Building Materials & Construction Management : Bricks and Stones Notes

Brick

Composition of Good Brick Earth

Following are the constituents of brick earth:

1. Alumina

It is the chief constituent of every kind of clay. A good brick earth should contain about 20 to 30 per cent of alumina. This constituent imparts plasticity to earth so that it can be moulded.

2. Silica

A good brick earth should contain about 50 to 60 per cent of silica. Presence of this constituent prevents cracking, shrinking and warping of raw bricks. It thus imparts uniform shape to the bricks.
Excess of silica destroys the cohesion between particles and bricks become brittle.

3. Lime

It should be present in a finely powdered state and not in lump.
Lime prevents shrinkage of raw bricks. Sand alone is infusible. But it slightly fuses at kiln temperature in presence of lime.
Excess of lime causes the brick to melt and hence, its shape is lost. Lumps of lime are converted into quick lime after burning and this quicklime slakes and expands in presence of moisture.

4. Oxide of Iron

About 5 to 5 per cent is desirable in good brick earth. It helps lime to fuse sand. It also imparts red color to bricks.
Excess of oxide of iron makes the bricks dark blue or blackish

5. Magnesia

A small quantity of magnesia in brick earth imparts yellow tint color to bricks and decreases shrinkage. But excess of magnesia leads to the decay of bricks.

Harmful Ingredients in Brick Earth

1. Lime

It causes unsoundness in brick if present in excess amounts.

2. Iron pyrites

If iron pyrites are present in brick earth, bricks are crystallized and disintegrated during burning.

3. Alkalies

These are mainly in the form of soda and potash

4. Pebbles

The presence of pebbles or grits of any kind is undesirable in brick earth because it will not allow the clay to be mixed uniformly and thoroughly which will result in weak and porous bricks.

5. Organic Matter

Presence of organic matter in brick earth assists in burning. But if such matter is not completely burnt, bricks become porous.

Manufacture of bricks

1. Preparation of clay

Clay of bricks is prepared in the following order:

Unsoiling
Digging
Cleaning
Weathering
Blending
Tempering

2. Moulding

Hand Moulding

Machine Moulding

Plastic Clay Machine
Dry Clay Machine

3. Drying

4. Burning: Burning of bricks is done either in clamps or in kilns.

(a) Clamps: Its shape in plan is generally trapezoidal. Floor of clamp is prepared in such a way that short end is slightly in the excavation and wider end is raised at an angle of about 15° from ground level.

(b) Kilns: A kiln is a large over which is used to burn bricks. The kilns which are used in the manufacture of bricks are of the following two types.

(i) Intermittent kilns (ii) Continuous kilns

(i) Intermittent Kiln: This may be over ground or underground they are classified in two ways: (a) intermittent up-drought kilns, (b) Intermittent down-drought kilns

Comparison between bull's trench kiln and Hoffman's kiln

Comparison between clamp Burning and kiln Burning

Tests For Bricks

1. Absorption

A brick is taken and it is weighted dry. It is then immersed in water for a period of 16 hours.
Then weight again and the difference in weight should not, in any case, exceed
(a) 20 per cent of weight of dry brick for first class bricks.
(b) 22.5 per cent for second class bricks.
(c) 25 per cent for third class bricks.

2. Crushing strength

Minimum crushing strength for first class bricks and for second class bricks

3. Hardness

In this test, a scratch is made on brick surface with the help of a finger nail. If no impression is left on the surface, brick is treated to be sufficiently hard.

4. Presence of soluble salts

Soluble salts, if present in bricks, will cause efflorescence on the surface of bricks.
It is immersed in water for 24 hours. It is then taken out and allowed to dry in shade. Absence of grey or white deposits on its surface indicates absence of soluble salts.
If the white deposits cover about 10% surface, the efflorescence is said to be slight.
When white deposits cover about 50% of surface thin it is said to be moderate.
If grey or white deposits are found on more than 50% of surface, the efflorescence becomes heavy and it is treated as serious.

