Introduction Cement

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CEMENT
A Cement is a binder, a substance that sets and hardeneds
independently, and can bind other materials together.

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HISTORY OF CEMENT

• Egyptians mostly used cementing materials, obtained by

burning gypsum.
• The Greeks and Romans used cementing materials
obtained by burning limestone.
• First manufacture of cement and patent by James Frost
and established in 1811.
• Joseph Aspdin took the patent of Portland cement on
21st October 1824.
• The fancy name of Portland was given owing to
resemblance of this hardened cement to the natural
stone occurring at Portland in England.

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 cont.
• In India, Portland cement was first manufactured in 1904
near Madras, by the south india industrial ltd. But this
venture failed.
• Between 1912 and 1913, the indian cement co. ltd was
established at porbander (gujrat) and by 1914 this
company was able to deliver about 1000 tons of portland
cement.
• German standard specification was drawn in 1877.
• British standard specification was drawn in 1904
• ASTM ( American standards for testing materials) in 1904

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Manufacture of Portland cement
Raw Materials Required are
1. Calcareous Materials: Example Limestone or Chalk.
2. Argillaceous Material such as Shale or clay

General processes
• The process of manufacture of cement consists of grinding
the raw materials, mixing them intimately in certain
proportions depending upon their purity and composition and
burning them in a kiln at a temperature of 1300 to 1500 oC, at
this temperature, the material sinters and partially fuses to
form nodular shaped clinker.
• The clinker is cooled and ground to fine powder with addition
of about 3 to 5 % of gypsum. The product formed by using this
procedure is Portland cement.
5
Main processes for manufacturing cement

Two main process for manufacture of cement is as

followed:
1 Wet Process
2 Dry Process

Note:
Above process depends upon whether the mixing and
grinding of raw materials is done in dry or wet condition.

6
Flow Chart Wet Process

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Wet Process

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9
Dry Process

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 Chemical composition for Portland cement
• The raw materials used for the manufacture of
cement consist mainly of lime, silica, alumina and
iron oxide.
• Chemical composition are

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Bogue’s Compounds
• The oxides present in the raw materials when subjected to
high clinkering temperature combine with each other to form
complex compounds. The identification of the major
compounds is largely based on R.H. Bogue’s work and hence it
is called Bogue’s Compounds.

• C stands for CaO, S stands for SiO2

• A for Al2O3, F for Fe2O3

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 Bogues equation
• The equations suggested by Bogue for calculating the
percentages of major compounds are given below.

C3S = 4.07 (CaO) – 7.60 (SiO2) – 6.72 (Al2O3) – 1.43(Fe2O3) –2.85 (SO3)
C2S = 2.87 (SiO2) – 0.754(3CaO.SiO2)
C3A = 2.65 (Al2O3) – 1.69 (Fe2O3)
C4AF= 3.04 (Fe2O3)

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14
• Tricalcium silicate and dicalcium 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 sum of the contents of C3A and C4AF has
decreased slightly in modern cements.
• Cements with a high total alumina and high ferric
oxide content is favourable to the production of high
early strengths in cement.
• Excess of lime will cause unsoundness in cement.
• Increase in silica content will make cement difficult to
fuse and form clinker.
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Cement and hydration of Portland cement can be
schematically represented below

