special aspects of construction

Building Materials and Construction

Compiled by Dr. Prashanth J. and Dr. Harish N.

8. SPECIAL ASPECTS OF CONSTRUCTION

Damp Proofing One of the essential requirements of a building is that it should be dry. Dampness in building

may occur due to bad design, faulty construction and use of poor quality of materials. Dampness

not only affects the life of building adversely, but also creates unhygienic condition for the

occupants. The treatment given to prevent leakage of water from roof is generally termed as

waterproofing, where as the treatment given to keep the walls, floors and basement dry is termed

as damp proofing.

A damp proof course (DPC) is a physical barrier inserted into the fabric of a building to stop

water passing from one place to another. This can be on a horizontal plane, stopping water rising

up from the ground by being sucked up by the dry masonry above, or vertically to stop water

passing from the outside of a building, though the masonry, to the inside. DPC's have taken

many forms through the ages and one of the earliest forms was to use a layer of slate in the

construction. Slate is still used but the less expensive plastic version is now more widely used.

Fig.: Horizontal DPC

Causes of Dampness

The dampness in building is a universal problem and the various causes, which are responsible

for the entry of dampness in a structure, are as follow.

1) Rising of moisture from ground: The ground on which the building is construction may be

made of soil, which easily allows the water to pass. Usually the building material used for

the foundations, absorb moisture by capillary action. Thus the dampness finds its way to

the floor through the sub structure.

Fig.: Rising of groundwater level Fig.: Action of rainwater



2) Action of rain: If the faces of wall, exposed to heavy showers of rain, are not suitably

protected, they become sources of dampness in the structure. Similarly the leaking roofs

also permit the rainwater to enter a structure.

3) Exposed of top wall: The parapet wall and compound wall also should be providing with a

damp proof course on the exposed tops. Otherwise the dampness entering through these

exposed tops of such walls may lead to serious result.

4) Condensation: The process of condensation takes place when warm humid air is cooled.

This is due to the fact that cool air can contain less invisible water vapour than warm air.

The moisture deposits on the walls, floors and ceiling. This is the main source causing

dampness in badly designed kitchens.

There are various miscellaneous causes for dampness as mentioned below:

1. If the site located on a site, which cannot be easily drained off, the dampness will be

entering the structure.

2. The orientation of a building is also an important factor, the wall obtaining less sunrise and

heavy shower of rain are liable to become damp.

3. The new constructed walls remain damp for short duration.

4. Very flat slope of a roof may also lead the penetration of rain water which is temporary

store on roof.

5. The dampness also caused due to bad workmanship in construction such as defective joints

in the roofs, improper connection of wall.

Effect of dampness

The building material such as bricks, timbers, concrete etc, has moisture content, which is not

harmful under normal condition. The rise in moisture content of these materials beyond the

certain level from where it becomes visible or when it deteriorates leads to the real dampness. In

absolute terms, the moisture content of different materials may be same, but the acceptable limit

differs from material to material. For instance, the presence of 10 percent by weight in timber is

not harmful. But the same level could saturate a brick or cause deterioration of plaster.

The structure is badly affected by dampness. The prominent effect of dampness is as follow.

1. A damp building gives rise to breeding of mosquitoes and creates unhealthy condition for

those who occupy it.

2. The metals used in the construction of material are corroded.

3. The decay of timber takes place rapidly due to dry-rot in a damp atmosphere.

4. The unsightly patches are formed on the wall surface and ceiling.

5. The materials used as floor covering are serious damaged.

6. It results in softening and crumbing of the plaster.

7. The materials used for wall decoration are damaged and it leads to difficult and costly

repairs.



8. The flooring gets loosened because of reduction in the adhesion when moisture enters

through the floor.

Methods of damp proofing

Following methods are used for prevent the defect of dampness in structure

1. Use of damp proof courses

2. Water proof or damp proof treatments

3. Integral damp-proofing treatments

4. Cavity wall construction

5. Guniting or shot concrete or shotcrete

6. Pressure grouting or cementation

1. Use of damp proof courses (DPC): These are layers or membranes of water repellent

materials such as bituminuous felts, mastic asphalt, plastic sheets, cement concrete, mortar,

metal sheets, stones etc which are interposed in the building structure at all locations

wherever water entry is anticipated or suspected. The best location or position of D.P.C. in

the case of building without basement lies at plinth level or structures without any plinth

level, it should be laid at least 15cm above ground level. The damp proof course provided

horizontally and vertically in floors, walls etc. In the case of basements, laying of D.P.C. is

known as taking Fig 14.1 shows the D.P.C. treatment above ground level.

