3rd Semester Civil

Concrete Technology

Tribhuwan kumar

Lecturer, NGP PATNA

(Dept. Of civil Engineering)

Unit –1

Ordinary Portland cement is one of the most widely used

type of Cement. In 1824 Joseph Aspdin gave the name as

Portland cement as it has similarity in colour and quality

found in Portland stone, which is a white grey limestone in

island of Portland, Dorset.

The principal raw materials used in the manufacture

of Ordinary Portland Cement are:

Argillaceous or silicates of alumina in the form of clays

and shales.

Calcareous or calcium carbonate, in the form of

limestone, chalk and marl which is a mixture of clay and

calcium carbonate.

The ingredients are mixed in the proportion of about two

parts of calcareous materials to one part of argillaceous

materials.

Properties of Cement • properties of cement – fineness, standard

consistency, initial & final setting time

compressive strength & soundness.

• grades of opc 33, 43 , 53 & their specification.

• Adulteration of cement (field test).

• Types of Cement

i) Rapid hardening cement

ii) Low heat cement

iii) Pozzolana Portland cement

iv) Blast furnace slag cement

v) White cement

Constituents of Cement.

The chief chemical constituents of Portland cement

are as follows:

Lime (CaO) 60 to 67%

Silica (SiO2) 17 to 25%

Alumina (Al2O3) 3 to 8%

Iron oxide (Fe2O3) 0.5 to 6%

Magnesia (MgO) 0.1 to 4%

Sulphur trioxide (SO3) 1 to 3%

Soda and/or Potash (Na2O+K2O) 0.5 to 1.3%

Fineness of Cement.

The size of the particles of the cement is its fineness. The

required fineness of good cement is achieved through

grinding the clinker in the last step of cement production

process. As hydration rate of cement is directly related to

the cement particle size, fineness of cement is very

important.

Importance of Cement Fineness

The fineness of cement affects hydration rate, and in turn,

the strength. Increasing fineness causes an increased

rate of hydration, high strength, and high heat generation.

Bleeding can be reduced by increasing fineness.

However, increased fineness can also lead to the

requirement of more water for workability,resulting in a

higher possibility of dry shrinkage.

Virtual Lab URL - http://civ02.vlabs.ac.in/exp6/index.html

YouTube link for Hindi- https://youtu.be/eP8_yrP8xc0

http://civ02.vlabs.ac.in/exp6/index.htmlhttps://youtu.be/eP8_yrP8xc0

Standard Consistency of

Cement.

As per IS:4031 Part 4 The standard consistency of a

cement paste is defined as that consistency which

will permit the Standard Vicat plunger to penetrate to

a point 5 to 7 mm from the bottom of the Vicat mould.

The percentage of water required for standard

consistency as taken as the minimum water required for

complete hydration of cement particles. That means, in

any case, the working Water Cement Ratio cannot go

below Normal Consistency.

The test to be conducted in controlled condition of

temperature 27±2˚C and Relative humidity 65±5%.

Virtual lab URL -

http://civ02.vlabs.ac.in/exp7/index.html

YouTube link for Hindi -

https://youtu.be/RQKfQcVewuo

http://civ02.vlabs.ac.in/exp7/index.htmlhttps://youtu.be/RQKfQcVewuo

Initial and final setting time of

concrete.

The initial setting time is the exact moment when the concrete starts to

harden. In theory, this time starts as soon as the water is added to the

cement. The final setting time is the moment the concrete has hardened

enough so that a five-millimetre square needle no longer penetrates the

surface.

Technical aspects of concrete setting time.

It is important that concrete does not set too quickly or too slowly. If the

initial setting time is too fast, the concrete will start to set while it is being

transported and before it can be poured. If the final setting time is too long,

the structure will not have enough strength to support the weight of

additional construction and machinery on top of it.

Note that setting should not be confused with hardening. Hardening of

concrete refers to the strengthening and solidifying of the material. Setting

is simply when the cement paste starts to reach a defined consistency by

losing its plasticity and workability.

The initial setting time is important to know for contractors and cement

suppliers as it determines how much time is needed for transport, placing

and compaction of the concrete. The final setting time also tells contractors

when the concrete will completely lose its plasticity and be able to support

its own shape and weight without formwork or supports. The final time is

the earliest point at which scaffolding and formwork can be removed.