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Hydration of Cement
• Anhydrous cement does not bind fine and coarse
aggregate. It acquires adhesive property only when
mixed with water.
• The chemical reactions that take place between cement
and water is referred as hydration of cement.
• The hydration of cement can be visualised in two ways.
The first is “through solution” mechanism. In this the
cement compounds dissolve to produce a supersaturated
solution from which different hydrated products get
precipitated.
• The second possibility is that water attacks cement
compounds in the solid state converting the compounds
into hydrated products starting from the surface and
proceeding to the interior of the compounds with time.
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Heat of Hydration
• The reaction of cement with water is exothermic. The
reaction liberates a considerable quantity of heat. This
liberation of heat is called heat of hydration.
a) In the figure the peak ascending A
refers to the heat evolved in
due to the reaction of
Aluminates and sulphates.
b) Descending peak A represents
This initial heat evolution
ceases quickly when the
solubility of aluminate is
depressed by gypsum.
c) The ascending peak B represents the heat evolved due to the
accounting ettrigate (hexa calcium aluminate tri sulphate
hydrate)-(cao)6 al2o3(so3)3.32H20 and also due to reaction C3S
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Heat of hydration can be predicted by following
H = aA + bB + cC + dD
Where H represents the heat of hydration in cal/g
• A, B, C, and D are the percentage contents
• of C3S, C2S, C3A and C4AF.
• a, b, c and d are coefficients representing the
contribution of 1 per cent of the corresponding
compound to the heat of hydration.

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20
 cont.

• Normal cement generally produces 89-90 cal/g in 7

days and 90 to 100 cal/g in 28 days.
• The reaction is faster in the early period and
continues indefinitely at a decreasing rate.
• It has been observed that after 28 days of curing,
cement grains have been found to have hydrated to a
depth of only 4μ.
• It has also been observed that complete hydration
under normal condition is possible only for cement
particles smaller than 50μ.

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Calcium Silicate Hydrates:
• During the course of reaction of C3S and C2S with water,
calcium silicate hydrate, abbreviated C-S-H and calcium
hydroxide, Ca(OH)2 are formed.
• Calcium silicate hydrates are the most important products. It
is the essence that determines the good properties of
concrete.
• It makes up 50-60 per cent of the volume of solids in a
completely hydrated cement paste.

2 (3 CaO.SiO2) + 6H2O→ 3 CaO.2 SiO2. 3H2O + 3Ca(OH)2

2C3S + 6H → C3S2H3 + 3Ca(OH)2

2 (2 CaO.SiO2) + 4 H2O→ 3Cao.2 SiO2. 3H2O + Ca(OH)2

2 C2S + 4 H → C3S2H3 + Ca (OH)2

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• C3S readily reacts with water and produces more heat of
hydration. It is responsible for early strength of concrete.
• C2S hydrates rather slowly. It is responsible for the later
strength of concrete. It produces less heat of hydration.

Calcium Hydroxide Ca(0H)2

• The other products of hydration of C3S and C2S is calcium
hydroxide.
• It constitutes 20 to 25 per cent of the volume of solids in the
hydrated paste.
• Calcium hydroxide reacts with sulphate present in soil or
water to form calcium sulphates which further reacts with C3A
and causes deterioration of concrete. This is known as
sulphate attack
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Calcium Aluminate Hydrates

• Due to the hydration of C3A , a calcium aluminate

system CaO – Al2O3 – H2O is formed.
• The cubic compound C3AH6 is probably the only
stable compound formed which remains stable up to
about 225°C.
• The reaction of pure C3A with water is very fast and
this may lead to flash set.
• To prevent this flash set, gypsum is added at the time
of grinding the cement clinker.

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Calcium alumina Ferrite hydrate

• On hydration, C4AF is believed to form a system of

the form CaO – Fe2O3 – H2O. A hydrated calcium
ferrite of the form C3FH6 is comparatively more
stable.
• This hydrated product also does not contribute
anything to the strength.
• The hydrates of C4AF show a comparatively higher
resistance to the attack of sulphates than the
hydrates of calcium aluminate.

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26
Diagrammatic representation of hydration
process
• T and formation of cement gel

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 cont.
• Fig. 1.8 (a) represents the state of cement particles immediately
when dispersed in an aqueous solution.
• Fig. 1.8 (b) represents the formation of coating on cement grain
by calcium silicate hydrates.
• Fig. 1.8 (c) represents formation of hydration product including
calcium hydroxide and bridge the gap between cement grains,
and paste stiffens into its final shape.
• Fig. 1.8 (d) represents final hydrated cement

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Structure of hydrated cement paste
The two phases in the concrete are
a) Paste phase
b) Aggregate phase

• In paste structure influences the behaviour of concrete to a

much greater extent. The strength, durability, the
permeability, the drying shrinkage, the elastic properties, the
creep and the volume change properties of concrete is greatly
influenced by paste structure.
• The aggregate phase has lesser significant that paste phase on
the properties of concrete.