General Principles to be observed while laying DPC are as under

The DPC should cover full thickness of wall excluding rendering.

The mortar bed upon which the DPC is to be laid should be made leveled, even and free

projections. Uneven base is likely to cause damage to DPC.

When a horizontal DPC is to be continued to a vertical face, a cement concrete fillet 75 mm

in radius should be provided at the junction, prior to the treatment.

Each DPC should be placed in correct relation to other DPC, so as to ensure a complete and

continuous barrier to the passage of water from floors, walls or roofs.

2. Water proof treatments: The surface treatment consists in filing up the pores of the

material exposed to moisture by providing a thin film of water repellent material over the

surface (internal / external). External treatment is effective in preventing dampness. Many

surface treatments, like pointing, plastering, painting, distempering etc are given to the

exposed surfaces and also to the internal surface . The most commonly used treatment to

protect the walls against dampness is lime cement plaster (1:6) (1-cement, 6-lime) mix

proportion. Generally employed as water proofing agent in surface treatments are sodium

or potassium silicate. Aluminium or zinc sulphate, Barium Hydroxide and magnesium

sulphate in alternate applications. Soft soap and alum also in alternate applications, unie



and unseed oil; coal tar, bitumen, waxes and fats; resins and gums. Waxes and fats are not

suitable in tropics as they melt with rise in temperatures.

3. Integral damp-proofing treatments: The integral treatment consists of adding certain

compounds to the concrete or mortar during the process of mixing, which when used in

construction acts as barriers to moisture penetration under different principles

i) Compounds like chalk, talc, faller’s earth etc have mechanical action principle (i.e.,)

they fill the pores present in the concrete or mortar and make them dense and water

proof.

ii) Compounds like denser and water proof sulphates, calcium chlorides etc work on

chemical action principle (i.e.) they react chemically and fill the pores to act as water-

resistant.

iii) The compounds like soaps, petroleum, oils fatty acids compounds such as sterates of

calcium, sodium ammonium etc work on the repulsion principle i.e., they are used as

admixture in concrete to react with it and become water repellent.

4. Cavity walls or hollow walls: A cavity wall consists of two parallel walls or leaves or

skins of masonry separated by a continuous air space or cavity. The provision of

continuous cavity in the wall per effectively prevent the transmission or percolation of

dampness from outer walls or leaf to inner wall or leaf. The following are the advantages of

cavity wall.

(i) As there is no contact between outer and inner walls of cavity wall, possibility of

moisture penetration is reduced to a minimum.

(ii) A cavity wall prevents the transmission of heat through wall.

(iii)A cavity wall offer good insulation against sound.

(iv) The cavity wall tends to reduce the nuisance of efflorescence.

(v) The cavity wall also provides benefits such as economy, better comfort and hygienic

conditions in buildings.

5. Guniting: (or shot concrete): The technique of guniting consists in forming an imperious

layer of rich cement mortar (1:3) or fine aggregate mix for water proofing over the exposed

concrete surface or over the pipes, cisterns etc for resisting the water pressure. By this

technique, an impervious layer of high compressive strength (600 to 700 kg/cm2) is

obtained and hence this is also very useful for reconditioning or repairing old concrete

works

6. Pressure grouting or (cementation): The mixture of cement, sand and water under

pressure into the cracks, voids or fissures present in the structural component or the ground.

In general, the foundations are given this treatment to avoid the moisture penetration. This



technique also used for repairing structures, consolidating ground to improve bearing

capacity, forming water cut-offs to prevent seepage etc.

Material used for damp proofing

Some of the commonly used for damp proofing materials are Hot bitumen, Mastic asphalt,

Bituminous felts, Metal sheets, Combination of sheets and felts, Stone, Bricks, Mortar, Cement

concrete, Plastic sheets etc.

Fire-proof construction

It is defined as the protection of the occupants of the building, contents and structure of the

building and adjacent buildings from the risks of fire and spread of fire. The objective is

achieved by using fire resistive materials in the construction. By suitable planning of the building

internally and in relation to adjacent building internally and in relation to adjacent building and

by providing suitable means of quick escape for the occupants. These measures are essential to

minimize the spread of fire and limit the total damage to a minimum.

