Sab 2112 - L12 Masonry

BRICK/BLOCK/STONE MASONRY

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Contents • Masonry materials • Types of masonry units • Manufacture of bricks and blocks • Characteristics and testing of bricks • Mortar for brickwork/masonry work

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MASONRY Type of construction whereby units are laid together to form a structure

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Masonry

Masonry Construction = masonry units + mortar Masonry units: Bricks Blocks Stones Made from a variety of non-organic material 5

MASONRY UNIT BLOCK

STONE

BRICK

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MASONRY STRUCTURE

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MASONRY STRUCTURES

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DESIRABLE CHARACTERISTICS • Strength • Durability • Resistance to water, noise and fire • Aesthetic • Other special requirements e.g. blast resistance 10

BRICKS

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Bricks • Bricks are produced in many formats: solid, perforated and hollow • Typically 215 x 102 x 65 mm (length x width x height) • Made of clay, sandcement, concrete and calcium silicate 12

Types of bricks (shape) Face shell

Central web End web

Cell

Solid End web

Perforate d holes 25 % of gross volume of the brick

Hollow

cavities exceeding 25 % of total volume of brick.

Frogge d volume of indentations must not exceed 20 % of gross volume.

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Types of Clay Bricks Three types of clay bricks: 1) Common – general use; not design to provide good finish or high strength; usually plastered, non-load bearing 2) Facing – for attractive appearance; no cracks; may or may not be load bearing; durable 3) Engineering – good strength and durability; high density; well fired (load bearing walls, retaining walls, sewers, embankments etc.) 14

Common Brick

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Facing Brick

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Facing Brick

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ENGINEERING BRICK

Column

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CLAY BRICKS Clay bricks continue to be the most important building units Raw materials are clay or shale Efficient material to use in terms of their energy consumption Strong and durable 19

Clay for Brick-making A variety clay composition and minerology deposited at different geological period; from soft sticky mud to shale Hence bricks are differ in their propertiescolour, texture, strength, density and durability Only 30-40% of brick making clay are clay minerals Clay minerals-size less than 2 microns; the amount and particle size present in the clay affect the cohesiveness, forming characteristics, drying and firing properties of the clay 20

Cont. Too much clay can result in high drying shrinkage; adding sand can reduce drying shrinkage Clays are hydrated aluminosilicates (predominance is silica and alumina); the main minerals are: kaolinite, Illite, montmorillonite Other mineral present in clays are: potash (K2O), Lime (CaO), Soda (Na2O), Magnesium (MgO) and iron (FeO, Fe2O3) Chemical analysis may be undertaken, together with minerological examination can assist in identifying the presence of chemicals and clay21

Manufacturing of clay bricks

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Stiff mud process PUG MILL

Grind clay

Preparation MIXER

Formation

EXTRUDE R WIRE

Drying

Firin g

Mix clay

Form clay strip

CUTTER

Cut bricks

TUNNEL DRYER

KILN

@ 40oC – 150 oC Dry bricks 24 – 48 hrs

Burn bricks @ 930 oC – 1320oC. 60-80 hrs.

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Manufacturing Clay Bricks 1) Clay Preparation Objectives: 1) improve homogeneity and plasticity of clay 2) control of physical and chemical properties such as shrinkage, colour and vitrification temperature 3) well prepared clay eliminate problems during the production process thereby reduces the rejection rates 24

Clay Preparation (cont.) Process Digging, crushing, sieving, grinding, proportioning, mixing, tempering Add chemicals for special purpose; eg. barium carbonate react with soluble salts producing insoluble product (expensive)

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MOULDING Process of giving shape to the bricks A variety of shaping methods that depends on the moisture content and consistency of the clay 26

Semi Dry Process Moisture content @ 10% Granular consistency, pressed in 4 stages After pressing be textured or sand faced Can be fired without going through drying stage Smooth finish 27

Stiff Plastic Process Moisture content @15% Extruded and then compacted into a mould under high pressure Many engineering bricks are made this way; clay containing large quantity of iron oxide help the fusion during firing Smooth finish

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Wire Cut Process Moisture content @ 20% Extruding a column of clay through a die and cut by tensioned wire Extrusion to a size which allow dry and firing shrinkage Perforated bricks are made this way, the perforation being formed during extrusion 29

Soft Mud Process Moisture content @ 30% Soft clay from shallow deposit Rolled in sand or sawdust and pressed manually into a mould

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DRYING OF BRICKS  Green bricks contain a considerable amount of moisture depending on the shaping process  The moisture content has to be further reduced before firing can be carried out Objectives:  Enable brick to be stacked higher in the kiln  Avoid too much shrinkage happening in the kiln which might cause the stack to become unstable  Enable firing temperature to be increased more rapidly 31