Indian Railways Institute of Civil Engineering URL -

http://www.iricen.gov.in/LAB/res/html/Test-20.html

http://www.iricen.gov.in/LAB/res/html/Test-20.html

COMPRESSIVE STRENGTH OF CEMENT.

Cement, basically is known by its compressive strength.Cement is

identified by its grade like 53 grade, 43 grade, 33 grade of

cement.This grade indicates the compressive strength of cement, i.e.

53 grade of cement indicates that compressive strength of cement

cube after 28 days of curing will be 53 N/mm2 (MPa) or 530 kg/cm2.

The compressive strength of the hardened cement is the essential

property when water is added in the cement. Cement hydrates and

shows cohesion and solidity. The strength of cement-based

compound, such as mortar or concrete depends upon the type and

nature of cement.

Basically, because of strength,nature of cement, both mortar and

concrete are very strong in compression and weak in tension, hence

testing of cement for compressive strength is most important because

it is the major purpose for which it is used.

Link of compressive test procedures and video by Indian Railway

Institute of Civil Engineering -

http://www.iricen.gov.in/LAB/res/html/Test-23.html

YouTube Link- https://youtu.be/DLqM2xxTCD4

http://www.iricen.gov.in/LAB/res/html/Test-23.htmlhttps://youtu.be/DLqM2xxTCD4

Soundness of Cement

Soundness of cement can be defined as its ability to retain its volume after

it gets hardened. This means that a properly sound cement will undergo

minimum volume change after it converts into the hardened state.

Soundness of cement is affected by the presence of excess lime (CaO) in

the cement. This excess lime hydrates very slowly and forms slaked lime

that occupies a larger volume than the original free calcium oxide. The

slow hydration process, therefore, affects the properties of hardened

concrete. The difference in the rate of hydration of free lime and slaked

lime leads to change in volume of hardened concrete. The cement which

exhibits this type of volume changes is described as unsound cement. In

the soundness test of cement, we determine the amount of excess lime.

Therefore, a limit has been set in the ordinary Portland cement regarding

the presence of free lime and is determined by test. In the soundness

test a specimen of hardened cement paste is boiled for a fixed time so

that any tendency to expand is speeded up and can be detected This test

can be conducted by Le-chatelier method and Autoclave Method.

3D Animation video URL - https://youtu.be/je5ztHs9tII

NPTEL Video demonstration- https://youtu.be/J7opp28cRe4

https://youtu.be/je5ztHs9tIIhttps://youtu.be/J7opp28cRe4

Grades of OPC

OPC is the most commonly used type of cement in the

world. OPC is the basic form of cement produced by inter-

grinding cement clinker with 3-5% gypsum.

Bureau of Indian Standards (BIS) has classified OPC into

3 different grades namely, OPC 33 Grade, OPC 43 Grade

and OPC 53 Grade cements. The grade number indicates

the minimum compressive strength that the cement is

required to attain at the end of 28 days eg., the minimum

compressive strength of 53 Grade OPC attained on the

28th day shall not be less than 53 MPa or 530 kg/sqcm.

It may be noted that OPC 33, OPC 43 and OPC 53

grades do not differ in chemical content. The only

difference is that the higher grade cements are ground

much finer during the final grinding process, creating a

product that is much stronger and more durable than the

less finely ground cement.

1. OPC 33 Grade

Cement

This grade of cement is used for general construction

under normal environmental condition. But low

compressive strength and availability of higher grades of

cement have impacted the use and demand of OPC 33.

IS Code – IS 269 : 1989 for Ordinary Portland Cement,

33 Grade.

Compressive Strength of OPC 33 – The average

compressive strength of at least three mortar cubes, is

taken into account while checking the compressive

strength. These mortar cubes are composed of one part

of cement and three parts of standard sand (1:3).a) 3 days

Not less than 16 N/mm2

b) 7 days Not less than 22 N/mm2

c) 28 days Not less than 33 N/mm2

2. OPC 43 Grade

Cement

This grade of cement is the most popular cement used in

the country today. OPC 43 is used for general RCC

construction where the grade of concrete is up to M30. It

is also used for the construction of precast items such as

blocks, tiles, asbestos products like sheets and pipes, and

for non-structural works such as plastering, flooring etc.

IS Code – IS 8112: 1989 for 43 Grade Ordinary Portland

Cement.

