UNIT 1

CONSTITUENT MATERIALS

1.1. Cement

 Cement is a mixture of limestone, clay, silica and gypsum. It is a fine powder which when mixed
with water sets to a hard mass as a result of hydration of the constituent compounds. It is the most
commonly used construction material.

 A hydraulic binder, i.e. a finely ground inorganic material which, when mixed with water, forms
a paste which sets and hardens by means of hydraulic reactions and processes and which, after
hardening, retains its strength and stability even under water.

1.2. Types of cement

1. Ordinary Portland cement 2. Low Heat Cement

3. Rapid hardening cement 4. Sulphates resisting Cement

5. Extra rapid hardening cement 6. Blast Furnace Slag Cement

7. Sulphate resisting cement 8. High Alumina Cement

9. White Cement 10. Air Entraining Cement

11. Coloured cement 12. Hydrographic cement

13. Pozzolanic Cement 14. Air Entraining Cement

Ordinary Portland cement (OPC)

This is by far the most common cement used in general concrete construction when there is no
exposure to sulphates in the soil or in ground water. Ordinary Portland cement is the cement most
widely used. It have an inadequate durability. Opc classified in to three grades i.e: 33 grade OPC, 43
grade OPC, 53 grade OPC.

33 grade OPC

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If the 28 days strength is not less than 33N/mm is called 33 grade opc.It is used for normal
grade of concrete upto M-20, plastering, flooring, grouting of cable ducts in PSC works etc. The
fineness should be between 225 and 280.

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43 grade OPC

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If the 28 days strength is not less than 43N/mm is called 33 grade OPC .It is the most widely
used general purpose cement. For concrete grades up to M-30 used in precast elements. For marine
structures but C3A should be between 5 - 8%.

53 grade OPC

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If the 28 days strength is not less than 33N/mm is called 53 grade OPC. For concrete grade
higher than M-30, PSC works, bridge, roads, multistoried buildings etc. For use in cold weather
concreting. For marine structures but C3A should be between 5 - 8%.

Rapid hardening cement

Rapid hardening cement is similar to Ordinary Portland cement but with higher tri-calcium
silicate (C3S) content and finer grinding. It gains strength more quickly than OPC, though the final
strength is only slightly higher. This type of cement is also called as High-Early Strength Portland
Cement. The one-day strength of this cement is equal to the three-day strength of OPC with the same
water-cement ratio. It is used where formwork has to be removed as early as possible in order to reuse it.
Rate of heat evolution is higher than in ordinary Portland cement due to the increase in C 3S and C3A,
and due to its higher fineness.

 It is used where high early strength is required.


 It is generally used for constructing road pavements, where it is important to open the road to
traffic quickly.

 It is used in industries which manufacture concrete products like slabs, posts, electric poles, block
fence, etc. because molds can be released quickly.

 It is used for cold weather concreting because rapid evolution of heat during hydration protects
the concrete against freezing. This type of cement does not use at mass concrete constructions.

Extra Rapid Hardening Portland Cement

This type prepare by grinding CaCl2 with rapid hardening Portland cement. The percentage of

CaCl2 should not be more than 2% by weight of the rapid hardening Portland cement.

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 By using CaCl2:

 The rate of setting and hardening increase (the mixture is preferred to be casted within 20
minutes).
 The rate of heat evolution increase in comparison with rapid hardening Portland cement, so it is
more convenient to be use at cold weather.
 The early strength is higher than for rapid hardening Portland cement, but their strength is equal
at 90 days.
 Because CaCl2 is a material that takes the moisture from the atmosphere, care should be taken to
store this cement at dry place and for a storage period not more than one month so as it does not
deteriorate.

Low Heat Portland Cement

Composition it contains less C3S and C3A percentage, and higher percentage of C2S in
comparison with ordinary Portland cement.

Properties

 Reduce and delay the heat of hydration and limit the heat of hydration of this cement. It has lower
early strength (half the strength at 7 days age and two third the strength at 28 days age) compared
with ordinary Portland cement.
 Its fineness is not less than 3200 cm2 /g

Uses

 It is used in mass concrete constructions: the rise of temperature in mass concrete due to
progression in heat of hydration -- cause serious cracks. So it is important to limit the rate of heat
evolution in this type of construction, by using the low heat cement.

Sulfate- resisting Cement

Composition

 Lower percentage of C3A and C4AF – which considers as the most affected compounds by
sulfates.
 Higher percentage of silicates – in comparison with ordinary Portland cement.
 For this type of cement – C2S represents a high proportion of the silicates.

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 Properties
 Low early strength.
 Its resulted heat of hydration is little higher than that resulted from low heat cement.
 Its cost is higher than ordinary Portland cement – because of the special requirements of
material composition, including addition of iron powder to the raw materials.

Portland Blast furnace

 Cement Production This type of cement consists of an intimate mixture of Portland cement
and ground granulated blast furnace slag. Slag – is a waste product in the manufacture of pig
iron.
 Chemically, slag is a mixture of 42% lime, 30% silica, 19% alumina, 5% magnesia, and 1%
alkalis, that is, the same oxides that make up Portland cement but not in the same proportions.
 The maximum percentage of slag use in this type of cement is limited by British standard
B.S. 146: 1974 to be 65%, and by American standard ASTM C595-76 to be between 25-65%.

Properties

 Its early strength is lower than that of ordinary cement, but their strength is equal at late ages
(about 2 months).
 The requirements for fineness and setting time and soundness are similar for those of
ordinary cement (although actually its fineness is higher than that of ordinary cement).
 The workability is higher than that of ordinary cement.
 Heat of hydration is lower that of ordinary cement. Its sulfate resistance is high.