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Paste phase
• Fresh cement paste is a plastic mass consisting of water and cement. With
the lapse of time, say one hour, the hardening paste consists of hydrates
of various compounds, unhydrated cement particles and water.
• With further lapse of time the quantity of unhydrated cement left in the
paste decreases and the hydrates of the various compounds increase.
Some of the mixing water is used up for chemical reaction, and some
water occupies the gel-pores and the remaining water remains in the
paste.
• After a sufficiently long time (say a month) the hydrated paste can be
considered to be consisting of about 85 to 90% of hydrates of the various
compounds and 10 to 15 per cent of unhydrated cement. The mixing
water is partly used up in the chemical reactions. Part of it occupies the
gel-pores and the remaining water unwanted for hydration or for filling in
the gel-pores causes capillary cavities.
• These capillary cavities may have been fully filled with water or partly with
water or may be fully empty depending upon the age and the ambient
temperature and humidity conditions.

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31
Transition Zone
• Transition Zone a third phase apart from the paste phase and
aggregate phase which represents the interfacial region
between the particles of coarse aggregate and hardened
cement paste.
• Transition zone is generally a plane of weakness and,
therefore, has far greater influence on the mechanical
behaviour of concrete.
• Although transition zone is composed of same bulk cement
paste, the quality of paste in the transition zone is of poorer
quality.
• Due to internal bleeding, water accumulate below elongated,
flaky and large pieces of aggregates. This reduces the bond
between paste and aggregate. Such a situation account for
the lower strength of transition zone than bulk cement paste
in concrete.
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 Cont.
• Due to drying shrinkage or temperature variation, the
transition zone develops micro cracks even before a structures
is loaded. When structure is loaded and at high stress levels,
these micro cracks propagate and bigger cracks are formed
resulting in failure of bond. Therefore, transition zone,
generally the weakest link of the chain, is considered strength
limiting phase in concrete.

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Water Requirement for hydration
• C3S requires 24% of water by weight of cement and C2S
requires 21%.
• On an average 23% of water by weight of cement is required
for chemical reaction with Portland cement compounds. This
23% of water chemically combines with cement and,
therefore, it is called bound water.
• A certain quantity of water is imbibed within the gel-pores.
This water is known as gel-water. It is estimated that about 15
per cent by weight of cement is required to fill up the gel-
pores.
• Therefore, a total 38 per cent of water by weight of cement is
required for the complete chemical reactions and to occupy
the space within gel-pores.

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Physical Test on Cement
Physical test on Cement are as follows:
1. Fineness Test http://www.youtube.com/watch?v=44yrGm2fxfU

2. Standard consistency test http://www.youtube.com/watch?v=MrwAjLwycN8

3. Setting Time Test http://www.youtube.com/watch?v=6Hh8i0lpuCs & http://www.youtube.com/watch?v=7ZvcKWUo1tg

4. Strength test http://www.youtube.com/watch?v=DWhHEh-27J4

5. Soundness Test http://www.youtube.com/watch?v=vqxAabDdmTE

http://www.youtube.com/watch?v=44yrGm2fxfU
http://www.youtube.com/watch?v=MrwAjLwycN8
http://www.youtube.com/watch?v=6Hh8i0lpuCs & http://www.youtube.com/watch?v=7ZvcKWUo1tg

http://www.youtube.com/watch?v=DWhHEh-27J4

http://www.youtube.com/watch?v=vqxAabDdmTE

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1. Fineness Test

Apparatus and Material:

IS sieve No. 9 (90 microns), Balance and OPC.
Procedure:
• Weigh correctly 100 grams of cement and take it on a standard
IS Sieve No. 9 (90 microns). Break down the air-set lumps in the
sample with fingers.
• Continuously sieve the sample giving circular and vertical
motion for a period of 15 minutes.
• Weigh the residue left on the sieve. This weight shall not exceed
10% for ordinary cement.
Note:
• Finer cement offers a greater surface area for hydration and
hence faster the development of strength.

