

• American CMU based on 8-inch module
• standard nominal size: 8”x8”x16”
• actual size is 3/4 inch less in each dimension
• actual size: 7 and 5/8 x 7 and 5/8 x 15 and 5/8

Question 4

What is a handy sizing feature of CMUs?

Answer 4

the height of a standard 8-inch CMU corresponds exactly to three courses of ordinary clay bricks

Question 5

What are some other common CMU sizes?

Answer 5

4”, 6”, 10” and 12” in width

Question 6

What are the three CMU classifications according to ASTM C90?

Answer 6

• normal-weight
• medium-weight
• light-weight

Question 7

What are the characteristics of light-weight blocks? (2)

Answer 7

• less expensive to transport and lay

- lower thermal conductivity

Question 8

What are the characteristics of medium-weight blocks?

Answer 8

most commonly specified

Question 9

What are the characteristics of normal or heavy-weight blocks? (3)

Answer 9

• more durable
• higher compressive strength
• better acoustical isolation between adjacent spaces

Question 10

Why should CMU walls be designed in dimensional units that correspond to the module of the block? (3)

Answer 10

• limit waste
• minimize the need to cut the block, or
• work with small pieces

Question 11

How are CMUs laid? (4)

Answer 11

• mortar is identical to that used for brick masonry
• similar to laying brick
• corner leads are laid first
• string lines and levels are used to keep walls straight, plumb, and level

Question 12

How does reinforced CMU improve the material?

Answer 12

reinforcing increases compressive strength, resistance to cracking, and resistance to lateral forces

Question 13

Describe the reinforcing techniques utilized in reinforced CMU. (2)

Answer 13

• vertical reinforcing in grouted cells

- lightweight horizontal reinforcing in mortar joints

Question 14

Describe the grouting process of reinforced CMU. (3)

Answer 14

• grouting can be low-lift or high-lift technique
• in most cases, only the cores with rebar are grouted
• occasionally, all vertical cores are filled

Question 15

What is unique about specially-shaped CMUs?

Answer 15

accommodate both vertical and horizontal reinforcing bars without modification

Question 16

How are openings spanned in concrete masonry? (3)

Answer 16

• steel lintel
• reinforced concrete brick
• precast concrete

Question 17

What are split-face blocks?

Answer 17

naturally textured surfaces with exposed aggregate

Question 18

What are five examples of decorative concrete masonry units?

Answer 18

• split-face block
• ribbed split-face units
• ground-face block
• glazed block
• glass block

Question 19

What are ground-face blocks? (2)

Answer 19

• after curing, block surface is ground smooth, creating a polished surface
• in any architectural block, the color of aggregates and cement can also vary

Question 20

Can CMUs be manufactured in a great variety of shapes and sizes?

Answer 20

yes