Uses

 Mass concrete it is possible to be use in constructions subjected to sea water (marine

constructions). May not be used in cold weather concreting.

Pozzolanic Cement

 Production This type of cement consists of an intimate mixture of Portland cement and
pozzolana. pozzolana content by 15-40% of Pozzolanic cement.
 Pozzolana, according to it is defined as a siliceous and aluminous material which in itself
possesses little or no cementitious value.

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  But will, in finely divided form and in the presence of moisture, chemically react with
calcium hydroxide at ordinary temperatures to form compounds possessing cementitious
properties.
 It is essential that pozzolana be in finely divided state as it is only then that silica can
combine with calcium hydroxide (produced by the hydrating Portland cement) in the
presence of water to form stable calcium silicates which have cementitious properties.
 Natural Pozzolanic materials, such as – volcanic ash - Industrial Pozzolanic materials, such
as – fired clay, rice husks ash Properties & Uses They are similar to those of Portland blast
furnace cement.

White Cement

 White Portland cement is made from raw materials containing very little iron oxide (less than
0.3% by mass of clinker) and magnesium oxide (which give the grey color in ordinary Portland
cement).
 China clay (white kaoline) is generally used, together with chalk or limestone, free from
specified impurities.
 Its manufacture needs higher firing temperature because of the absence of iron element that
works as a catalyst in the formation process of the clinker.
 In some cases kreolite (sodium-aluminum fluoride) might be added as a catalyst. The
compounds in this cement are similar for those in ordinary Portland cement, but C4AF
percentage is very low. Contamination of the cement with iron during grinding of clinker has
also to be avoided. For this reason, instead of the usual ball mill, the expensive nickel and
molybdenum alloy balls are used in a stone or ceramic-lined mill.
 The cost of grinding is thus higher, and this, coupled with the more expensive raw materials,
makes white cement rather expensive.
 It has a slightly lower specific gravity (3.05-3.1), than ordinary Portland cement. The strength is
usually somewhat lower than that of ordinary Portland cement.

Colored Portland Cement

 It is prepared by adding special types of pigments to the Portland cement. The pigments added to
the white cement (2-10% by weight of the cement)
 when needed to obtain light colors, while it added to ordinary Portland cement when needed to
obtain dark colors.

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  The 28-day compressive strength is required to be not less than 90% of the strength of a
pigment-free control mix, and the water demand is required to be not more than 110% of the
control mix.
 It is required that pigments are insoluble and not affected by light. They should be chemically
inert and don't contain gypsum that is harmful to the concrete.

Anti-bacterial Portland Cement

 It is a Portland cement with an anti-bacterial agent which prevents microbiological fermentation.

 This bacterial action is encountered in concrete floors of food processing plants where the
leaching out of cement by acids is followed by fermentation caused by bacteria in the presence
of moisture.

Hydrophobic Cement

 It is prepared by mixing certain materials ( stearic acid, oleic acid, … etc by 0.1-0.4%) with
ordinary Portland cement clinker before grinding, to form water repellent layer around the
cement particles, so as the cement can be store safely for a long period. This layer removes
during mixing process with water.

Expansive Cement

 It has the property of expanding in its early life so as to counteract contraction induced by
drying shrinkage.

Portland Slag Cement ( PSC)

 Thus the cement produced with slag, clinker and gypsum is called Portland Slag Cement ( PSC).

Used

 Concrete pavements Structures and foundations Mass concrete applications, such as dams
Precast concrete, such as pipe and block Pre-stressed or post-tensioned concrete. Concrete
exposed to water and marine applications High-performance/high-strength concrete, used
typically in high-rise buildings or bridges to give 100 year service life.
 Portland Slag Cement improves the Properties of Fresh Concrete, improves Concrete Strength
and Elastic Modulus, reduce Permeability and Corrosion, Improves Resistance to Alkali-
Aggregate Reaction, Mitigate Sulfate Attack, Reduce Heat and Cracking in Mass Concrete

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Types of Cement Composition Purpose

Rapid Hardening Increased Lime content Attains high strength in early days it is used in
Cement concrete where form work are removed at an
early stage.

Quick setting cement Small percentage of aluminium Used in works is to be completed in very short
sulphate as an accelerator and reducing period and concreting in static and running
percentage of Gypsum with fine water
grinding

Low Heat Cement Manufactured by reducing tri-calcium It is used in massive concrete construction like
aluminate gravity dams

Sulphates resisting It is prepared by maintaining the It is used in construction exposed to severe

percentage of tricalcium aluminate sulphate action by water and soil in places like

Cement below 6% which increases power canals linings, culverts, retaining walls,
against sulphates siphons etc.,

Blast Furnace Slag It is obtained by grinding the clinkers It can used for works economic considerations
Cement with about 60% slag and resembles is predominant.
more or less in properties of Portland
cement

High Alumina Cement It is obtained by melting mixture of It is used in works where concrete is subjected
bauxite and lime and grinding with the to high temperatures, frost, and acidic action.
clinker it is rapid hardening cement
with initial and final setting time of
about 3.5 and 5 hours respectively

White Cement It is prepared from raw materials free It is more costly and is used for architectural
from Iron oxide. purposes such as pre-cast curtain wall and
facing panels, terrazzo surface etc.,

Coloured cement It is produced by mixing mineral They are widely used for decorative works in
pigments with ordinary cement. floors

Pozzolanic Cement It is prepared by grindin pozzolanic It is used in marine structures, sewage works,
clinker with Portland cement sewage works and for laying concrete under
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 water such as bridges, piers, dams etc.,

Air Entraining It is produced by adding indigenous air This type of cement is especially suited to
Cement entraining agents such as resins, glues, improve the workability with smaller water
sodium salts of Sulphates etc during cement ratio and to improve frost resistance of
the grinding of clinker. concrete.

