Presentation on theme: "BRICKS. Bricks are obtained by moulding clay in rectangular blocks of uniform size and then by drying and burning these blocks. As bricks are of uniform."— Presentation transcript:
Bricks are obtained by moulding clay in rectangular blocks of uniform size and then by drying and burning these blocks. As bricks are of uniform size, they can be properly arranged, light in weight ----------------------------------replace stones
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Size of the Brick Standard size 19cm X 9cm X 9cm 19cm X 9cm X 4cm Nominal size 20cm X 10cm X 10cm – Nominal size is the thikness of motar with brick size Size of Brick used
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. These bricks are used for superior work of permanent nature. CLASSIFICATION OF BRICKS
Second class 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 may have hair cracks and their edges may not be sharp and uniform. These bricks are commonly used at places where brickwork is to be provided with a coat of plaster
Third class bricks: ground-moulded and they are burnt in clamps. not hard and they have rough surfaces with irregular and distorted edges. give dull sound when struck together. used for unimportant and temporary structures and at places where rainfall is not heavy.
Fourth class bricks: These are over burnt with irregular shape and dark color. These bricks are used as aggregate for concrete in foundations, floors, roads, etc. the over burnt brick have a compact structure ----sometimes found to be stronger that even the first class bricks.
Composition Following are the constituents of good brick earth. 1.Alumina chief constituent of clay A good brick earth should contain 20 to 30 percent of alumina. imparts plasticity to earth -------moulded. If alumina is present in excess, raw bricks shrink and warp during drying and burning.
2. Silica A good brick earth should contain about 50 to 60 percent of silica. Silica exists in clay either as free or combined form. Presence of silica prevents crackers, shrinking and warping of raw bricks. It thus imparts uniform shape to the bricks.
3. Lime A small quantity in finely powdered state prevents shrinkage of raw bricks. Excess of lime causes the brick to melt and hence, its shape is lost due to the splitting of brick
4. Oxide of iron A small quantity of oxide of Iron -- 5 to 6 percent is desirable in good brick to imparts red colour 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 to bricks decreases shrinkage. excess of magnesia leads to the decay of bricks. The ingredients like, lime, alkalies, pebbles, organic matter should not present in good brick earth
Manufacture of bricks: The manufacturing of brick, the following operations are involved I.Site selection II.Preparation of brick earth III.Moulding of brick IV.Drying of bricks V.Burning of bricks 1.Unsoiling 2.Digging 3.Cleaning 4.Weathering 5.Grinding 6.Blending 7.Tempering
(i)Selection of site Must have suitable clay In sufficient quantity Location---water table should be atleast 1m below kiln floor
(ii) Preparation of clay :- The preparation of clay involvesfollowing operations Unsoiling Top layer of 20cm depth is removed as it contain impurities- organic matter, roots. Digging Clay is dug out from ground and spread on level ground about 60cm to 120cm heaps. Cleaning Stones, pebbles, vegetable matter etc removed and converted into powder form.
Weathering Clay is exposed to atmosphere from few weeks to full season. Grinding hard clay with lumps are crushed in clay crushing rollers Blending Clay is made loose and any ingradient to be added to it is spread out at top and turning it up and down in vertical direction Tempering Clay is brought to a proper degree of hardness, then water is added to clay and whole mass is kneaded or pressed under the feet of men or cattle for large scale, done in pug mill
iii) Moulding of bricks Hand or machine Mould- Rectangular boxes open at bottom Wood or steel
Hand moulding Ground is levelled Sprinkle fine sand Dip mould in water and place on grnd Lumps of clay are dashed in to it Pressed and filled----fill corners Surplus clay removed by using a stricker Mould is lifted up Raw brick remains
Machine moulding When, -large scale production -Clay is hard -Plastic clay machine---wire cut bricks -Dry clay machine---powdered clay filled in moulds ---pour water----pressed----results in hard, well shaped
Drying The damp bricks, if burnt, are likely to be cracked and distorted. Hence moulded bricks are dried Bricks are laid along and across the stock in alternate layers. 5-7 % moisture content Mostly natural or artificial drying
Burning: to impart hardness, strength and makes them dense and durable. Burning --- clamps or in kilns. Clamps are temporary structures and to manufacture bricks on small scale. Kilns are permanent structures and they are adopted to manufacture bricks on a large scale.
Clamp Temporary structures Stacked in layers with gaps for firewood 6-8 weeks Strong tough bricks Quality not uniform No skilled labour Kilns Masonry structures ----permanent Continuous Uniform quality Need skilled labour
Qualities of Good Brick Bricks should be table moulded, well burnt in kilns, copper coloured, free from cracks and with sharp and square edges uniform shape and should be of standard size clear ringing sound when struck each other
bright homogeneous and compact structure free from voids should not absorb water more than 20 percent by weight for first class bricks 22 percent by weight for second class bricks when soaked in coldwater for a period of 24 hours
Tests on bricks A brick is generally subjected to following tests to find out its suitability of the construction work. – Compressive strength – Absorption – Hardness – Presence soluble salts – Shape and size – Soundness – Structure – Absorption A good should not absorb not more than 20 percent of weight of dry brick
Compressive strength: Smooth the surface, immerse in water for 24 hrs in compression testing machine It is pressed till it breaks @ 14 N/mm 2 per minute Compr strength = max load at failure/loaded area of brick
Absorption Oven dried for 1 day @ 100 0 C 27 0 C for 24 hrs A good should not absorb not more than 20 percent of weight of dry brick %water absorption = ((w 2 -w 1 )/w 1 ) X 100 Hardness Scratch with finger nail -- No impression is left on the surface the brick is treated to be sufficiently hard
Presence of soluble salts (efflorescence) The bricks should not show any grey or white deposits after immersed in water for 24 hours (HW) Shape and size It should be standard size and shape with sharp edges
Soundness The brick should give clear ringing sound struck each other Structure The structure should be homogeneous, compact and free from any defects
Warpage Measured with – Flat surface of steel/glass – Steel measuring rule Clean the surface Place on the flat Measure greatest distance using the rule