Building Construction2. Masonry

CE 2330Civil Engineering Materials and Construction

Learning outcomes

• List and classify different types of masonry• Describe the construction methodology

and arrangement for stone and brick masonry

• Explain differences between different types of masonry walls

IntroductionMasonry consists of blocks made out of stone, bricks,

concrete and other materials, joined together by mortar. Various types of masonry units are used in construction:

1. Concrete blocks – could be solid or hollow2. Clay bricks3. Stone4. Structural clay tiles – These are larger than clay bricks

and are used for lightweight masonry such as partition walls and filler panels

5. Glass blocks – Used in cold regions, especially when there is a need for natural light in the interior

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) sufficient tensile strength to retain shape after forming, and (3) ability of particles to fuse together at high temperatures.

Clays - Classification

Depending on their composition, clays are divided into

(a) Calcareous clays – approx. 15% CaCO3and burn to a yellowish colour, and

(b) Non-calcareous clays – contains aluminosilicates with feldspar and iron oxide (2 – 10%), colour on burning is determined by the iron oxide content.

Manufacture of bricks

• Bricks are manufactured by grinding or crushing the clay in mills and mixing with water 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.

Bricks – Classification

Functional:• 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 should not be used in places exposed to heavy rains.

2. Burnt bricks – Commonly used.

Brick dimensions

• Similar to concrete blocks, nominal dimensions are used for bricks also. Typically, company manufactured bricks have a depression on the top and bottom surfaces with an imprint (usually of the company name). This depression is called a ‘frog’, and causes and improvement in the bond 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

Brick types

Properties of bricks

Durability of bricks depends on their absorption potential. Bricks with high absorption are prone to efflorescence.

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

The compressive strength of bricks depends on:• Composition of the clay• Method of brick manufacturing, and• The degree of firing

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.).

Efflorescence

Stone

• Similar to the ancient times, large blocks (more than 1 m on each side) of stones are often used for architecturally appealing construction. Such large pieces that are finished and ‘dressed’ are known as ‘dimension stone’.

• The choice of a particular type of tone for construction depends on many parameters, such as the mineralogy of the rock, the mechanical properties of the rock, as well as the resistance to weathering.

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

Grout and Plaster

• Grout is highly flowable concrete consisting of PC, lime, sand, fine gravel, and water. It is used to 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 providing an even surface on top of the brick walls. It also acts as a protective layer to the brick wall.

Other masonry materials

• Surkhi• Terra cotta• Earthenware and stoneware• Gypsum

Types

• Stone• Brick• Concrete block• Reinforced brick• Composite

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)

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

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

Masonry terms - graphically

Section through a wall

Traditional

Modern

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

Masonry cement / combination of (a) Lime and pozzolan, 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 to

heavy pressure require stiff mortars• Lime mortar – above plinth level; cement mortar

– below ground

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 masonry wall. Thus, thin mortar layers produce stronger walls compared to thick layers.