Types of Tests on Bricks for Building Construction Works

Various types of tests on bricks are conducted to check the qualities of bricks for construction purposes. Tests on bricks are conducted at construction site as well as in laboratory. Bricks are oldest and important construction materials because of their durability, reliability, strength and low cost.

To produce good quality of structure, good quality materials are required. To decide the quality of the materials some tests are to be conducted on bricks. The tests which are required to find the suitability of bricks for construction purposes are discussed below.

Types of Tests On Bricks for Construction Purpose

Following tests are conducted on bricks to determine its suitability for construction work.

1. Absorption test
2. Crushing strength test
3. Hardness test
4. Shape and size
5. Color test
6. Soundness test
7. Structure of brick
8. Presence of soluble salts (Efflorescence Test)

1. Absorption Test on Bricks

Absorption test is conducted on brick to find out the amount of moisture content absorbed by brick under extreme conditions. In this test, sample dry bricks are taken and weighed. After weighing these bricks are placed in water with full immersing for a period of 24 hours. Then weigh the wet brick and note down its value. The difference between dry and wet brick weights will give the amount of water absorption. For a good quality brick the amount of water absorption should not exceed 20% of weight of dry brick.

2. Crushing Strength or Compressive Strength Test on Bricks

Crushing strength of bricks is determined by placing brick in compression testing machine. After placing the brick in compression testing machine, apply load on it until brick breaks. Note down the value of failure load and find out the crushing strength value of brick. Minimum crushing strength of brick is 3.50N/mm2.if it is less than 3.50 N/mm2, then it is not useful for construction purpose.

3. Hardness Test on Bricks

A good brick should resist scratches against sharp things. So, for this test a sharp tool or finger nail is used to make scratch on brick. If there is no scratch impression on brick then it is said to be hard brick.

4. Shape and Size Test on Bricks

Shape and size of bricks are very important consideration. All bricks used for construction should be of same size. The shape of bricks should be purely rectangular with sharp edges. Standard brick size consists length x breadth x height as 19cm x 9cm x 9cm.

To perform this test, select 20 bricks randomly from brick group and stack them along its length , breadth and height and compare. So, if all bricks similar size then they are qualified for construction work.

5. Color Test of Bricks

A good brick should possess bright and uniform color throughout its body.

6. Soundness Test of Bricks

Soundness test of bricks shows the nature of bricks against sudden impact. In this test, 2 bricks are chosen randomly and struck with one another. Then sound produced should be clear bell ringing sound and brick should not break. Then it is said to be good brick.

7. Structure of Bricks

To know the structure of brick, pick one brick randomly from the group and break it. Observe the inner portion of brick clearly. It should be free from lumps and homogeneous.

8. Efflorescence Test on Bricks

A good quality brick should not contain any soluble salts in it. If soluble salts are there, then it will cause efflorescence on brick surfaces.To know the presence of soluble salts in a brick, placed it in a water bath for 24 hours and dry it in shade. After drying, observe the brick surface thoroughly. If there is any white or grey color deposits, then it contains soluble salts and not useful for construction.

Types of Stairs Used in Building Construction

Types of stairs used in building construction is broadly based on the shape of the stairs. Straight stairs, Turning stairs and Continuous stairs are broad types of stairs.

A stair is a set of steps leading from one floor of a building to another, typically inside the building. The room or enclosure of the building, in which the stair is located is known as staircase. The opening or space occupied by the stair is known as a stairway.

Types of Stairs – Classification of stairs:

Stairs can be broadly classified into three types:

1. Straight stairs
2. Turning stairs
3. Continuous stairs

1. Straight stairs

Generally for small houses, available width is very retractable. So, this type of straight stairs are used in such conditions which runs straight between two floors. This stair may consists of either one single flight or more than one flight with a landing.

2. Turning stairs

Turning stairs are sub classified as:

1. Quarter turn stairs
2. Half turn stairs ( dog legged stairs)
3. Three – quarter turn stairs
4. Bifurcated stairs

3. Quarter turn stairs

A quarter turn stair is the one which changes its direction either to the right or to the left but where the turn being affected either by introducing a quarter space landing or by providing winders. In these type of stairs the flight of stair turns 90 degrees art landing as it rises to connect two different levels. So it is also called as L-stair. Again these quarter turn stairs are two types.

