3. Cement Definition Cement is a substance acts as a binding
agent for materials. It is obtained by burning the mixture of
calcareous material such as limestone and argillaceous materials
such as clay at a high temperature. There are two main constituents
in portland cement: Argillaceous materials - clay Calcareous
materials calcium carbonate.
5. Setting action of cement When water is added to cement,
ingredients of cement react chemically with water and forms
chemical compounds which impart strength to the cement. This is
known as setting action of cement. Chemical compounds produced are
Tricalcium aluminate Tricalcium silicate Dicalcium silicate Tetra
calcium alumino ferrite. Usually cement attains about 70% of its
final strength in 28 days and about 90% of its final strength in
one year or so.
6. Manufacture of portland cement There are three operations
involved in manufacture of portland cement: Mixing of raw materials
Burning Grinding Mixing of raw materials There are two methods in
mixing of raw materials of cement: Dry process Wet process.
7. Argillaceous material crushing Fine grinding storage
Calcareous material crushing Fine grinding storage Mixing in
correct proportion Dry process
8. Storage tanks for raw mix Rotary kiln Formation of clinkers
cooler Grinding of clinkers in ball mills and tube mills Storage in
silos Weighing &packing in bags distribution gypsum Coal
dust
9. Wet process Calcareous material limestone Argillaceous
material clay crushing crushing storage storage channel Grinding
mill Formation of slurry
10. Correcting basin Storage tank pumping Rotary kiln Formation
of clinkers cooler Grinding of clinkers in ball mills Storage in
silos Weighing and packing in bags distribution gypsum Coal
dust
11. Burning Burning is carried out in rotary kiln. Diameter of
kiln is 250-300 cm, length is 90-120 m and inclined about 1 in 20
to 30. It is supported on rollers. Refractory lining is provided on
the inner surface. Slurry is injected at upper end and it descends
to burning zone carbon- dioxide gets evaporated and forms nodules.
Temperature is about 1500-1700 c. In burning zone the lime and clay
in the slurry get chemically fused to form hard balls of portland
cement known as clinkers (Size 5 to 10mm).
12. Rotary kiln from storage tank slurry dust nodules rotary
arrangement coal dust burning zone refactoy lining air Support
cooler clinkers
13. Grinding Grinding is done in ball mills and tube mills.
Gypsum is added about 3 to 4 percent during grinding. Gypsum
controls initial setting time of cement. Finely ground cement is
stored in silos. It is weighed and packed in bags. Each bag
contains 50Kg of cement. The bags are stored in dry places.
14. Properties of cement It is an excellent binding material.
Gives strength to masonry. Possesses a good plasticity. Offers a
good resistance to moisture. Easily workable. It hardens quickly
after addition of water. The colour of cement should be uniform.
Cement should be free from lumps. Cement should feel smooth when
touched or rubbed in between fingers.
15. If a small quantity of cement is thrown into a bucket of
water, it should sink and should not float on the surface. Average
compressive strength of cement mortar should not be lass than 11.5
N/mm2 at 3days and 17.5 N/mm2 at 7days. Average tensile strength of
cement mortar should not be less than 2 N/mm2 at 3days and 2.5
N/mm2 at 7days. The initial setting time should not be less than 30
mins and final setting time should not be more than 600 mins. The
loss of ignition should be within 4% The specific surface of cement
should not be less than 2250 cm2 /gm. If the cement is sieved on 90
micron sieve for 15 mins, the residue by weight should be within
10%.
16. Uses of cement It is used for constructing engineering
structures such as dams, bridges, storage reservoirs. Used for
making joints for pipes, drains. Used for preparation of
foundations, footpath. Used for manufacture of precast pipes,
fencing posts. Used for masonry work, plastering, pointing. Used
for laying floors, roofs and constructing lintels. Used for
protecting the structures from weather.
17. Types of cement Quick setting cement Low heat cement High
alumina cement Expanding cement Rapid hardening cement Acid
resistant cement Sulphate resisting cement White cement Coloured
cement Blast furnace cement Pozzolana cement Air entraining cement
Masonry cement Oil-well cement Redi-set cement High strength cement
Hydrophobic cement
18. Testing of cement Testing of cement can be brought under
two categories: Field testing Laboratory testing Field testing
sufficient to subject the cement to field tests when it is used for
minor works. Open the bag and take a look at the cement. There
should not be any visible lumps. The colour of the cement should
normally be greenish grey. Thrust your hand into the cement bag. It
must give you a cool feeling. Take a pinch of cement and feel
between the fingers. It should give a smooth and gritty
feelings.
19. Take a handful of cement and throw it on a bucket full of
water, the particles should float for some time before they sink.
Take about 100 grams of cement and a small quantity of water and
make a stiff paste (cake should not disturb when take into the
water) Laboratory testing - for using cement in major works, the
laboratory test are carried out. The following are carried out in
laboratory: Fineness test (sieve analysis) Setting time
test(standard consistency) Strength test(compressive strength)
Soundness test(le chatelier) Heat of hydration test(vacuum flask
method) Chemical composition test
20. Strength test: Compressive strength is most important. The
standard sand is used for finding the strength of cement. Fineness
test Fineness of cement is important bearing on the rate of
hydration and on rate of gain of strength. Finer cement offers a
greater surface area and hence faster and greater the development
of strength. Fineness of cement is tested in two ways: By sieving.
