02 masonry
TRANSCRIPT
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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.