Drying of Bricks (cont.) Important for green bricks with high moisture content; Temperature being increased while humidity progressively decreased Low rate of drying to avoid stresses that cause cracking and distortion Dried until approximately at critical moisture content (leather-hard) Sufficiently rigid and strong for handling and stacking Chamber or tunnel dryers takes 1 or 2 days, 32 natural drying takes 6 weeks

FIRING OF BRICKS  Changes their physical structure and give them good mechanical properties and resistance to water  Sintering of clay increases the strength and decreases the soluble salt without loss of shape  Silica and alumina do not melt, they are fused together with metallic oxides THREE stages of firing: 1) 100 °C – water evaporation 2) 400 ºC – burning of carbonaceous matter 33 3) 900 – 1200 °C – sintering of clay

Firing of Bricks (cont.) Clay composition and chemical changes during firing influence the final colour of bricks Fe2 oxidation produce red colour bricks Large amount of lime produce yellowish-brown colour bricks 34

Properties of clay bricks Physical properties • Colour • Texture • Size • Density

Engineering properties • Compressive strength • Water Absorption • Initial rate of suction • Efflorescence and soluble salt content

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Colour and texture • Variety of colours: red, yellow, brown etc • Depending on mineral content and firing temperature • Variety of textures: smooth, rough, bark face etc.

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Density • Varies from 1300 – 2200 kg/m3 • Important for thermal and acoustic property of wall – Heavier wall better sound and thermal insulation – Solid units have higher thermal conductivity

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Size Header face

102.5 mm

Bed face

Stretcher face

Bed joint

65 mm

Head joint

215 mm

Actual size 215 X102.5 X 65 mm often called work size (BS)

Coordinating size (brick size +mortar thickness) 225 X112.5 X 75 mm

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Size Dimensional tolerance (MS 76/BS 3921): • Sizes of bricks must not be outside the ranges shown in Table 1 • Must not exceed the coordinating size • Test method – overall measurement of 24 bricks

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Table 1: Limits of sizes (MS/BS) Coordinating size (mm)

Work size Overall measurement of (mm) 24 bricks Maximum (mm)

225 112.5 75

215 102.5 65

5235 2505 1605

Minimum (mm)

5085 2415 1515

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Test Methods for Dimension

Length

Width

Height

Dimensional deviations • Overall measurements of 24 bricks 41

Compressive strength • Most important mechanical properties • Measure of quality • Use for classifying bricks • Varies in accordance to materials and manufacturing methods • Available in strengths of 5 – 100 N/mm2

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Test Methods for Bricks Compressive strength • Select 10 bricks from a stack • Bricks are immersed in water for 24 hours before testing • Faces are capped between 3 mm ply sheets or packed before testing to reduce the effects of roughness, lack of plane and platen effects • Bricks loaded normal to its bed face. Tested until failure. Compressive strength is calculated as the average of 10 bricks as below: Compressive strength

=

maximum load N/mm2 bed face area 43

Compressive Strength

Compressive Machine

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Water Absorption • Water absorption is the quantity of water that could be absorbed by the unit • Indicate porosity • Varies widely, clay units from 4.5 to 21%, calcium silicate units from 7 to 21% and concrete units from 7 to 10% • Clay bricks which absorb between 4.5 and 7.0% of their weight can be used as damp-proof course material

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Water Absorption • Highly absorptive clay bricks remove water from mortar preventing complete hydration of cement • Relation of water absorption to flexural strength of masonry

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Water Absorption Two types of tests: 1) 24 hours cold immersion test (Partially saturated condition) 2) 5 hr. boiling test (Fully saturated condition

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24 hours cold immersion test (ASTM C67) – Select 5 bricks from a stack – Dry bricks in the oven @110ºC for not less than 24 hrs – Cool the specimen and weigh each brick (Wd) – Immerse the dry bricks in clean water at 15 to 30ºC for 24 hours – Remove the bricks and weigh each brick (Ws) – Calculate the absorption of each brick as follows: Absorption % =

 Ws - Wd for the 10 bricks Report the average100 absorption  

Wd

 

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5 hours Boiling Test • Select 10 bricks. • Heat at 110 °C for not less than 48 hours – dry bricks. • When cool, weigh the bricks and record the dry mass (wd) • Then boil for 5 hours and then allow to cool naturally in the water a minimum of 16 hours and a maximum of 19 hours. • Weigh each brick and record the wet mass (ws) • Water absorption A %=

 W - Wd  100 s   Wd  49

Classification of clay bricks according to compressive strengths and absorption (BS) Designations Average compressive strength not less than (N/mm2)

Average absorption not greater than (% by weight)

Engineering A

70

4.5

Engineering B

50

7.0

Damp-proof course 1

5

4.5

Damp-proof course 2

5

7.0 50

Characteristic flexural strengths and levels of water absorption (BS 5628 Pt. 1, 1985) Characteristic flexural strength, fkx N/mm2 Plane of failure parallel Plane of failure perpendicular to to bed joints bed joints (i)