Compressive Strength of OPC 43 –

a) 3 days Not less than 23 N/mm2

b) 7 days Not less than 33 N/mm2

c) 28 days Not less than 43 N/mm2

3. OPC 53 Grade

Cement

OPC 53 is used when we need higher strength concrete.

In concrete mix design, for concrete M20 and above we

can achieve 8 to 10% saving in cement with the use of

OPC 53.

This cement grade is used for specialized works such as

prestressed concrete components, precast items such as

paving blocks, building blocks etc, runways, concrete

roads, bridges, and other RCC works where the grade of

concrete is M25 and above.

IS Code – IS 12269 : 1987 for Specification for 53 grade

ordinary portland cement.

Compressive Strength of OPC 53

a) 3 days Not less than 27 N/mm2

b) 7 days Not less than 37 N/mm2

c) 28 days Not less than 53 N/mm2

Adulteration of Cement

(Field Test)

Sometimes it may be required to perform cement quality tests at a site within a very short period of time for evaluating the condition of the supplied cement. In most of the cases, it is not

possible to have any laboratory test in the short period of time. Therefore, the quality check is

performed with the help of some basic field tests.

Field Tests of Cement –

Date of Manufacturing: As the strength of cement reduces with age, the date of manufacturing of cement bags should be checked. It should not be older then 3 months.

Cement Color: The color of cement should be uniform. It should be typical cement color i.e. gray color with a light greenish shade.

Whether Hard Lumps are Formed: Cement should be free from hard lumps. Such lumps are formed by the absorption of moisture from the atmosphere.

Temperature Inside Cement Bag: If the hand is plunged into a bag of cement, it should be

feel cool inside the cement bag.

Smoothness Test: When cement is touched or rubbed in between fingers, it should give a

smooth feeling. If it felt rough, it indicates adulteration with sand.

Water Sinking Test: If a small quantity of cement is thrown into the water, it should float some

time before finally sinking.

Glass Plate Test: A thick paste of cement with water is made on a piece of a glass plate and it

is kept under water for 24 hours. It should set and not crack.

Types of Cement

1) Rapid

Hardening Cement

Rapid hardening cement attains high strength in the early

days; it is used in concrete where formworks are removed

at an early stage. Its initial and final setting times are

similar to ordinary portland cement (OPC).

Its 3 days strength is equal to 7 days strength of OPC.

This cement has increased lime content and higher c3s

content and finer grinding, which gives higher strength

development than OPC at an early stage.

2) Low Heat Cement

Low heat cement is produced by maintaining the

percentage of tricalcium aluminate below 6% by

increasing the proportion of C2S. A small quantity of

tricalcium aluminate makes the concrete to produce low

heat of hydration.

Low heat cement suitable for mass concrete construction

like gravity dams, as the low heat of hydration, prevents

the cracking of concrete due to heat.

This cement has increased power against sulphates and

is less reactive and initial setting time is greater than

OPC.

3) Portland Pozzolana

Cement (PPC)

It is prepared by grinding pozzolanic clinker with Portland

cement. It is also produced by adding pozzolana with the

addition of gypsum or calcium sulfate or by intimately and

uniformly blending Portland cement and fine pozzolana.

This cement has a high resistance to various chemical

attacks on concrete compared with ordinary portland

cement, and thus, it is widely used.

It is used in marine structures, sewage works, sewage

works, and for laying concrete underwater, such as

bridges, piers, dams, and mass concrete works, etc.

4) Blast Furnace Slag

Cement

Slag is the residual waste obtained from steel

manufacturing industries.

It has pozzolonic properties.

Blast furnace slag cement is obtained by grinding the

clinkers with about 60% slag and resembles more or

less in properties of Portland cement. It can be used

for works where economic considerations are

predominant.

5) White Cement

It is prepared from raw materials free from Iron oxide

and is a type of ordinary portland cement, which is

white.

It is costlier than any other cement.

Used for architectural purposes. such as precast

curtain wall and facing panels, terrazzo surface, etc.

and for interior and exterior decorative work like

external renderings of buildings, facing slabs,

floorings, ornamental concrete products, paths of

gardens, swimming pools, etc.

