Experiment No: 10

Sampling and Testing Brick

Introduction

The durability and performance of masonry structures rely heavily on the quality of the bricks used. Testing bricks according to ASTM C67 ensures they meet the necessary standards for construction. This test method covers the procedures for sampling and testing the physical properties of fired brick and structural clay tile. By following these tests, the suitability of bricks for construction projects can be ascertained.

Scope

These test methods outline the procedures for sampling and testing brick and structural clay tiles. While they may not apply to every type of unit, the tests include evaluating modulus of rupture, compressive strength, absorption, saturation coefficient, resistance to freezing and thawing, efflorescence, initial rate of absorption, and determining weight, size, warpage, length change, and void area.

 

Purpose

 

To test brick masonry units for modulus of rupture, compressive strength, absorption, saturation coefficient, effect of freezing and thawing, efflorescence, initial rate of absorption and determination of weight, size, warpage, length change, and void area.

ASTM Designation

 

ASTM C167— Sampling and Testing Brick.

 

Terminology

 

Clay—

A mineral aggregate composed mostly of hydrous silicates of alumina, which is flexible when adequately crushed and moistened, hard when dry, and vitreous when subjected to high temperatures.

Absorption (Clay Product) -

The weight of water absorbed by a clay masonry unit during immersion under specified conditions, represented as a ratio to the dry weight of the unit.

Brick –  

A solid masonry unit of clay or shale, usually formed into a rectangular prism while plastic and burned or fired in a kiln. Brick is a ceramic product.

Building brick —

Brick intended for construction that is not specifically manufactured for texture or color.

Floor brick —

Smooth, solid brick, highly resistant to abrasion, used as finished floor surfaces.

 

Significance and Use

Bricks are used for numerous purposes, including building, face and aesthetics, floor construction, and paving. Building bricks (ordinary bricks) are used as a structural material and are generally solid and durable. Facing bricks are used for facing and aesthetic purposes and are available in varied sizes, colors, and textures. Floor bricks are used on polished floor surfaces and are often smooth and dense, with good resistance to abrasion.

 

Sampling

Selection and Preparation of Test Specimens

 

The tests involve selecting full-size brick or solid masonry units from a lot, including a range of colors, textures, and sizes. The specimens must be free of dirt, mud, mortar, or other foreign materials unrelated to the manufacturing process. Brushes used to remove foreign material should have plastic or horsehair bristles. Wire brushes should not be used for testing preparation. Untreated specimens exhibiting foreign material should be discarded to prevent damaged or contaminated ones from being tested.

Number of Specimens

 

For modulus of rupture, compressive strength, abrasion resistance, and absorption determinations, at least ten bricks must be selected for 1,000,000 brick lots or fraction thereof, and five additional specimens from each 500,000 brick or fraction thereof for larger lots.

Specimen Preparation

Weight Determination:

Drying

Test specimens should be dried in an oven at 230-239°F (110-115°C) for 24 hours until two consecutive weighing show a weight loss increase of no more than 0.2% of the last recorded weight.

Cooling

After drying, specimens should be stored in a drying room at a temperature of 75-85°F (24-8)°C with a relative humidity of 30-70%. Store them separately for at least 4 hours until the surface temperature is within 5°F (2.8°C). Avoid using specimens that are warm to the touch for tests requiring dry units. The specimens should be kept in the drying room until tested.

Weighing and Report

Five dry full-size specimens must be weighed using a scale with a capacity of 3000 g and a sensitivity of 0.5 g. Results should be reported separately for each specimen, with the average of all tested specimens.

1    Modulus of Rupture (Flexure Test)

·        Test specimens should be supported flatwise, applying load in the direction of the unit's depth. Load the specimen on a span 1 in. less than the basic unit length and loaded at midspan. If specimens have recesses, place them on the compression side. Apply the load to the upper surface of the specimen through a steel bearing plate ¼ in. thick and 1 ½ in. wide, at least equal to the specimen's width.

