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Building Construction

2. Masonry

CE 2330Civil Engineering Materials and Construction

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Clay Bricks Clay is composed of silica, alumina, and small

quantities of Fe, Mn, S, and phosphates. The properties of clay necessary for brick-

making are: (1) plasticity to allow moulding and

shaping when mixed with water, (2) sufficienttensile strength to retain shape after forming,

and (3) ability of particles to fuse together at high

temperatures.

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Clays - ClassificationDepending on their composition, clays are

divided into(a) Calcareous clays approx. 15% CaCO3

and burn to a yellowish colour, and

(b) Non-calcareous clays containsaluminosilicates with feldspar and ironoxide (2 10%), colour on burning isdetermined by the iron oxide content.

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Manufacture of bricks Bricks are manufactured by grinding or

crushing the clay in mills and mixing withwater to make it plastic.

The plastic clay is then moulded, textured,dried, and then fired. The firing

temperature is typically between 900 and

1200 oC. The average density of bricks is 2 g/cc.

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Bricks ClassificationFunctional:

Building bricks Facing bricks

Floor bricks

Paving bricks

Based on manufacturing process:

1. Unburnt bricks / sun dried bricks: These are very weak, and can

be used only for temporary and cheap structures. These shouldnot be used in places exposed to heavy rains.

2. Burnt bricks Commonly used.

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Brick dimensions Similar to concrete blocks, nominal dimensions

are used for bricks also. Typically, companymanufactured bricks have a depression on thetop and bottom surfaces with an imprint (usuallyof the company name). This depression is called

a frog, and causes and improvement in thebond between the brick and mortar.

Standard brick measures 19 x 9 x 9 cm (with 1

cm mortar joint 20 x 10 x 10 cm) Traditional brick measures 23 x 11 x 7 cm

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Brick types

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Properties of bricksDurability of bricks depends on their absorption

potential. Bricks with high absorption are proneto efflorescence.

In general, clay bricks are durable, fire resistant,poor conductors of heat, and have moderateinsulating properties.

The compressive strength of bricks depends on:

Composition of the clay

Method of brick manufacturing, and

The degree of firing

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Efflorescence Efflorescence on brickwork is commonly observed when

salts dissolved in moisture get deposited on the surface. It produces ugly damp patches, eats through the surface

coatings, and gradually disintegrates the structure.

The salts are typically sulphates of Mg, Ca, or Na, as

well as certain nitrates, carbonates, and chlorides.

The source of these salts can be groundwater, mortar

used for the masonry, or the brick itself (when it is

porous, underburnt etc.).

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Efflorescence

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Stone Similar to the ancient times, large blocks (more

than 1 m on each side) of stones are often usedfor architecturally appealing construction. Suchlarge pieces that are finished and dressed areknown as dimension stone.

The choice of a particular type of tone forconstruction depends on many parameters,such as the mineralogy of the rock, the

mechanical properties of the rock, as well as theresistance to weathering.

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Lime Lime (CaO) is obtained from limestone (composed of

CaCO3

) by calcination.

Hydration of lime:

CaO + H2O Ca(OH)2 Setting

Ca(OH)2 + CO2 CaCO3 + H2O Hardening

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Grout and Plaster Grout is highly flowable concrete consisting of

PC, lime, sand, fine gravel, and water. It is usedto fill the cores or voids in hollow masonry.

Plaster, on the other hand, is a mixture of PC,

lime, sand, and water, and is used for providingan even surface on top of the brick walls. It also

acts as a protective layer to the brick wall.

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Other masonry materials Surkhi

Terra cotta

Earthenware and stoneware

Gypsum

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Types Stone

Brick

Concrete block

Reinforced brick Composite

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Terms associated with masonry Course: Horizontal layer of masonry unit;

thickness of course??? Header and stretcher

Bed lower surface of brick/stone in a course

Natural bed bedding plane of rocks

Bond arrangement of masonry units

Quoins Exterior angle or corner of wall Face surface of wall exposed to weather

(opposite: back)

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Terms (contd.) Facing material used in the face

Joint Bed joint, cross joint and vertical joints Closers and bats cut bricks

Frog depression on top surface of brick

Sill, Lintel, Jamb parts of window opening Plinth horizontal projecting course of stone or

brick, provided at base of wall above ground

level Corbel Projecting stone from wall serving as

support

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Terms (contd.) Coping covering of stone, terra cotta,

concrete or brick on top of wall(weathering and throating)

Arches and gables

Column (W < 4t)

Pier (W > 4t)

Pilaster Pier monolithic with wall and

projecting beyond

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Masonry terms - graphically

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Section through a wall

Traditional

Modern

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Mortars for masonry Lime (hydraulic or semi-hydraulic) / PC or

Masonry cement / combination of (a) Lime andpozzolan, or (b) Lime and PC

Clay / mud for low strength

Avoid excess water (generally, max w/(c+l) =0.65)

Thinner joints more fluidity; joints subjected toheavy pressure require stiff mortars

Lime mortar above plinth level; cement mortar below ground

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Mortar is used for:

Bonding masonry units together

Serving as seating material for the units

Levelling and seating the units

Providing aesthetic quality to the structure.