Hydrographic cement It is prepared by mixing water This cement has high workability and strength
repelling chemicals

1.3. Chemical composition & Properties of cement

 The raw materials used for the manufacture of cement consist mainly of lime, silica, alumina and
iron oxide. These oxides interact with one another in the kiln at high temperature to form more
complex compounds.

 The relative proportions of these oxide compositions are responsible for influencing the various
properties of cement; in addition to rate of cooling and fineness of grinding.

Oxide Per cent content

CaO 60–67
SiO2 17–25
Al2O3 3.0–8.0
Fe2O3 0.5–6.0
MgO 0.1–4.0
Alkalies ( K2O, Na2O) 0.4–1.3
SO3 1.3–3.0

 The identification of the major compounds of cement is largely based on Bogue’s equations and
hence it is called “Bogue’s Compounds”. The four compounds usually regarded as major
compounds are listed in the table

Name of Compound Formula Abbreviated Formula

Tricalcium silicate 3 CaO.SiO2 C3S

Dicalcium silicate 2 CaO.SiO2 C2S
Tricalcium aluminate 3 CaO.Al2O3 C3A
Tetracalcium
aluminoferrite 4 CaO.Al2O3.Fe2O3 C4AF

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  In addition to the four major compounds, there are many minor compounds formed in the kiln.
Two of the minor oxides namely K2O and Na2O referred to as alkalis in cement are of some
importance and Expressed in terms of Na2O.

 These alkalis basically react with active silica in aggregate and produce what is called alkali-
silica gel of unlimited swelling type under favorable conditions of moisture and temperature in
voids and cracks and further it causes disruption and pattern cracking.

 Tricalcium silicate and di calcium silicate are the most important compounds responsible for
strength.
 Together they constitute 70 to 80 per cent of cement. The average C3S content in modern
cement is about 45 per cent and that of C2S is about 25 per cent.

 The calculated quantity of the compounds in cement varies greatly even for a relatively small
change in the oxide composition of the raw materials.

 To manufacture a cement of stipulated compound composition, it becomes absolutely
necessary to closely control the oxide composition of the raw materials.

 SO3 also appear in cement analysis which comes from adding gypsum (4-6) % during clinker

gridding. The Iraqi and British specification for normal high rapid Portland cement pointed
that SO3 content must be between ( 3-2.5 )% according to type of cement and C3A content.

 The percentage of Mgo in cement which is come from Magnesia compounds in raw material.
is about ( 4-1)% and 5% as maximum range to control expansion from hydration of this oxide
in hard concrete.

 An increase in lime Cao content beyond a certain value makes it difficult to combine with
other compounds and free lime will exist in the clinker which causes unsoundness in cement.
 Insoluble residue is that part of the Cement non-soluble in hydrochloric acid HCl and arise
mainly from non-active silica to form cement compounds dissolved in this acid therefore it
express the completeness of the chemical reactions inside the rotary kiln.

1.4. Hydration

 The reaction of cement with water is called hydration. The reaction liberates a considerable
quantity of heat. This can be easily observed if a cement is gauged with water and placed in a
thermos flask.
 The hydration of cement is happening in two ways as follows.
1. Solution through Hydration
 In this, the cement compounds dissolve in water to produce a super – saturated solution, from
which different hydrated products get precipitated.

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2. Solid state Hydration
 In this, the water attacks cement compounds in the solid state and converting them into hydrated
products
 The solution through mechanism takes places in the early stages of hydration when large quantity
of water is available.
 Hydration process is not an instantaneous one. The reaction is faster in the early stage and
continues indefinitely, at a decreasing rate. The hydration process cannot be completed even in a
year or more even the cement is very finely ground.
 The hydration process is an Exo thermic reation and hence it liberates the heat. The quantity of
heat, in joules per hour of hydrated cement evolved in the complete hydration process, as a given
temperature is called heat of hydration.
Products of hydration :
1. Calcium Silicate hydrates (C- S- H)
2. Calcium alumininum hydrates (C- A- H)
3. Calcium Hydroxide (Ca(OH)2)
 When water is added to cement each of Bogue’s compound undergo hydration and
contributes to final cement product. Only the calcium silicate contribute to strength.
 Tri – calcium silicate is responsible for most of early strength(first 7 days).
 Di – Calcium Silicate, which reacts more slowly, contributes only to the strength at later
times
Tri calcium silicate + water Calcium Silicate hydrates + Calcium Hydroxide + Heat

1.5. Testing of cement

 Field test
 Laboratory test

Field tests on cement

 Field tests on cements are carried to know the quality of cement

supplied at site. It gives some idea about cement quality based on
colour, touch and feel .
 The colour of the cement should be uniform. It should be grey colour with a light greenish shade.
The cement should be free from any hard lumps. Such lumps are formed by the absorption of
moisture from the atmosphere. Any bag of cement containing such lumps should be rejected
 The cement should feel smooth when touched or rubbed in between fingers. If it is felt rough, it
indicates adulteration with sand.

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  If hand is inserted in a bag of cement or heap of cement, it should feel cool and not warm. If a
small quantity of cement is thrown in a bucket of water, the particles should float for some time
before it sink.
 A thick paste of cement with water is made on a piece of glass plate and it is kept under water
for 24 hours. It should set and not crack.
 A block of cement 25 mm ×25 mm and 200 mm long is prepared and it is immersed for 7 days
in water. It is then placed on supports 15cm apart and it is loaded with a weight of about 34 kg.
The block should not show signs of failure.

