CONCRETE MATERIALS AND MIXTURE

CONCRETE MATERIALS AND





MIXTURE














This topic covers the compositions of

concrete materials and mixture.





It also includes the relation of the concrete

mix strength with the mixture ratios and

workability of wet concrete.

Introduction








• Concrete is the most versatile material for all


types of construction works and has been used


for innumerable construction works, either as



plain concrete or as reinforced concrete or as


precast concrete, or pre-stressed concrete or in


many other forms.



• In building industry, the concrete is mainly used


for purposes, foundations, columns, beams,


slabs, stair cases, lintels, doors, window frames,


sun-shades, storage tanks, etc.



1.1 Basic properties of Normal Weight




Concrete (NWC)











• The various constituents of concrete are



– Cement



– Fine aggregate



– Coarse aggregates and



– Water




• In Reinforced Concrete Steel is also used.

1.1.1 What is Cement?








• Cement usually gray.



• It is the product which is obtained by burning and


crushing to powder a well proportioned mixture of


calcareous (limestone) and argillaceous materials

(clay).



• A material with adhesive and cohesive properties


which make it capable bonding material fragments


into a compact whole.


• Cement + water + fine agg. + coarse agg. = concrete



• Cement + water + fine agg. = cement slurry/plaster


• Cement + lime + water + fine agg. = mortar



Ordinary

Portland
cement Rapid
Quick Hardening
setting
cement Portland
cement



Portland
Blast Portland

Furnace Sulphate
slag resistant
cement cement

Type of

Cement



High Pozzolana
Alumina cement

cement







White and Low Heat
coloured Portland
cement Air cement
entraining
portland
cement

1. Ordinary Portland Cement



- It is also known as Normal setting cement.


- It is general purpose cement suitable for all


purpose.


- It is used in Road pavements, buildings, culverts,


water pipes etc.


- In the other sense it is used every where except


in places where special properties of other types

are required.



- Out of the total consumption of different types


of cement 90% of this type is used.

Types of
Cement Composition Purpose




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






Small percentage of Used in works is to be completed

Quick setting aluminium sulphate as an in very short period and
accelerator and reducing
cement percentage of Gypsum with concreting in static and running
fine grinding water







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

Types of
Cement Composition Purpose



It is prepared by It is used in construction

Sulphates maintaining the percentage exposed to severe sulphate
of tricalcium aluminate
action by water and soil in places
resisting Cement below 6% which increases like canals linings, culverts,
power against sulphates retaining walls, siphons etc.,









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

of Portland cement









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

Types of Composition Purpose
Cement





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



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






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

1.1.1.2 Properties of cement in




concrete mixture





The chemical composition in cement

1. Cement Ingredient and its function

– Lime: It makes the cement sound and provides strength to the cement. Excess
of it in original form causes the cement to expand and disintegrate.

– Silica: It provides strength to the cement. In excess it slows down the setting
of cement.

– Alumina: It provides quick setting property to the cement. In excess it
weakens the strength of cement.

– Calcium Sulphate (Gypsum): It helps in increasing the initial setting time of
cement.

– Iron Oxide: It provides colour, hardness and strength to the cement.
– Magnesium Oxide: It provides colour and hardness to the cement. Excess of it
in free state makes the cement unsound.

– Sulphur Trioxide: In small quantity it makes the cement sound and in excess it
makes the cement unsound.

– Alkalies: In excess it causes efflorescence.

1.1.1.2 Properties of cement in




concrete mixture





The chemical composition in cement



2. The composition of different kind of portland cement





Sl. Compound Formula Abbreviation Range
No.



1 Dicalcium silicate 2(CaO)SiO C S 21 to 45%
2
2

2 Tricalcium silicate 3(CaO)SiO C S 25 to 50%
2
3


3 Tricalcium Aluminate 3(CaO)Al O C A 5 to 11%
3
2
3

4 Tetra Calcium 4(CaO)Al O C AF 9 to 14%
4
2
3
Aluminum Ferrite Fe O
2
3

1.1.1.2 Properties of cement in




concrete mixture





The chemical composition in cement



3. Abbreviation function



C S C A
2 3
• It hydrates slowly. • It is fast reacting with large amount
• It hardens more slowly of heat generation.

• It provides ultimate strength to the • It causes initial setting of cement.
cement. • It is weak against sulphate attack.

• It has more resistance to chemical
attack. C AF

• 4 It is comparatively inactive.

