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CE625A: Masonry Structures/Dr Durgesh Rai/IITK/2015 1
Masonry Materials
UnitsDurgesh C. Rai
Professor
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
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• Significant physical properties of clays– Plasticity– Fusibility– Tensile strength– Shrinkage
Clay Brick unitsClay Brick units ……
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• 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
Clay Brick unitsClay Brick units ……
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• Manufacturing Bricks…– Brick forming machine
Clay Brick unitsClay Brick units ……
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• Manufacturing Bricks…– Firing in Clamps/Scoves
Clay Brick unitsClay Brick units ……
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• Manufacturing Bricks…– Bull’s Trench Kiln
• Continuous
Clay Brick unitsClay Brick units ……
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• Manufacturing Bricks…– Hoffman’s Kiln
Clay Brick unitsClay Brick units ……
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Engineering PropertiesEngineering Properties
• Absorption– Related to degree of burning of clay particles, fusing
temperatures and porosity
• Durability– Incipient fusion– Partial Vitrification
• Thermal Conductivity• Acoustics• Fire Resistance
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• Compressive strength– Properties of clays and methods of manufacture
• Stiff mud process produces bricks of higher compressivestrength
– Degree of firing• For given clay and method of manufacture, higher firing
temperature produces bricks of higher strength and lowerabsorption
• Flexural Strength
– Factors affecting are same as those for compressive strength• Elastic Modulus• Split Tensile Strength
Engineering PropertiesEngineering Properties ……
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Physical PropertiesPhysical Properties
• Colour– Iron oxide content controls, but depends on
• Oxidizing (red) or reducing (purple) environs
• Texture– Smooth or sand finished
• Form and size variation– Air 2-8%– Fire 2.5-10%
• Dimensional stability
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Water Absorption Water Absorption
• Total Water Absorption =Weight of water absorbed after 24 hrs in cold water
Total dry weight
(a) Saturation Coefficient C/B Ratio =Weight of water absorbed after 24 hrs in cold water .Total absorption after 5hr boiling + 24 hr in cold water
C/B ratio is measure of freeze-thaw durability and should not be greater than 0.78.
Secondary pores filledby boiling water
Primary pores filled bycold water
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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
Uniform drying and Shrinkage
Bond action between mortar and brick
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• Compressive Strength– North American bricks
• 3-30ksi (21-210 MPa)• Nominal Strength (8-15ksi) (56-105 MPa)
– Indian Bricks• > 3.5 MPa• 10-20 MPa common for bricks in North India
Engineering PropertiesEngineering Properties ……
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• Modulus of ElasticityEb=1400-5000 ksi (9.8-35.0 GPa)
• Modulus of Rupture f r =1.5 Pl/bt 2
• Sahlin: f r /f b varies ~0.1-0.32
• Coefficient of Thermal Expansion0.0045-0.0072 mm/m/°C (Fire clays → Shale → Surface clays)
Engineering PropertiesEngineering Properties ……
l
t
b
P
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Tensile Strength of Brick UnitsTensile Strength of Brick Units
Split tensile strength, f t (ASTM C 1006-07)Flat position
On edge position
L
Split tensile failure
Alignment Jig
Flat Position On Edge Position
2t
P f LH
P
P
H
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Tests on BricksTests on Bricks
• Flowchart– Dry Bricks in oven for 24 hours– Weigh dry bricks (determine density)– Run IRA
– Dry Bricks– Run Modulus of Rupture Test– Run Absorption Test
• Soak in cold water for 24 hours
– Run Saturation Coefficient Test (optional)• Soak half-bricks in boiling water 5 hours
– Run flat-wise Compressive Test (Cap and crush)
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IS 1077: BricksIS 1077: Bricks
• Class of bricks– Based on compressive strength
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IS 1077: BricksIS 1077: Bricks
• Dimension of bricks
– Common brick size• Approx. 235 ×110×70 mm ( 9×4.5×2.75 in .)