Laboratory test on cement

 Fineness Test
 Setting Time Test
 Strength Test
 Soundness Test
 Heat Of Hydration Test
 Chemical Composition Test

Fineness Test
 The fineness of cement has an important bearing on the rate of hydration and hence on the rate
of gain of strength and also on the rate evolution of heat.
 Finer cement offers a greater surface area for the hydration and hence faster development of
strength. The disadvantages of finer grains are susceptible to air set and early deterioration.
 Increase in fineness of cement is also found to increase the drying shrinkage of concrete. In
commercial cement it is suggested that there should be about 25-30% of particle of less than 7 µ
in size.
Fineness of cement is tested in two way that is,
 Sieving method
 Air permeability method

Standard consistency test

 The standard consistency of cement is defined as that consistency which will permit a vicat
plunger having 10mm diameter and 50mm length to penetrate to a depth of 33-35mmfrom the top
of the mould.

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 Procedure for standard consistency
 Take about 500 gms of cement and prepare a paste with a weighed quantity of water (say 24 % by
weight of cement) for the first trial.
 The paste must be prepared in a standard manner and filled into the Vicat mould within 3-5
minutes. After completely filling the mould, shake the mould to expel air.
 A standard plunger, 10 mm diameter, 50 mm long is attached and brought down to touch the
surface of the paste in the test block and quickly released allowing it to sink into the paste by its
own weight.
 Take the reading by noting the depth of penetration of the plunger. Conduct a 2nd trial (say with
25 per cent of water) and find out the depth of penetration of plunger.
 Similarly, conduct trials with higher and higher water/cement ratios till such time the plunger
penetrates for a depth of 33-35 mm from the top.
 That particular percentage of water which allows the plunger to penetrate only to a depth of 33-35
mm from the top is known as the percentage of water required to produce a cement paste of
standard consistency.
 This percentage is usually denoted as P. The test is required to be conducted in a constant
temperature (27° + 2°C) and constant humidity (90%).
Setting Time Test
 The term setting time is a combination of initial and final setting time of the cement.
 Initial setting time is regarded as the time elapsed between the moments that the water is added
to the cement to the time that the paste starts losing its plasticity. Initial setting time starts after 30
minutes.
 Final setting time is 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 attained sufficient firmness to
resist certain defined pressure. The actual construction dealing with cement paste. Final setting
time of the cement is not more than 10hr.
The following procedure is adopted Vicat Appartus shown in figure.
 Take 500 gm. of cement sample and guage it with 0.85 times the water required to produce
cement paste of standard consistency (0.85 P).
 The paste shall be gauged and filled into the Vicat mould in specified manner within 3-5 minutes.
Start the stop watch the moment water is added to the cement. The temperature of water and that
of the test room, at the time of gauging shall be within 27°C ± 2°C.

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 Vicat Appartus
Initial Setting Time
 Lower the needle (C) gently and bring it in contact with the surface of the test block and quickly
release.
 Allow it to penetrate into the test block. In the beginning, the needle will completely through the
test block. But after some time when the paste starts losing its plasticity, the needly may penetrate
only to a depth of 33-35 mm from the top.
 The period elapsing between the time when water is added to the cement and the time at which
the needle penetrates the test block to a depth equal to 33-35 mm from the top is taken as initial
setting time.

Final Setting Time

 The cement shall be considered as finally set when, upon, lowering the attachment gently cover
the surface of the test block, the centre needle makes an impression, while the circular cutting
edge of the attachment fails to do so. In other words the paste has attained
 Such hardness that the centre needle does not pierce through the paste more than 0.5 mm.

Strength Test
 The compressive strength of hardened cement is the most important of all the properties.
Therefore, it is not surprising that the cement is always tested for its strength at the laboratory
before the cement is used in important works.
 Strength tests are not made on neat cement paste because of difficulties of excessive shrinkage
and subsequent cracking of neat cement.
 Strength of cement is indirectly found on cement sand mortar in specific proportions. The
standard sand is used for finding the strength of cement. It shall conform to IS 650-1991.

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 Procedure
 Take 555 gms of standard sand (Ennore sand), 185 gms of cement (i.e., ratio of cement to
sand is 1:3) in a non-porous enamel tray and mix them with a trowel for one minute, then add
water of quantity 3.0 % of combined weight of cement and sand
 Mix the three ingredients thoroughly until the mixture is of uniform colour. The time of
mixing should not be less than 3 minutes nor more than 4min.
 Immediately after mixing, the mortar is filled into a cube mould of size 7.06 cm. The area of
the face of the cube will be equal to 50 sq cm. Compact the mortar either by hand compaction
in a standard specified manner or on the vibrating equipment (12000 RPM) for 2 minutes.
 Keep the compacted cube in the mould at a temperature of 27°C ± 2°C and at least 90 %
relative humidity for 24 hours.
 After 24 hours the cubes are removed from the mould and immersed in clean fresh water
until taken out for testing.
 Three cubes are tested for compressive strength at the periods of 7,14,28 days. The
compressive strength shall be the average of the strengths of the three cubes for each period
respectively. The strength requirements for various types of cement is shown in Moulding of
70.7 mm Mortar Cube Vibrating Machine.

Soundness Test

 It is very important that the cement after setting shall not undergo any appreciable change of
volume. Certain cements have been found to undergo a large expansion after setting causing
disruption of the set and hardened mass.
 The testing of soundness of cement, to ensure that the cement does not show any appreciable
subsequent expansion is of prime importance.
 The unsoundness in cement is due to the presence of excess of lime than that could be
combined with acidic oxide at the kiln. This is also due to inadequate burning or insufficiency
in fineness of grinding.