Mortar designation

(ii) and (iv) (iii)

(i)

(ii) and (iii)

(iv)

Clay bricks having a water absorption less than 7%

0.7

0.5

0.40

2.0

1.5

1.2

Between 7 % and 12 %

0.5

0.4

0.35

1.5

1.1

1.0 51

Over 12 %

0.4

0.3

0.25

1.1

0.9

0.8

Initial rate of suction (IRS)

• The rate at which bricks absorb water from mortar during laying • Measured in kg/m2/min. For clay bricks generally range from 0.25 – 2.05 kg/min/m2 Low values < 0.25 kg/min/m2 High values > 1.5 kg/min/m2 • Necessary for bond between bricks and mortar • Water tightness • Critical for highly stressed masonry structures

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Initial Rate of Suction • Select 10 bricks • Dry bricks in the oven • When cool, weigh the bricks and record the dry mass (m1). • Then immerse the dry brick in water for 1 min. Depth of immersion is 3± 1mm • After 1 min remove the wet bricks and weigh (m2) • Calculate initial rate of suction using formula below: 1000(m - m ) 2 2 1 IRS (kg/m /min) = A A is the area of the immersed face of the brick in mm2 53

Efflorescence and Soluble Salt Content • Efflorescence is the white deposits (salts) on brick surfaces • Salts from bricks, ground and environment • Usually occurs on new brickwork • Affect appearance but often harmless • Bricks exceeding the “heavy”category should be rejected 54

Efflorescence and Soluble Salt Content

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Efflorescence and Soluble Salt Content

Spalling effects of bricks

Source of water

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Levels of efflorescence (MS/BS) Nil

No perceptible deposit of salt

Slight

Up to 10% of the area of the face covered with a deposit of salt, but unaccompanied by powdering or flaking of the surface.

Moderate

More than 10% but not more than 50% of the area of the face covered with a deposit of salts but unaccompanied by powdering or flaking of the surface.

Heavy

More than 50% of the area of the face covered with a deposit of salts and/or powdering or flaking of the surface. 57

Applications

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Calcium Silicate Bricks (sand-lime) • Consists of 90-95% sand (majority passing 1.15 mm sieve) • lime (aggregate lime ratio by weight of 10 – 20 : 1) • water 59

Manufacturing Mixing

Pressin g Autoclav e

Mixing of sand, lime, pigments and water Pressed under very high pressure to give shape and compaction High pressure steam curing combining lime and sand to form calcium silicate. 60

Properties of Calcium Silicate Bricks • Size • Colour • Water absorption • Strength • Shrinkage

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Size and Colour

• Size – similar to clay bricks • Colour – Calcium silicate and are usually light grey and other paler shades 62

Paving Units

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Water Absorption • Varies between 6 to 16 % • Absorption is less relevance for calcium silicate and concrete units

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Strength • Compressive strength is the criteria • Typically strength varies from 14 – 27.5 N/mm2

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Compressive Strengths Classes and Requirements of Calcium Silicate (BS187) Designations

Class

Mean compressive Shrinkage not strength of 10 bricks greater than not less than (%) (N/mm2)

Load-bearing brick or facing brick

7 6 5 4 3

48.5 41.5 34.5 27.5 20.5

Facing brick or common brick

2

14.0

0.040

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CONCRETE BRICK AND BLOCK

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Blocks • Three main types of blocks Solid blocks – blocks containing no formed cavities Hollow blocks – blocks containing cavities which fully penetrate the block Cellular blocks – blocks containing cavities which do not fully penetrate the block 69

Block

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Block

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Concrete Bricks and Blocks • Bricks are units with size not exceeding 337.5mm in length, 225mm in width and 112.5mm in height. Bigger than this are called blocks • Lengths 400 – 600 mm, heights 150 – 300 mm Thickness 60 – 250 mm • Consists of aggregates, cement and water • May contain additives such as air entraining agents, pozzolanic material, colouring pigments 72

Concrete bricks and blocks

Standard blocks Screening blocks

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Manufacturing of Concrete Blocks Cement,

Aggregates are stored separately by density and gradation, then weighed and transported by conveyor to mixer.

Separate and weigh aggregate

aggregate, water, pigments and other admixtures are combined to form damp but not wet mix.

Mixing

Curing Curing is done under saturated conditions. Temperature may be raised to accelerate hydration (steam curing) for 18 hours, or autoclaving (high pressure)

Mix is fed into a mould and consolidate d by vibration

Moldin g

Ejectio n Units in sets of three ejected from moulds.

