07: Cement

Question 1

This is a binder, a substance that sets and
hardens and can bind other materials together.

Answer 1

Cement

Question 2

This is the mixture of calcareous, siliceous, argillaceous and other substances.

Answer 2

Cement

Question 3

This is the principal binding material of modern time.

Answer 3

Cement

Question 4

COMPARISON OF CHEMICAL AND PHYSICAL
CHARACTERISTICS:

Answer 4

SiO2 content (%) (Silica): 17% – 25%

Al2O3 content (%) (Alumina): 3% – 8%

Fe2O3 content (%) (Iron oxide): 0.5% – 6%

CaO content (%) (lime): 60% – 67%

Gypsum (Calcium Sulphate): 1% – 4%

Specific gravity: 3.15

General use in concrete: Primary binder

Question 5

This is the most common type of cement in
general use around the world, used as a basic ingredient of concrete and mortar.

Answer 5

Portland Cement

Question 6

This forms nearly two-third (2/3) of the cement. Its proportion has an important effect on the cement. Sufficient quantity of this material forms di-calcium silicate (C2SiO2) and tri-calcium silicate in the manufacturing of cement.

Answer 6

Lime

Question 7

This material, in excess, causes the cement to expand and disintegrate.

Answer 7

Lime

Question 8

The quantity of this material should be enough to form di-calcium silicate and tri-calcium silicate in the manufacturing of cement. It gives strength to the cement.

Answer 8

Silica

Question 9

This material, in excess, causes the cement to set slowly.

Answer 9

Silica

Question 10

This supports to set quickly to the cement. It also lowers the clinkering temperature.

Answer 10

Alumina

Question 11

This material, in excess, reduces the strength of the cement.

Answer 11

Alumina

Question 12

This gives color to the cement. It gives hardness and strength to the cement.

Answer 12

Iron Oxide

Question 13

It also helps in giving colour to the cement.

Answer 13

Magnesia

Question 14

This material, in excess, makes the cement unsound.

Answer 14

Magnesia

Question 15

At the final stage of manufacturing, this material is added to increase the setting of cement.

Answer 15

Gypsum

Question 16

PRODUCTION PROCESSES OF CEMENT

Answer 16

Quarrying, Dredging, and Digging
Grinding
Blending
Burning
Finish Grinding
Packaging/Shipping

Question 17

This is accomplished by using explosives to blast the rocks from the ground. After blasting, Excavators (or power shovels) are used to load dump trucks or small railroad cars for transportation to the cement plant, which is usually nearby.

Answer 17

Quarrying of Limestone and Shale

Question 18

The ocean floor is ___ to obtain the shells, while clay and marl are dug out of the ground with power shovels.

Answer 18

Dredged

Question 19

After the raw materials have been transported to the plant, the limestone and shale which have been blasted out of the quarry must be crushed into smaller pieces. Some of the pieces, when blasted out, are quite large. The pieces are then dumped into primary crushers which reduce them to the size of a softball.

Answer 19

Grinding

Question 20

In this process, the raw materials are changed to powdered form in the presence of water.

Answer 20

Wet Process of Grinding

Question 21

In this process, raw materials are pulverized by using a Ball mill, which is a rotary steel cylinder with hardened steel balls. When the mill rotates, steel balls pulverize the raw materials which form slurry (liquid mixture). The slurry is then passed into storage tanks, where correct proportioning is done. Proper composition of raw materials can be ensured by using wet process than dry process. Corrected slurry is then fed into rotary kiln for burning.

Answer 21

Wet Process of Grinding

Question 22

This process is generally used when raw materials are soft because complete mixing is not possible unless water is added.

Answer 22

Wet Process of Grinding

Question 23

This process of fine grinding is accomplished with a similar set of ball or tube mills; however, water is not added during the grinding. The dry materials are stored in silos where additional mixing and blending may be done.

Answer 23

Dry Process of Grinding

Question 24

In this process calcareous material such as lime stone (calcium carbonate) and argillaceous material such as clay are ground separately to fine powder in the absence of water and then are mixed together in the desired proportions. Water is then added to it for getting thick paste and then its cakes are formed, dried and burnt in kilns. This process is usually used when raw materials are very strong and hard.

Answer 24

Dry Process of Grinding

Question 25

Difference between Wet and Dry Manufacturing of Cement

Answer 25

Wet Process:
Raw materials mixed with water
Ground to form a slurry
Homogenized and stored.

Dry Process:
Raw materials ground to a powder
Dried using waste process gases.
Blended and stored.

Advantages and disadvantages:

Wet Process:
Facilitates grinding.
Higher water usage.

Dry Process:
Saves on fuel costs for drying.
Lower water usage.

Water addition:
Wet process: Water added before mixing.
Dry process: Water added during mixing.