Unit 2nd

Presentation 2nd

3rd Sem Civil

Concrete Technology

TRIBHUWAN KUMAR

Lecturer, NGP PATNA

Dept. Of Civil Engineering

Unit –2Properties of Aggregates :

2.1 Classification of Aggregates.

2.2 Properties of aggregates :

2.3 Bulking of sand, phenomenon of bulking, its effect on concrete mix proportion..

2.4 Determination of crushing & impact value of coarse aggregate and flakiness index .

Aggregates are inert granular materials such as sand,

gravel, or crushed stone that, along with water and

cement, are an essential ingredient in concrete.

Aggregates are used in concrete to provide economy in

the cost of concrete. Aggregates act as filler only. These

do not react with cement and water.

But there are properties or characteristics of aggregate

which influence the properties of resulting concrete mix.

In any concrete, Aggregates forms about 70%-75% of the

total volume of concrete, are divided into two distinct

categories--fine and coarse. Fine aggregates generally

consist of natural sand or crushed stone with most

particles passing through 4.75mm IS sieve and retain on

75micron IS sieve .Coarse aggregates are any particles

passing through 75mm IS Sieve and retain on 4.75mm IS

Sieve.

Classification of Aggregates

ACCORDING TO SIZE

Fine Aggregate

Coarse Aggregate

All in Aggregate

1) FINE AGGREGATE

It is the aggregate whose particles passing through

4.75mm IS sieve and retain on 75micron IS sieve.

It is used to fill the voids created by coarser Agg.

2) COARSE AGGREGATE

It is the aggregate whose particles passing through

75mm IS Sieve and retain on 4.75mm IS Sieve.

3) ALL IN AGGREGATE

It is the aggregate composed of both fine aggregate and

coarse aggregate.

Classification of Aggregates

According to Shape :-

Rounded aggregate- Due to its smooth textured and rounded shape, It gives goodworkability 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 – These Aggregates are naturally irregular or partially rounded. It is also not suitable for construction works due to its

lack of interlocking properties.

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- The aggregate is said to be flaky when its least dimension is less than 3/5th (or 60%) of its mean dimension. Mean dimension is the average size

through which particles pass and the sieve size on which these are retained. Flaky

aggregate tends to be oriented in one plane which affects the durability.

Elongated aretained- The aggregate is said to be

elongated when its greater dimension i.e. length is greater

than 9/5th or 180% of its mean dimension.

Properties of Aggregate

1) Size and Shape

The size and shape of the aggregate particles greatly influence the quantity of cement required in concrete mix and hence ultimately economy of

concrete. For the preparation of economical concrete mix on should use largest coarse aggregates feasible for the structure. IS-456 suggests

following recommendation to decide the maximum size of coarse aggregate to be used in P.C.C & R.C.C mix.

Maximum size of aggregate should be less than One-fourth of the minimum dimension of the concrete member.

One-fifth of the minimum dimension of the reinforced concrete member.

Remember that the size & shape of aggregate particles influence the properties of freshly mixed concrete more as compared to those of hardened

concrete types.

2) SURFACE TEXTUREThe development of hard bond strength between aggregate particles and cement paste depends upon the surface texture, surface roughness and

surface porosity of the aggregate particles.

If the surface is rough and porous, maximum bond strength develops. In porous surface aggregates, the bond strength increases due to setting of

cement paste in the pores.

3) SPECIFIC GRAVITY

The ratio of weight of oven dried aggregates maintained for 24 hours at a temperature of 100 to 1100C,

to the weight of equal volume of water displaced by saturated dry surface aggregate is known as

specific gravity of aggregates.

Specific gravity is a mean to decide the suitability of the aggregate. Low specific gravity generally

indicates porous, weak and absorptive materials, whereas high specific gravity indicates materials of

good quality. Specific gravity of major aggregates falls within the range of 2.6 to 2.9.

4) BULK DENSITY

It is defined as the weight of the aggregate required to fill a container of unit volume. It is generally

expressed in kg/litre.

Bulk density of aggregates depends upon the following 3 factors.

* Degree of compaction

* Grading of aggregates

* Shape of aggregate particles

5) FINENESS MODULUS

Fineness modulus is an empirical factor obtained by adding the cumulative percentages of aggregate

retained on each of the standard sieves ranging from 80 mm to 150 micron and dividing this sum by 100.

Fineness modulus is generally used to get an idea of how coarse or fine the aggregate is. More fineness

modulus value indicates that the aggregate is coarser and small value of fineness modulus indicates that

the aggregate is lloads.