3.1. Newel quarter turn stairs

These type of stairs have clearly visible newel posts at the beginning of flight as well as at the end. At the quarter turn, there may either be quarter space landing or there may be winders.

3.2. Geometrical quarter turn stairs

In geometrical stairs, the stringer as well as the handrail is continuous without any newel post at the landing area.

4. Half turn stairs

In case of half turn stairs its direction reversed, or changed for 180o. Such stairs are quite common. Again these are three types.

4.1. Dog-legged stairs

Because of its appearance in sectional elevation this name is given. It comes under the category of newel stairs in which newel posts are provided at the beginning and end of each flight.

4.2. Open newel half turn stair

In this type of open newel half turn stairs, stair has a space or well between the outer strings. This is the only aspect in which it differs from the doglegged stair.

4.3. Geometrical half turn stairs

In case of geometrical half turn stairs the stringers and the hand rails are continuous, without any intervening newel post. These stairs may contains either with half space landing or without landing.

5. Three quarter turn stairs

The direction of stairs changed three times with its upper flight crossing the bottom one in the case of three quarter turn stairs. These stairs are may either be newel or open newel type. This type stairs are generally used when the vertical distance between two floors is more and as well as length of the stair room is limited.

6. Bifurcated stairs

Bifurcated stairs are commonly used in public building at their entrance hall. This has a wider flight at the bottom, which bifurcates into two narrower flights, one turning to the left and other to the right, at landing.it may be either of newel type with a newel post or of geometrical type with continuous stringer and hand rails.

7. Continuous stairs

This type of stairs neither have any landing nor any intermediate newel post. They are geometric in shape. These are may be of following types.

• Circular stairs
• Spiral stairs
• Helical stairs

Circular stairs or spiral stairs are usually made either of R.C.C or metal, and is placed at a location where there are space limitations. Sometimes these are also used as emergency stairs, and are provided at the back side of a building. These are not comfortable because of all the steps are winders and provides discomfort.

A helical stair looks very fine but its structural design and construction is very complicated. It is made of R.C.C in which a large portion of steel is required to resist bending, shear and torsion.

Tests on Building Stones – Strength and Properties of Stones

There are various tests on building stones to know its properties and suitability for various construction works. Tests on building stones provides physical and chemical properties as well as strength and hardness properties.

Tests on Building Stones

Following are different tests on building stones:

1. Acid test
2. Attrition test
3. Crushing test
4. Crystalline test
5. Freezing and thawing test
6. Hardness Test
7. Impact test
8. Water absorption test
9. Microscopic Test
10. Smith’s Test

Acid Test on Building Stone

This test is carried out to understand the presence of calcium carbonate in building stone. A sample of stone weighing about 50 to 100 gm is taken. It is placed in a solution of hydrophobic acid having strength of one percent and is kept there for seven days. Solution is agitated at intervals.

A good building stone maintains its sharp edges and keeps its surface free from powder at the end of this period. If the edges are broken and powder is formed on the surface, it indicates the presence of calcium carbonate and such a stone will have poor weathering quality.

This test is usually carried out on sandstones.

Attrition Test on Building Stone

This test is done to find out the rate of wear of stones, which are used in road construction. The results of the test indicates the resisting power of stones against the grinding action under traffic.

The following procedure is adopted:

1. Samples of stones is broken into pieces about 60mm size.
2. Such pieces, weighing 5 kg are put in both the cylinders of Devil’s attrition test machine. Diameter and length of cylinder are respectively 20 cm and 34 cm.
3. Cylinders are closed. Their axes make an angle of 30 degree with the horizontal.
4. Cylinders are rotated about the horizontal axis for 5 hours at the rate of 30 rpm.
5. After this period, the contents are taken out from the cylinders and they are passed through a sieve of 1.5mm mesh.
6. Quality of material which is retained on the sieve is weighed.
7. Percentage wear worked out as follows:

Percentage wear = (Loss in Weight/Initial Weight) x 100 

Crushing Test on Building Stone

Samples of stone is cut into cubes of size 40 x 40 x 40 mm sizes of cubes are finely dressed and finished. Maximum number of specimen to be tested is three. Such specimen should be placed in water for about 72 hours prior to test and therefore tested in saturated condition.

