Bricks lecutre

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BRICKS

Civil Engineering Materials

Fall Semester 2014

Department of Civil Engineering

Iqra National University Peshawar

Civil Engineering Materials

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Building Materials

• Building stones

• Bricks and clay products

• Cement concrete

• Timber and wood products

• Metals and alloys

• Paints, varnishes, distempers

• Asphalt, bitumen and tar

• Plastics and fibers

• Glass

• Asbestos, adhesives and abrasives


Bricks and Clay Products


Clay Products

• Clay Products

– Bricks

– Tiles

– Fire clays and fire bricks

– Terracotta

– Earthenware

– Clay pipes

• Bricks

– Block of tampered clay or ceramic material molded to desired shape and size, sun dried and if required burnt to make it more strong, hard and durable


Bricks

• Commonly it is rectangular in shape

– Length = twice width of brick + thickness of mortar

– Height = multiple of width of brick

– Usual size available in Pakistan is 8¾ x 4¼ x 2 ¾ inches to make it 9 x 4.5 x 3 inches with mortar

– Indian Standard size 19 x 9 x 9 cm and 19 x 9 x 4 cm to make it 20 x 10 x 10 cm and 20 x 10 x 5 cm with mortar

• Bricks are most common form of structural clay products; others being tiles, pipes, terracotta, earthenware, stoneware, and porcelain

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Historical Development

Began as low walls of stones or caked mud

Sun-dried bricks - With the availability of fire became burnt

bricks

Invention of kilns made mass production of bricks easy

Limestone turned into lime mortar replaced mud as mortar

In Mesopotamia, palaces and temples were built of stone and

sun-dried bricks in 4000 B.C.

The Egyptians erected their temples and pyramids of stones by

3000 B.C.

By 300 B.C., Greeks perfected their temples of limestone and

marble

Romans made the first large-scale use of masonry arches and

roof vaults in their basilica, baths and aqueducts



Medieval and Islamic civilizations perfected masonry vaulting to a high degree of development - Islamic craftsmen built palaces, markets, and mosques of bricks and often faced them with brightly glazed tiles

Europeans built fortresses and cathedrals using pointed vaults and flying buttresses

In America and Asia other cultures were building with stones

During industrial revolution, machines were developed to quarry and cut stones, mould bricks, and speed the transportation of these materials to site of building

Portland cement came into wide use and this enabled the construction of masonry building of greater strength and durability



Late in 19th century tall buildings were built, of steel and

reinforced concrete (pored into simple forms), economically

Development of hollow concrete forms in 19th century averted

the extinction of masonry as a building material - Cavity wall,

developed by the British during the earlier part of the 19th

century also contributed to the survival of masonry as a building

material

This facilitated the introduction of thermal insulation

High strength mortars, high-strength masonry units, and

complex shapes of masonry units extended the use of masonry

for buildings



• Through the mid-1800s – Primary Building Materials

• Late 1800s – New Products Developed

– Ended Masonry’s Dominance

• 20th Century Developments

– Steel Reinforced Masonry

– High Strength Mortars

– High Strength Masonry Units

– Variety of Sizes, Colors, Textures & Coatings

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Adobe

• Spanish-American name applied to sun-dried brick and to the clay soil from which the brick is made

• Adobe soil is composed of very fine mixture of clay, quartz, and other minerals

• Adobe soil has great plasticity when moist, but when dry is so coherent that tillage is almost impossible

• Soil is used combined with straw, molded and baked in sun for 7 to 14 days

• Used in regions of low rainfall and dampness


Civil Engineering Uses

• Construction of exterior and interior walls,

partitions and boundary walls

• Construction of piers, abutments

• Construction of footings

• Construction of miscellaneous load

bearing structures


Classification of Bricks

Bricks

Sun Dried

Katcha

Un Burnt

Burnt

Pucca

Practice Usage Finish Manufacture Burning Strength


Classification of Bricks

• Sun Dried, Un-burnt or Kacha Bricks

– After molding dried in sun, and are used in

the construction of temporary structures

which are not exposed to rains.

• Burnt or Pucca Bricks

– Burnt in an oven called kiln to provide

strength and durability


Classification of Burnt Bricks

Burnt

Bricks

Practice Usage Finish Manufacture

1st Class

2nd Class

3rd Class

4th Class

Common

Brick

Facing

Brick

Engg

Brick

Sand

Faced

Rustic

Hand

Made

Machine

Made

Burning

Pale Bricks

Under Burnt

Body Bricks

Well Burnt

Arch Bricks

Over Burnt

Strength

Class A

Class B

Classes

350 to 35



Field Practice • First Class Bricks

– Thoroughly burnt, deep red, cherry or copper color

– Straight edges, square corners, smooth surface

– Free from flaws, cracks, stones and nodules

– Uniform texture & ringing sound

– No scratch marks with fingernails

– Water absorption 12-15% of dry weight in 24 hours

– May have only slight efflorescence

– Crushing strength not less than 10.5 N/mm2

– Recommended for pointing, exposed face work, flooring and reinforced brick work