6) CRUSHING VALUE

The aggregates crushing value gives a relative measure of resistance of an aggregate to crushing under

gradually applied compressive load. The aggregate crushing strength value is a useful factor to know

the behavior of aggregates when subjected to compressive loads.

Bulking of Sand

Bulking of sand is an important volumetric change that takes place in

the sand when they are moist. Sand increase in volume, to the extent

of 20-30 percent, when they contain moisture between 2-8 percent.

This is because moisture in small proportions forms thin films around

the sand grains.

Fine sands bulk greater than coarse sand.

As regards the rate of bulking of sand, it has been observed that it is

related to two factors.

(i) percentage of moisture content in the sand.

(ii) gram-Size of the sand particles.

Thus, the bulking effect is maximum when the moisture content in the

sand is between 4-6 percent. As the water content increases, this

effect goes on decreasing, becoming negligible at 15-20 percent

moisture content.

When water is added to dry and loose sand, a thin film of water is

formed around the sand particles. Interlocking of air in between the

sand particles and the film of water tends to push the particles apart

due to surface tension and thus increase the volume. But in case of

fully saturated sand the water films are broken and the volume

becomes equal to that of dry sand.

AGGREGATE CRUSHING

VALUE (IS:2386-PART

4-1963)

Aggregate crushing value test on coarse aggregates

gives a relative measure of the resistance of an

aggregate crushing under gradually applied compressive

load.

Aggregate crushing value is a numerical index of the

strength of the aggregate and it is used in construction of

roads and pavements.

Crushing value of aggregates indicates its strength.

Lower crushing value is recommended for roads and

pavements as it indicates a lower crushed fraction under

load and would give a longer service life and a more

economical performance.

MHRD Virtual lab link - http://ts-

nitk.vlabs.ac.in/transportation-

engineering/exp/crushing-value/index.html

YouTube link NITTTR Chandigarh-

https://youtu.be/lE7LFOuGKyI

http://ts-nitk.vlabs.ac.in/transportation-engineering/exp/crushing-value/index.htmlhttps://youtu.be/lE7LFOuGKyI

Aggregate Impact test

The aggregate impact value gives a relative measure of the

resistance of an aggregate to sudden shock or impact, which in

some aggregates differs from its resistance to a slow

compressive load.

The property of a material to resist impact is known as toughness. Due to

movement of vehicles on the road the aggregates are subjected to impact

resulting in their breaking down into smaller pieces

The aggregates should therefore have sufficient toughness to resist their

disintegration due to impact. This characteristic is measured by impact

value test.

The aggregate impact value is a measure of resistance to sudden impact

or shock, which may differ from its resistance to gradually applied

compressive load.

Test Theory ( Iricen link) -

http://www.iricen.gov.in/LAB/res/html/Test-16.html

YouTube link (Lab/hindi) -

https://youtu.be/x4ekpMEERxI

http://www.iricen.gov.in/LAB/res/html/Test-16.htmlhttps://youtu.be/x4ekpMEERxI

Flakiness index

RELEVANCE AND IMPORTANCE

It is not desirable to use flaky particles in construction of roads especially in surface course.

This is because when the load acts along the thin axis (along the axis of minimum moment of

inertia) of the flaky flat particles then they may get broken down easily. In order to avoid such

condition, the particles have to be tested for their flakiness index values to check their

suitability in using for construction of roads. This the reason of the test being carried out.

TEST DESCRIPTION:

Flakiness Index of aggregate is the percentage by weight of aggregate particles whose least

dimension is less than 0.6 of their mean dimensions. This test is applicable to aggregates

having size larger than 6.3mm.

To calculate the flakiness index of the given sample of aggregates, the weight of each fraction

of aggregates passing and retaining on the specified set of sieves is noted first. The pieces of

aggregates are made to pass through the slot of specified thickness of gauge and then they

are weighed. Then the flakiness index is calculated as the total weight of material passed

through various thickness gauges, expressed as a percentage of total weight of the sample

gauged.

Flakiness Index = [W2/ W1] x 100

Where, W2= Weight passed from 0.6 x dmean size

W1= Total weight of aggregates

Flakiness Index of aggregates used in road construction should be less than 15% and normally

does not exceed 25%

Link (NITTTR CHANDIGARH) - https://youtu.be/acfJIG9o8iw

https://youtu.be/acfJIG9o8iw

3rd Sem,Civil

Concrete Technology

TRIBHUWAN KUMAR Lecturer,NGP PATNA

Civil Engineering

Unit- 3

Properties of Concrete

different grades of concrete as per provisions of IS 456- 2000.

minimum grade of concrete for different exposure conditions.