National building code classifies the construction into four classes, namely type 1, type 2, type 3

and type 4 on the basis of fire-resistance offered by building components for 4-hours, 3-hours, 2-

hours and 1-hour respectively. To achieve the objective of fire-resistance, due considerations

should be made in design and construction of the structural members and use of combustible

material should be avoided as far as possible in the construction

a) Walls and columns

b) Floor and roofs

c) Wall openings

d) Building fire escape elements (i.e.,) stair, staircase, corridors, entrances etc.

Fire protection requirements

1. It should be the objective of every engineer and architect while planning and designing the

building that the structure offer sufficient resistance against fire so as to afford protection to

the occupants, use of fire-resisting materials and construction techniques and providing

quick and safe means of escape in the building.

2. All the structural elements such as floors, walls, columns, beams etc should be made of fire

resisting materials.

3. The construction of structural elements such as walls, floors, columns, lintels, arches etc

should be made in such a way that they should continue to function atleast for the time,

which may be sufficient for occupants to escape safely in times of fire.

4. The building should be so planned or oriented that the elements of construction or building

components can with stand fire for a given time depending upon the size and use of

building, to isolate various compartments so as to minimize the spread of fire suitable



separation is necessary to prevent fire, gases, and smoke from spreading rapidly through

corridors, staircases left shafts etc.

5. Adequate means of escape are provided for occupants to leave the building quickly and

safely in terms of outbreak of fire.

6. In multi-storeyed office buildings suitable equipment for detecting, extinguishing and

warning of fire should be installed in the niches.

In important buildings, in addition to the fire-resisting materials and adopting fire resistant

construction, the following general measures of fire-safety are also recommended.

(i) Alarm system

(ii) Fire extinguishing arrangements

(iii) Escape routes for public buildings

Sound proof Construction

Control of noise transmission is essential to minimize the disturbing effect of sound passing from

one room to another, through walls, partitions, and floors or ceilings. Good planning in respect of

the location of building as well as the placement of quiet and noisy areas in the building itself

plays an important roles in controlling noise transmission.

The sound insulation of wall is governed by weight of the wall. It is seen that a solid one brick

thick wall plastered on both sides, proves quite effective as a sound insulation partition wall.

This can also be achieved by a suitable combination of materials which are light in weight.

Transmission of sound takes place more easily through floors. Even bare concrete and timber

floors do not function effectively as barrier against impact sound. A floating floor resting on a

resilient material like glass wool, mineral wool, quilt, hairfelt, cork, rubber etc., has an increased

rating for impact sound insulation.

Among many, following are the most significant factors affecting acoustical planning and

design:

a) Noise: The unwanted sound is called a noise. The hall or room should be properly insulated

from external and internal noise.

b) Reverberation Time: Reverberation is the persistence or prolongation of sound in a hall even

after the source stopped emitting sound. The reverberation time is taken by the sound to fall

below the minimum audibility level. In order to have good acoustic effect, the reverberation time

has to be maintained at optimum value. The reason is, if the reverberation time is too small, the

loudness becomes inadequate. As a result the sound may not reach to the listener. Thus, this

gives the hall a dead effect. On the other hand, if the reverberation time is too long, it will lead to



more confusion due to mixing of different style. Hence, to maintain good effect reverberation

time should be maintained.

c) Loudness: The uniform distribution of loudness in a hall or a room is an important factor for

satisfactory hearing. Sometimes, the loudness may get reduced due to excess of sound- absorbing

materials in a hall or a room.

d) Echo: An echo is heard due to reflection of sound from a disaster sound- reflecting object. If

the time interval between the direct sound and reflected sound is less than 0.066 seconds, the

reflected sound is helpful in increasing the loudness. But, sounds arriving later than these cause

confusion.

e) Echelon effect: It refers to the generation of a new separate sound due to multiple echoes. A

set of railings or any regular reflecting surface is said to produce the echelon effect. This echelon

effects effect affects the quality of the original sound.

f) Focusing and Interference Effects: The presence of any concave surface or any other curved

surface in the hall or room may make the sound to be concentrated at this focus region. As a

result, the sound may not be heard at all at other regions. These regions are referred as dead

space. Hence, such surfaces must be avoided.