5. Shape and Size

Its shape should be truly rectangular with sharp edges.
20 bricks are randomly selected of standard (19 × 9 × 9 cm) for good quality bricks, the results should be within the following permissible limits:
Length – 368 cm to 392 cm
Width – 174 cm to 186 cm
Height – 174 to 186 cm

6. Soundness

In this test, two bricks are taken and they are struck with each other.
Bricks should not break and a clear ringing sound should be produced.

7. Structure

It should be homogenous compact and free from any defects such as holes, lumps, etc.
High duty fire-clays can resist temperature range of 1482°C to 1648°C; medium duty fire-clays can resist temperature range of 1315°C to 1482°C and low duty fire-clays can resist temperature up to 870°C only.

Quality of Good Bricks

The bricks should be table-moulded, well burnt in kilns, copper-coloured free from cracks and with sharp and square edges.
The bricks should be uniform in shape and should be of standard size.
The bricks should give a clear metallic ringing sound when struck with each other.
The bricks when broken or fractured should show a bright homogeneous and uniform compact structure free from voids.
The brick should be sufficiently hard. No impression should be left on brick surface, when it is scratched with finger hail.
The bricks should not break into pieces when dropped flat on hard ground from a height of about one meter.
The bricks, when soaked in water for 24 hour should not show deposits of white salts when allowed to dry in shade.
No brick should have the crushing strength below 5.50 N/MM².

Classification of Bricks

The bricks can broadly be divided into two categories:

1. Unburnt Bricks: The unburnt or sun dried bricks are dried with the help of heat received from the sun after the process of moulding. These bricks can only be used in the construction of temporary and cheap structures. Such bricks should not be used at places exposed to heavy rains.

2. Burnt Bricks: These are classified in four categories:

First Class Bricks
- These bricks are table-moulded and of standard shape and they are burnt in kilns.
- The surfaces and edges of the bricks are sharp square smooth and straight.
- First class bricks have all qualities of good bricks.
- These bricks are used for superior work of permanent nature.
Second Class Bricks
- These bricks are ground moulded and they are burnt in kilns.
- The surface of these bricks is somewhat rough and shape is also slightly irregular.
- These bricks are commonly used at places where bricks work is to be provided with a coat of plaster.
Third Class Bricks
- These are ground moulded and they are burnt in clamps.
- These bricks are not hard and they have rough surface with irregular and distorted edges.
- These bricks gives dull sound when struck together.
- They are used for unimportant and temporary structures.

Size and Weight Of Bricks(For India)

Standard size of bricks is 19 cm × 9 cm × 9 cm
Normal size (with mortar) is 20 cm × 10 × 10 cm.
The commonly adopted nominal size of traditional bricks is 23 cm × 11.4 cm × 7.6 cm.
It is found that the weight of 1 m³ of bricks earth is about 1800 kg. Hence the average weight of a brick will be about 3 to 3.50 kg.

Shape of Bricks

1. Bulinose Brick

A brick moulded with a rounded angle is termed as a bulinose. It is used for a rounded quoin.
A connection which is formed when a wall takes a turn is known as quoin.

2. Channel Bricks

These bricks are moulded to the shape of a gutter or a channel and they are very often glazed.
These bricks are used to function as drain.

3. Coping bricks

These bricks are made to suit the thickness of walls on which coping is to be provided.
Such bricks take various forms such as chamfered half-round or saddle-back.

4. Cownose Bricks

A brick moulded with a double bulinose on end is known as cownose.

5. Curved Sector Bricks

These bricks are in the form of curved sector and they are used in the construction of circular brick masonry pillars, brick chimneys.
The perforation may be circular, square, rectangular or any other regular shape in cross-section.
The water absorption after immersion for 24 hour in water should not exceed 15% by water.
Compressive strength of perforated bricks should not be less than 7 N/mm² on gross area.

6. Hollow Bricks

These are also known as cellular or cavity bricks. Such bricks have wall thickness of about 20 mm to 25 mm. They are prepared from special homogeneous clay. They are light in weight about one third the weight of the ordinary bricks of the same size. The use of such bricks leads to speedy construction. They also reduce the transmission of heat, sound and damp. They are used in the construction of brick partitioning.