Field Practice • Second Class Bricks

– Small cracks and distortions permitted

– Water absorption 16-20% of dry weight allowed

– Crushing strength not less than 7.0 N/mm2

– Recommended for all hidden work and centering of RBC

• Third Class Bricks, Pilla Bricks – Under burnt, Soft and light colored producing dull sound

– Water absorption 25% of dry weight

– Recommended for temporary structures

• Fourth Class Bricks, Jhama, Khingar – Over burnt and badly distorted in shape and size

– Brittle in nature

– Ballast of these bricks used for foundation and floors and as road metal



Strength Based • Classes

– 350 (35 N/mm2) 125 (12.5 N/mm2)

– 300 (30 N/mm2) 100 (10 N/mm2)

– 250 (25 N/mm2) 75 (7.5 N/mm2)

– 200 (20 N/mm2) 50 (5 N/mm2)

– 175 (17.5 N/mm2) 25 (2.5 N/mm2)

– 150 (15 N/mm2)

• Sub Classes – Subclass A. Tolerance 0.3% in dimensions

– Subclass B. Tolerance 0.8% in dimensions

• Heavy Duty. Compressive strength > 40 N/mm2



• Basis of Usage

– Common Brick. General multi-purpose

– Facing Brick. Good appearance, color, textured,

durable under severe exposure

– Engineering Bricks. Strong, impermeable, smooth

and hard

• Basis of Finish

– Sand Faced Brick. Textured surface by sprinkling

sand inside mold

– Rustic. Mechanically textured finish



• Basis of manufacturing method

– Hand Made. Hand molded

– Machine Made. Wire cut, pressed and molded bricks

• Basis of Burning

– Pale Bricks are under burnt

– Body Bricks are well burnt in central portion of kiln

– Arch Bricks are over burnt. Also called clinker


Comparison of Stones and Bricks

• Stone – Natural material

– Heavier

– High dressing cost

– Costly except in hilly areas

– Less porous, good for hydraulic structures

– Greater strength

– Better heat conductor

– Weather resistant

– Superior quality stone is monumental and decorative

• Bricks – Manufactured from clay

– Lighter

– Moldable to any shape

– Cheaper except in hilly areas

– More porous, needs water proof treatment

– Reasonable for normal loads

– Poor heat conductor

– Needs pointing and plastering

– Architectural effect is achievable


Ingredients of Good Brick Earth

• Brick earth is formed by the disintegration of igneous rocks. Potash feldspars, orthoclase or microcline yield clay minerals which decompose to yield kaolinite, a silicate of alumina. On hydration it gives a clay deposit Al2O3. 2H2O called kaolin.

• Alumina or clay 20-30% by weight

• Silica or sand 35-50% by weight

• Silt 20-35% by weight

• Remaining ingredients 1-2% by weight – Lime (CaO)

– Magnesia (MgO)

– Iron oxides

– Alkalis (Sodium potash, etc)

• Water



• Silica, Sand – Present as free sand or silicate. Its presence in clay produces hardness, resistance to heat, durability and prevents shrinkage and warping.

• Alumina – Fine grained mineral compound. Moldable plastic when wet, becomes hard, shrinks, warps and cracks when dry.

• Lime – Acts as binder for brick particles. Reduces shrinkage when present in small amount, excess causes the brick to melt and lose shape.



• Magnesia – Provides darker yellow color

with iron. Usually less than 1%.

• Iron Oxide – Helps fusion of brick and

provides light yellow to red color to brick.

Should not be present as iron pyrites



• Harmful Substances – Lime in excess or in lumps and pebbles, gravel, etc

– Iron Pyrites

– Alkalis in excess

– Organic Matter

– Carbonaceous Materials

• Additives – Fly Ash – silicates help in strength development

– Sandy Loam – controls drying of plastic soil

– Rice Husk Ash – controls excessive shrinkage

– Basalt Stone Dust – modifies shaping, drying & firing


Operations in Manufacturing of Bricks

• Preparation of Brick Earth

– Un-soiling

– Digging

– Weathering

– Blending

– Tempering

• Molding of Bricks

• Drying of Bricks

• Burning of Bricks


Preparation of Brick Earth

• Un-soiling – Removal of top 20 cm organic matter and freeing from gravel, coarse sand, lime etc

• Digging – additives spread, soil excavated, puddled, watered and left over for weathering

• Weathering – heaps left for one month for oxidation and washing away of excessive salts in rain

• Blending – sandy earth and calcareous earth mixed in right proportions with right amount of water

• Tempering – kneading of blended soil with feet or with a pug mill to improve plasticity and homogeneity


Pug Mill


Manufacturing of Burnt Bricks

• Molding – giving right shape

– Hand molding • Ground molding. Molded on sand. No frog in bricks

• Table molding. Molded on stock boards with frog

– Machine molding • Plastic method or Stiff-Mud process. Molded stiff clay bar

cut by wire into brick size pieces. Structural clay products

• Dry Press method. Moist powdered clay fed into machine to be molded into bricks. Roof, floor and wall tiles

• Drying – Removing 7-30% moisture present during molding stage. This controls shrinkage, fuel and burning time. Natural open air driers in shades