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Manufacturing

Handling of aggregates in a plant

Block machine in operation 75

Properties of Concrete Blocks (BS 6073) Type

Face size (440 × 215 mm) Thickness (mm)

Solid

75 100

Solid or cellular or hollow

140 150 190 200 215

Minimum average compressive strengths of unit (N/mm2)     7.0 – 21.0  

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Glass Blocks

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Stone

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Stones

Most common • Limestone • Granite • Marble • Slate

Marble quarry

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Applications

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MORTAR FOR BRICKWORK

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MASONRY MORTAR

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MORTAR

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MORTAR A mixture of materials for jointing masonry units Made up of sand, a binder such as cement or lime, and water The thickness of mortar in brickwork is normally 10 mm thick and should not exceed 15 mm because of high shrinkage 85

FUNCTION OF MORTAR Joint the units together Seals any gaps to resist wind and rain penetration Take up the tolerances between building units, fill up the holes between the units 86

REQUIREMENTS Should be able to support the weight of the brick Should not segregate, easy to spread and align the units Adhere to the vertical face of the units Should impart sufficient strength to the whole unit

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REQUIREMENTS (cont.) Should permit movement (unless this is negligible or joints are provided). When movement occurs, it should take place in the form of microcracks within the mortar rather cracking of the bricks or blocks “mortar must not be stronger than the units it is bonding” Should be durable, resisting the penetration of water through the units Should contribute to the aesthetic appearance of the wall 88

SAND FOR MORTAR Well graded – even distribution of particle sizes from fine to coarse. In well graded sand the void is one-third of the total volume Sand containing silt and clay should not be used which can lead to unacceptable shrinkage movement Sand lack in finer particles causes poor water retention resulting in a harsh unmanageable mortar 89

BINDER MATERIALS Hydraulic lime

From limestone contaminated with clay which gave the resulting hydraulic properties Relatively weak and slow setting Only suitable for thick wall and low stress Lime-sand mortars are obsolete 90

ORDINARY PORTLAND CEMENT Principal binding ingredients in modern binders Cement and sand (1:3) by volume produces high strength, good durability, density and hardness For most application such properties are not required. Can be replaced with pozzolanic materials 91

MASONRY CEMENT Premixed binder, 75% OPC, 25% inert fine mineral filler and powdered air entraining admixture On no account should masonry cement be used in place of OPC in making up the other type of mortar 92

SULPHATE RESISTING CEMENT Sulphate Resisting Portland Cement may be used in place of OPC to combat sulphate attack where prolong wet condition are likely The soluble sulphates are either from the ground or in clay bricks The proportion of the mortar constituents are not altered 93

Table 15 BS 5628:Part3

Increasing

Increasing

Strength and Ability to

Masonry Cement: Lime: sand cement:sand

Cement:Sand with Superpl.

1:0 to ¼:3

-

-

1:1/2:4 to 4.5

1:2.5 to3.5

1:3 to 4 1:5 to 6

Improving

accommodate 1:1:5 to 6

1:4 to 5

durability

movements

1:5.5 to 6.5 1:7 to 8

(arrow upward) (arrow downward)

1:2:8 to 9

1:3:10 to 12 1:6.5 to 7

1:8

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NON-HYDRAULIC LIME Insufficient setting and hardening strength to make them as a total binder Added as a binder constituent to produce cement: lime: sand mortar Lime has good water retentive properties which give good workability characteristics and promote bonding of the Portland cement Have better resistance to rain penetration 95

AIR-ENTRAINERS  As an alternative to lime as a binder supplement, the reduced volume can be made with minute bubbles by adding air-entraining agent  In powder/liquid form but must be intended for mortar  Air entrainment must not exceed 12% of the volume because it reduces the bond strength  At 15% or above the bonding performance is seriously impart  Induces good plasticity/workability characteristics 96

Linear Thermal Movement of Masonry unit and Mortar Material

Coeff. Of Linear Thermal Expansion (x 10-6 /K)

Fired-clay masonry units

4-8

Concrete masonry units

7 - 14

Calcium silicate masonry units

11 - 15

Mortars

11 - 13 97

Moisture movement and Thermal properties of Common Building Materials Material

Reversible moisture movement

+- 0.5-2.5

Irreversible moisture Coeff. Of Thermal movement Exp. (x10-6/ K)

4 - 70

-

_ _

10 - 18

Concrete

+-0.02-0.10

-(0.03-0.08)

7 - 14

Dense concrete agg. products

+-0.02-0.04

-(0.02-0.06)

6 – 12

Lightweight agg. conc.

+-0.02-0.06

-(0.02-0.06)

8 - 12

Aerated (autoclave) products

+-0.02-0.03

-(0.05-0.06)

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Calcium silicate brick

+-0.01-0.05

-(0.01-0.04)

8 - 14

+-0.02

+(0.02-0.07)

5 - 898

Timber Steel

Clay brick

Thank You HAVE A NICE DAY

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