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  It is also likely that too high a proportion of magnesium content or calcium sulphate content
may cause unsoundness in cement.
 For this reason the magnesia content allowed in cement is limited to 6 %.The apparatus is
shown in Fig..
 It consists of a small split cylinder of spring brass or other suitable metal. It is 30 mm in
diameter and 30 mm high. On either side of the split are attached two indicator arms 165 mm
long with pointed ends.
 Cement is gauged with 0.78 times the water required for standard consistency (0.78 P), in a
standard manner and filled into the mould kept on a glass plate.
 The mould is covered on the top with another glass plate. The whole assembly is immersed in
water at a temperature of 27°C – 32°C and kept there for 24 hours. Measure the distance
between the indicator points.
 Submerge the mould again in water. Heat the water and bring to boiling point in about 25-30
minutes and keep it boiling for 3 hours.
 Remove the mould from the water, allow it to cool and measure the distance between the
indicator points. The difference between these two measurements represents the expansion of
cement.
 This must not exceed 10 mm for ordinary, rapid hardening and
low heat Portland cements. If in case the expansion is more than
10 mm as tested above, the cement is said to be unsound.
The Le Chatelier test detects unsoundness due to free lime only.

Heat of Hydration
 The reaction of cement with water is called hydration. The reaction liberates a considerable
quantity of heat. This can be easily observed if a cement is gauged with water and placed in a
thermos flask.
 Much attention has been paid to the heat evolved during the hydration of cement in the interior of
mass concrete dams. It is estimated that about 120 calories of heat is generated in the hydration of
1 gm. of cement.
 From this it can be assessed the total quantum of heat produced in a conservative system such as
the interior of a mass concrete dam. A temperature rise of about 50°C has been observed.
 This unduly high temperature developed at the interior of a concrete dam causes serious
expansion of the body of the dam and with the subsequent cooling considerable shrinkage takes
place resulting in serious cracking of concrete.

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  The use of lean mix, use of pozzolanic cement, artificial cooling of constituent materials and
incorporation of pipe system in the body of the dam as the concrete work progresses for
circulating cold brine solution through the pipe system to absorb the heat, are some of the
methods adopted to offset the heat generation in the body of dams due to heat of hydration of
cement.
 Test for heat of hydration is essentially required to be carried out for low heat cement only. This
test is carried out over a few days by vaccum flask methods, or over a longer period in an
adiabatic calorimeter.
 When tested in a standard manner the heat of hydration of low heat Portland cement shall not be
more than 65 cal/gm. at 7 days and 75 cal/g, at 28 days.

Chemical Composition Test

 A fairly detailed discussion has been given earlier regarding the chemical composition of cement.
 Both oxide composition and compound composition of cement have been is cussed.
 At this stage it is sufficient to give the limits of chemical requirements. The Ratio of percentage of
lime to percentage of silica, alumina and iron oxide, when calculated by the formulae,

 Not greater than 1.02 and not less than 0.66. The above is called lime saturation factor.

1.6. IS Specifications
 Ordinary Portland Cement (OPC) – Grade 43 is a high strength cement confirming to IS 8112
– 1989. Following table explains the specifications, requirements of BIS and test results for OPC.

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 Specifications Minimum Requirements for
OPC as per IS : 8112 -1989
2
Fineness (cm /gm ) specific surface 2250
Setting time( intial) 30 min
Setting time (intial) 600min
Compressive Strength(kg/cm2)
3 days 230
7days 330
28 days 430

1.7. Aggregates

 Aggregates are the important constituents in concrete. They give body to the concrete, reduce
shrinkage and effect economy.
 Earlier, aggregates were considered as chemically inert materials but now it has been recognized
that some of the aggregates are chemically active and also that certain aggregates exhibit
chemical bond at the interface of aggregate and paste. The mere fact that the aggregates occupy
70–80 per cent of the volume of concrete, their impact on various characteristics and properties of
concrete is undoubtedly considerable. The study of aggregates can best be done under the
following sub-headings:
o Classification
o Source
o Size
o Shape
o Texure
o Strength
o Specific gravity and bulk density
o Moisture content
o Bulking factor
o Cleanliness
o Soundness
o Chemical properties
o Thermal properties
o Durability
o Sieve analysis
o Grading

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 Source
 Almost all natural aggregate materials originate from bed rocks. There are three kinds of
rocks, namely, igneous, sedimentary and metamorphic.
Size
 The largest maximum size of aggregate practicable to handle under a given set of
conditions should be used. Perhaps, 80 mm size is the maximum size that could be
conveniently used for concrete making. Using the largest possible maximum size will
result in (i) reduction of the cement content (ii) reduction in water requirement (iii)
reduction of drying shrinkage. Aggregates are divided into two categories from the
consideration of size
(i) Coarse aggregate (ii) Fine aggregate.
 The size of aggregate bigger than 4.75 mm is considered as coarse aggregate and aggregate
whose size is 4.75 mm and less is considered as fine aggregate.
 The shape of aggregates is an important characteristic since it affects the workability of
 Concrete. It is difficult to really measure the shape of irregular body like concrete aggregate
which are derived from various rocks.

1.8. Classifying aggregate according to nature of formation

Classification Description Examples

Rounded Fully water worn or completely River or seashore gravels; shaped by
attrition
Irregular or rounded Naturally irregular or partly Pit sands and gravels; land Partly

Angular Possessing well-defined edges formed at Crushed rocks of all types; talus;
the intersection of roughly planar faces screes

Flaky Material, usually angular, of which the Laminated rocks

thickness is small relative to the width
and/or length

One of the first field investigations for a concrete construction project is to search for sources of
aggregates which will give material of good quality at economical rates. Suitability of aggregate will
depend upon the geological history of the region. The aggregate as per nature of formation may be
divided into two types.