The mortar is the weakest part of a masonrywall. Thus, thin mortar layers producestronger walls compared to thick layers.

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Applying mortar for the joint

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Mortar joints

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Stone masonry Classification Rubble (undressed blocks

of stone) masonry and ashlar (accuratelydressed stone) masonry

Rubble masonry Avoid long continuous

vertical joints; arrange to get loaddistributed over maximum area

Ashlar masonry Stone height is 25 30

cm; height of all stones in single course isequal

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Uncoursed random rubble masonry

Random rubble: built to courses

Uncoursed square rubble masonry

Square rubble: built to courses

Types of rubble masonry

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Square rubble: regular coursed

Polygonal rubble masonry

Types of rubble masonry

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Fine tooled ashlar masonry Chamfered ashlar masonry

Types of ashlar masonry

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Guess the types!

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Brick masonry

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Bricks rules for bonding Uniform size bricks (L = 2t + tmortar) for uniform

lap

Lap not less than brick along length and brick across thickness

Discourage use of brickbats

In alternate course, CL of header coincides withCL of stretcher in the course above and below it

Vertical joints in alternate courses along sameperpend

Stretchers to be used only in the facing

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Types of bonds Stretcher bond (only for brick walls)

Header bond (only for 1 brick walls)

English bond strongest

Flemish bond aesthetically pleasing (butuses more bats; more skill and mortar

required)

Zig-zag bond

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Types of bondsStretcher bond

Flemish bondEnglish bond

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Concrete blocks

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Concrete blocks1. Lightweight units (Density < 1.68 g/cc)

Prepared using lightweight aggregates2. Medium-weight units (Density between

1.68 and 2.00 g/cc)

3. Normal weight units (Density > 2.00 g/cc)

Lightweight units are most widely used because of the ease of handlingand transport. They also possess better thermal, fire resistance, and

insulation properties.

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Normal or rapid hardening Portland cement is used in the

manufacture of concrete blocks. The concrete mix is very stiff, and

the block units are moulded under pressure.

Concrete blocks are further classified as being load bearing or non

load bearing. In the case of load bearing blocks, a minimum

compressive strength requirement has to be satisfied.

Concrete masonry units are specified by their nominal dimensions.The nominal dimension is equal to the actual block dimension plus

the thickness of the mortar joint (typically 10 mm).

Concrete masonry walls are sometimes reinforced with steel to

provide better lateral load resistance. This is especially useful inearthquake-prone areas.

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Important aspects of bricklaying

Use presoaked bricks

Corner of wall constructed first (bed joint 1cm thick)

Use of taut cord to maintain level

Verticality of perpends checked withstraight edge and square

Jointing and pointing after wall isconstructed; joints to be cleaned andfinished after every days work

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Building a masonry wall

Taut cordfor level

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Supervision of brickwork No soaking when fat lime or mud mortar is

used Frog on top while laying

Thick walls joint grouting also Uniformly raised; or use toothing

18 25 mm expansion joints for every 30

45 m length of wall

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Joints in walls

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Composite masonry

Brick-stone composite

Reinforced brick

masonry

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Reinforced masonry

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Plastering for masonry Older structures lime mortar

New structures cement mortar (typically1:4 or 1:6)

Why is it necessary?

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Masonry walls Walls provide strength and stability,

weather resistance, durability, firsresistance, thermal and sound insulation

Classification:

- Load bearing (superimposed load + selfweight)

- Non-load bearing (only self weight)

+ Internal

+ external (panel or in-fill walls)

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Special walls Partition wall could be load-bearing

Party wall separating adjoining buildings Curtain walls only for lateral loads

Cross wall construction Internal wallsbear all the load

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Load bearing walls Solid masonry wall

Cavity wall (cavity could be filled byinsulating or waterproofing material)

Faced wall (when facing and backing are

of different materials)

Veneered wall (Faade)

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Types of walls

Veneered

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Design considerations Loads avoid large openings and large

concentrated loads, reduce eccentricity Mortar strength 30 stability problem)

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References Various web sources

Wikipedia http://faculty.delhi.edu/hultendc/A220-

Week2-Lecture-Web.html

Building Construction by B C Punmia

Building Design and Drawing by Balagopal

T S Prabhu et al.