http://www.youtube.com/watch?v=44yrGm2fxfU
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Sieve

37
W
• C

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Standard Consistency Test
Apparatus and Material: vicat apparatus, Balance, vicat plunger,
Vicat mould, non porous dish, measuring jar and OPC

plunger

Initial Final
Setting needle Setting needle
40
 cont.
Procedure:
• Take about 500 gms of cement and prepare a paste with a
weighed quantity of water (say 24 per cent 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.

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 cont.

• Similarly, conduct trials with higher and higher water/cement

ratios till such time the plunger penetrates for a depth of
5mm - 7mm from the top.
• That particular percentage of water which allows the plunger
to penetrate only to a depth of 5-7 mm from the bottom of
the mould is known as the percentage of water required to
produce a cement paste of standard consistency. This
percentage is usually denoted as ‘P’.

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Setting Time Test
Apparatus and Material: vicat apparatus, Balance, Initial setting ,
Vicat mould, non porous dish, measuring jar, stop watch and OPC

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Procedure for initial setting time

• Take 500 gm of cement in a non porous dish.

• The cement paste is prepared by mixing the cement with 0.85
times the water required to produce cement paste of
standard consistency (0.85 P).
• Start the stop watch the moment water is added to the
cement.
• The paste is filled into the Vicat mould within 3-5 minutes and
placed under rod bearing needle.
• The temperature of water and that of the test room, at the
time of gauging shall be within 27°C ± 2°C.
• The needle is lowered gently in contact with the surface at the
test block and quickly released allowing to penetrate into the
test block.

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 cont.

• In the beginning, the needle penetrates the mould

completely. The procedure is repeated until the needle fails to
penetrate the test block by 5 mm from the bottom of the
mould.
• The initial setting time of the cement paste is defined the
period elapsing between the time when the water is added to
the cement and the time at which the needle fails to
penetrate the test block about 5 mm from the bottom of the
mould.

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Procedure for final setting time

• Take 500 gm of cement in a non porous dish.

• The cement paste is prepared by mixing the cement with 0.85 times
the water required to produce cement paste of standard
consistency (0.85 P).
• Start the stop watch the moment water is added to the cement.
• The paste is filled into the Vicat mould within 3-5 minutes and
placed under rod bearing needle.
• The temperature of water and that of the test room, at the time of
gauging shall be within 27°C ± 2°C.
• The needle is replaced by final setting time needle with an annular
attachment.
• The cement is considered as finally set when upon applying the
needle gently to the surface of the test block, the needle makes an
impression there, but the attachment fails to do so.

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Strength Test

Apparatus and Material: 50 cm2 cube mould (7.07 cm X 7.07 cm)

, OPC, sand, Vibrating machine and compression testing
Machine.

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Procedure.
• Cement mortar cube are prepared by mixing 1 part of cement
𝑃
, 3 parts of sand and ( +3 ) % of water. Where P is % of water
4
required for producing normal consistency paste of cement
and 3 indicating 3 % of combine weight of cement and sand.
• The mould is filled with the mortar and vibrate using vibrating
machine for 2 minutes.
• After 24 hours of casting, the block is removed from the
mould and cured in water.
• The specimen is tested in compression after curing for 3 days
and 7 days in a compression testing machine and 3 day
compression value 16 Mpa and 7 days 22 Mpa.
• Compression strength is determined by dividing the load by
area of the specimen which is 50 cm2.