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  Natural Aggregates
 Artificial Aggregates

Natural aggregates

 These aggregates are obtained from natural deposit of sand and gravel or from quarries by cutting
rocks. Cheapest among them will be the natural sand and gravel which have been reduced to their
present size by natural agents such as water, wind and snow etc. River deposits are the most
common and have good quality.
 The second most commonly used source of aggregates is quarried bed rock material. Crushed
aggregates are made by breaking down natural bed rocks into requisite graded particles through a
series of blasting, crushing and screening, etc.
Artificial aggregates
 Amongst the artificial aggregates brick ballast and air cooled blast furnace slag are most
common. Broken brick may be used for mass concrete but is not used for reinforced concrete
work unless the crushing strength is high.
 Blast furnace slag is not commonly used on account of the possible corrosion of steel due to the
sulpher content of slag. Concrete made with blast furnace slag aggregate has good fire resisting
qualities. Other artificial aggregates such as foamed slag, expanded clay, shale and slate are also
used for producing light weight concrete.

Classify aggregates according to size

According to size the aggregates are classified as:
 Fine Aggregate
 Coarse Aggregate
 All in Aggregate
Fine aggregate
 It is the aggregate most of which passes 4.75 mm IS sieve and contains only so much coarser as is
permitted by specification.
According to source fine aggregate may be described as:
 Natural Sand– it is the aggregate resulting from the natural disintegration of rock and
which has been deposited by streams or glacial agencies
 Crushed Stone Sand– it is the fine aggregate produced by crushing hard stone.
 Crushed Gravel Sand– it is the fine aggregate produced by crushing natural gravel.
According to size the fine aggregate may be described as coarse sand, medium sand and
fine sand.

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  Specifications classify the fine aggregate into four types according to its grading as fine
aggregate of grading Zone-1 to grading Zone-4. The four grading zones become
progressively finer from grading Zone-1 to grading Zone-4. 90% to 100% of the fine
aggregate passes 4.75 mm IS sieve and 0 to 15% passes 150 micron IS sieve depending
upon its grading zone.
Coarse aggregate
 It is the aggregate most of which is retained on 4.75 mm IS sieve and contains only so much
finer material as is permitted by specification. According to source, coarse aggregate may be
described as:
 Uncrushed Gravel or Stone– it results from natural disintegration of rock
 Crushed Gravel or Stone– it results from crushing of gravel or hard stone.
 Partially Crushed Gravel or Stone– it is a product of the blending of the above two aggregate.
According to size coarse aggregate is described as graded aggregate of its nominal size i.e. 40
mm, 20 mm, 16 mm and 12.5 mm etc. for example a graded aggregate of nominal size 20 mm
means an aggregate most of which passes 20 mm IS sieve.
 A coarse aggregate which has the sizes of particles mainly belonging to a single sieve size is
known as single size aggregate. For example 20 mm single size aggregate mean an aggregate
most of which passes 20 mm IS sieve and its major portion is retained on 10 mm IS sieve.

All in aggregate
It is the aggregate composed of both fine aggregate and coarse aggregate. According to size All-
in-aggregate is described as all-in-aggregates of its nominal size, i.e. 40mm, 20mm etc. For example, all
in aggregate of nominal size of 20mm means an aggregate most of which passes through 20 mm IS sieve
and contains fine aggregates also.

Classify aggregate according to its shape

According to shape the aggregate is classified as
 Rounded aggregate
 Irregular or partly rounded aggregate
 Angular aggregate
 Flaky aggregate
 Elongated aggregate
 Flaky and elongated aggregate

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 Rounded aggregate

The aggregate with rounded shape has the minimum

percentage of voids ranging from 32 to 33%. It gives
minimum ratio of surface area to given volume and
hence requires minimum water for lubrication. It gives
good workability for the given amount of water and
hence needs less cement for a given water cement
ratio. The only disadvantages is that the interlocking
between its particles is less and hence the development
of bond is poor. This is why rounded aggregate is not suitable for high strength concrete and for
pavements subjected to tension.

Irregular or partly rounded aggregate

The aggregate with irregular shape has higher percentage of voids ranging from 35 to 37%. It
gives lesser workability than rounded aggregate for the given water content. Water requirement is higher
and hence more cement is needed for constant water cement ratio. The interlocking between aggregate
particles is better than rounded aggregate but not adequate to be used for high strength concrete and
pavements subjected to tension.

Angular aggregate
The aggregate with angular shape has the maximum percentage of void ranging from 38 to 45%.
It requires more water for lubrication and hence it gives least workability for the given water cement ratio.
For constant water cement ratio and workability the requirement of cement increase. The interlocking
between the aggregate particles is the best and hence the development of bond is very good. This is why
angular aggregate is very suitable for high strength concrete and for pavements subjected to tension.

Flaky aggregate
th
The aggregate is said to be flaky when its least dimension is less than 3/5 (or 60%) of its mean
dimension. Mean dimension is the average size through which the particles pass and the sieve size on
which these are retained. For example, mean size of the particles passing through 25 mm sieve and
retained on 20 mm sieve is (20+25)/2=22.5 mm. if the least dimension is less than 3/5 x (22.5) = 13.5
mm, then the material is classified as flaky. Flaky aggregate tends to be oriented in one plane which
affects the durability.

21
Elongated aggregate
The aggregate is said to be elongated when its length is greater than 180% of its mean dimension.

Flaky & elongated aggregate

Aggregate is said to be flaky and elongated when it satisfies both the above conditions. Generally
elongated or flaky particles in excess of 10 to 15% are not desirable.

