Traditional Material - Bricks

Stones, bricks, cement, lime and timber are the traditional materials used for civil engineering constructions for several centuries. In this chapter types, properties, tests and uses of these materials is explained.

1.2 BRICKS

Brick is obtained by moulding good clay into a block, which is dried and then burnt. This is the oldest building block to replace stone. Manufacture of brick started with hand moulding, sun drying and burning in clamps. A considerable amount of technological development has taken place with better knowledge about to properties of raw materials, better machinaries and improved techniques of moulding drying and burning.

The size of the bricks are of 90 mm × 90 mm × 90 mm and 190 mm × 90 mm × 40 mm. With mortar joints, the size of these bricks are taken as 200 mm × 100 mm × 100 mm and 200 mm × 100 mm × 50 mm.

1.2.1 Types of Bricks

Bricks may be broadly classified as:

(i) Building bricks

(ii) Paving bricks

(iii) Fire bricks

(iv) Special bricks.

(i) Building Bricks: These bricks are used for the construction of walls.

(ii) Paving Bricks: These are vitrified bricks and are used as pavers.

(iii) Fire Bricks: These bricks are specially made to withstand furnace temperature. Silica bricks belong to this category.

(iv) Special Bricks: These bricks are different from the commonly used building bricks with respect to their shape and the purpose for which they are made. Some of such bricks are listed below:

(a) Specially shaped bricks

(b) Facing bricks

(c) Perforated building bricks

(d) Burnt clay hollow bricks

(e) Sewer bricks

( f ) Acid resistant bricks.

(a) Specially Shaped Bricks: Bricks of special shapes are manufactured to meet the requirements of different situations. Some of them are shown in Fig. 1.3.

 (b) Facing Bricks: These bricks are used in the outer face of masonry. Once these bricks are provided, plastering is not required. The standard size of these bricks are 190 × 90 × 90 mm or 190 × 90 × 40 mm.

(c) Perforated Building Bricks: These bricks are manufactured with area of perforation of 30 to 45 per cent. The area of each perforation should not exceed 500 mm2. The perforation should be uniformly distributed over the surface. They are manufactured in the size 190 × 190 × 90 mm and 290 × 90 × 90 mm.

(d) Burn’t Clay Hollow Bricks: Figure 1.4 shows a burnt clay hollow brick. They are light in weight. They are used for the construction of partition walls. They provide good thermal insulation to buildings. They are manufactured in the sizes 190 × 190 × 90 mm, 290 × 90 × 90 mm and 290 × 140 × 90 mm. The thickness of any shell should not be less than 11 mm and that of any web not less than 8 mm.

 (e) Sewer Bricks: These bricks are used for the construction of sewage lines. They are manufactured from surface clay, fire clay shale or with the combination of these. They are manufactured in the sizes 190 × 90 × 90 mm and 190 × 90 × 40 mm. The average strength of these bricks should be a minimum of 17.5 N/mm2 . The water absorption should not be more than 10 per cent.

( f ) Acid Resistant Bricks: These bricks are used for floorings likely to be subjected to acid attacks, lining of chambers in chemical plants, lining of sewers carrying industrial wastes etc. These bricks are made of clay or shale of suitable composition with low lime and iron content, flint or sand and vitrified at high temperature in a ceramic kiln.

1.2.2 Properties of Bricks

The following are the required properties of good bricks:

(i) Colour: Colour should be uniform and bright.

(ii) Shape: Bricks should have plane faces. They should have sharp and true right angled corners.

(iii) Size: Bricks should be of standard sizes as prescribed by codes.

(iv) Texture: They should possess fine, dense and uniform texture. They should not possess fissures, cavities, loose grit and unburnt lime.

(v) Soundness: When struck with hammer or with another brick, it should produce metallic sound.

(vi) Hardness: Finger scratching should not produce any impression on the brick.

(vii) Strength: Crushing strength of brick should not be less than 3.5 N/mm2. A field test for strength is that when dropped from a height of 0.9 m to 1.0 mm on a hard ground, the brick should not break into pieces.

(viii) Water Absorption: After immercing the brick in water for 24 hours, water absorption should not be more than 20 per cent by weight. For class-I works this limit is 15 per cent.

(ix) Efflorescence: Bricks should not show white patches when soaked in water for 24 hours and then allowed to dry in shade. White patches are due to the presence of sulphate of calcium, magnesium and potassium. They keep the masonry permanently in damp and wet conditions.

(x) Thermal Conductivity: Bricks should have low thermal conductivity, so that buildings built with them are cool in summer and warm in winter.