Question 26

After the rock is crushed, plant chemists analyze the rock and raw materials to determine their mineral content. The chemists also determine the proportions of each raw material to utilize in order to
obtain a uniform cement product. The various raw materials are then mixed in proper proportions and prepared for fine grinding.

Answer 26

Blending

Question 27

____ the blended materials is the key in the process of making cement. The wet or dry mix is fed into the kiln, which is one of the
largest pieces of moving machinery in the industry.

Answer 27

Burning

Question 28

It is generally twelve feet or more in diameter and 500 feet or more in length, made of steel and lined with firebrick. It revolves on large roller bearings and is
gradually slanted with the intake end higher than the output end.
As the kiln revolves, the materials roll and slide downward for approximately four hours. In this zone, where the heat can reach 3,000 degrees Fahrenheit, the materials become incandescent and change in color from purple to violet to orange. Here, the gases are driven from
the raw materials, which actually change the properties of the raw materials. What emerges is “clinker” which is round, marble-sized, glass-hard balls which are harder than the quarried rock. The clinker is then fed into a cooler where it is cooled for storage.

Answer 28

Burning

Question 29

These are used for the pyroprocessing stage of manufacture of Portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates.

Answer 29

Cement Kiln

Question 30

This is the solid material produced by the cement kiln stage that has sintered into lumps or nodules, typically of diameter 3-25 mm

Answer 30

Clinker

Question 31

The cooled clinker is mixed with a small amount of gypsum, which will help regulate the setting time when the cement is mixed with other materials and becomes concrete. Here again there are primary and secondary grinders. The primary grinders leave the clinker, ground to the fineness
of sand, and the secondary grinders leave the clinker ground to the fineness of flour, which is the final product ready for marketing.

Answer 31

Finish Grinding

Question 32

The final product is shipped either in bulk (ships, barges, tanker trucks, railroad cars, etc.) or in strong paper bags which are filled by machine.

Answer 32

Packaging/Shipping

Question 33

TYPES OF CEMENT (MAJOR STANDARD)

Answer 33

ASTM C150
EN 197

Question 34

TYPES OF ASTM C150 CEMENT

Answer 34

Type I Portland cement is known as common or general-purpose cement.
Type II gives off less heat during hydration.
Type III has relatively high early strength.
Type IV Portland cement is generally known for its low heat of hydration.
Type V is used where sulfate resistance is important.

Question 35

55% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 2.8% MgO, 2.9% (SO3), 1.0% Ignition loss,
and 1.0% free CaO

Portland cement is known as common or general-purpose cement. It is generally assumed unless another type is specified. It is commonly used for general construction especially when making precast and precast-prestressed concrete that is not to be in contact with soils or ground water.

Answer 35

Type I (ASTM C150)

Question 36

51% (C3S), 24% (C2S), 6% (C3A), 11% (C4AF), 2.9% MgO, 2.5% (SO3), 0.8% Ignition loss, and 1.0% free CaO.

This type of cement costs about the same as type I.

A limitation on the composition is that the (C3A) shall not exceed 8%, which reduces its vulnerability to sulfates. This type is for general construction exposed to moderate sulfate attack and is meant for use when concrete is in contact with soils and ground water, especially in the western United States due to the high sulfur content of the soils. Because of similar price to that of type I, this type is much used as a general purpose cement, and the majority of Portland cement sold in North America meets this specification.

Answer 36

Type II (ASTM C150)

Question 37

57% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 3.0% MgO, 3.1% (SO3), 0.9% Ignition loss,
and 1.3% free CaO

This cement is similar to type I, but ground finer.

Some manufacturers make a separate clinker with higher C3S and/or C3A content, but this is increasingly rare, and the general purpose clinker is usually used, ground to a specific surface area typically 50–80% higher. The gypsum level may also be increased a small amount. This gives the concrete using this type of cement a three-day compressive strength equal to the seven-day compressive strength of types I and II. Its seven-day compressive strength is almost equal to 28-day compressive strengths of types I and II. The only downside is that the six-month strength of type III is the same or slightly less than that of types I and II. Therefore, the long-term strength is sacrificed a little. It is usually used for precast concrete manufacture, where high one-day strength allows fast turnover of molds. It may also be used in emergency construction and repairs and construction of machine bases and gate installations.

Answer 37

Type III (ASTM C150)

Question 38

28% (C3S), 49% (C2S), 4% (C3A), 12% (C4AF), 1.8% MgO, 1.9% (SO3), 0.9% Ignition loss, and 0.8% free CaO.

The percentages of (C2S) and (C4AF) are relatively high and (C3S) and (C3A) are relatively low.