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IS 1077: BricksIS 1077: Bricks
• Water Absorption
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Compressive Stress-Strain Curves of Brick Units-Research at IIT Kanpur (Kaushik et al 2007)
Four brick manufacturers:M: MBFB: BajrangO: OnkarS: Sarang
Average Dimensions:Length 230 mmWidth 110 mmHeight 75 mm
CompressiveCompressive Behaviour Behaviour ——Clay BricksClay Bricks
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Typical crushing failure
Test Setup
CompressiveCompressive Behaviour Behaviour ——Clay BricksClay Bricks
306095 [0.29]0.0065 [0.34]20.8 [0.33]Avg (40 specimens)
6534 [0.10]0.0057 [0.28]20.6 [0.17]S (10 specimens)
7516 [0.26]0.0070 [0.39]28.9 [0.23]O (10 specimens)
5030 [0.34]0.0060 [0.19]16.1 [0.08]B (10 specimens)
5300 [0.15]0.0072 [0.18]17.7 [0.23]M (10 specimens) Eb (MPa)Failure strain f b (MPa)Brick type
[] – COV
0
5
10
15
20
25
30
0.000 0.002 0.004 0.006 0.008 0.010 0.012Strain
C o m p r e s s i v e
S t r e s s , M P a
MB
O
SAverage
bb
bb
bb
bb
bb
f E
f E
f E
f E
f E
300
317S
260O
312B
300M
Eb - slope between0.05 f b - 0.33 f b
CompressiveCompressive Behaviour Behaviour ——Clay BricksClay Bricks
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Eb ≈ 150 f b to 500 f b
Variation of f b with Eb
C r – Correlation Coefficient (Poor C r for Eb ≈ 300 f b )
0
2000
4000
6000
8000
10000
12000
0 10 20 30 40Brick compressive strength, MPa
B r i c k e l a s t i c m o d u l u s ,
M P a
M bricks
B bricks
O bricks
S bricks
40 brick specimens
C r =0.39
bb f E 300
bb f E 150
bb f E 500
CompressiveCompressive Behaviour Behaviour ——Clay BricksClay Bricks
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IRA and f b are more closely correlated
Too low IRA, bricks may float on mortarToo high IRA, rapid suction of water in mortar by bricks
Poor Brick-Mortar Bond
IRA test is not mandatory as per IS:3495 (1992)
CompressiveCompressive Behaviour Behaviour ——Clay BricksClay Bricks
010
20
30
40
0 1 2 3IRA, kg/m2/min
C o m p . s t r e s s ,
M P a
C r = - 0.77
8 10 12 14 16WA, %
C r = - 0.24
IRA vs. WA
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Fly sh Bricksly sh Bricks34
Fly Ash BricksFly Ash BricksAdvantages
– Higher cold crushing strength (10-15 MPa)– Low water absorption (13-15%)
• Reduced efflorescence– Smooth and uniform size
• Requires less quantity ofcement mortar & no plaster
– Lower bulk density (1600 kg/m3 )• Reduces dead weight
on load bearing walls• Saves transportation cost
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Methods of Manufacturing Methods of Manufacturing
• Primary Ingredients– Fly ash (Grade 1 or 2 of IS 3812)– Sand– Lime (Hydraulic Class C of IS 712)
– Chemical accelerators, small quantity such asGypsum, cement, etc.• Mixing
– In the first stage, only dry mixing is done– About 8- 10% water, 0.2% (by weight) chemical
accelerator is added in the second stage mixing.– This admixture is further subjected to thorough
mixing in the third stage.36
Methods of Manufacturing Methods of Manufacturing ……
Moulding – Fly ash is a non-plastic material
• Raw mix is subjected to a pressure of ~25 MPain a suitable hydraulic press
Double acting brick press (CybertekEngineering, Faridabad) Brick Press (CBRI, Roorkee )
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Methods of Manufacturing Methods of Manufacturing ……
• Drying – Green bricks exposed to natural drying
for about 48-60 hours• Depending upon weather conditions
• Steam Curing – Semi- dried bricks cured in Autoclaves
(steam chamber) at a desired pressure & temperature– Steam cured finished bricks stacked in open
• They gain further strength
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SpecificationsSpecifications
• IS 12894-2002– Dimensions same as clay bricks– Compressive Strength
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SpecificationsSpecifications
• IS 12894-2002– Water Absorption
– Efflorescence
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C Blocks C Blocks
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Autoclaved Aerated Concrete Autoclaved Aerated Concrete
DEPARTMENT OF CIVIL ENGINEERING, IIT KANPUR
AAC Blocks(Fortune EkoTech)
AAC Blocks(Fortune EkoTech)
Cellular structure of AAC(Tanner, 2003)
Cellular structure of AAC(Tanner, 2003)
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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