By determination of specific surface by air- permeability.
21. Setting time test An arbitrary division has been made for
the setting time of cement as initial setting and final setting
time. Initial setting time- is the time elapsed between the moment
that the water is added to the cement to the time that the paste
starts losing its plasticity. Final setting time the time elapsed
between the moment the water is added to the cement and the time
when the paste has completely lost its plasticity and has
sufficient firmness to resist pressure. The test is carried out in
vicat apparatus.
22. Concrete Definition Concrete may be defined as a building
material obtained by mixing cement, fine, coarse aggregates and
water in suitable proportions. It is plastic mixture after curing
it becomes hard mass. The coarse aggregates are broken stone,
broken bricks or gravel, the fine aggregate is sand or surki and
the binding material is lime or cement. Fresh concrete or plastic
is a freshly mixed material which can be moulded into any shape.
The relative quantities of cement, aggregates and water together
control the properties in the wet state as well as in the hardened
state. Constituents of Concrete Cement Fine aggregate and Coarse
aggregate Water
23. Advantages of Concrete It is plastic when freshly prepared
and can be moulded to any shape. Concrete does not lose its
strength with age and does not require maintenance. The proportion
of mix can be suitable designed to give concrete of required
strength. It is durable and not affected by weather. It affords
quickness and ease of a construction. It can be given various
finishes. Concrete is water repellent and can be made water proof.
Concrete can be made fire proof or light weight or chemical
resistant by using suitable admixtures.
24. Properties of Concrete Concrete has high compressive
strength depends on the proportion of cement, sand, coarse
aggregates and water used. It hardens with age and process of
hardening continuous for long time even after it has attained
sufficient strength, but the rate of hardening decreases with age.
It is free from corrosion and atmospheric effects. It is weak in
tension. Steel reinforcement is placed in cement concrete at
suitable places to take up the tensile stresses called as RCC. It
shrinks in the initial stage and during hardening. This can be
minimized by proper curing.
25. Workability The property of freshly mixed concrete which
determines the ease and homogenous with which it can be mixed,
placed, compacted and finished Factors Affecting Workability Water
content Mix proportions Size of aggregates Shape of aggregates
Surface texture of aggregates Grading of aggregates Use of
admixtures
26. Water content Water content in a given volume of concrete
will have significant influences on the workability. Higher the
water content, higher be the fluidity which affects workability.
Mix proportion Aggregate/cement ratio is an important factor
influences workability. Higher the aggregate/cement ratio, leaner
is the concrete. Size of aggregate Bigger the size of the
aggregate, less is the surface area and less is the amount of
water. It will give better workability.
27. Shape of aggregate The shape of aggregate influences
workability. Angular, elongated or flaky aggregate makes the
concrete harsh when compared with rounded aggregates. Surface
texture The total surface area of rough textured aggregate is more
than the surface area of smooth rounded aggregate of same volume.
Grading of aggregate It influences maximum workability. Better the
grading, less the void content and higher the workability. Use of
aggregate Use of air-entraining and pozzolanic material gives
better workability.
28. Measurement of workability The following tests are commonly
employed to measure workability: Slump test K Slumper Compacting
factor test - Compacting factor apparatus Flow test Flow table
Kelly ball test Kelly ball Vee bee consistometer test- VBR
Segregation : Separation of the constituent materials of concrete
Bleeding : Water from the concrete comes out of the surface of the
concrete Water Cement ratio : Ratio of weight of water used to that
of cement. It depends upon strength, workability and method of
compaction
29. Process of manufacture of concrete The various stages of
manufacture of concrete are: Batching Mixing Transporting Placing
Compacting Curing Finishing
30. Batching The measurement of materials for making concrete
is known as batching. Volume batching Gauge box Weigh batching
weight machine Mixing Mixing of materials is essential for the
production of uniform concrete. There are two methods for mixing
concrete: Hand mixing Machine mixing.
31. Transporting concrete Concrete can be transporting by a
variety of methods and equipments. Mortar pan Wheel barrow, Hand
cart Bucket and Rope way Truck mixer and Dumpers Belt conveyors
Chute Skip and Hoist Pumps and Pipeline
32. Placing concrete Placing concrete within earth mould. e.g.:
foundation concrete for a wall or column. Placing concrete within
large earth mould or timber plank formwork. e.g.: road slab and
airfield slab. Placing concrete in layers within timber or steel
shutters. e.g.: mass concrete in dam construction or construction
of concrete abutment or pier. Placing concrete within usual from
work. e.g.: columns, beams and floors. Placing concrete under
water.
33. Compaction of concrete Compaction of concrete is the
process adopted for expelling the entrapped air from the concrete.