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Soundness Test

Apparatus and Material: Le Chatelier mould, Stove, and OPC

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Procedure
• The mould is placed on a glass plate and filled with cement paste by
mixing cement with 0.78 times Of P. where P is standard
consistency value.
• The mould is covered with another piece of glass plate and a small
weight is placed on it.
• The whole assembly is submerged immediately in water at a
temperature of 27 to 32 oC and kept there for 24 hours.
• The mould is removed from water and the distance seperating the
indicator points is measured.
• The mould is submerged again in water and the water is heated till
it reaches the boiling point in 25 to 32 minutes.
• The mould is kept in boiling water for 3 hours. The mould is
removed from water, allowing to cool and the distance between the
indicator points is measured again.
• For a good cement the expansion should not exceed 10 mm. the
change in distance is a measure of the unsoundness.

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 Types of Cement
a) Ordinary Portland Cement
(i ) Ordinary Portland Cement 33 Grade– IS 269: 1989
(ii ) Ordinary Portland Cement 43 Grade– IS 8112: 1989
(iii ) Ordinary Portland Cement 53 Grade– IS 12269: 1987

(b) Rapid Hardening Cement – IS 8041: 1990

(c) Extra Rapid Hardening Cement – –
(d) Sulphate Resisting Cement – IS 12330: 1988
(e) Portland Slag Cement – IS 455: 1989
(f ) Quick Setting Cement – –
(g) Super Sulphated Cement – IS 6909: 1990
(h) Low Heat Cement – IS 12600: 1989

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 cont.

(i) Portland Pozzolana Cement – IS 1489 (Part I) 1991 (fly ash

based) – IS 1489 (Part II) 1991 (calcined clay based)
j) Air Entraining Cement – –
(k) Coloured Cement: White Cement – IS 8042: 1989
(l) Hydrophobic Cement – IS 8043: 1991
(m) Masonry Cement – IS 3466: 1988
(n) Expansive Cement – –
(o) Oil Well Cement – IS 8229: 1986
(p) Rediset Cement – –
(q) High Alumina Cement – IS 6452: 1989
(r) Very High Strength Cement ––

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(b) Rapid Hardening Cement – IS 8041: 1990
.
• Also called as High early strength cement.
• Rapid Hardening Cement develops the strength at the age of three
days, the same strength as that is expected of OPC at seven days.
• More fineness of grinding (specific surface area not less that 3250
cm2 per gram) and Higher C3S and lower C2S content.
• Should not be used in mass concrete construction.

The use of rapid heading cement is recommended in the following

situations:
(a) In pre-fabricated concrete construction.
(b) Where formwork is required to be removed early for re-use
elsewhere.
(c ) Road repair works
(d ) In cold weather concrete where the rapid rate of development of
strength reduces the vulnerability of concrete to the frost damage.

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C. Extra Rapid Hardening Cement
• Extra rapid hardening cement is obtained by intergrinding calcium
chloride with rapid hardening Portland cement.
• The normal addition of calcium chloride should not exceed 2 per
cent by weight of the rapid hardening cement.
• It is necessary that the concrete made by using extra rapid
hardening cement should be transported, placed and compacted
and finished within about 20 minutes.
• It is also necessary that this cement should not be stored for more
than a month.
• Extra rapid hardening cement accelerates the setting and hardening
process.
• 25 % more strength than RHC at one or two days and 10-20 % more
at 7 days and same as that of OPC at 90 days
• Specific surface area is 5000 to 6000 cm2 /gm
• Size of particles are generally less than 3 microns.
• Difficult to store as it is liable to air set.
• There is small amount of initial corrosion of reinforcement.

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D Sulphate resisting cement

• Sulphate react both with free calcium hydroxide in set cement to

form calcium sulphate and with hydrate of calcium aluminate to
form calcium sulpho aluminate, the volume of which is
approximately 227 % of the original aluminates.
• Their expansion within the form work of hardened cement paste
results in cracks and subsequent disruption.
• This is known as sulphate attack and is greatly accelerated if
accompanied by alternate wetting and draying which normally
takes places in marine structure in zone of tidal variations.
• To remedy the sulphate attack, the use of cement with low C3A
content is found to be effective and this type of cement is known as
sulphate resisting cement.
• This has high silica content and C3A content is limited to 5%.
Recommended for
1Concrete to be used in marine condition.
2 In foundation and basement.

