CE625A: Masonry Structures/Dr Durgesh Rai/IITK/2015 1 Masonry Materials Units Durgesh C. Rai Professor Department of Civil EngineeringIndian Institute of Technology Kanpur Kanpur - 208 01 6 Clay Bricks lay Bricks http://www.brick.com 3 Classification Classification • Clay Bricks – Most Common – Two types of • Un-burnt • Burnt • Clay – Chemical composition • Silica & Alumina 4 Clay Brick units Clay Brick units • Raw materials – Clay • Types Surface clays : sedimentary formation Shales : Clays subjected to high p ressure until they b ecome slate Fire clay : Deeper sites, refractory like properties – Iron oxide – Hydrated silicates of alumina – Miscellaneous impurities (e.g., Ca, Mg, Na, Ti, K) – Metallic oxide gives color to fired product
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Department of Civil Engineering Indian Institute of Technology Kanpur
Kanpur - 208 016
Clay Brickslay Bricks
http://www.brick.com
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ClassificationClassification
• Clay Bricks– Most Common– Two types of
• Un-burnt
• Burnt• Clay
– Chemical composition• Silica & Alumina
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Clay Brick unitsClay Brick units
• Raw materials– Clay
• TypesSurface clays : sedimentary formationShales : Clays subjected to high pressure until they become slateFire clay : Deeper sites, refractory like properties
– Iron oxide– Hydrated silicates of alumina– Miscellaneous impurities (e.g., Ca, Mg, Na, Ti, K)– Metallic oxide gives color to fired product
• Manufacturing Bricks– Winning and storage of raw materials
• Usually mined from open pits
– Preparation• Grinding • Sieving • Pug mills
– Forming• Tempering
To produce homogeneous , plastic mass ready for moulding Mixing water to clays in pug mills
Clay Brick unitsClay Brick units ……
C E 6 2 5 - M a s o n r y s t r u c t u r e s / D r
D u r g e s h
R a i /
I I T K / 2 0 1 2
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• Manufacturing Bricks…– Forming
• Three processesStiff mud process
12-15% water by weightPugging and De-airing gives increased strengthForms clay strip through extruder-wire cutter
Soft mud process20-30% of water by weightCast in moulds – sand struckLubricated with water
Dry press process7-10% of water by weightSteel moulds under pressure of 3.4-10 MPa
Clay Brick unitsClay Brick units ……
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• Manufacturing Bricks…– Drying
• Control temperature & humidityTo avoid excessive cracking
– Firing• 40-150 hours
Clays soften slowly and melt and fuse gradually when subjected to risingtemeperaturesThis fusibility of clay makes it hars, solid and of low absorbing capacity
• Fusion stagesIncipient stage: Soft particle stick together Vitrification stage: Clays form solid, non-absorbent mass (875-1300°C)Viscous stage: Clay mass breaks down and tends to become molten (should avoidthis stage)
– Cooling• Important stage• 48-72 hours• Rapid cooling will cause cracking
Water Absorption and Initial Rate of Absorption- Gives information about quality of bricks
f bWAIRA
WA: Water Absorption capacity of the brick material
IRA: Suction of water from mortar due to capillaryaction in bricks (per minute, per unit area, brickimmersed in about 3 mm deep water)
Water Absorption Water Absorption ……
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(b) Initial Rate of AbsorptionIRA = (W 1-W)/Anet
W 1=Weight of brick after 1 min in 1/8’’ (3 mm) waterW= Dry weight of the brick
• IRA < 30g/min/30in 2
Usually IRA is 5.0-40.0g/min/30in2 (0.25-2.05 kg/min/m2 )IRA < 0.25 kg/min/m2
Bricks may float on mortar, if the brick is dampLow Absorption-Low suction Units
IRA > 1.5 kg/min/m2
Highly absorptivePoor bond if dry thin layer of mortar is kept next to itShould be wet before (3-24 hrs),but surface is dry when laid with mortar
Water Absorption Water Absorption ……
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(b) Initial Rate of Absorption• High IRA is undesirable because of
Rapid drying of mortar Poor bond strength between brick and mortar Poor non-structural performancedue to water penetration into masonrySoaking of units is desired if IRA > 1.5 kg/min/m2
Water Absorption Water Absorption ……
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Engineering PropertiesEngineering Properties
• Compressive Strength– Depends on
• Clays• Type of manufacturing process
• Degree of burning
• Tested Flat-wise (ASTM C67) f b = P/Anet
– If Anet>A gross (75%), then use Anet = A gross• Since core will add strength because of
Light-weight cementitious material with closed cellular structureLow strength and stiffness compared to conventional masonryEasily cut into any shape with hand toolsGood fire, thermal and acoustic resistance
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Concrete Masonry UnitsConcrete Masonry Units
• Manufacturing – Developed by Swedish architect Johan Axel Eriksson in 1900s– AAC is a mixture of cement, sand, lime, gypsum and
aluminium powder which is steam cured– Aluminum powder reacts with calcium hydroxide and water
to form hydrogen, which increases the volume by two to threetimes.
– At the end of the foaming process, the hydrogen escapes intothe atmosphere and is replaced by air.
– Finally, the blocks are cured in an autoclave, producing a
final material, with about one-fifth to one-third the density ofstructural concrete.– Can be cut and nailed like wood and good thermal insulation