CONCRETE TECHNOLOGY
UNIT 1
By ~ Kunal Pravin Dhole
{Part- 1} Cement and Aggregates
Historical Notes
In 1824, Joseph Aspdin cooked a mixture of limestone and clay into lumps and then crushed them into a fine
powder. When he mixed this powder with water and fine aggregate, he found that it made a strong mortar
that would harden underwater. He obtained a patent for this product and called it Portland cement.
Cement – A powder fine powder of silica, lime, iron oxide, magnesia, Alumina, etc hardens when mixed with
water and is used to bind different materials together.
Manufacturing of Ordinary Portland Cement
1. Wet Process –
In this method, the crushed raw materials are fed to the ball mill, and a small quantity of water is
added.
Now, the steel balls will again crush and mix the raw materials along with water to form a slurry.
The slurry is then passed through silos (vertical chambers to store something), where proper
proportioning of the constituents takes place. The slurry at last has around 40 % of moisture content
in it.
The slurry is then passed through rotary kiln (cylindrical horizontal pipe which is rotating) wherein the
nodules are formed (small stones like shape). The Temperature is maintained in kiln at around 1600oC.
This temperature leads to conversion of nodules to clinkers.
The clinker is later cooled, and a small quantity of Gypsum about 3% is added. The addition of gypsum
is important as it avoids the flash setting of cement.
Finally, the cement is fed into the silos after which it is later supplied to the Cement Packing Plant.
2. Dry process –
It is a new process with is mostly used in modern days. Unlike wet process more focus is given to
reduction in power and fuel utilization in Dry method.
In dry process, the calcareous and argillaceous materials are reduced to 25 mm size with the help of
crushers in a ball mill.
After proper Grinding, both materials are mixed to proper proportion before being fed to rotary kiln.
Before material is brought up inside the kiln it is pre heated at around 850oC for around 2 hours.
The product which is obtained from rotary kiln is called as clinkers, which is in size between 3mm and
20mm.
Addition of 2-3% of Gypsum is done to decrease the flash setting property and setting time of clinkers.
The final product obtained is Calcium Silicate hydrate (CSH) gel, with calcium hydroxide being the by
product.
Hydration of Cement – Hydration of cement is a series of chemical reactions which occurs when water is
added to cement, causing it to harden and become solid with the liberation of heat. This process forms Calcium
silicate Hydrate Gel (CSH), Calcium Hydroxide (CH) which is essential for the strength and durability of
Concrete structures. The reaction emits the heat reaching temperature up to 60oC.
1|Page
, Bogue’s Compounds
Bogue’s Compound Composition % Properties
Tricalcium Silicate C3S 30-50 Responsible for early Strength development of cement.
Dicalcium Silicate C2S 20-45 It hardens slowly; however, leads to the development of
Ultimate Strength.
It also makes Cement Resistant to Chemical Attacks
Tricalcium Aluminate 8-12 It results in the flash setting of cement and has highest heat
C3A of hydration.
Tetracalcium 6-10 It contributes to flash set to some extent.
Aluminoferrite
Chemical Composition of cement
Constituent Composition % Description
Lime (CaO) 60 – 65 Key Ingredient in cement that
gives its strength and ability to
bind together.
Silica (SiO2) 15 – 25 It gives strength to cement. Excess
of it can delay setting time of OPC.
Alumina (Al2O3) 3–8 It helps to quickly set the cement
Calcium Sulphate (CaSO4) 3–4 Controls the rate at which the
cement sets
Iron Oxide (Fe2O3) 3–4 It imparts color to cement
Magnesia (MgO) 0.1 – 3 It contributes to hardness and
toughness of cement.
Sulphur 1–3 Used to give Soundness to cement.
Excess of it may decrease Cement
Soundness.
Alkalies (Soda, Potash) 0.5 – 1.3 Plays major role in Alkali –
Aggregate reaction. Excess may
lead to efflorescence
Properties of Cement –
1. Physical property –
Fineness – The size of particle determines the fineness. The smaller the particle the finer is cement.
Cement fineness is critical as cement hydration rate is directly proportional to cement particle size.
Soundness – Soundness is cement’s Ability to resist against the shrinkage after it has hardened.
Excessive free lime and magnesia causes delayed expansion, which is why good cement maintain it’s
volume after it hardens.
Consistency – Consistency is the ability of cement paste to flow. The Vicat Test is used to determine it.
In Vicat Test, a regular consistency cement paste is used in Vicat Apparatus. The plunger of the equipment
is lowered till it touches cement’s top surface. Depending on the consistency of cement, the plunger will
penetrate it to a particular depth.
Setting time – Cement sets and hardens when sufficient water is added to it. The initial setting time
should be as short as possible and final setting time should be as long as possible. It depends on W/C
ratio, Fineness, Chemical Content and presence of Admixtures.
Heat of Hydration – When water is added to cement, it undergoes hydration, which is a chemical
reaction. Hydration produces heat, which can affect the quality of the cement and aid in keeping the
curing temperature stable in cold weather.