and fire resistance of concrete
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Concrete Masonry UnitsConcrete Masonry Units
• Manufacturing
321.725.424.415.013.4 Water Absorption (%)
0.4
2.4
2.7
0.58
709
AACblock
0.7
0.4
9.1
1.6
0.88
1600.0
B
Fly-AshClayProperties
On edge
Flat position
0.50.51.7
0.40.31.0Tensile Strength(MPa)
5.35.421.9Compressive Strength (MPa)
4.44.42.7IRA (kg/m 2 /min)
0.910.82-Saturation Coefficient
1520.01740.01774.0Density (kg/m3
)
ABA
Comparison of Conventional Units and AAC Blocks
Tests conducted at IIT Kanpur (2012)
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Concrete Blocksoncrete Blocks46
Concrete Masonry UnitsConcrete Masonry Units
• Dimensions B×H×L– Specified dimension 3/8” < Nominal dimension– Actual dimension within 1/8” (3mm) of
Specified dimension• Example
Nominal Dimension: 200×200×400 mmSpecified Dimension: 190×190×390 mm
– Tapered holes, top-thicker web for better mortar placementand ease of lifting out of moulds
L
H
B
47 No. 47
Concrete Masonry UnitsConcrete Masonry Units
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• Concrete Blocks
Physical RequirementsPhysical Requirements ……
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Concrete Masonry UnitsConcrete Masonry Units
• IS 2185 (Part 1):2005
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Concrete Masonry UnitsConcrete Masonry Units
• IS 2185 (Part 1):2005
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RAW MATERIALSRAW MATERIALS
• Constituents– Portland Cement– Pozzolanas
• Reduce expansive characteristic
• Add surface resistance– Other Admixtures
• Air entrainment, pigments, water repellants, …
– Aggregates• Normal Weight
>125 pcf (2000 kg/m3 )
• Light Weight<105 pcf (1680 kg/m3 )
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METHODS OF MANUFACTURING METHODS OF MANUFACTURING
• Separate and weigh aggregates– Aggregate stored by density and gradation– Weighed– Transported
• Mixing – Cement + Aggregate + water + pigments+
admixtures to create damp (but not wet) mix
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• Moulding – Feed to mould– Consolidated by vibration (feed time)– Press mix into mould– Second vibration cycle consolidates mix (finish time)
• Ejection
– Come out in a set of 3 supported on steel pallets• Bottom of mold cavities
– Put in kiln for 6-8 hrs
METHODS OF MANUFACTURING METHODS OF MANUFACTURING ……
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• Curing – Done under saturated conditions– Elevate temperature for accelerated hydration– Store outside for continued curing
METHODS OF MANUFACTURING METHODS OF MANUFACTURING ……
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METHODS OF MANUFACTURING METHODS OF MANUFACTURING ……
• Production Plant
http://www.besser.com 56
Engineering PropertiesEngineering Properties
• Absorption– Weight changes after 24hr immersion in cold water
• 200–350 kg/m 3
• Total Linear shrinkage– Up to 0.065% for Type I Units
• Moisture Content– 25-45%• Compressive Strength
– 14-42 MPa (lower values in India!)• Tensile Strength
– 1.75-3.50 MPa• Deformational Properties
– Em=750 f’m ; Gm=0.4Em ; m=0.28
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Physical RequirementsPhysical Requirements
• IS 2185 (Part 1) :2005 Concrete Blocks
12.015.0 A(15.0)
MinimumCompressiveStrength ofindividualunits (MPa)
MinimumCompressiveStrength (MPa)
Density ofBlock(kg/m3)
GradeType
10.012.5 A(12.5)8.010.0 A(10.0)7.08.5 A(8.5)5.67.0 A(7.0)4.45.5 A(5.5)3.64.5 A(4.5)
2.83.5Not less than1500
A(3.5)Hollow loadbearing unit(Open & closedcavities)
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• IS Concrete Blocks
Physical RequirementsPhysical Requirements ……
2.83.5Less than1500 but not
less than1100
B (3.5)Hollow non-loadbearing unit(open & closedcavity)
MinimumCompressiveStrength ofindividualunits (MPa)
MinimumCompressiveStrength (MPa)
Density ofBlock(kg/m3)
GradeType
3.24.0C(4.0)4.05.0Not less than
1800C(5.0)Solid Load
bearing units
4.05.0B(5.0)
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• Concrete Blocks Machines
Physical RequirementsPhysical Requirements ……
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• Concrete Blocks Machines– Besser Machine in India in 1950’s– Sindhu Resettlement Corporation– Gandhidham city– 2001 Bhuj Earthquake
Physical RequirementsPhysical Requirements ……