CEMENT

Kardan University

Uploaded BY: Engr.Ahmad Sameer

CEMENT

Introduction ·  Popular as building material.·  Material with adhesive & cohesive properties.·  To bind the fine & coarse aggregate together ·  To fill voids in between fine & coarse aggregate particle form a compact mass.

COMPOSITION OF CEMENT• Calcium Oxide (CaO) = 60 – 65%• Silica (SiO2) = 20 – 25%

• Aluminum Oxide = 4 - 8%• Ferrous Oxide = 2 – 4 %• Magnesium Oxide = 1 – 3 %

CEMENT

There are 3 kind of mixture/concrete can be created using cement that are: Cement Grout- A mixture of cement & water  Cement Mortar - A mixture of cement & sand & water to form a paste. Cement concrete- A composite product which is obtained by mixing of cement, water, inert matrix of sand and gravel / crushed stone.

CEMENTPORTLAND CEMENTMade by mixing substances containing Calcium Carbonate such as chalk / limestone,with substances containing silica , alumina and iron oxide such as clay/ shale.

• Clay/shale: SiO2 Silica (silicon oxide) abbreviated S

Fe203 Ferrite (iron oxide) abbreviated F

Al203 Alumina (aluminium oxide) abbreviated A

 • Limestone/chalkCaC03 Calcium carbonate abbreviated C

 • then the mixture heated and became clinker.• Clinker then grounded to powder.• The hardening Portland cement is a chemical process during which heat is evolved.

Why is it called "portland" cement?Joseph Aspdin, an English mason who patented the product in 1824, named it portland cement because it produced a concrete that resembled the color of the natural limestone quarried on the Isle of Portland, a peninsula in the English Channel

Types of Cement

Depending upon our requirements i.e. using it at a suitable place, we use different types of cement.

• Rapid Hardening or High early strength Cement• Quick setting Cement• High Alumina Cement• Portland Slag Cement• Low Heat Cement• Air Entraining Cement• White Cement• Coloured Cement• Portland Pozzolona Cement

Rapid Hardening Cement

This type cement gets the strength faster than OPC, However its Initial and Final setting is same as those of OPC. It contains more of Tri-Calcium Silicate and is more finely grounded. It gives out more Heat while setting so it is as such unsuitable for massive concrete. It is Used for the Structures which are Subjected to loads early e.g. Roads, Bridges.

Quick Setting cement

It sets faster than the Ordinary Portland Cement. Its Initial Setting Time is 5 minutes and the Final Setting Time is not more 30 minutes. It is required for making concrete that is required to set early as for lying under water or in running water. Initial setting being very little there is always the danger of concrete having undergone its initial setting. Thus this type of cement is used in more special cases.

• High Alumina Cement

It is manufactured by the burning of bauxite ore and lime stone in correct proportions and at high temperature. The resulting product is then ground finely. It develops Strength Rapidly. It is of black colour and resists well the attack of chemicals especially of sulphates and sea water. Its ultimate strength is much higher than OPC. Its initial setting takes more than 2 hours and the final set takes place immediately thereafter. Most of the heat it gives in the first 10 hrs as a result it can be conveniently used in freezing temperatures. At ordinary temperature it is used in thin layers.

• Portland Slag Cement

It is obtained by mixing clinker, gypsum and granulated slag in a proper proportion. The Properties of this cement is very similar to that of OPC which are as under. It has lesser heat of hydration and has better resistance of soils, sulphates of alkali metals, alumina and iron. It has better resistance to acidic water. This type of cement is mostly used in Marine Works.

• Low Heat Cement

The Heat Generated by cement while setting may cause the structure to crack in case of concrete. This Heat generation is controlled by keeping the percentage of Tri-Calcium Silicate and that of Tri-Calcium Aluminate low. Its initial setting and Final setting times are nearly the same as those of OPC. It is not very suitable for Ordinary structures because the use of cement will delayed time of drying. It will also need more curing.

• Air Entraining Cement

It is the OPC mixed with some air entraining agents. The common air entraining agents are oils, fats and fatty acids etc. These materials have the property of entraining air in the form of fine air bubbles. The bubbles render the concrete to become more plastic, workable and more resistant to freezing. However because of air entrainment the strength of concrete reduces and as such the quantity of air so entrained should not exceed 5%.

• White Cement

It is the cement of pure white colour and having same properties as those of Ordinary Portland Cement. Greyish colour of cement is due to iron oxide (FeO). White cement is manufactured from chalk and clay free from Iron Oxide. Oil fuel and not the coal is used for the burning of this cement.It is much more costly than ordinary cement.  .

• Coloured Cement

Various coloured cement are prepared when required in special cases. Suitable pigments are added with OPC to get red or brown cement but for other colours 5 – 10% of desired pigments are grounded with white cement. Pigments used should be chemically inert and also durable so as they must not fade due to the effect of lights sun or weather.

• Portland Pozzolona Cement

Portland Pozzolona cement is produced by grinding together Portland cement and Pozzolona. This cement has properties similar to those of OPC and can therefore be used for all general purpose. Portland Pozzolona cement produces less heat of hydration and offers greater resistance to attack of aggressive water or sulphates bearing than OPC. Portland Pozzolona cement are particularly used in marine works. It takes a little longer to gain strength. Ultimate Strength of this cement is more than OPC

HYDRATION It's a process of chemical reaction between cement and water.

It results first in setting (the concrete become solid) and then hardening (increase of strength and stiffness).