Texture
Surface texture is the property, the measure of which depends upon the relative degree to which
particle surfaces are polished or dull, smooth or rough. Surface texture depends on hardness, grain size,
pore structure, structure of the rock, and the degree to which forces acting on the particle surface have
smoothed or roughened it. Hard, dense, fine-grained materials will generally have smooth fracture
surfaces

Strength
When we talk of strength we do not imply the strength of the parent rock from which the
aggregates are produced, because the strength of the rock does not exactly represent the strength of the
aggregate in concrete. The test for strength of aggregate is required to be made in the following situations:
(i ) For production of high strength and ultra high strength concrete.
(ii ) When contemplating to use aggregates manufactured from weathered rocks.
(iii ) Aggregate manufactured by industrial process.

1.9. Aggregate tests

Aggregate crushing value
 Strength of rock is found out by making a test specimen of cylindrical shape of size 25 mm
diameter and 25 mm height.
 This cylinder is subjected to compressive stress. Different rock samples are found to give
different compressive strength varying from a minimum of about 45 MPa to a maximum of 545
MPa.
 As said earlier, the compressive strength of parent rock does not exactly indicate the strength of
aggregate in concrete. For this reason assessment of strength of the aggregate is made by using a
sample of bulk aggregate in a standardized manner. This test is known as aggregate crushing
value test.
 Aggregate crushing value gives a relative measure of the resistance of an aggregate sample to
crushing under gradually applied compressive load. Generally, this test is made on single sized
aggregate passing 12.5 mm and retained on 10 mm sieve.

22
  The aggregate is placed in a cylindrical mould and a load of 40 ton is applied through a plunger.
The material crushed to finer than 2.36 mm is separated and expressed as a percentage of the
original weight taken in the mould.
 This percentage is referred as aggregate crushing value. The crushing value of aggregate is
restricted to 30 per cent for concrete used for roads and pavements and 45 per cent may be
permitted for other structures.

Aggregate Impact Value

 With respect to concrete aggregates, toughness is usually considered the resistance of the material
to failure by impact.
 Several attempts to develop a method of test for aggregates impact value have been made. The
most successful is the one in which a sample of standard aggregate kept in a mould is subjected to
fifteen blows of a metal hammer of weight 14 Kgs. falling from a height of 38 cms.
 The quantity of finer material (passing through 2.36 mm) resulting from pounding will indicate
the toughness of the sample of aggregate. The ratio of the weight of the fines (finer than 2.36 mm
size) formed, to the weight of the total sample taken is expressed as a percentage.
 This is known as aggregate impact value IS 283-1970 specifies that aggregate impact value shall
not exceed 45 per cent by weight for aggregate used for concrete other than wearing surface and
30 per cent by weight, for concrete for wearing surfaces, such as run ways, roads and pavements.

Aggregate Abrasion Value

Apart from testing aggregate with respect to its crushing value, impact resistance, testing the
aggregate with respect to its resistance to wear is an important test for aggregate to be used for road
constructions, ware house floors and pavement construction. Three tests are in common use to test
aggregate for its abrasion resistance.

23
 (i) Deval attrition test (ii) Dorry abrasion test (iii) Los Angels test.

Deval Attrition Test

 In the Deval attrition test, particles of known weight are subjected to wear in an iron cylinder
rotated 10000 times at certain speed. The proportion of material crushed finer than 1.7 mm size is
expressed as a percentage of the original material taken.
 This percentage is taken as the attrition value of the aggregate. This test has been covered by IS
2386 (PartIV) – 1963. But it is pointed out that wherever possible Los Angeles test should be
used.

Dorry Abrasion Test

 This test is not covered by Indian Standard Specification. The test involves in subjecting a
cylindrical specimen of 25 cm height and 25 cm diameter to the abrasion against rotating metal
disk sprinkled with quartz sand.
 The loss in weight of the cylinder after 1000 revolutions of the table is determined. The hardeness
of the rock sample is
Expressed in an empirical formula Hardness = 20 – Loss in Grams/3
 Good rock should show an abrasion value of not less than 17. A rock sample with a value of less
than 14 would be considered poor.

Los Angeles Test

 Los Angeles test was developed to overcome some of the defects found in Deval test. Los
Angeles test is characterised by the quickness with which a sample of aggregate may be tested.
The applicability of the method to all types of commonly used aggregate makes this method
popular.
 The test involves taking specified quantity of standard size material along with specified number
of abrasive charge in a standard cylinder and revolving if for certain specified revolutions.
 The particles smaller than 1.7 mm size is separated out. The loss in weight expressed as
percentage of the original weight taken gives the abrasion value of the aggregate. The abrasion
value should not be more than 30 per cent for wearing surfaces and not more than 50 per cent for
concrete other than wearing surface.

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Specific gravity of aggregate
 About 2kg of the aggregate sample is washed thoroughly to remove fines, drained and then
0
placed in the wire basket and immersed in distilled water at a temperature between 22 to 32 C
with a cover of at least 50 mm of water above the top of the basket
 Immediately after the immersion the entrapped air is removed from the sample by lifting the
basket containing it 25 mm above the base of the tank and allowing it to drop 25 times at the rate
of about one drop per second. The basket and the aggregate should remain completely immersed
in water for a period of 24±0.5 hours afterwards.
 The basket and the sample are then weighed while suspended in water at a temperature of 22 to
0
32 C. The weight is noted while suspended in water (W1) g.
 The basket and the aggregate are then removed from water and allowed to drain for a few minutes,
after which the aggregates are transferred to one of the dry absorbent clothes.
 The empty basket is then returned to the tank of water, jolted 25 times and weights in water
(W2)g.
 The aggregates placed in the dry absorbent clothes are surface dried till no further moisture could
be removed by this clothe.
 Then the aggregate is transferred to the second dry cloth spread in a single layer, covered and
allowed to dry for at least 10 minutes until the aggregates are completely surface dry. 10 to 60
minutes drying may be needed. The surface dried aggregate is then weighed W3 g.
 The aggregate is placed in a shallow tray and kept in an oven maintained at a temperature of
0
110 C for 24 hours. It is then removed from the oven, cooled in air tight container and weighed

W4 g.