Load bearing surface is then covered with plaster of paris of about 5mm thick plywood. Load is applied axially on the cube in a crushing test machine. Rate of loading is 140 kg/sq.cm per minute.

Crushing strength of the stone per unit area is the maximum load at which the sample crushes or fails divided by the area of the bearing face of the specimen.

Crystalline Test on Building Stone

At least four cubes of stone with side as 40mm are taken. They are dried for 72 hrs and weighed. They are then immersed in 14% solution of Na2SO4 for 2 hours. They are dried at 100 degree C and weighed. Difference in weight is noted.

This procedure of drying, weighing, immersion and reweighing is repeated at least 5 times. Each time, change in weight is noted and it is expressed as a percentage of original weight.

Crystallization of CaSO4 in pores of stone causes decay of stone due to weathering. But as CaSO4 has low solubility in water, it is not adopted in this test.

Freezing and thawing test

Stone specimen is kept immersed in water for 24 hours. It is then placed in a freezing machine at -12 degC for 24 hours. Then it is thawed or warmed at atmospheric temperature.

This should be done in shade to prevent any effect due to wind, sun rays, rain etc. this procedure is repeated several times and the behaviour of stone is carefully observed.

Hardness Test on Building Stone

For determining the hardness of a stone, the test is carried out as follows:

1. A cylinder of diameter 25mm and height 25mm is taken out from the sample of stone.
2. It is weighed.
3. The sample is placed in Dorry’s testing machine and it is subjected to a pressure of 1250 gm.
4. Annular steel disc machine is then rotated at a speed of 28 rpm.
5. During the rotation of the disc, coarse sand of standard specification is sprinkled on the top of disc.
6. After 1000 revolutions, specimen is taken out and weighed.
7. The coefficient of hardness is found out from the following equation:

Coefficient of hardness = 20 – (Loss of weight in gm/3)

Impact Test

For determining the toughness of stone, it is subjected to impact test in a Page Impact Test Machine as followed:

1. A cylinder of diameter 25mm and height 25mm is taken out from the sample of stones.
2. It is then placed on cast iron anvil of machine.
3. A steel hammer of weight 2 kg is allowed to fall axially in a vertical direction over the specimen.
4. Height of first blow is 1 cm, that of second blow is 2 cm, that of third blow is 3 cm and so on.
5. Blow at which specimen breaks is noted. If it is nth blow, ‘n’ represents the toughness index of stone.

Microscopic Test

The sample of the test is subjected to microscopic examination. The sections of stones are taken and placed under the microscope to study the various properties such as

1. Average grain size
2. Existence of pores, fissures, veins and shakes
3. Mineral constituents
4. Nature of cementing material
5. Presence of any harmful substance
6. Texture of stones etc.

Smith’s Test

This test is performed to find out the presence of soluble matter in a sample of stone. Few chips or pieces of stone are taken and they are placed in a glass tube. The tube is then filled with clear water. After about an hour, the tube is vigorously stirred or shaken.

Presence of earthy matter will convert the clear water into dirty water. If water remains clear, stone will be durable and free from any soluble matter.

Water Absorption Test

The test is carried out as follows:

1. From the sample of stone, a cube weighing about 50gm is prepared. Its actual weight is recorded as W1 gm.
2. Cube is then immersed in distilled water for a period of 24 hrs.
3. Cube is taken out of water and surface water is wiped off with a damp cloth.
4. It is weighed again. Let the weight be W2 gm.
5. Cube is suspended freely in water and its weight is recorded. Let this be W3 gm.
6. Water is boiled and cube is kept in boiling water for 5 hours.
7. Cube is removed and surface water is wiped off with a damp cloth. Its weight is recorded. Let it be W4 gm.

From the above observations, values of the following properties of stones are obtained.

Percentage absorption by weight after 24 hours =(W2 – W1) x 100 / W1

Percentage absorption by volume after 24 hours = (W2 – W1) x 100 / (W2 – W3)

Volume of displaced water = W2 – W3

Percentage porosity by volume = (W4 – W1) x 100 / (W2 – W3)

Density =W1 / (W2 – W3) kg/m3

Specific Gravity = W1 / (W2 – W3)

Saturation Coefficient = (Water Absorption/Total Porosity) = (W2 – W1) / (W4 – W1)