Water cement ratio ,Definition of w/c ratio, Duff Abraham w/c

law.

Definition of workability, factors affecting workability of

concrete. Determination of workability of concrete by slump

cone test, compaction factor test & vee bee consistometer.

CONCRETE MIX DESIGN.

Testing of concrete

• Introduction

Concrete is a mixture of portland cement, water, aggregates, and in some cases, admixtures.

The cement and water form a paste that hardens and bonds the aggregates together.

Concrete is often looked upon as “man made rock”.

Concrete is the most widely used construction material in the world.

Grade of concrete is defined as the minimum strength the concrete must

posses after 28 days of construction with proper quality control. Grade of

concrete is denoted by prefixing M to the desired strength in MPa. For example,

for a grade of concrete with 20 MPa strength, it will be denoted by M20, where

M stands for Mix.

These grade of concrete is converted into various mix proportions. For

example, for M20 concrete, mix proportion will be 1:1.5:3 for

cement:sand:coarse aggregates.

Grade of concrete construction is selected based on structural design

requirements.

• Different grades of concrete

Minimum grade of concrete for different

exposure conditions

Water Cement Ratio

The ratio between the water and cement by weight is known as Water-Cement Ratio.

The quantity of water added to the cement while preparing concrete mixes has been known to exert tremendous influence on the quality of concrete.

It was first discovered in 1918 A.D. Abraham had evaluated this aspect of concrete proportioning and stated:

The strength of Concrete / Mortar is dependent on the net quantity of water used per sack of cement.

Cement and water are the only two chemically active elements in concrete.

By their combination they form a glue-like binder paste, which surrounds and coats the particles of the inert mineral aggregates, sets and upon hardening binds the entire product into a composite mass.

Functions of Water in Concrete.

1. It hydrates the cement, which is an essential chemical reaction for formation of complex silicate crystalline gels that are responsible for the strength of the cement.

2. It lubricates all the concrete ingredients, by passing around them in the form of films. Hence it is responsible for the plasticity and mobility of concrete which define its workability.

Too much water can increase the workability, but it will also adversely effect the strength and durability of concrete.And water used in a small amount can increase the strength and durability of concrete but will decrease its workability.

That’s why it is needed to carefully select the quantity of water which should be used in the mix. It can be seen that lower water cement ratio could be used when the concrete is vibrated to achieve higher strength, whereas, comparatively, higher water cement ratio is required when concrete is hand compacted.

https://civilseek.com/concrete-definition-and-concrete-ingredients/https://civilseek.com/properties-of-hardened-concrete/

Workability of Concrete

Workability of concrete is the property of freshly mixed concrete which determines the ease and homogeneity with which it can be mixed, placed, consolidated and finished’ as defined by ACI Standard.

ASTM defines it as “that property determining the effort required to manipulate a freshly mixed quantity of concrete with minimum loss of homogeneity”.

Workability is directly proportional to water cement ratio. An increase in water-cement ratio increases the workability of concrete.

Factors Affecting Workability of Concrete

The workability requirements for a concrete construction depends on:

Water cement ratio

Type of construction work

Method of mixing concrete

Thickness of concrete section

Extent of reinforcement

Method of compaction

Distance of transporting

Method of placement

Environmental condition

Tests for Workability of Concrete

a) Slump Test

The concrete slump test measures the consistency of fresh concrete before it sets. It is performed to check the workability of freshly made concrete, and therefore the ease with which concrete flows.

The test is carried out using a metal mould in the shape of a conical frustum known as a slump cone that is open at both ends and has attached handles. The tool typically has an internal diameter of 100 mm at the top and of 200 mm at the bottom with a height of 300 mm.

The cone is placed on a hard non-absorbent surface. This cone is filled with fresh concrete in THREE stages. Each time, each layer is tamped 25 times with a bullet-nosed metal rod measuring 5/8 in (16 mm) in diameter.At the end of the third stage, the concrete is struck off flush with the top of the mould. The mould is carefully lifted vertically upwards, so as not to disturb the concrete cone.

