buildinng conctruction

1. Aggregates
Aggregates are mixed with cement and water to provide bulk and to modify the
physical and chemical properties of the mix. There are several
properties of aggregates:
 Clean: Free from any organic substancessuch as dust or other
fine materials.
 Hard/strong: Most cement in construction is used to resist
compressive forces.
 Durable: Must be able to resist forces over a long time period.
 Capable of good adhesion: The cement paste needsto physically bind to
other aggregates and grip effectively.
 Good shape: Smooth and round aggregates provide good workability,
whereas angular and rough aggregates tend to give better compressive
strength.
The two most common sources for aggregates are rivers (smooth) or
crushed rock from quarries (rough), both make very good concrete.
 Fine: < 5 mm (sand or crushed rock)
 Coarse: > 5 mm (naturally occurring gravel or crushed rock)
Grading of aggregates
Grading is the distribution of sizes of particles in aggregates,usually expressed in
terms of cumulative percentages larger or smaller than eachother.It is important
in terms of preventing voids.
For grading, a sample of aggregate is placed in a container of sieves of successively
reducing sizes. The container is vibrated for a specified period and
the aggregate retained on each sieve is measured. This provides a profile of the
distribution of different particle sizes in the aggregate.
Lime
Lime is one of the basic building material used mainly as lime mortar in
construction. The raw materialsused to produce building lime are either chalk or
limestone. Whenchalk or limestone is burnt at a very high temperature it turns
into quicklime. This material cannot be used for building work in this state so it
undergoestreatment by adding water to it – this process is known as slaking. The
end product is hydrated lime.
Applications of Lime in Building Construction
1. Masonry Construction-For the construction of the monument, retaining
walls. Also, used in load bearing walls.
2. Structural Applications like canopies, arches, domes of different size and
form
3. Used for construction of wall structures like wells, fountains and water
channels

2. 4. Used for plastering purposes- For different types like decorative,plain
plastering
5. Used to make intricate patterns as well as geometrical profiles
6. Used for finishing works
Cement
Cement is a substance used for binding and hardening
other materials. Water and cement set and harden through a chemical reaction
known as 'hydration'. The process of hardening is described as 'curing', which
requires particular conditions of temperature and humidity.
Cement can be mixed with a fine aggregate and water to produce mortar, used
in masonry construction as a bedding and adhesive to bind and fill the gaps
between adjacent blocks of brick, concrete or stone.
It can be also be mixed with water, aggregates (such as gravel, sand or rock), and
sometimes admixtures, to form concrete, and can be used to make renders
and screeds.The ratio of water and cement will determine the
overall strength and quality of the mix.
The exact properties of the cement paste are very important ie:
 It must be fluid enough for some time after mixing to allow the mix to be
formed into its final shape.
 It must then set and gain strength so that it binds the aggregates together to
produce a strong material.
Types of cement
1. Portland cement
Almost all concrete is made with Portland cement. It is also the
principal cement used in most masonry mortars and renders.It
is manufactured by heating together limestone (or chalk) and clay (or shale) in large
rotary kilns. The chemistry of Portland cement largely consistsof calcium silicate
which reacts with water to form a strong, durable cement paste.
2. Low heat blast-furnace Portland cement
This is a special blended cement with low heat of hydration characteristicsfor mass
concreting. The advantage of this kind of cement over ordinary Portland cement is
that, although it has a slower strength gain, it has a higher ultimate strength,as
well as better workability.
3. Rapid hardeningcement
This hardensfaster than Portland cement, as it includesmore silicates,however,
the final strength is only slightly higher. The one-day strength of this cement is