A limitation on this type is that the maximum percentage of (C3A) is seven (7%), and the maximum percentage of (C3S) is thirty-five (35%). This causes the heat given off by the hydration reaction to develop at a slower rate. However, as a consequence the strength of the concrete develops slowly. After one or two years the strength is higher than the other types after full curing. This cement is used for very large concrete structures, such as dams, which have a low surface to volume ratio. This type of cement is generally not stocked by manufacturers but some might consider a large special order. This type of cement has not been made for many years, because Portland-pozzolan cements and ground granulated blast furnace slag addition offer a cheaper and more reliable alternative.

Answer 38

Type IV (ASTM C150)

Question 39

38% (C3S), 43% (C2S), 4% (C3A), 9% (C4AF), 1.9% MgO, 1.8% (SO3 ), 0.9% Ignition loss, and 0.8% free CaO.

This cement has a very low (C3A) composition which accounts for its high sulfate resistance. The maximum content of (C3A) allowed is 5% for this type of Portland cement. Another limitation is that the (C4AF) + 2(C3A) composition cannot exceed 20%. This type is used in concrete to be exposed to alkali soil and ground water sulfates which react with (C3A) causing disruptive expansion. It is unavailable in many places, although its use is common in the western United States and Canada. As with type IV, this type of Portland cement has mainly been supplanted by the use of ordinary cement with added ground granulated blast furnace slag or tertiary blended cements containing slag and fly ash.

Answer 39

Type V (ASTM C150)

Question 40

Portland cement Comprising Portland cement and up to 5% of minor additional constituents

Answer 40

Type I (EN 197)

Question 41

Portland-composite cement Portland cement and up to 35% of other single constituents

Answer 41

Type II (EN 197)

Question 42

Blast furnace cement Portland cement and higher percentages of blast furnace slag

Answer 42

Type III (EN 197)

Question 43

Pozzolanic cement Portland cement and up to 55% of pozzolanic constituents (volcanic ash)

Answer 43

Type IV (EN 197)

Question 44

Composite cement Portland cement, blastfurnace slag or fly ash and pozzolana Constituents that are permitted in Portland-composite cements are artificial pozzolans (blast furnace slag, silica fume, and fly ashes) or natural pozzolans (siliceous or siliceous aluminous materials such as volcanic ash glasses, calcined clays and shale).

Answer 44

Type V (EN 197)

Question 45

TYPES OF CEMENT (GENERAL)

Answer 45

1. Ordinary Portland Cement
2. Sulphate Resisting Cement
3. Rapid Hardening Cement (or) High Early Strength cement
4. Quick Setting Cement
5. Low Heat Cement
6. High Alumina Cement
7. Air Entraining Cement
8. White Cement

Question 46

It is the variety of artificial cement. It is called Portland cement because on hardening (setting) its colour resembles to rocks near Portland in England. It was first of all introduced in 1824 by Joseph Asp din, a bricklayer of Leeds, England.

Answer 46

Ordinary Portland Cement

Question 47

Constituents and Chemical Composition of Ordinary Portland Cement

Answer 47

Lime (CaO) 60 - 63%
Silica (SiO2) 17 - 25%
Alumina (Al2O3) 03 - 08%

Iron oxide (Fe2O3) 0.5 - 06%
Magnesia (MgO) 1.5 - 03%
Sulphur Tri Oxide (SO3) 01- 02%
Gypsum 01 - 04%

Question 48

It is modified form of O.P.C and is specially manufactured to resist the sulphates. In certain regions/areas where water and soil may have alkaline contents and O.P.C is liable to disintegrate, because of unfavourable chemical reaction between cement and water, S.R.C is used. This cement contains a low %age of C3A not more than 05%. This cement requires longer period of curing. This cement is used for hydraulic structures in alkaline water and for canal and water courses lining. It develops strength slowly, but ultimately it is as strong as O.P.C.

Answer 48

Sulphate Resisting Cement

Question 49

This cement contains more %age of C3S and less %age of C2S. The property at early stage is due to finer grinding, burning at higher temperature and increased lime content. The strength obtained by this cement in 4 days is same as obtained by O.P.C in 14 days. This cement is used in highway slabs which are to be opened for traffic quickly. This is also suitable for use in cold weather areas. One type of this cement is manufactured by adding calcium chloride (CaCl2 ) to the O.P.C in small proportions. Calcium chloride (CaCl2 ) should not be more than 02%. When this type of cement is used, shuttering material can be removed earlier.

Answer 49

Rapid Hardening Cement (or High Early Strength Cement)

Question 50

When concrete is to be laid under water, this kind of cement is to used. This cement is manufactured by adding small %age of aluminum sulphate (Al2SO4 ) which accelerates the setting action. The setting action of such cement starts with in 5 minutes after addition of water and it becomes stone hard in less than half an hour.