In addition to focusing there should not be interference of direct and reflected waves. This is

because, a constructive interference may produce sound of maximum intensity in some places

and a destructive interference may produce sound of minimum intensity in other places. Thus,

there will be an uneven distribution of sound intensity.

g) Resonance: Resonance occurs due to the matching of frequency. If the window panels and

sections of wooden portions have not been tightly fitted, they may start vibrating, thereby

creating an extra sound in addition to the sound produced in the hall or room.

Joints

It is well known that almost all building materials expand or contract due to change in

temperature and variation in moisture content. The magnitude of such expansion or contraction

depends upon the type of material used in construction and the variation in the temperature and

moisture content. In a continuous structure, the cumulative effect of the dimensional changes in

the building elements on account of the above may be considerable. In case components of such

a structure are not allowed free movements, internal stresses will be set up which may result in

formation of cracks. This may in turn endanger the stability of the structure. Such a problem

gains special importance in tropical countries like India, where large variations occur in the

atmospheric temperature and humidity. Thus special provisions should be made to control or

isolate thermal and other movements to avoid danger to a structure. This is achieved by breaking

the continuity of a structure, by introducing joints at regular intervals. These joints sub-divide the

building into smaller units and also permit free movement of each unit.



Joints can be divided into the following different categories.

(i) Expansion joints

(ii) Isolation joints

(iii) Contraction joints

(iv) sliding joints

(v) Construction joints.

Expansion joints

These joints are provided to accommodate the expansion of adjacent building parts and to relieve

compressive stresses that may otherwise develop. Total expansion (I) of a structure can be

obtained by the formula

I = co-efficient of linear expansion x length of the structure in centimetre x change of

temperature in degree F

Based on this formula, it is seen that a structure 30 m long expands linearly by about 10 mm.

through a temperature change of 500 F. In general, buildings of ordinary size and regular shape in

plan can resist the stresses caused by dimensional changes and as such do not require provision

of expansion joints. However, provision of one or more expansion joints is considered necessary

when the continuous length of a structure exceeds 45 m. There is wide divergence of opinion

regarding proper spacing of expansion joints. In India, the recommended maximum centre to

centre spacing of expansion joints is 30 m. In addition, expansion joints should be provided

where a structure changes direction for instance in L, T, H and U shaped structures. Where two

or more expansion joints are considered necessary it is desirable to locate the joints in such a

way that the distance of joints from the nearest continuous corner does not exceed 15 m.

Fig: Plans showing location of expansion joint in buildings of different shapes

The joint is formed by providing an initial gap between the adjacent building parts which gets

widened or shortened while accommodating the contraction or expansion of the building. The

width of the gap should be sufficient to accommodate the maximum thermal-induced movements



likely to be encountered. Normally it varies between 10 mm to 40 mm. There should be complete

discontinuity of masonry, reinforcement or concrete at the joint and the gap should permit

unobstructed movement of adjacent parts.

Construction Joints

Joint provided at locations where the construction is stopped either after the day's work or due to

any other reason is known as construction joint. Installation of construction joint becomes

necessary to ensure proper bond between the old work and the new one. If possible it must be

planned in such a way that after the day's work end the need for construction joint must not arise.

However, often it is difficult to complete the concreting for large work in one operation and as

such special measures are necessary to be taken to achieve prefect continuity between the old

concrete that has already set and hardened and the new concrete to be laid subsequently.

From consideration of structural stability, it is necessary to ensure construction joints are

provided at pre-determined locations. Following factors should be kept in view while deciding

the installation of construction joint.

(1) The construction joint should be located along or near the plane of minimum shear

(2) The joint should be vertical or horizontal as the case may be except that, in an inclined or

curved member, the joint should be at right angle to the axis of the member.

(3) The concrete at the vertical joint should be finished against a stop-board especially fixed

for the purpose. As far as possible a key of tongue and groove type should be provided at

all construction joints. The key is normally formed by fixing beveled edged strip of wood

to a stop-board. In case of large works, key made up of sheet is used to permit repetitive

use. There is a tendency to provide more depth for the key. It is however, seen that key

formed by use of a 25 x 50 mm beveled edged strip is sufficient for slabs ranging from 12

cm to 18 cm in thickness.

The stop-board has to be slotted to allow reinforcement to extend old concrete to the new

one. The details of formation of from the construction joint in a slab are shown in Fig.