3. equal to the three-day strength of Portland cement with the same water-cement
ratio. It is mainly used where formwork has to be removed for reuse.
4. Sulphate resisting cement
Sulphates exist in rain and sea water and can be harmful to building materials.
Sulphate resisting cement is a type of modified Portland cement that can be used
in conditions where concrete is exposed to the risk of deterioration due to sulphate
attack.
5. High alumina cement
High alumina cement (HAC, sometimes known as calcium aluminate cement (CAC)
or aluminous cement) is composed of calcium aluminatesrather than calcium
silicates.It is manufactured from limestone or chalk and bauxite.
6. Ferro-cement
Ferro-cement is a composite material made up of mortar and light wire steel mesh.
It is a highly versatile form of reinforced concrete.
Mortar
Mortar is a uniform mixture of sand, lime, cement and water in appropriate
proportions. The mixture is used in paste form as a binding material of
bricks/blocks in masonry wall construction.
Good Mortar should:
1. Have sufficient strengthfor which it is required
2. Be workable so that the brick layer can handle it with ease
3. Have a good bond with units which are bedded in it
4. Be durable and resistant to chemical attack
5. Be produced at an economic cost.
Forms of mortar:
a. Cement mortar: this is usually mixed in ratios of 1:3 and is suitable for
bonding exposed brickwork, such as parapets, boundary walls and brick
work for foundations.
b. Lime mortar: It is also mixed in proportions of 1:3 (Lime:Sand) and is
suitable for internal use and dry areas
c. Gauged mortar: It is usually in proportions 1:1:6 (Cement: Lime: Sand) and
is suitable for most conditions
Concrete
Concrete is an artificial rock made from a mixture of coarse aggregates, sand, a
cement binder and water. It can be moulded to any required shape and its load
bearing capabilities can be increased by casting in steel reinforcing bars.

4. There are several types of concrete.
Dense concrete
Lightweight concrete
Air entrained concrete.
The three main constituents used to manufacture concrete are:
• Cement
• Aggregates
• Water.
Manufacture of concrete
The manufacture of hardened concrete involves two stages. These are the plastic
(setting) stage and the rigid (hardening) stage. During both of these stagesthe
chemical process of hydration occurs, where the cement reactswith the water. The
aggregate, althoughpresent, does not take part in the chemical reaction.
cement + aggregate + water concrete + heat
Plastic stage
1. Mixing. The constituentsare mechanically mixed together in the correct
proportions to give a homogeneous(same consistency throughout) concrete
mixture. During mixing,the cement and water produce a paste, and a film is
formed around each aggregate particle. The finer aggregate particles fill the voids
between the coarse aggregate.
2. Placing. The concrete mixture is placed into a mould to obtain the required
shape.
3. Compaction. The concrete mixture may need to be vibrated to remove any air
voids formed during placing. This is known as compaction of the concrete mixture
Rigid stage
When the concrete mixture has set in the mould, the hardening process starts.
Curing. This is the process of retaining water in the concrete mix and maintaining
the temperature of the concrete at about 20°C, which ensuresthat the cement
binds the aggregate particlestogether and that the concrete hardens at a
favourable rate. Curing is carried out by protecting the concrete from the weather.
The exposed concrete surface is covered with a water-resistant material such as
plastic or with damp canvas or hessian. This stops evaporation.
The concrete mix.
It is important in the manufacture of concrete to mix the aggregates, cement and
water in the correct proportions, in order to obtain the correct workability and
strength required for the job. A typical mix contains the followingproportions of
ingredients:
1 part cement : 2 parts of fine aggregate : 4 parts of coarse aggregate : 0.5 parts of
water

5. Type of mix. The proportions of the concrete may be mixed by one of two methods:
• Mixing by volume
Mixing by volume Specified mixes are based on the aggregate and the cement being
dry when measured. Specified examplesof nominal mixes:
Mass concrete 1:3:6
Reinforced concrete 1:2:4.
• Mixing by mass.
For any concrete mix, the mass of each of the ingredientsneeds to be known
accurately. These are called the batch quantities. An accurate knowledge of the
batch quantities enablesthe properties of the concrete to be forecast to a good
precision. The properties of concrete are today much better understood. There are
many varietiesof concrete. This is because:
1. the ingredientscan be varied;
2. the relative proportions of the ingredients can also be varied.
Workability. The measurement of workability of fresh concrete is of importance in
assessing the practicability of placing and compacting the mix and also in
maintaining consistency throughout the job. In addition workability tests can be
used as an indirect check on the water content and therefore on the water/cement
ratio of the concrete