Answer 50

Quick Setting Cement

Question 51

In this cement the heat of hydration is reduced by tri calcium aluminate (C3A) content. It contains less %age of lime than ordinary port land cement. It is used for mass concrete works such as dams etc.

Answer 51

Low Heat Cement

Question 52

This cement contains high aluminate %age usually between 35-55%. It gains strength very rapidly with in 24 hours. It is also used for construction of dams and other heavy structures. It has resistance to sulphates and action of frost also.

Answer 52

High Alumina Cement

Question 53

This type of cement was first of all developed in U.S.A to produce such concrete which would have resistance to weathering actions and particularly to the action of frost. It is found that the bubbles while applying cement, increases resistance to frost action. This also improves workability and durability. It is recommended that air contents should be 03-04 % by volume. Natural resins, fats, oils are used as its agents.

Answer 53

Air Entraining Cement

Question 54

This cement is called snowcrete. As iron oxide gives the grey colour to cement, it is therefore necessary for this cement to keep the content of iron oxide as low as possible. Lime stone and china clay free from iron oxide are suitable for its manufacturing. This cement is costlier than O.P.C. It is mainly used for architectural finishing in the buildings.

Answer 54

White Cement

Question 55

TO CHECK THE QUALITY OF CEMENT IN THE FIELD:

Answer 55

1. Colour greenish grey.
2. One feels cool by thrusting one’s hand in the cement bag.
3. It is smooth when rubbed in between fingers.
4. A handful of cement thrown in a bucket of water should float at first and after few seconds it will go under water.

Question 56

QUALITY TESTS OF CEMENT:

Answer 56

(1) Fineness Test
(2) Consistency Test / Setting Time Test
(3) Setting Time Test
(4) Compressive Strength Test

Question 57

Finer cements react quicker with water and develop early strength, though the ultimate strength is not affected. However finer cements increase the shrinkage and cracking of concrete.

Answer 57

Fineness Test

Question 58

The fineness is tested by:

Break with hands any lumps present in 100 grams of cement placed in IS sieve No.9 and sieve it by gentle motion of the wrist for 15 minutes continuously. The residue when weighed should not exceed 10 percent by weight of the cement sample.

Answer 58

Sieve Analysis

Question 59

This test is performed to determine the quantity of water required to produce a cement paste of standard or normal consistency. Standard consistency of cement paste may be defined as the consistency which permits the Vicate’s plunger (10 mm, 40 to 50 mm in length) to penetrate to a point 5 mm to 7 mm from the bottom ( or 35 mm to 33 mm from top) of Vicat mould. When the cement paste is tested within the gauging time ( 3 to 5 minutes) after the cement is thoroughly mixed with water. ____ is used for performing this test.

Answer 59

Consistency Test

Vicat apparatus is used for performing this test.

Question 60

In cement hardening process, two instants are very important, i.e. initial setting and final setting.

Answer 60

Setting Time Test

Question 61

The process elapsing between the time when water is added to the cement and the time at which the needle ( 1 mm square or 1.13 mm dia., 50 mm in length) fails to pierce the test block ( 80 mm dia. and 40 mm high) by about 5 mm, is known as ____ of Cement.

Answer 61

Initial Setting Time (Test)

Question 62

The process elapsing between the time when water is added to the cement and the time at which a needle used for testing this setting upon applying gently to the surface of the test block, makes an impression thereon, while the attachment of the needle fails to do so, is known as ___ of Cement.

Answer 62

Final Setting Time (Test)

Question 63

IMPORTANT NOTES ON SETTING TIME TEST OF CEMENT

Answer 63

• Importance of Setting Time: Cement should set neither too quickly nor too slowly to ensure proper concrete placement and strength development.
• Initial Setting Time: Marks when cement paste begins losing plasticity, crucial for transportation, placement, and compaction of concrete.
• Final Setting Time: Indicates complete loss of plasticity, allowing safe removal of scaffolding or forms, and signifies sufficient hardening for concrete to attain desired shape and strength.
• Hydration Process: Primary chemical reaction between cement and water occurs during setting, influencing concrete’s mechanical properties.
• Transportation and Workability: Setting time directly impacts transportation, placement, and compaction of concrete, affecting construction efficiency and quality.

Question 64

This test is very important. In this test, three moulds of (face area 50 cm²) are prepared and cured under standard temperature conditions and each cube tested by placing it between movable jaws of the compressive strength testing machine. The rate of increasing load is zero in the beginning and varies at 350 kg/cm² per minute. The load at which the cube gets fractured divided by the cross sectional area of the cube, is the compressive strength of the cube. The average of the compressive strengths of three cubes is the required compressive strength of the cement sample.

Answer 64

Compressive Strength Test