ASTM C67
Flexure and Compression Testing Brick and Clay Tile

ASTM C67 Test Fixture – Universal Grip Data Sheet (PDF)

ASTM C67/C67M covers the standard test methods for sampling and testing brick and structural clay tile. It includes modulus of rupture (flexure), compressive strength, absorption, saturation coefficient, freezing and thawing, efflorescence, initial rate of absorption and dimensional checks. The flexure, breaking load and compression tests are run on a universal testing machine; this page covers those tests and the fixtures used for them.

Flexure Test (Modulus of Rupture)

• Whole, dry brick tested flatwise (on its bed face)

• Supported on two rounded supports, span not more than 178 mm (7 in); supports free to rotate so the brick sits evenly

• Load applied at mid-span through a steel bearing plate 6 mm (¼ in) thick and 38 mm (1½ in) wide

• Loading rate not more than 8,896 N/min (2,000 lbf/min)

• Record the maximum load and the position of the fracture

Modulus of rupture: S = 3W(L/2 − x) / (bd²), where W = maximum load, L = span, x = distance from mid-span to the fracture plane, b = width and d = depth of the brick.

Example: a brick 3.625 in wide and 2.25 in deep breaks at 3,000 lbf on a 7 in span, 0.25 in from mid-span. S = 3 × 3,000 × (3.5 − 0.25) / (3.625 × 2.25²) = 29,250 / 18.35 = 1,594 psi (11.0 MPa).

Compressive Strength Test

• Specimens are half bricks (full height and width, about half the length), usually the halves left from the flexure test

• Bearing faces capped (gypsum or sulfur) or ground flat and parallel

• Loaded between steel platens, one with a spherical seat, larger than the specimen

• Apply up to half the expected maximum load at any convenient rate, then the rest at a uniform rate so failure occurs in 1 to 2 minutes

Compressive strength: C = W / A, where A is the average gross area of the bearing faces.

Example: a half brick 3.625 × 4.0 in (A = 14.5 in²) fails at 145,000 lbf. C = 145,000 / 14.5 = 10,000 psi (69 MPa). Strong brick can need a high-capacity compression machine.

Fixtures for ASTM C67

• Universal Grip 10,000 lb three-point bend fixture with articulating supports that rotate freely across the brick, so an uneven brick still sits evenly

• Steel loading nose plate 1/4 in thick, 1.5 in wide and 4 in long

• Standard 4 in wide rollers for brick 3.625 × 2.25 × 8 in (depth × height × length); custom widths available

• Spherically seated compression platens that cover the whole bearing face of the specimen

The same three-point fixture is used for the flexure (modulus of rupture) and breaking load tests.

Similar Specifications

• ASTM C62, C216 and C652 – building, facing and hollow brick specifications that call up C67

• ASTM C78 – flexural strength of concrete (third-point loading)

• ASTM C1314 – compressive strength of masonry prisms

ASTM C67 FAQ

What span is used for the C67 flexure test?

Not more than 178 mm (7 in), with the load applied at mid-span through a steel bearing plate.

How fast is the flexure test loaded?

At a rate not exceeding 8,896 N/min (2,000 lbf/min).

What specimen is used for compressive strength?

A half brick of full height and width, capped or ground flat, loaded so failure occurs in 1 to 2 minutes after the first half of the expected load.

Why use articulating supports?

Brick faces are rarely perfectly flat. Supports that rotate let the brick bear evenly, so it is not twisted during the test. Confirm all dimensions and rates against your copy of ASTM C67.