MASONRY - Materials for Civil and Construction Engineers - page 308

T ABLE 8.2 Strength Requirements of Concrete Masonry Units
(ASTM C90 and C129)

Minimum Compressive Strength
Based on Net Area MPa (psi)

Type Average of Three Units Individual Units

Load bearing 13.1 (1900) 11.7 (1700)

Non-load-bearing 4.1 (600) 3.5 (500)

Sample Problem 8.1

A hollow concrete masonry unit has actual gross dimensions of
The unit is tested in a compression machine with the following results:

7 - 5/8 in. * 7 - 5/8 in.

* 15 - 5/8 in.

Failure Load = 250 kips

366.9 in 3 Net volume of

a. Calculate the gross area compressive strength.
b. Calculate the net area compressive strength.

Solution

119.141 in 3 a. Gross

Gross area compressive
b. Net
Net area compressive

area = 7.625 * 15.625 =

strength = 250,000/119.141 = 2,098.4 psi

48.118 in 2 area = 366.9/7.625 =

strength = 250,000/48.118 = 5,195.6 psi

The amount of water absorption of concrete masonry units is controlled
by ASTM standards to reduce the effect of weathering and to limit the
amount of shrinkage due to moisture loss after construction (ASTM C90).
The absorption of concrete masonry units is determined by immersing the
unit in water for 24 hours (ASTM C140). The absorption and moisture con-
tent are calculated as follows.

W s - W d

kg/m 3 Absorption = * 1000 (8.1)

1 2

W s - W i

W s - W d

lb/ft 3 Absorption 1 2 = * 62.4 (8.2)

W s - W i