Ce 625 a Masonry Materials Units 2015

8/9/2019 Ce 625 a Masonry Materials Units 2015

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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

3

ClassificationClassification

• Clay Bricks– Most Common– Two types of

• Un-burnt

• Burnt• Clay

– Chemical composition• Silica & Alumina

4

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


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


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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





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• Manufacturing Bricks…– Brick forming machine


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• Manufacturing Bricks…– Firing in Clamps/Scoves


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• Manufacturing Bricks…– Bull’s Trench Kiln

• Continuous


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• Manufacturing Bricks…– Hoffman’s Kiln



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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


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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


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• 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


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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)


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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• Dimension of bricks

– Common brick size• Approx. 235 ×110×70 mm ( 9×4.5×2.75 in .)

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• 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


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


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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


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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)


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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• 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)



Concrete Blocksoncrete Blocks46


• 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


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• Concrete Blocks

Physical RequirementsPhysical Requirements ……



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• IS 2185 (Part 1):2005

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• 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


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• Production Plant

http://www.besser.com 56


• 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


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


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• Concrete Blocks Machines– Besser Machine in India in 1950’s– Sindhu Resettlement Corporation– Gandhidham city– 2001 Bhuj Earthquake


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Ce 625 a Masonry Materials Units 2015