·        Ensure test specimen supports are rotated freely in longitudinal and transverse directions, and adjust them to avoid exerting force in these directions.

·        The loading rate must not exceed 2000 lb./f (8896 N)/min, but this requirement is met if the moving head of the testing machine immediately prior to application of the load is not more than 0.05 in. (1.27 mm)/min.

·        Calculate and report the modulus of rupture of each specimen to the nearest 1 psi (0.01 MPa) as follows:

S = 3W (l/2 – x)/ bd²

 

Where,

S = modulus of rupture of the specimen at the plane of failure, lb/in.² (Pa)

W = maximum load indicated by the testing machine, lb (N)

l = distance between the supports, in. (mm)

b = net width, of the specimen (face to face minus voids) at the plane of failure, in. (mm)

d = depth, (bed surface to bed surface), of the specimen at the plane of failure, in. (mm), and

x = average distance from the midspan of the specimen to the plane of failure measured in the direction of the span along the centerline of the bed surface subjected to tension, in. (mm).

 

2    Compressive Strength Test

The test specimens should comprise dry half bricks, matching the complete height and breadth of the unit, with a length equivalent to half the full length of the unit, ±1 inches (25.4 mm). If the test specimen, as previously described, exceed the capacity of the testing machine, the test specimens shall comprise dry brick pieces, maintaining the complete height and width of the unit, with a length no less than one quarter of the total length of the unit, and possessing a gross cross-sectional area perpendicular to the bearing of no less than 14 in.² (90.3 cm²). Test specimens must be obtained through any method that produces a specimen with approximately flat and parallel ends, without causing breaking or cracking. Five specimens will be taken for testing.

Capping Test Specimens

                  ·        All specimens shall be dry and cool and capping procedure should be carried out.

·        To conduct a compression test on bearing surfaces, fill the depressions with a mortar made of Type III cement and sand. Age the specimens for 48 hours before capping. If the recess exceeds 1⁄2 in., use a brick or tile slab section or metal plate as a core fill. Cap the test specimens using one of two procedures.

·        To create Gypsum Capping, coat the two opposite bearing surfaces of each specimen with shellac and let it dry thoroughly. Bed one of the dry shellacked surfaces in a thin paste of calcined gypsum on an oiled nonabsorbent plate, such as glass or machined metal. The plate should be plane, rigid, and not deflected during capping. Lightly coat it with oil or other suitable material. Repeat this process with the other shellacked surface, ensuring opposite bearing surfaces are parallel and perpendicular to the specimen's vertical axis. Age the caps for at least 24 hours before testing the specimens. The thickness of the caps will be approximately the same and not exceeding 1⁄8 in. (3.18 mm).

·        Sulfur-Filler Capping involves using a mixture of 40-60% sulfur and ground fire clay or other inert material. Four square steel bars are placed on a surface plate to form a rectangular mold. The sulfur mixture is heated in a thermostatically controlled heating pot to maintain fluidity. The mold is filled to a depth of 1⁄4 in. (6.35 mm) with molten sulfur material. The specimen is held at right angles to the capping surface, and the caps should be approximately the same thickness. The unit is left undisturbed until solidification is complete, and the caps should cool for at least 2 hours before testing the specimens.

Procedure

·        Test the brick specimens flatwise, applying the load in the direction of the brick's depth.

·        The testing machine must fulfill the Practices of ASTM E4, which require an upper bearing consisting of a spherically seated, hardened metal block attached to the upper head. The block should be free to turn and the perimeter shall have at least 1⁄4 in. (6.35 mm) clearance from the head to accommodate specimens. The bearing surface should have a diameter of at least 5 in. (127.00 mm). A hardened metal bearing block should be used beneath the specimen to minimize wear on the machine's lower platen. The bearing block surfaces should have a hardness of HRC60 (HB 620) and not depart from plane surfaces by more than 0.001 in. (0.03 mm). When the bearing area of the spherical bearing block is insufficient, a steel plate with surfaces machined to true planes should be placed.