Heat is liberated during hydration process. Thus, during the hardening process, the concrete is being continually warmed by internal heat generated

WHAT IS SETTING ? When cement is mixed with sufficient water, within 1 or 2

hr after the mixing, the sticky paste losses its fluidity ; within a few hours after mixing, noticeable stiffening commences.

Setting can be divided to 2 stage that is: a) Initial Set b) Final Set

Initial set is when the paste begin to stiffen Final set is when the paste beginning to harden and able to sustain some loads.

Initial Setting Time is the time lapse from the addition of water in the mix to the initial set.

Initial Setting Time and Final Setting Time can be determine by using Vicat Apparatus in laboratory.

They are measure at lab. As the time required for the cement paste to withstand a certain arbitrary pressure.

The time taken for a 1-mm diameter needle in the Vicat apparatus to penetrate a depth of 25mm into the cement past sample is the initial setting time.

The final setting time is reached when in the modified Vicat apparatus only the needle penetrates the surface, while the attachment fails to do so.

The rate of setting is also a measure of the rate of heat of hydration.

Test of Cement

•Consistency test•Compressive strength test•Tensile strength test

VICAT’S APPARATUS

VICAT APPARATUS

                  

Consistency Test • It is used to determine the % of water required for

preparing cement pastes for other tests• Procedure:

1. Take 300g cement, add 30% or 90g of water

2. Mix water and cement on a non-porous surface. Mixing should be done.

• Fill the mould of Vicat apparatus.

• The interval between the addition of water to the commencement of filling the moulds is known as the time of gauging.

Among the factors affect the setting time are: a) Fineness of cement b) Chemical composition c) Amount of water

Gypsum added to clinker to retard setting and prevent flash set.

Flash set is defined as the rapid development of permanent rigidity of the cement paste along with high heat.

False set is the rapid development of rigidity without the evolution of heat .

Compressive strength

• Mortar of cement & sand is prepared, 1:3.• Water is added, water cement ratio 0.4:1• It is placed in moulds & form cubes of sides 70.6 or 76 mm.

• The cement required is 185 or 235g• Compacted in vibrating machine in 2 min.

• Moulds placed in damp cabin for 24 hrs

• Specimens are removed & placed in water for curing.

• It is tested in compressive testing machine after 3 and 7 days.

•Every side is calculated and average is taken.

•For 3 days: > 115 kg/cm2 or 11.5 N/mm2

• for 7 days: > 175 kg/cm2 or 17.5 N/mm2

Tensile Strength

• Procedure:

1. Mortar is prepared cement(1) : Sand (3)

2. Water is added 8%

3. Mortar is placed in briquette moulds

• Typical briquette is formed. • A small heap is formed at its top.• It is beaten down by a standard spatula till water appears on the surface.

• Same procedure is repeated for other sides of briquettes.

• 12 standard briquettes are prepared• The quantity of cement may be 600g for 12 briquettes

• It is kept in damp cabin for 24 hrs.• It is carefully removed from mould and submerged in clean water for curing.

• It is tested in testing machine after 3 and 7 days

• The cross section of briquettes at least section is 6.45 cm2

• Ultimate tensile stress = failing load

6.45

• After 3 days: > 20 kg/cm2

• After 7 days: > 25 kg/cm2

HARDENINGHardening is the development of strength over an

extended period of time, is completed for months or years.

Hydration is the key for strength development in concrete.

Hydration process are gradual and require continuous presence of water.

Adding water to the cement would cause temperature of the mixture rise rapidly due to reaction between Tricalcium Aluminate and water that is initially quite rapid.

This is because of since it takes some time for the gypsum to dissolve sufficiently to control the reaction of Tricalcium Aluminate.

Gypsum prevents flash setting that happen due to the reaction of Tricalcium Aluminate.

Thereafter, setting and gradual hardening take place by the reaction of Tricalcium Silicate and Dicalcium Silicate with water.

Atmosphere doesn't take part in hydration process

Hydration process can't take place completely without enough water in the mixture.

Hydration rate depends surface area of clinker expose and fineness of grinding.

Rate of hydration decreases continuously with age as the resistance to water penetration of unhydrated cement grains progressively rises.

Characteristics of Cement• Color • Physical properties• Presence of lumps• Strength

Colour

Colour should be uniform

Typical cement colour (gray colour with light greenish shade)

It gives an indication of excess of lime or clay and the degree of burning.

Physical propertiesFeel smooth when touched or rubbed in between fingers.

If felt rough, indicates adulteration with sand.If hand is inserted in cement bag, hand feels cool and not warm.

If it immersed in water, it should sink and should not float

A paste of cement feel sticky If it contains clay & silt as adulterant, it give earthy smell.

Presence of Lumps

• It should free from hard lumps.• It is due to the absorption of moisture from atmosphere.

• If a bag contains lumps it should be rejected.

Strength• It is tested by three methods:

1. Briquettes with a lean or weak mortar are made (75mm x 25mm x 12mm).

The proportion of cement & sand is 1:6.

Immersed in water for 3 days.• If cement is good it will not be broken easily and difficult to

convert powder form.

2. A block is prepared (25 x 25 x 200) and immersed in water for 7 days.

• Then it is placed on supports 150 mm apart and loaded 340N.

• It should not show signs of failure.

3. Thick paste of cement with water is made on thick glass and kept in water for 24 hours.

• It should set and not crack

THE END