Weight of saturated aggregate suspended in water with basket = W1 g

Weight of basket suspended in water = W2 g
Weight of saturated aggregate in water = (W1-W2)g = Ws g
Weight of saturated surface dry aggregate in air = W4 g
Weight of water equal to the volume of the aggregate = (W3-Ws) g

Water absorption of aggregate

 The sample should be thoroughly washed to remove finer particles and dust, drained and then
o
placed in the wire basket and immersed in distilled water at a temperature between 22 and 32 C.

25
  After immersion, the entrapped air should be removed by lifting the basket and allowing it to
drop 25 times in 25 seconds. The basket and sample should remain immersed for a period of 24 +
½ hrs afterwards.
 The basket and aggregates should then be removed from the water, allowed to drain for a few
minutes, after which the aggregates should be gently emptied from the basket on to one of the dry
clothes and gently surface-dried with the cloth, transferring it to a second dry cloth when the first
would remove no further moisture. The aggregates should be spread on the second cloth and
exposed to the atmosphere away from direct sunlight till it appears to be completely surface-dry.
The aggregates should be weighed (Weight „A‟).
o
 The aggregates should then be placed in an oven at a temperature of 100 to 110 C for 24hrs. It
should then be removed from the oven, cooled and weighed (Weight „B‟).

Formula =[(A–B)/B]x100%.
 Two such tests should be done and the individual and mean results should be reported.

1.10. Water and its quality

 Water is an important ingredient of concrete as it actively participates in the chemical reaction
with cement .since it helps to form the strength giving cement gel the quantity and quantity of
water is required to be looked into very carefully. In practice very often great control on
properties of cement and aggregates is exercised but the control on the quantity of water affects
the strength it is necessary to go into the purity and quality of water.

Impurity Tolerable concentration

Sodium and potassium carbonates and bi 1000ppm,if this is exceeded
carbonates
Chlorides 500 ppm

SO3 1000 ppm

Alkali Carbonates and Bicarbonates 1000 ppm
Turbidity 2000 ppm
pH Shall be less than 6
Total dissolved salts 15000ppm
organic material 3000ppm
Water quality stranded of concrete.

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Function of Water in Concrete:
Three water serves the following purpose:
 To wet the surface of aggregates to develop adhesion because the cement pastes adheres quickly
and satisfactory to the wet surface of the aggregates than to a dry surface.
 To prepare a plastic mixture of the various ingredients and to impart workability to concrete to
facilitate placing in the desired position and
 Water is also needed for the hydration of the cementing materials to set and harden during the
period of curing.
The quantity of water in the mix plays a vital role on the strength of the concrete. Some water which have
adverse effect on hardened concrete.

Potable water as mixing water

 The common specifications regarding quality of mixing water is water should be fit for drinking.
Such water should have inorganic solid less than 1000 ppm.
 This content lead to a solid quantity 0.05% of mass of cement when w/c ratio is provided 0.5
resulting small effect on strength. But some water which are not potable may be used in making
concrete with any significant effect.
H
 Dark color or bad smell water may be used if they do not posses deleterious substances. P of
water to even 9 is allowed if it not tastes brackish.
 In coastal areas where local water is saline and have no alternate sources, the chloride
concentration up to 1000 ppm is even allowed for drinking.
 But this excessive amount of alkali carbonates and bicarbonates, in some natural mineral water,
may cause alkali-silica reaction.

The effect on concreting for different types of contamination or impurities are described below:
Suspended Solids:
 Mixing water which high content of suspended solids should be allowed to stand in a setting
basing before use as it is undesirable to introduce large quantities of clay and slit into the
concrete.
Acidity and Alkalinity:
 Natural water that are slightly acidic are harmless, but presence of humid or other organic acids
may result adverse effect over the hardening of concrete. Water which are highly alkaline should
also be tested.

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Algae:
 The presence of algae in mixing water causes air entrainments with a consequent loss of strength.
The green or brown slime forming algae should be regarded with suspicion and such water should
be tested carefully.
Sea Water:
 Sea water contains a total salinity of about 3.5%(78% of the dissolved solids being NaCl and 15%
MgCl2 and MgSO4), which produces a slightly higher early strength but a lower long-term
strength. The loss of strength is usually limited to 15% and can therefore be tolerated. Sea water
reduces the initial setting time of cement but do not effect final setting time.

Chloride:
 Water containing large amount of chlorides tends to cause persistent dampness and surface
efflorescence. The presence of chlorides in concrete containing embedded steel can lead to its
corrosion.

Moisture Content of Aggregate:

 Aggregate usually contains some surface moisture. Coarse aggregate contains more than 1% of
surface moisture but fine aggregate can contain in excess of 10%. This water can represent a
substantial proportion of the total mixing water indicating a significant importance in the quality
of the water that contributes surface moisture in aggregate.

Quantity of water
 C3S requires 24% of water by weight of cement and c2s requires 21%. It has also been an
estimate that on an average 23% of water by weight of cement is required for chemical reaction
with OPC cement.

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