(xi) Sound Insulation: Heavier bricks are poor insulators of sound while light weight and hollow bricks provide good sound insulation.

(xii) Fire Resistance: Fire resistance of bricks is usually good. In fact bricks are used to encase

steel columns to protect them from fire.

1.2.3 Tests on Bricks

The following laboratory tests may be conducted on the bricks to find their suitability:

(i) Crushing strength

(ii) Absorption

(iii) Shape and size and

(iv) Efflorescence.

(i) Crushing Strength: The brick specimen are immersed in water for 24 hours. The frog of the brick is filled flush with 1:3 cement mortar and the specimen is stored in damp jute bag for 24 hours and then immersed in clean water for 24 hours. The specimen is placed in compression testing machine with 6 mm plywood on top and bottom of it to get uniform load on the specimen. Then load is applied axially at a uniform rate of 14 N/mm2 . The crushing load is noted. Then the crushing strength is the ratio of crushing load to the area of brick loaded. Average of five specimen is taken as the crushing strength.

(ii) Absorption Test: Brick specimen are weighed dry. Then they are immersed in water for a period of 24 hours. The specimen are taken out and wiped with cloth. The weight of each specimen in wet condition is determined. The difference in weight indicate the water absorbed. Then the percentage absorption is the ratio of water absorbed to dry weight multiplied by 100. The average of five specimen is taken. This value should not exceed 20 per cent.

(iii) Shape and Size: Bricks should be of standard size and edges should be truely rectangular with sharp edges. To check it, 20 bricks are selected at random and they are stacked along the length, along the width and then along the height. For the standard bricks of size 190 mm × 90 mm × 90 mm. Lengthwise: 3680 to 3920 mm

Widthwise: 1740 to 1860 mm

Heightwise: 1740 to 1860 mm.

The following field tests help in acertaining the good quality bricks:

(i) uniformity in size

(ii) uniformity in colour

(iii) structure

(iv) hardness test

(v) sound test

(vi) strength test.

(i) Uniformity in Size: A good brick should have rectangular plane surface and uniform in size. This check is made in the field by observation.

(ii) Uniformity in Colour: A good brick will be having uniform colour throughout. This observation may be made before purchasing the brick.

(iii) Structure: A few bricks may be broken in the field and their cross-section observed. The section should be homogeneous, compact and free from defects such as holes and lumps.

(iv) Sound Test: If two bricks are struck with each other they should produce clear ringing sound. The sound should not be dull.

(v) Hardness Test: For this a simple field test is scratch the brick with nail. If no impression is marked on the surface, the brick is sufficiently hard

(vi) Efflorescense: The presence of alkalies in brick is not desirable because they form patches of gray powder by absorbing moisture. Hence to determine the presence of alkalies this test is performed as explained below:

Place the brick specimen in a glass dish containing water to a depth of 25 mm in a well ventilated room. After all the water is absorbed or evaporated again add water for a depth of 25 mm. After second evaporation observe the bricks for white/grey patches. The observation is reported as ‘nil’, ‘slight’, ‘moderate’, ‘heavy’ or serious to mean

(a) Nil: No patches

(b) Slight: 10% of area covered with deposits

(c) Moderate: 10 to 50% area covered with deposit but unaccompanied by flaking of the surface.

(d) Heavy: More than 50 per cent area covered with deposits but unaccompanied by flaking of the surface.

(e) Serious: Heavy deposits of salt accompanied by flaking of the surface.

1.2.4 Classification of Bricks Based on their Quality

The bricks used in construction are classified as:

(i) First class bricks

(ii) Second class bricks

(iii) Third class bricks and

(iv) Fourth class bricks

(i) First Class Bricks: These bricks are of standard shape and size. They are burnt in kilns. They fulfill all desirable properties of bricks.

(ii) Second Class Bricks: These bricks are ground moulded and burnt in kilns. The edges may not be sharp and uniform. The surface may be some what rough. Such bricks are commonly used for the construction of walls which are going to be plastered.

(iii) Third Class Bricks: These bricks are ground moulded and burnt in clamps. Their edges are somewhat distorted. They produce dull sound when struck together. They are used for temporary and unimportant structures.

(iv) Fourth Class Bricks: These are the over burnt bricks. They are dark in colour. The shape is irregular. They are used as aggregates for concrete in foundations, floors and roads.

1.2.5 Uses of Bricks

Bricks are used in the following civil works:

(i) As building blocks.

(ii) For lining of ovens, furnaces and chimneys.

(iii) For protecting steel columns from fire.

(iv) As aggregates in providing water proofing to R.C.C. roofs.

(v) For pavers for footpaths and cycle tracks.

(vi) For lining sewer lines.