Brick Molds


Table Molding


Plastic Molding


Strikes


Extruded – Wire Cut Extruded – Smooth

Wood Mold Extruded – Raked


Method

of Drying

Bricks



• Burning Stages – Dehydration (400-650 °C). Water smoking stage in

which water from pores driven off

– Oxidation (650-900 °C). Carbon eliminated and ferrous iron oxidized to ferric form. Sulphur is removed

– Vitrification (900-1250 °C). Mass converted into glass like substance

• Incipient vitrification. Clay just softens to adherence

• Complete vitrification. Maximum shrinkage

• Viscous vitrification. Soft molten mass, loss in shape, glossy structure on cooling



• Clamp or Pazawah Burning – Alternate layers of bricks and fuel encased in mud plaster.

– Fuel consists of grass, cow dung, litter, wood, coal dust

– Brick layer consists of four to five courses of brick

– 25,000 to 100,000 bricks in three months cycle

• Kiln Burning – Intermittent kiln. Loaded, fired, cooled and unloaded before

next loading

– Continuous kiln. Bricks are loaded, fired, dried and cooled simultaneously in different chambers. Example: Bull’s trench kiln and Hoffman’s kiln


Clamp or

Pazawah


Intermittent

Kiln


Hoffman’s

Continuous

Kiln


Bull’s Trench Kiln


Bull’s

Trench

Kiln


Characteristics of Good Bricks

• Size and shape – uniform size, rectangular surfaces, parallel sides, sharp straight edges

• Color – uniform deep red or cherry

• Texture and compactness – uniform texture, fractured surface should not show fissures, holes, grits or lumps of lime

• Hardness and soundness – not scratchable by finger nail. Produce metallic ringing sound

• Water absorption – should not exceed 20% wt

• Crushing strength – not less than 10.5 N/mm2

• Brick earth – free from stones, organic matter


Special

Forms

of

Bricks

a. Round ended

brick

b. Cant brick

c. Splay brick

d. Cornice brick

e. Compass brick

f. Bull nosed brick

g. Perforated brick

h. Hollow brick

i. Coping brick

j. Plinth level brick

k. Split brick (Queen

closer)

l. Split brick (King

closer)


Specially Shaped Bricks



Testing of Bricks

• Dimension Test. Sample size 50. 20 pieces selected to determine length, width and height tolerances.

• Compressive strength Test. Sample prepared from smooth, parallel face, brick is soaked 24 hours and stored under damp jute bags for 24 hours followed by further immersion in water for three days. Load applied @ 14 N/mm per minute till failure. Maximum load at failure divided by average area of bed face gives compressive strength.


Testing of Bricks

• Absorption Test. – 24 hours immersion cold water test.

• Dry bricks oven dried at 105° ± 5° C

• Room temperature cooled bricks weighed W1

• Bricks immersed in water at 27° ± 2° C for 24 hrs

• Soaked bricks weighed W2

• Water absorption in % = (W2 – W1)/W1 x 100

– Five hours boiling water test • Oven dried bricks weight W1

• Bricks immersed in water and boiled for 5 hours and then cooled down at room temperature in 16-19 hours

• Cooled down weight as W3

• Water absorption in % = (W3 – W1)/W1 x 100


Testing of Bricks

• Efflorescence Test. Ends of brick kept in 150 mm dia porcelain/glass dish containing 25 mm deep water at 20°–30°C till all water is absorbed – Nil imperceptible efflorescence

– Slight deposit covers area < 10% of exposed area

– Moderate deposit covers exposed area 10% to 50%

– Heavy deposit covers exposed area > 50%

– Serious deposits are heavy and powder or flake away the surface


Defects of Bricks

• Over-burning. Burnt beyond complete vitrification

• Under-burning. Burnt less not to cause complete vitrification

• Bloating. Spongy swollen mass over the surface due to excess carbonaceous matter and sulphur

• Black Core. Due to bituminous matter or carbon

• Efflorescence. Grey white crystallization of alkalis on the surface, due to water absorption

• Chuffs. Deformation due to rainwater falling or hot bricks

• Checks or Cracks. Due to lumps of lime getting in contact with water

• Spots. Dark sulphur spots due to iron sulphides

• Blisters. Broken blisters due to air entrapped during molding

• Laminations. Thin lamina produced due to air entrapped in voids of clay


Brick Masonry

• Brick sides

– Header

– Stretcher

• Brick Bonds

– English

• Brick Masonry Patterns

– Herringbone

– Basket weave

– Flemish



Basic Brickwork Terminology

Bed

Joint

Head

Joint

Course - horizontal layer of brick


Basic Brickwork Terminology

Header - Bonds two wythes together

Wythe: vertical layer 1 unit thick

Soldier - Laid on its end, face parallel

Rowlock -

laid on face,

end visible

Stretcher - long dimension horizontal

& face parallel to the wall


Joint Color that “Blends” w/ Brick Color



Concave Joints


Raked Joints



Simulated Precast Concrete Lintel

(actually a steel lintel supports the assembly)


Arch