Prior to laying new concrete the stop-board is removed and the face of the concrete that has

already hardened is treated and prepared as under.

(a) If the new concrete is to be laid within 48 hours, the face of the old concrete is cleaned with

wire brush and water and a coat of cement mortar (of the same composition as that of

concrete) is applied before placing new concrete.

(b) If new concrete is to be laid after 48 hours, the face of the old concrete is first roughened

by chiseling. It is then cleaned of scum, loose aggregates and other foreign matter, wetted

and a coat of cement mortar (of the same composition as that of the concrete) is applied

before placing new concrete.



Fig.: Details relating to formation of construction joint

A: View showing stop board with wooden key fixed to slab shuttering

B, C: Alternative detail of keys

D: Section showing dimension of key

E: Section showing stop-board in position for forming construction joint

Location of Construction Joints for Different Members

The recommended position for construction joints in different structural components is as under.

(i) For slabs: In case of slabs supported on two sides, the construction joints should be vertical

and parallel to the main reinforcement. Alternatively, it can also be provided at the middle of

span at right angles to main reinforcement. In case of two way slabs, the joint can be provided

near the middle either spans.

(ii) For Beams: In case of beams, the construction joint should be located at the middle or within

the middle third of span and it should be vertical. In case of L or T beams, the rib of the beam

should be concreted along with the flange slab. In case, however, a construction joint between

slab and beam becomes unavoidable (especially in case of long and deep beans) the rib of the

beam can be concreted up to 25 mm below the level of soffit of the slab and the construction

joint can be provided there.

(iii) For columns: In case of columns, the construction joint should be formed horizontally by

stopping the concrete in column about 75 mm below its junction with lowest soffit of the beam

or bottom of haunching (if any). The operation of concreting above the construction joint should

be taken up after a gap of at least 4 hours.

(iv) For walls: The horizontal construction joint in walls should be located at the top of plinth,

top or bottom of window opening or at any other convenient height. In case of concrete or

R.C.C. walls, the location of horizontal construction joints is governed by the following factors:

Convenience in setting the formwork.

Ease of access for compaction and supervision of concreting.



The continuity at the joint is achieved by the formation of key. The key is formed by use of

beveled edged planks on the inner face of wall shuttering (Refer Fig. below). Prior to pouring

concrete above the joint, the beveled edged planks are removed and the surface of old concrete is

prepared in manner as described earlier in the article.

Fig.: Details of planking for construction joint in wall and shape of joint after casting

Introduction to aluminum

Aluminum is silver white in colour with a brittle metallic lustre on freshly broken surface. It is

malleable, less ductile than copper but excels zinc, tin, and lead. Aluminum is harder than tin.

Aluminum is very light, soft, strong and durable, has low thermal conductivity but is a good

conductor of electricity. Aluminum can be riveted and welded, but cannot be soldered. It can be

tempered at 350° C. The melting point is 657° C, tensile strength is 117.2 N/mm2 in the cast

form and 241.3 N/mm2 when drawn into wires. Aluminum is found to be resistant to the attack

of nitric acid, dissolves slowly in concentrated sulphuric acid and is soluble in hydrochloric acid.

At normal temperature it is not affected by sulphur, carbonic acid, carbonic oxide, vinegar, sea

water, etc., but is rapidly corroded by caustic alkalis.

Aluminum alloys

Aluminum is commonly alloyed with copper silicon, magnesium or zinc to improve its

mechanical properties. Some aluminum alloys also contain one or more of the metals

manganese, lead, nickel, chromium, titanium, and beryllium. A large part of the aluminum

production is utilized in making light, stiff, corrosion-resistant alloys with these metals.

Aluminum alloys may be classed as the cast alloys, which are shaped by casting and wrought

alloys, which are worked into different shapes by mechanical operations. Cast alloys are

generally binary alloys containing copper or silicon, and sometimes magnesium. Wrought alloys

contain copper, magnesium, silicon and manganese that form precipitation hardening alloys with

aluminum. Following are some of the aluminum alloys.



Duralumin contains 3–5% copper, 0.51–1% magnesium and 0–0.07% manganese. 0.3–0.6%

iron and 0.3%–0.6% silica are present as impurities. It is highly resistant to corrosion. Wire and

sheets are drawn from duralumin.