·        Speed of Testing: The test involves applying a load up to half of the expected maximum load at a convenient rate, then adjusting the machine's controls to ensure the remaining load is applied uniformly within 1 to 2 minutes.

Calculation and Report:

 

Calculate and report the compressive strength of each specimen to the nearest 10 psi (0.01 MPa).

Compressive strength, C = W / A

where:

C = compressive strength of the specimen, lb/in.² (or kg/cm²)

W = maximum load, lb, (or kg) (or N), indicated by the testing machine, and

A = average of the gross areas of the upper and lower bearing surfaces of the specimen, in.² (or cm²).

 

3    Absorption Test

Test Specimen: Five specimens shall be required for testing.

Saturation: Fully immerse the dry, cooled specimen in clean water (soft, distilled, or rain water) at a temperature of 15.5 to 30°C for the designated time, without prior partial immersion. Remove the specimen, eliminate the surface moisture using a wet towel, and measure the specimen's weight. complete weighing of each specimen within 5 min after taking the specimen from the bath.

Calculation and Report:

Calculate and report the cold water absorption of each specimen to the nearest 0.1 % as follows:

Absorption, % = 100 (W_s - W_d)/ W

where:

W_d = dry weight of the specimen, and

W_s = saturated weight of the specimen after submersion in cold water.

 

4     Efflorescence Test

Apparatus:

Trays and Containers: Watertight shallow pans or trays constructed of corrosion-resistant metal or other material that will not give soluble salts when in contact with distilled water containing leachings from brick. The pan should be of such dimensions that it will provide not less than a 1-in. (25.4-mm) depth of water.

Brush: A soft-bristle brush.

Test Specimens

The test specimens consist of ten full-size bricks, sorted into five pairs for uniform appearance. Any dirt that might be mistaken for efflorescence should be removed by brushing, and the specimens should be dried and cooled.

Procedure

·        To test specimens, immerse one specimen from each pair in distilled water to a depth of approximately 1 in. (25.4 mm) for 7 days in a drying room. When multiple specimens are tested in the same container, separate them by a minimum of 2 inches (50.8 mm).

·        The second specimen from each of the five pairs should be stored in the drying room without water contact.

·        After 7 days, inspect the first set of specimens and then dry both sets in a drying oven for 24 hours.

Examination and Rating

After drying, compare and observe the top and all four faces of each specimen from a distance of 10 ft. under an illumination of not less than 50 footcandles (538.2 lm/m2). If no difference is noted, report "not effloresced." If a noticeable difference due to efflorescence is noted, report "effloresced." Report the appearance and distribution of the efflorescence.

 

5     Measurement of Warpage

Apparatus

Steel Straightedge

Rule or Measuring Wedge:

A steel rule with divisions of 1⁄32 in. (or 1 mm) from one end, or an alternative: a steel measuring wedge 2.5 in. (60 mm) in length, 0.5 in. (12.5 mm) in width, and 0.5 in. (12.5 mm) in thickness at one end, tapering from a line 0.5 in. (12.5 mm) from one end to zero thickness at the other end. The wedge must be graduated in 1⁄32-in. (or 1-mm) divisions and numbered to show the thickness of the wedge between the base, AB, and the slope, AC.

 

Fig.  Measuring Wedge

 

Flat Surface

A flat surface made of steel or glass should be 12 by 12 inches and plane to within 0.001 inch (0.025 mm).

Brush

A soft-bristle brush.

Sampling

·        Use the sample of ten bricks selected for determination of size.

·        The specimens should be tested as received, with any dirt removed by brushing.

Procedure

Concave Surfaces

To measure concave surface warpage, place a straightedge along the surface, choosing the location with the greatest departure from straightness. Measure the distance from the brick surface to the straightedge using a steel rule or wedge, measure this distance to the nearest 1⁄32 in. (1 mm), and record it as the concave warpage of the surface.