The concrete then slumps (subsides). The slump of the concrete is measured by measuring the distance from the top of the slumped concrete to the level of the top of the slump cone.

b) Compaction Factor Test

c) Vee-bee test

Concrete Mix Design

Mix design is defined as process of selecting suitable ingredients of concrete and determining their relative proportions with the objective of producing concrete of certain minimum strength with respect to requirement of workability at site, without sacrificing durability of concrete.

Concrete Mixes are primarily divided into the two different types :

a) Nominal Mix:

Nominal Mix is generally adopted for small scale constructions. In this type of mix, the mix ratios and concrete constituent proportions are prefixed and specified. Eg: M20(1:1.5:3); the quantity of cement, sand and aggregate is batched in volume as per the fixed ratio 1:1.5:3. From the above table till M25 grade, the concrete proportions are called as Nominal mix concrete.

b) Design Mix:

Design mix concrete is adopted for high rise constructions. In this type of mix, the mix ratios are decided by an Engineer after analysing the properties of individual ingredients of concrete. Like, cement is tested for Fineness modulus and Specific gravity of cement in the lab while deciding the Design mix ratio. There is No Pre-fixed ratio, and ingredients are are batched in weight. From the above table, concrete grades more than M25 falls in Design mix.In Simple, Design Mix refers to the ratios which are decided by the designer.

Compressive test of Concrete The compressive strength of the concrete cube test provides an idea

about all the characteristics of concrete. By this single test one judge that

whether Concreting has been done properly or not. Concrete compressive

strength for general construction varies from 15 MPa (2200 psi) to 30 MPa

(4400 psi) and higher in commercial and industrial structures.

Compressive strength is the ability of material or structure to carry the loads on

its surface without any crack or deflection.

For cube test two types of speciused is used i.e. either cubes of 15cm X 15cm

X 15cm or 10cm X 10cm x 10cm depending upon the size of aggregate are

used. For most of the works cubical molds of size 15cm x 15cm x 15cm are

commonly used.

This concrete is poured in the mold and appropriately tempered so as not to

have any voids. After 24 hours, molds are removed, and test specimens are put

in water for curing. The top surface of these specimen should be made even

and smooth. This is done by placing cement paste and spreading smoothly on

the whole area of the specimen.

These specimens are tested by compression testing machine after seven days

curing or 28 days curing. Load should be applied gradually at the rate of 140

kg/cm2 per minute till the Specimens fails. Load at the failure divided by area of

specimen gives the compressive strength of concrete.

Age Strength percent

1 day 16%

3 days 40%

7 days 65%

14 days 90%

28 days 99%

CONCRETE TECHNOLOGY QUALITY CONTROL OF CONCRETE

Unit-04

NEW GOVT. POLYTECHNIC, PATNA-13

Index

Sr.No Title

1 Introduction

2 Quality control application in concrete construction

3 Where does quality control begin?

4 How does quality control continue?

5To know the quality of concrete, We

can do the several tests.

6 Material Used in Concrete

7 Formwork2

Introduction

What is concrete?

Concrete is a most widely used construction material, commonly made by mixing of

Cement with Fine Aggregate, Coarse Aggregate, Water and Admixture.

What is quality of concrete?

For the building structure to be durable, more strength and also for aesthetic,

accomplishing a quality concrete is of supreme importance. This is because the vital factor

which determines or makes a building look elegant, gives a building more strength and

durability the concrete’s quality.

Low strength and low durable concrete structures have damaged millions of lives and

properties in past decades. So, in order to achieve a quality and a durable building structure,

maintaining the quality and standard of concrete is paramount.

Quality is perceived differently by different people. Yet, everyone understands what is

meant by “quality”. In a manufactured product, the customer as a user recognizes the quality

of fit, finish, appearance, function, and performance.

The quality of service may be rated based on the degree of satisfaction by the customer

receiving the service. The relevant dictionary meaning of quality is “the degree of Excellence”

3

Quality control application in concrete construction

Mechanical properties of the reinforcement to be used.

Dimension of the reinforcement.

Location of the reinforcement in construction before concrete poured.

Location of pre-stressing ducts.

Properties of the cement used in the concrete.

Properties of the concrete mix designed of use in the structure.

Control of the coarse aggregates and fine aggregates going into the concrete.

Mixing of the concrete.

Transport of the concrete to the construction site.

Slump of the concrete.

Pouring of the concrete.

Control of water addition.

Vibration/Compaction of the concrete.

Preparation of areas where different concrete pours are done.