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E Portland Slag cement

• Portland slag cement is obtained by mixing portland cement

clinker, gypsum and granulated blast furnace slag in suitable
proportions and grinding the mixture to get a thorough and
intimate mixture between the constituents.
• It may also be obtained by separately grinding portland
cement clinked, gypsum and ground granulated blast furnace
slag and later mixing them intimately.
• The
Major Advantage are
a Reduced heat of hydration
b Reduced permeability
c Increased resistance to chemical attacks.

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f Quick Setting cement

• Sets very early

• By reducing gypusum content at time of clinker grinding
• For under water construction and grouting operations.

g Super Sulphated Cement

• 85% for granulated slag+10-15% of hard burnt gypsum+5% of
portland cement clinker.
• Specific surface area must not be less than 4000 cm2/gm
• Low heat of hydration 40-45 cal/gm at 7 days and 45 to
50 cal /gm at 28 days.
• Used for foundations, marine works,.

57
h Low Heat Cement
• Low C3S and C3A contents and high C2S content.
• Slow rate of gain of strength but ultimate strength is same as
that of OPC cement.
• 7 days- not more than 65 cal/gm.
28 days- not more than 75 cal/gm
• Specific surface area is not less than 3200 cm2/gm.

58
I Portland pozzolana Cement
• PPC is manufactured by the intergrinding of OPC clinker with 10
to 25% of pozzolanic material.
Ca(OH)2+pozzolana+waterC-S-H (gel)
• Less heat of Hydration and offers greater resistance to the
attack of aggressive water than OPC.
• Useful in marine structures and hydraulic construction.

Advantage
a Economical b Improvement of permeability c low heat of
Hydration.

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J Air Entraining Cement
• Air entraining agent+OPC clinker at the time ginder.
• These agents in powder or liquid forms are added to the the
extent of 0.025-0.1% by weight of cement clinked.
• Air entraining cement will produce at time of mixing, tough,
tiny, discrete non coalescing air bubbles in the body of concrete
which will modify the properties of plastic concrete w.r.t
workability, segregation and bleeding.
• It will modify the properties of hardened concrete w.r.t
resistance to frost action.

60
K Coloured cement ( White cement)
• Coloured cement consists of portland cement with 5-10 % of
pigment.
• Cement and pigment are grinded together.
• The raw materials used are high purity limestone (96% caco3 and less
than 0.07% iron oxide), China clay with iron content of about (0.72 to
0.8%), silica sand, flour spar as flux and selenite as retarder.

L Hydrophobic cement
• Hydrophobic cement is obtained by grinding O.P.C clinker with water
repellent film forming substance such as oleic and stearic acid.
• The water repellant film formed around each grain of cement,
reduces the rate of deteriorationof the cement during long storage,
transport, or under unfavourable condition.
• Cost slightly higher than OPC.

61
M Masonry cement
• Masonry cement is made with a combination such material which
when used for making mortar, incorporating all the good properties
of lime mortar and discards all the not so ideal properties of cement
mortar.
• Mostly used for masonry construction
• Contains certain amount of air entraining agent and mineral
admixture to improve plasticity and water retentivity.

N Expensive cement
• ordinary Portland cement shrinks while setting due to loss of free
water. This is known as drying shrinkage.
• a slight expansion with time will prove to be advantageous for
grouting purpose.
• This type of cement which suffers no overall change in volume on
drying is known as expansive cement.
• 8-20 parts of the sulphoaluminate clinker are mixed with 100 parts of
the Portland cement and 15 parts of the stabilizer

62
O Oil-Well Cement
• Cement slurry is used to seal off the annular space between
steel casing and rock strata and also to seal off any other
fissures or cavities in the sedimentary rock layer.
• The cement slurry has to be pumped into position, at
considerable depth where the prevailing temperature may be
upto 175°C. The pressure required may go upto 1300 kg/cm2.
• It may also have to resist corrosive conditions from sulphur
gases or waters containing dissolved salts. The type of cement
suitable for the above conditions is known as Oil-well cement.

