Compressive Strength of Brick

                                       

                                               

Bricks are mainly used in construction of wall, floor, cornices and
arches. Brick chips are also used as a substitute of stone chips in concrete
mix where stone is not available. In all the above-mentioned cases, compression
load governs. Due to this, compressive strength of bricks is an important parameter.

Specified compressive strength

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According
to BDS 2002

Grade

Mean
Strength (kg/cm2 )

Minimum
Strength (kg/cm2 )

S

280

245

A

175

154

B

140

105

 

According
to Indian Standard (IS 1077:1992)

Classification

Average
Strength (N/mm2)

Average
Strength (kg/cm2)

35

35

350

30

30

300

25

25

250

20

20

200

17.5

17.5

175

15

15

150

12.5

12.5

125

10

10

100

7.5

7.5

75

5

5

50

3.5

3.5

35

  

Compressive Strength Test of Bricks

The
determination of Compressive Strength Test of Brick is carried out under the
specification of ASTM C67-03.

Sampling of Brick:

Selection of Test Specimen:

Full-size representative bricks should be
sampled randomly to cover the whole range color, texture and sizes from a shipment.

Number of Test Specimen:

At least 10 bricks should be chosen from each
lot of 1000000 bricks or fraction thereof. For larger lots, five individual
bricks should be chosen from each lot of 500000 bricks or fraction thereof.
Each sample must be marked for identification purposes. Markings must not cover
more than 5% of the superficial area of the sample.

Weight determination:

Drying:
The test specimens should be dried in a ventilated oven at 230 to 239o
F (110 to 115oC) for at least 24 hours and until two successive
weighting at intervals of 2 hours show an increment of loss not greater than
0.2% of the last previously determined weight of the specimen.
Cooling:
After drying, the specimens need to be cooled in a drying room. The temperature
must be kept 75+15 o F (24+8oC), with a relative
humidity between 30 and 70%.
Materials Used:

Cement: Quick hardening cement

Sand: Locally available good quality sand

Capping Material: Capping is usually done
either using gypsum or Sulphur clay mixture. For the later, a mixture containing
40 to 60 weight % Sulphur, the remainder being fire clay or other suitable
inert material passing a No.100 sieve with or without plasticizer is used.

Apparatus:

Capping Mold: Four 1 inch (25.4 mm) square
steel bars on the surface plate to form a rectangular mold approximately ½ inch
(12.7 mm) greater in either inside dimension than the brick specimen used.

Testing Machine

Test Procedure

Preparation of the Sample:
Dry half bricks with full height and width of the unit and length equal to one
half of the full length of the unit + 1 inch (25.4 mm).  Ends should be plane and parallel.
Capping the Specimen:
1. If the surface which will become the bearing surfaces during the compression
test are recessed or paneled, the depressions have to be filled with a mortar
composed of 1 part by weight of quick hardening cement and 2 parts by weight of
sand. The specimens are to be aged at 48 hours before capping them. Where the
recess exceeds ½ inch (12.7 mm) , a brick or tile slab section or metal plate is
used as a core fill.

2. The capping mold is to be placed.

3. The Sulphur mixture is to be heated in a
thermostatically controlled heating pot to a temperature sufficient to maintain
fluidity for a reasonable period of time after contact with the surface being
capped. Care is required to prevent overheating and the liquid is to be stirred
before using.

4. The mold should be filled to a depth of ¼ inch
with molten Sulphur material. The surface is to be placed in the liquid
vertically.

5. The unit must remain undisturbed for
minimum 2 hours until solidification.

Testing the Specimen:

1.    
Brick specimens are to be
tested flat wise. The specimen is to be centered under the spherical upper
bearing within 1/16 inch.

                  

                         Figure : Compressive Strength Test of
Brick

2.    
The load should be applied
up to one half of the expected maximum load, at any convenient rate. Then the
remaining load has to be applied at a uniform rate in 1-2 minutes.

Calculation:

          
Compressive Strength, C= (W/A)

Where,
W= Calibrated maximum load

A= Average of the gross
areas of the upper and lower bearing surfaces of the specimen.