C S
3 • It has poor cementing value.
• It hydrates more rapidly. • It is slow in reaction with small

• It develops early strength. heat generation.
• It generates heat more rapidly and has

less resistance to chemical attack.

1.1.1.2 Properties of cement in




concrete mixture





Concrete hydration process






• The chemical reaction between cement and water is


known as hydration of cement. The reaction takes


place between the active components of cement

(C AF, C A , C S and C S ) and water
3
2
3
4
• Concrete hydration process stages

Stage 1 - Rapid heat generation

Stage 2 - Dormant period


Stage 3 - Acceleration period

Stage 4 - Deceleration

Stage 5 - Steady state



1.1.1.2 Properties of cement in




concrete mixture






The storage of cement








• Dry cement in bags is stored in a dry place



protected from the weather




• For large construction sites this is usually a



secure storage area






Keep the cement dry and

Keep away form both wetness and dampness

1.1.2.1 Properties of aggregate in




concrete






• Classification and sources of the aggregates

• Criteria of aggregates


• Function of aggregates and its relation to the strength of concrete

Aggregate






• The term aggregate is used to describe the



gravels, crushed stones and other materials



which are mixed with cement and water to


make concrete.




• Generally occupy 70%-80%




of the volume of concrete.




• Have important influence



on concrete properties.

Classification and sources of the aggregates










Aggregates are classified in following three



ways:




• Unit weight classification



• Size classification




• Sources classification

Classification of the aggregates according to their



unit weight







Normal Aggregate




• Crushed rock, sand and gravel, broken


bricks






Light Weight Aggregate





• Pumice, expanded shale, expanded clay







Heavy Weight Aggregate



• Magnetite, heamatite, limonite

Classification of the aggregates according to the size






Coarse Aggregate




•Aggregates predominately retained on the

4.75mm sieve, max size can be as a large
150mm







Fine Aggregate





•Aggregates passing 4.75mm & predominately
retained on the 75µm sieve

Classification of the aggregates according to the sources










• Taken from natural deposit without


changing their nature during the process of


Natural production such as crushing and grinding.

Aggregates








• Man-made materials produced as a main


product or an industrial by-product. E.g.

Manufactured expanded perlite(lightweight aggregate)

Aggregates

Criteria of Aggregate









• Aggregate should have the following criteria:




a. Hard and strong



b. Free and undesirable impurities(clean)




c. Chemically stable




d. Abrasion resistance




e. Durable

Function of aggregates and its relation




to the strength of concrete





• Reduce the cost of concrete



• Well graded aggregates produce workable yet



cohesive concrete


• Reduce the heat of hydration of concrete



• Reduce the shrinkage of concrete



• Control of surface hardness



• Colour or light reflecting properties



• Control of density



• Control of fire

1.1.3 Water








• Key ingredient for concrete to cause hydration of


cement.


• Only right amount of water used would produce a


strong and dense concrete.


• Quality and quantity of water influence the


strength of concrete.


• The water cement ratio influenced by:



a. The grade of concrete


b. The nature and type of aggregates


c. Workability

d. Durability

1.1.3.1 Behavior of water in concrete




mixture





• Role of water in concrete mixture:


a. To enable hydration process


b. To lubricate the concrete mixture (gravel, sand and
cement) in order to facilitate placing


c. To wash aggregates


d. For curing process


• Potable water can be used in concrete mixing without

testing its quality.


• Natural water can be used will depend on the fitness of

water without prior treatment.


• Specification for test on water for making concrete can

be obtained in BS 3148:1959 or MS 7.3:1971

1.1.3.1 Behavior of water in concrete




mixture





• Effect impurities may lead to:


a. Interfere the setting time of cement

b. Adverse effect to the strength of concrete

c. Staining in concrete surface


d. Corrosion to the reinforcement of the steel reinforced
concrete


• Do not used water that:

a. Have excessive impurities


b. Contain acid

c. Contain algae

d. High alkaline


• Use of sea water may lead to efflorescence and cause

problems with decorative finishes.

1.2 Advantages And Disadvantages of




concrete in construction industry.





• Advantages of concrete


– Economical in long run


– High compressive strength with minimal corrosive and
weathering effects


– Fresh concrete can be moulded into any shape or size

according to specifications


– able to combine with other structural materials

(reinforced concrete)

– Unlimited structural application (foundations, alls, roads,

buildings, airfields, dams, bridges, and etc)


– It is durable, fire resistant and requires little maintenance

– Fresh concrete can be pumped and laid to high and

difficult positions also





828m 452m

1.2 Advantages And Disadvantages of




concrete in construction industry.