Concave Edges

To measure concave edge warpage, place a straightedge between the ends of the edge and select the greatest distance from the brick edge to the straightedge. Measure this distance using a steel rule or wedge to the nearest 1⁄32 in. (1 mm) and record the concave warpage.

Convex Surfaces

To measure convex surface warpage, place the unit in contact with a plane surface with the corners equidistant from the plane surface. Measure the distance to the nearest 1⁄32 in. (1 mm) of each corner from the plane surface using a steel rule or wedge, and record the average of the four measurements as the convex warpage.

Convex Edges

Measure the convex warpage of an edge by placing a straightedge between its ends and selecting the greatest distance from the brick edge to the straightedge. Use a steel rule or wedge to measure this distance to the nearest 1⁄32 in. (1 mm).

 

Report

Record all warpage measurements of each specimen tested to the nearest 1⁄32 in. (0.8 mm).

LAB Assignment Questions:

1.      Why is it important to sample and test bricks?

2.      What properties of bricks are typically evaluated during testing?

3.      What is the purpose of following standards like ASTM C67 for testing bricks?

4.      What are the typical tests conducted on bricks as per ASTM C67?

5.      What is meant by 'sampling' in the context of brick testing?

6.      Why is sampling necessary before testing bricks?

7.      What is the recommended method of selecting bricks for testing according to ASTM C67?

8.      What is the minimum number of bricks that should be tested from a batch for reliable results?

9.      What are the criteria for rejecting a brick during sampling?

10.  How can visible defects or irregularities affect the performance of the brick?

11.  How is the compressive strength of a brick determined?

12.  Can you describe the procedure for testing the compressive strength of a brick?

13.  What is the significance of the compressive strength of bricks in construction?

14.  What factors can affect the compressive strength of bricks?

15.  How do you calculate the compressive strength of a brick from the test results?

16.  What is water absorption in bricks, and why is it important?

17.  Can you describe the procedure for testing the water absorption of bricks?

18.  Why is it necessary to soak the brick for 24 hours in this test?

19.  What is the permissible water absorption percentage for bricks used in construction?

20.  How does excessive water absorption affect the performance of bricks in a structure?

21.  How does water absorption relate to the durability of bricks?

22.  What is efflorescence in bricks, and how does it occur?

23.  What is the test for determining efflorescence in bricks?

24.  How do you categorize the levels of efflorescence (e.g., none, slight, moderate, heavy, serious)?

25.  What are the potential consequences of efflorescence on brick masonry structures?

26.  What is the modulus of rupture test, and why is it performed on bricks?

27.  How does it relate to the flexural strength of the brick?

28.  What is the purpose of the initial rate of absorption (IRA) test, and how is it performed?

29.  How does the presence of soluble salts in bricks affect their performance in masonry?

30.  What are the thermal properties of bricks, and why are they tested?

31.  Which ASTM standard governs the testing of bricks?

32.  What are the key requirements of ASTM C67 for brick testing?

33.  What are the quality control measures taken during brick sampling and testing to ensure reliable results?

34.  What are the typical values or ranges of compressive strength, water absorption, and efflorescence for good-quality bricks?

35.  What are the limitations of ASTM C67 when it comes to testing bricks?

36.  How do you ensure that the brick specimen is prepared properly before conducting the compressive strength test?

37.  What safety precautions should be taken during the testing of bricks?

38.  What could cause discrepancies between test results from different bricks in the same batch?

39.  What are the acceptance criteria for bricks based on the different tests?

40.  How do you interpret the results of the compressive strength test for bricks?

41.  What would be the implications of a low compressive strength result?

42.  How do you interpret the results of the water absorption test?

43.  What would high water absorption indicate about the quality of a brick?

44.  What are the reasons for a brick to fail the efflorescence test?

45.  How can efflorescence in brick masonry be prevented?

References

ASTM C67: Standard Test Methods for Sampling and Testing Brick and Structural Clay Tile.