63
P Rediset Cement
• The cement allows a handling time of just about 8 to 10
minutes.
• The strength pattern is similar to that of ordinary Portland
cement mortar or concrete after one day or 3 days. What is
achieved with “REDISET” in 3 to 6 hours can be achieved with
normal concrete only after 7 days.
• More heat of hydration
• The rate of shrinkage is fast but the total shrinkage is similar to
that of ordinary Portland cement concrete.

Application
(a ) very-high-early (3 to 4 hours) strength concrete and mortar,
(b) patch repairs and emergency repairs,
(c ) quick release of forms in the precast concrete products
industry,
64
(q ) High Alumina Cement
• High alumina cement is obtained by fusing or sintering a
mixture, in suitable proportions, of alumina and calcareous
materials and grinding the resultant product to a fine powder.
• The raw materials used for the manufacture of high alumina
cement are limestone and bauxite.

65
(r) Very high strength cement
(a) Macro-defect-free cements
• MDF refers to the absence of relatively large voids or defects
which are usually present in conventional mixed cement pastes
because of entrapped air and inadequate dispersion.
• In the MDF process 4-7% of one of several water-soluble
polymers (such as hydroxypropylmethyle cellulose,
polyacrylamide of hydrolysed polyvinylacetate) is added as
rheological aid to permit cement to be mixed with very small
amount of water.
• At final processing stage entrapped air is removed by applying
a modest pressure of 5 MPa.
• With this process a strength of 300 MPa for calcium aluminate
system and 150 MPa for Portland cement system can be
achieved.

66
(b) Densely Packed System (DSP).
• Normal Portland cement and ultra-fine silica fume are mixed.
• The size of cement particles may very from 0.5 to 100μ and
that of silica fume varies from 0.005 to 0.5μ.
• Silica fume is generally added from 5 to 25 %.
• A compressive strength of 270 MPa have been achieved with
silica fume substituted paste.

(c) Pressure Densification and Warm Pressing

• Compressive strength as much as 650 MPa and tensile strength
up to 68 MPa have been obtained by warm pressing Portland
and calcium aluminate cements.
• Enormous increases in strength resulted from the removal of
most of the porosity and generation of very homogeneous, fine
micro-structures with the porosities as low as 1.7%.

67
(d) High Early Strength Cement.
• Lithium salts have been effectively used as accelerators in high
alumina cement.
• Resulted in very high early strength in cement and a marginal
reduction in later strength.
• Strength as high as 4 MPa has been obtained within 1 hour and
27 MPa has been obtained within 3 hours time and 49 MPa in
one day.
(e) Pyrament Cement
• In this cement no chlorides are added during the
manufacturing process.
• Pyrament cement produces a high and very early strength of
concrete and mortar which can be used for repair of Air Field
Run-ways.

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(f) Magnesium Phosphate Cement (MPC)
• Magnesium Phosphate Cement, an advanced cementing
material, giving very high early strength mortar and concrete
has been developed by Central Road Research Institute, New
Delhi.
• MPC is a prepacked mixture of dead burn magnesite with fine
aggregate mixed with phosphate. It sets rapidly and yields
durable high strength cement mortar.
• This cement can be used for rapid repair of damaged concrete
roads and airfield pavements.

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 Cont.
The following materials are used for making MPC:
• Magnesite (MgCO3) when calcined at or above 1500°C gives
dead burnt magnesite (DBM). This material is ground to a
fineness of 300-350 m2/kg (Blaines).
• This is mixed with commercially available crystalline Mono
Ammonium Phosphate after grinding into fine powder passing
600μ seive, and other ingredients like sodium tri-
polyphosphate in the form of fine powder, di-sodium
tetraborate (Borax), fine aggregate (crushed dolomite sand)
and water.
• The DBM and sand mixture is added into cold phosphate and
borax solution (12-15°C) and mixed for one minute. This mix is
applied for the purpose of repair. It is air cured and is ready for
opening traffic within 4-5 hours.
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