2|Page
UNIT 1
By ~ Kunal Pravin Dhole
{Part- 1} Cement and Aggregates
Historical Notes
In 1824, Joseph Aspdin cooked a mixture of limestone and clay into lumps and then crushed them into a fine
powder. When he mixed this powder with water and fine aggregate, he found that it made a strong mortar
that would harden underwater. He obtained a patent for this product and called it Portland cement.
Cement – A powder fine powder of silica, lime, iron oxide, magnesia, Alumina, etc hardens when mixed with
water and is used to bind different materials together.
Manufacturing of Ordinary Portland Cement
1. Wet Process –
In this method, the crushed raw materials are fed to the ball mill, and a small quantity of water is
added.
Now, the steel balls will again crush and mix the raw materials along with water to form a slurry.
The slurry is then passed through silos (vertical chambers to store something), where proper
proportioning of the constituents takes place. The slurry at last has around 40 % of moisture content
in it.
The slurry is then passed through rotary kiln (cylindrical horizontal pipe which is rotating) wherein the
nodules are formed (small stones like shape). The Temperature is maintained in kiln at around 1600oC.
This temperature leads to conversion of nodules to clinkers.
The clinker is later cooled, and a small quantity of Gypsum about 3% is added. The addition of gypsum
is important as it avoids the flash setting of cement.
Finally, the cement is fed into the silos after which it is later supplied to the Cement Packing Plant.
2. Dry process –
It is a new process with is mostly used in modern days. Unlike wet process more focus is given to
reduction in power and fuel utilization in Dry method.
In dry process, the calcareous and argillaceous materials are reduced to 25 mm size with the help of
crushers in a ball mill.
After proper Grinding, both materials are mixed to proper proportion before being fed to rotary kiln.
Before material is brought up inside the kiln it is pre heated at around 850oC for around 2 hours.
The product which is obtained from rotary kiln is called as clinkers, which is in size between 3mm and
20mm.
Addition of 2-3% of Gypsum is done to decrease the flash setting property and setting time of clinkers.
The final product obtained is Calcium Silicate hydrate (CSH) gel, with calcium hydroxide being the by
product.
Hydration of Cement – Hydration of cement is a series of chemical reactions which occurs when water is
added to cement, causing it to harden and become solid with the liberation of heat. This process forms Calcium
silicate Hydrate Gel (CSH), Calcium Hydroxide (CH) which is essential for the strength and durability of
Concrete structures. The reaction emits the heat reaching temperature up to 60oC.
1|Page
, Bogue’s Compounds
Bogue’s Compound Composition % Properties
Tricalcium Silicate C3S 30-50 Responsible for early Strength development of cement.
Dicalcium Silicate C2S 20-45 It hardens slowly; however, leads to the development of
Ultimate Strength.
It also makes Cement Resistant to Chemical Attacks
Tricalcium Aluminate 8-12 It results in the flash setting of cement and has highest heat
C3A of hydration.
Tetracalcium 6-10 It contributes to flash set to some extent.
Aluminoferrite
Chemical Composition of cement
Constituent Composition % Description
Lime (CaO) 60 – 65 Key Ingredient in cement that
gives its strength and ability to
bind together.
Silica (SiO2) 15 – 25 It gives strength to cement. Excess
of it can delay setting time of OPC.
Alumina (Al2O3) 3–8 It helps to quickly set the cement
Calcium Sulphate (CaSO4) 3–4 Controls the rate at which the
cement sets
Iron Oxide (Fe2O3) 3–4 It imparts color to cement
Magnesia (MgO) 0.1 – 3 It contributes to hardness and
toughness of cement.
Sulphur 1–3 Used to give Soundness to cement.
Excess of it may decrease Cement
Soundness.
Alkalies (Soda, Potash) 0.5 – 1.3 Plays major role in Alkali –
Aggregate reaction. Excess may
lead to efflorescence
Properties of Cement –
1. Physical property –
Fineness – The size of particle determines the fineness. The smaller the particle the finer is cement.
Cement fineness is critical as cement hydration rate is directly proportional to cement particle size.
Soundness – Soundness is cement’s Ability to resist against the shrinkage after it has hardened.
Excessive free lime and magnesia causes delayed expansion, which is why good cement maintain it’s
volume after it hardens.
Consistency – Consistency is the ability of cement paste to flow. The Vicat Test is used to determine it.
In Vicat Test, a regular consistency cement paste is used in Vicat Apparatus. The plunger of the equipment
is lowered till it touches cement’s top surface. Depending on the consistency of cement, the plunger will
penetrate it to a particular depth.
Setting time – Cement sets and hardens when sufficient water is added to it. The initial setting time
should be as short as possible and final setting time should be as long as possible. It depends on W/C
ratio, Fineness, Chemical Content and presence of Admixtures.
Heat of Hydration – When water is added to cement, it undergoes hydration, which is a chemical
reaction. Hydration produces heat, which can affect the quality of the cement and aid in keeping the
curing temperature stable in cold weather.
2|Page