Hand compaction: Rodding Ramming Tamping. Compaction by vibration
Internal vibrator (needle vibrator) Formwork vibrator (external
vibrator) Table vibrator Platform vibrator Surface vibrator (screed
vibrator). Compaction by pressure and jolting Compaction by
spinning.
34. Curing of concrete Curing is the process of maintaining a
satisfactorily moisture content and favorable temperature. The
following are the curing methods: Water curing Membrane curing
Application of heat Miscellaneous Water curing Water curing can be
done in the following: Immersion Ponding Spraying Wet covering
35. Membrane curing Bituminous compounds Polyethylene
Waterproof paper Rubber. Application of heat The exposure of
concrete to higher temperature can be done in the following manner:
Steam curing at ordinary pressure Steam curing at high pressure
Curing by infra-red radiation Electrical curing.
36. Miscellaneous methods of curing Calcium chloride is used as
a surface coating or as a admixture. Finishing Finishing operation
is the last operation in making concrete. Surface finish can be
grouped as follows: Formwork finishes centering work Surface
treatment Applied finishes. Miscellaneous Finishes : Non - Slip
Finish, Coloured finish, Water resistant floor finish
37. Tests of fresh concrete Slump test Kelly ball test. Tests
on hardened concrete Non-destructive testing-does not cause any
destructive of the element. Semi-destructive testing-cause
negligible damage of the element. Non-destructive testing: Rebound
hammer test. Ultrasonic pulse velocity test. Semi-destructive
testing: Windsor probe test
38. Rebound hammer test It consists of spring-controlled mass
that slides on a plunger within tubular housing. When the plunger
is pressed the spring controlled mass rebounds. Depends on surface
hardness of concrete. Related to compressive strength. The rebound
is read on graduated scale and the value is designated as rebound
number or rebound index.
39. Uses: It is used for estimating the compressive strength.
Establishing the uniformity of concrete. Assessing the quality of
one element of concrete in relation to another. Limitations:
Results are affected by the angle of test, surface smoothness, and
mix proportion. It is only suitable for close-textured
concrete.
40. Rebound hammer concrete impact spring compression spring
surface plunger hammer mass housing
41. Types of concrete Normal density Air-entraining Polymer
concrete composites Sulphur impregnate concrete Fibre reinforced
concrete(FRC). Roller compacted concrete Super plasticized Coloured
Pumped Ready mixed concrete(RMC) Ferro cement Light weight Recycled
Heavy weight No slump No fine Vacuum Spinned Hot
42. FRC Composite material consisting of mixture of cement
mortar and discontinuous discrete, uniformly dispersed suitable
fibres. Types: a) SFRC- steel fibre reinforced concrete b) CFRC-
carbon fibre reinforced concrete c) GFRC- glass fibre reinforced
concrete d) HFRC- hybrid fibre reinforced concrete. SFRC- steel
fibre reinforced concrete Made up of rusted steel. Used in road
pavements, bridge decks.
43. CFRC- carbon fibre reinforced concrete Has high tensile
strength. Durability. HFRC- hybrid fibre reinforced concrete Made
up of polypropylene, nylon fibres, asbestos. Durability High
tensile strength.
44. Quality of concrete Good workability No segregation No
bleeding High strength Durability Impermeability Elasticity
Shrinkage Least thermal expansion.
45. Advantages of concrete Availability of concrete is easy.
Easy handling. Easy transportation. More economical. Monolithic
character gives better appearance. Disadvantages of concrete
Expansion joints are required. Construction joints are provided to
avoid cracks. Sustain loads develops creep in structure. Due to low
tensile strength, concrete is required to be reinforced to avoid
cracks. Soluble salts in concrete cause efflorescence of moisture
reacts with them.
46. Concrete chemicals They are used in cement as an additive,
in mortar and concrete as admixtures. Such additives and admixtures
is called as concrete chemicals or construction chemicals. It
includes the following materials: Plasticizers and super
plasticizers. Retarding plasticizers and retarders. Accelerating
plasticizers and accelerators. Air-entraining agent. Water proofing
material. Polymer bonding agents.
47. Floor hardness and dust proofers. Concrete curing
compounds. Polymer mortar for repair and maintenance. Adhesive for
tiles, marbles and granite. Mould releasing agents. Grouting
agents. Decorative and protective paint. Concrete repair system.
Installation aids.
48. Queries: Two marks: What is cement and list out its
chemical composition? What are the process of cement manufacturing?
What are the methods of testing in cement? What is meant by
workability? What is concrete and explain mix proportion of
concrete? What are the testing methods involved in fresh concrete
and hardened concrete? What are the qualities of concrete? Describe
the advantage of concrete? Describe the disadvantages of concrete?
What Is meant by concrete chemicals?
49. 16 marks: Describe the manufacturing of cement(dry and wet
process)? What are the different types of cement? explain their
properties and uses? Describe the field testing and laboratory
testing method in cement? Explain in detail the process of concrete
manufacturing? Explain the method of non-destructive testing in
detail? What tests are used to determine the workability of fresh
concrete? explain in detail: What are the different types of
concrete? explain their properties and uses? Explain the various
types of concrete chemicals in detail?