Magnalium is an alloy of aluminum and magnesium (6 percent). It has got very good

mechanical properties and is a little lighter than pure aluminum. It is easy to work, exceptionally

strong, and ductile and is widely used as deoxidizers in copper smelting operations.

Aldural is obtained when a coating of aluminum is given to duralumin and has better corrosion

resisting properties.

Aluminum-copper alloy contains copper up to 4 per cent. Less liable to burning the alloy

produces light castings that are stronger and tougher than that made from aluminum. It is mainly

used in automobile industry for casting.

Aluminum-zinc alloy contains zinc up to 15 percent and is used for light casting which can be

easily machined or forged into desired form. These are very sensitive to high temperatures in

melting and in solid form exhibit low strength and brittleness.

Aluminum-silicon alloy contains 5 to 15 percent silicon. They have excellent casting qualities,

including excellent fluidity and freedom from hot-shortness, permit the pouring of thin intricate

sections. They also have high resistance to corrosion, are good conductors of heat, and have low

thermal expansion.

Uses of aluminum

Pure aluminum is very soft and is unsuitable for structural purposes. Satisfactory properties are

derived by alloying copper, manganese, zinc, silicon, nickel with aluminum. It is most suitable

for making door and window frames, railings of shops and corrugated sheets for roofing system.

Aluminum sheets are used over doors in bathrooms to protect them from getting rot and for

stamping into a variety of shapes. Aluminum powder is used for making paint. Aluminum is

extensively used in making parts of internal combustion engine, airplanes, utensils and packings

for medicines, chocolates, etc. Aluminum alloys are widely used for the manufacture of rolled

sections, such as angles, channels, I-sections, round and rectangular pipes, rivets and bolts.

Introduction to plastics

Plastics are made from resin with or without fillers, plasticisers and pigments. These are organic

materials of high molecular weight which can be moulded to any desired form when subjected to

heat and pressure in the presence of a catalyst. Plastics are replacing glass, ceramics and other

building materials due to the low temperature range in which they can be brought to the plastic

state and the consequent ease of forming and fabrication and also for their low cost and easy

availability.



Classification of Plastics

Based on behavior with respect to heating, plastics can be divided into two types:

2) Thermo-setting plastics and

3) Thermo-plastics

Thermo-setting plastics: Thermo setting plastics set into permanent shape when heat and

pressure are applied to them. Reheating will not soften them again. They set at a temperature

varying from 127°C to 177°C. This plastic is soluble in alcohol and certain organic solvents,

when they are in thermo-plastic stage. These properties are utilized for making paints and

varnishes from these paints. This plastic is strong, hard and durable and is available in a variety

of colours.

Thermo-plastics: Thermo-plastics become soft when heated and hardens when cooled;

regardless of the number of times the process is repeated. The process of softening and hardening

may be repeated for an indefinite number of times provided the temperature during heating is not

so high as to cause chemical decomposition. It is thus possible to shape and reshape these

plastics by means of heat and pressure. Scraps obtained from old worn-out articles can be

effectively used again.

Properties of Plastics

1. Plastics are electrical insulators. They have low thermal and electrical conductivity.

2. Plastics are clear and transparent. They can be given beautiful and brilliant colours.

3. Its specific gravity varies from 1 to 1.6.

4. Tensile strength of plastics is about 70 N/mm2.

5. Plastics have excellent corrosion resistance to chemicals, solvents and moisture.

6. The plastics are not ductile.

7. Most of the plastics have very low melting point. Some have as low as 50°C.

8. It can be moulded in any desired shape.

9. It can be sawn, drilled and punched like wood and can be welded.

10. It is a shock absorbing material.

Uses of Plastics

1. Plastic is a versatile material whose properties can be changed to suit varying requirements

when used at different places and in different situations in a building.

2. Thermo plastics or polyvinyl (P.V.C. or P.V.A.) are used for floors in the form of sheets or

tiles.