• Disadvantages of concrete



– Low tensile strength and cracks easily



– Shrinks on drying and expands on wetting will lead to

cracks


– Expands and contracts with the changes in


temperature


– Creep (prestressed concrete production)


– Liable to disintegrate by alkali and sulphate attack



– Lack of ductility inherent in concrete to be used

earthquake resistant design.



1.3 Fundamental of concrete mixture








• The process of selecting suitable ingredients of

concrete to comply minimum properties of strength,


durability, and consistency with higher workability and

economical


• Selection of materials depends on:


a. Structural requirements


b. Function and environment where the concrete will be
exposed


c. Site condition


d. Production, transport, placement, compaction and
finishing


e. Characteristics of the available raw materials

1.3 Fundamental of concrete mixture





• The usefulness of concrete for various



concrete grade/ nominal strength :





Concrete Nominal Use


Grade strength


7 7 Non reinforced concrete
10 10


15 15 Reinforced concrete with lightweight

aggregates

20 20 Reinforced concrete with normal weight

25 25 aggregates



30 30 Pre-tensioning concrete




40 40 Post-tensioning concrete

50 50

1.3.1 Types of concrete mixture











• There is three types of concrete mixture:




a. Standard/prescribed mix



b. Designed mix



c. Nominal mix

1.3.1.1 Prescribed mix









• The rate is usually based on weight of mixture



(CP110)




• Level of concrete represents the expected


minimum characteristic strength




• In some cases, the engineers set the mixing



ratio and the contractor must provide the



mixtures as required.

1.3.1.2 Designed mix









• The rate is usually based on volume of mixture




• Usually contractor is responsible to select



concrete mix ratio to achieve required


strength at the appropriate workability.




• A few designed mix will be prepared to obtain



a good and quality concrete mixture

1.3.1.3 Nominal mix









• The rate is usually based on volume of mixture




• A few designed mix will be prepared to obtain



only minimal strength



• Content low cement and less durable




• Can be done if the weight and density of the



materials is known




• Mixtures preparation are must encouraged by


engineers

1.3.2 Proportion of concrete mixture








• Mix ratio usually for example 1:2:4 (cement:


sand: coarse aggregate), 1:3:6 and 1:5:10


depended on its purpose and application.



• The use of concrete for various concrete mix


ratio:

1.3.3 Admixtures








• Is a material added to the batch of concrete mixture either

before or during its mixing to alter its properties such as

workability, curing temperature range, set time or colour.


• Reason for using admixture:

a. Increase slump and workability


b. Retard or accelerate initial setting

c. Reduce or prevent shrinkage


d. Modify the rate or capacity for bleeding


e. Reduce segregation

f. Retard or reduce heat evolution during early hardening


g. Increase strength

h. Increase durability or resistance to severe conditions of


exposure


i. Decrease permeability of concrete

1.3.3 Admixtures








• Types of chemical admixture:


– Air entraining


– Water-reducing

– Retarders


– Accelerators

– Superplasticizers


– Water proofing


• Types of mineral admixture:


– Pozzolanic reaction

– Agricultural ash


– Industrial ash

1.3.3.1 Air entraining








• This material is added in concrete mix for the



entrainment of air into concrete



• Addition of this material would increase the


durability of concrete to frost without



increasing cement content



• The types of agent used are natural wood


resin, various sulfonated compounds, some



animal and vegetable fat and oils and


synthetic detergents.



1.3.3.2 Water reducing








• Also known as plasticizer


• Is a surface active agent to support the cement

distribute efficiently in the water.



• Adding this material in concrete mix would increase

the workability of mix


• Require less water to make a concrete equal slump or

increase a slump of concrete at the same water

content


• As a result the followings can be achieved:


– Higher workability with strength unchanged


– Higher strength with workability unchanged

– Less cement for same strength and workability



1.3.3.3 Retarders









• Retarders are used to prolong or delay the



setting time of cement paste in concrete.




• The following aspect can be achieved through


addition of this material:




a) Maintain workability at high temperatures




b) Reduce rate of heat evolution




c) Extend placing times

1.3.3.3 Retarders









• Some of materials used to retard the set of a



concrete mixture are tartaric acid, sugar, salt,


lignin and borax. These material should be



added to the mixing water.




• For example an addition of 0.2% of sugar by



weight of cement will retard setting time



down to 3 days or more.