7. Paving bricks

These bricks are prepared from clay containing a higher percentage of iron. Excess iron vitrifies the bricks at a low temperature. Such bricks resist better the abrasive action of traffic. Paving bricks may be plain or checkered.

8. Perforated Bricks

Perforated bricks are used in the construction of brick panels for lightweight structures and multi-storeyed framed structures.

STONES

1.GENERAL CLASSIFICATION OF STONES

The building stones are obtained form rocks which as classified in following three ways.

Geological classification
Physical classification
Chemical classification

1.1. Geological classification

(i) Igneous rocks is formed by the cooling of molten magma

Example :- Plutonic rocks – Granite

Hypabyssal rocks – dolerite

Volcanic rocks – Basalt

(ii) Sedimentary rocks are formed by the deposition of products of weathering on pre-existing rocks. residual deposits, sedimentary deposits, chemical deposits and organic deposits are the type of sedimentary deposits.

Example :- Gravel, sandstone, limestone, gypsum etc

(iii) Metamorphic rocks are formed by the change in character in pre-existing rocks.

Example :- quartzite anthracite.

1.2. Physical classification

Based on general structure of rock.

(i) Stratified rocks :- It possess plane of stratification. The sedimentary rocks are distinctly stratified rocks.

(ii) Unstratified rocks :- The structure may be crystalline granular or compact granular.

(iii) Foliated Rocks :– It is a very common case of metamorphic rocks.

1.3. Chemical classification

(i) Siliceous Rocks- Silica Predominates.

Example :- Granite, Quartzites

(ii) Argillaceous Rocks- Argil or clay predominates

Example :- Slates, laterites

(iii) Calcareous Rocks- Carbon Predominates.

Example :- Limestone, Marble.

2.TESTS FOR STONE

2.1. Acid Test

In the test, a sample of stone weighing about 0.5N to 1N is taken and placed in a solution of hypo chloric acid having strength of one percent for seven days. The solution is agitated at intervals. A good building stone maintains its sharp edges.

2.2. Attrition test

Test is conducted to find out the wear of stones which are used in road construction. The results of the test indicate the resisting power of stones against grinding action under traffic.

2.3. Crushing Test

The compressive strength of stone is found out with test. The sample of stone cut into cubes of size 40mm × 40mm × 40mm are used.

2.4. Crystallization Test

In this test, four cubes of side 40mm are taken and dried for 72 hours and weighed. They are then 14% solution of Na₂SO₄ for 2 hrs and dried at 100°C. The difference in weight is noted and each time difference is noted in on at least 5 samples.

2.5. Freezing and thawing test

The specimen of stone is kept immersed in water for 24 hours and the placed at a freezing temperature of —12ºC for 24 hours. It is then thawed or warmed at atmospheric temperature.

2.6. Hardness Test

A cylinder of diameter 25 mm and height 25 mm is taken and weighed. It is placed in Dorry’s testing machine and pressed at a pressure of 12.5 N. The disc of machine is rotated at a speed of 28 rpm. During the rotation of disc the coarse and sand of standard specification it sprinkled on top of disc. After 1000 revolutions, specimen is taken and weighed.

2.7. Microscopic Test

In this test, a sample of stone is subjected to microscopic examination for various properties such as average grain size, existence of pores, fissures, mineral constituents and texture of stone.

3.QUALITIES OF GOOD BUILDING STONE

(i) For a good structural stone, the crushing strength should be greater than 100 N/mm².

(ii) The stones to be used for work should be decent in appearance and be capable of preserving their color for a long time.

(iii) A good building stone should be durable.

(iv) The stones should be such that they can be easily conserved, moulded cut and dressed.

(v) For a good building stone, its fracture should be sharp even bright and clear with grains.

(vi) The coefficient of hardness worked out in hardness test should be greater than π to be used in road work.

(vii) If the wear in the attrition test is more than 3 percent, the stone is not satisfactory.

(viii) For a good building stone, its specific gravity should be greater than 2.7 or so

(ix) All stones more or less porous, percentage absorption by weight after 24 hours should not exceed 0.6

(x) A good building stone should have compact fine cry stalling structure free from patches.