3. Plastic is used in the form of corrugated sheets and plain sheets as a roofing material.

4. Plastic is used as electrical conduits and electrical insulators.

5. Plastics are used as films for water proofing, damp-proofing.

6. Plastics are used in the manufacture of Flush doors and window frames.

7. Plastics are used in the manufacture of paints and varnishes.



8. Plastic is used to produce pipes to carry cold water

9. Plastic is used in the manufacture of water storage tanks.

10. Plastic is used in the manufacture of furnitures.

11. Plastic is used to produce water resistant adhesives etc.

Disadvantages of Plastics

1. Most of the plastics possess low resistance.

2. They are not very hard.

3. They exhibit high creep.

4. They have high coefficient of thermal expansion.

5. Plastics disintegrate gradually and because of the effects of light, air and temperature, they

lose strength, become soft and get dull as time passes

Plastics with reinforcement

Fibre-reinforced polymer (FRP), also Fibre-reinforced plastic, is a composite material made of a

polymer matrix reinforced with fibres. The fibres are usually glass, carbon, or aramid, although

other fibres such as paper or wood or asbestos have been sometimes used. The polymer is

usually an epoxy, vinylester or polyester thermosetting plastic, and phenol formaldehyde resins

are still in use. FRPs are commonly used in the aerospace, automotive, marine, and construction

industries.

FRP provides an unrivalled combination of properties:

- Light weight

- High strength-to-weight ratio

- Design freedom

- High levels of stiffness

- Chemical resistance

- Good electrical insulating properties

- Retention of dimensional stability across a wide range of temperatures

Introduction to glass

Glass is an amorphous substance having homogeneous texture. It is a hard, brittle, transparent or

translucent material. It is the most common material glazed into frames for doors, windows and

curtain walls. The most common types used in building construction are sheet, plate, laminated,

insulating, tempered, wired and patterned glass. Most ordinary colourless glasses are alkali-lime

silicate and alkali-lead silicate with tensile and compressive strengths of about 30–60 N/mm2 and

700–1000N/mm2, respectively and modulus of elasticity in the range 0.45 × 10

5 to 0.8 × 10

5

N/mm2. The strength is very much affected by internal defects, cords and foreign intrusions. The

main shortcoming of glass is its brittleness which depends on a number of factors, the chief one

being the ratio of the modulus of elasticity of the material to its tensile strength.



Properties of Glass

1. It is extremely brittle and is available in beautiful colours.

2. It is affected by alkalies, but not by air or water.

3. It has amorphous structure.

4. It has no definite melting point.

5. It can be polished.

6. It absorbs and refracts light,

7. It is not easily affected by chemicals.

8. It can be cast into any desired shape.

9. Glass can be welded by fusion.

10. It may be transparent and translucent

11. It is possible to modify some of its properties like hardness, fusibility, refractive power etc.

12. It is an excellent electrical insulator

Uses of Glass

1. Soda-lime glass is used in the manufacture of glass tube other laboratory apparatus, plate

glass, window glass etc.

2. Potash-lime glasses used in the manufacture of combustion tubes etc

3. Potash-lead glass is used in the manufacture of lenses, prisms electric bulbs, artificial gems

etc

4. Common glass is used in the manufacture of medicine bottles.

5. The colored glass is used for window panels, fancy articles, decorative tiles etc.

6. Plate glass is used for looking glass, and large paneled glass for high class houses, glazing

of shop fronts, wind screens of vehicles etc.

7. Perforated glass is used for panels in ventilators.

8. Wired glass is used for fire resisting doors and windows.

9. Ultra-violet ray glass is used in windows of schools, hospitals etc.

10. Soluble glass is used for preparing acid resistant cement.

11. Glass wool is used as filter in air conditioners for electric insulation, for heat insulation.

12. Bullet-proof glass is used for glazing bank teller booths and cash booths, Jewellery stores,

display cases etc.

Ferrocement

Ferrocement is a composite material in which the filler material (called matrix), cement mortar,

is reinforced with fibres, usually steel mesh dispersed throughout the composite, which results in

better structural performances than individual ones. The fibres impart tensile strength to the

mass.



It is a type of thin-wall reinforced concrete commonly constructed of hydraulic-cement mortar

reinforced with closely spaced layers of continuous and relatively small wire mesh. The mesh

may be made of metallic or other suitable materials. Ferrocement has a very high tensile

strength-to-weight ratio and superior cracking behavior in comparison to conventional reinforced

concrete. Unlike conventional concrete, ferrocement reinforcement can be assembled into its

final desired shape and the mortar can be plastered directly in place without the use of a form.

Ferrocement consists of Cement, Fine Aggregate, Water, Admixture, Mortar Mix, Reinforcing

mesh, Skeletal Steel and Coating.

Fig.: Different types of welded wire meshes Fig.: Typical Cross Section of Ferrocement

Advantages of Ferro-Cement:

Basic raw materials are readily available in most countries.

Fabricated into any desired shape.

Low labour skill required.

Ease of construction, low weight and long lifetime.

Low construction material cost.

Better resistance against earthquake.

Very high tensile strength- to- weight ratio.

Disadvantages of Ferro-Cement:

Structures made of it can be punctured by collision with pointed objects.

Corrosion of the reinforcing materials due to the incomplete coverage of metal by mortar.

It is difficult to fasten to Ferro-cement with bolts, screws, welding and nail etc.

Large no of labors required.

Cost of semi-skilled and unskilled labors is high.

Tying rods and mesh together is especially tedious and time consuming.



Properties of ferrocement

It is very durable, cheap and versatile material.

Low w/c ratio produces impermeable structures.

Less shrinkage, and low weight.

High tensile strength and stiffness.

Better impact and punching shear resistance.

Undergo large deformation before cracking or high deflection.

Applications of ferrocement

The excellent crack control and impermeability characteristics of ferrocement make it suitable

for liquid retaining structures, boat building, gas containers, caissons, canal lining, etc. Since it is

cheaper than steel and R.C.C. and can be cast in thin sections it is most suitable for low cost

roofing, precast units, manhole covers, casings, etc. and is the most appropriate building material

for the construction of domes, vaults, shells, grid surfaces, corrugated sheets and folded plates.

Fiber reinforced concrete (FRC)

Because of its low tensile strength and impact resistance, plain cement concrete is considered to

be a brittle material. It has now been established that by addition of small diameter, short length,

and randomly distributed fibres it is possible to bring about marked improvements in the tensile

strength and impact resistance properties of concrete. The fibre could be of steel, glass of

asbestos. Concrete with fibre is termed as fibre reinforced concrete. The extent of improvement

in the properties of fibre reinforced concrete depends upon various factors like material of fibre,

their shape, size, pattern of distribution and magnitude (volume percentage) in the concrete mix.

Out of various possible types of fibre reinforced concrete the following two types are mostly

being recommended.

Steel fibre reinforced concrete

Glass fibre reinforced concrete

I. Steel Fibre Reinforced Concrete: This type of concrete is formed by adding steel fibres in

the ingredients of concrete. Steel fibres are normally produced by cutting 10 to 60 mm length of

low carbon steel wires to 0.25 to 0.75 mm in diameter. Besides round fibres use of fat sheet steel

fibres is also common. Flat sheet steel fibre are produced by shearing 0.15 mm to 0.40 mm thick

steel plates in widths ranging from 0.25 to 0.90 mm and length 10 mm to 60 mm. Steel fibres

have a tendency cluster together which creates difficulties in ensuring their uniform random

distribution in the concrete. This difficulty is overcome by using fibre-bundles (Fibre loosely

assembled in the form of bundles with the help of water soluble glue). The steel fibre in the

fibre-bundles separate out during the process of mixing concrete and get distributed in a random

fashion in the concrete mix. By addition of 2 to 3% of fibres (by volume) it is possible to achieve

two to three times increase in the flexural strength of concrete and substantial increase in



explosion resistance, crack resistance and other properties of the concrete. Steel fibre reinforced

concrete is considered suitable for the construction of pavements, bridge decks pressure vessels,

tunnels lining etc.

II. Glass Fibre Reinforced Concrete: It is observed that strength of glass fibre increases as its

diameter is reduced. It is also seen that although small diameter glass fibres are reasonably strong

in tension, they are very brittle and cannot be used in long lengths. Moreover, glass fibres get

corroded due to the effect of alkali present in portland cement. Thus to utilize glass fibres as

micro-reinforcement they are suitably treated (coating with epoxy resin compounds etc.) to

protect them from alkali attack. It is seen that addition of 10% of glass fibre (by volume) brings

almost two folds increase in tensile strength and substantial increase in impact resistance of

concrete. Investigations are on to use glass fibre reinforced concrete in the manufacture of

precast products like spun pipes, wall cladding etc.

References:

Sushil Kumar, “Building Construction”, Standard Publishers Distributors.

S. C. Rangwala, “Building Construction”, Charter Publishing House.

S. K. Duggal, “Building Materials”, 3rd

revised edition, New Age International Publishers.

Various Internet sources

special aspects of construction

Documents