Control of compression test samples

Control of formwork removal.

Where does quality control begin?

It begins in the production of material used in concrete ( Sampling and Testing):

Portland Cement

Pozzolana

Coarse and Fine Aggregate

Uniformity of concrete production will be no greater than the uniformity of materials used in the concrete.4

How does quality control continue?

Handling and stockpiling

Batching and Mixing

Sampling and testing fresh concrete

Slump

Air Content

Unit weight

Temperature

Transporting and placing the freshly mixed concrete.

To know the quality of concrete,

We can do the several tests.

(1)Tests on Fresh Concrete

a)The Slump test

b)The Compacting Factor Test

(2)Tests on Hardened Concrete

a)Compression Test

b)Tensile Strength Test(Split Cylinder Test)

c) Flexural Strength Test

5

(1)Tests on Fresh Concrete

(a)The Slump TestThe mound for the slump test has the shape of frustum of a cone, 300mm high, The

Diameter of the base is 200 mm and at the top is 100mm.

If the slump is:

25-50 =Low Workability

50-100 =Medium Workability

100-150 = High Workability

6

(b) The Compacting Factor Test

Compacting factor is less than 0.75 = low workability concrete.

Compacting factor is less than 0.92 = High workabilityconcrete.

Compacting Factor Machine

7

(2)Tests on Fresh Concrete

(a)Compression Test

To determine the characteristic strength of the concrete. Size of concrete cylinder is 150mm

dia 300mm long.

Compression test of concrete Cylinder

(b)Tensile Strength Test (Split Cylinder Test)

When the cylinder split the tensile strength of concrete is determined.

8

(c) Flexural Strength Test

Test to determine the tensile strength of concrete in flexure have been largely

superseded by the indirect tensile strength test, although it is still specified occasionally on

pavement and other similar projects where the strength of concrete in flexure, or bending,

is of prime importance.

9

Material Used in Concrete

1) Cement

2) Water

3) Aggregate

4) Admixture

(1) Cement

A mixture of compounds made by burning limestone and clay together at very high temperature ragging

from 1400 ®C to 1500 ®Cather production of Portland Cement begins with the quarrying of limestone.CaCO3.Then Mixed

with Clay(or Shale),sand and iron ore and ground together to form a homogenous powder.

(2) Water

Water is the key ingredient. When water mixed with a cement, forms a paste that binds the aggregates

together. water causes the hardening of concrete through process call hydration.The water needs to be pure in order to

prevent side reaction from occurring which may weaken the concrete or otherwise interfere with hydration process.The

ratio of cement and water is the most critical factor in the production of ‘perfect’ concrete. Too much water can reduces

concrete strength but high workability.Too little water will make the concrete unworkable but high strength.

10

(3) Aggregate

Chemically inert, solid bodies, held together by the cement. Come in various shapes, sizes and material

ranging from fine particles of sand to large, coarse rock. Soft, porous aggregate can result in weak concrete with low wear

resistance. Hard aggregate can make strong concrete with high resistance to abrasion Should be clean, Hard and strong,

Usually washed to remove any Dust, Silt, Clay, Organic matter.

(4) Admixtures

A material ,other than aggregate ,cement and water added in small quantities to the mix in order to

produce some desired modification, either to the physical or chemical properties of the mix or of the hardened product.

The most common admixture affect plasticity, air entrainment and curing time.

11

• Formwork (shuttering) in concrete construction

is used as a mold for a structure in which fresh

concrete is poured only to harden subsequently.

• The construction of formwork takes time and

involves expenditure up to 20 to 25% of the cost of

the structure or even more. The design of these

temporary structures are made to economic

expenditure. The operation of removing the

formwork is known as stripping. Stripped formwork

can be reused. Reusable forms are known as panel

forms and non-usable are called stationary forms.

Requirements of Good Formwork

• It should be strong enough to withstand all types of dead and live

loads.

• It should be rigidly constructed and efficiently propped and braced both

horizontally and vertically, to retain its shape.

• The joints in the formwork should be tight against leakage of cement

grout.

• Construction of formwork should permit removal of various parts in

desired sequences without damage to the concrete.

• The material of the formwork should be cheap, readily available, and

should be suitable for reuse.

• The formwork should be set accurately to the desired line, and levels

should have a plane surface.

• It should be as light as possible.

• The material of the formwork should not warp or get distorted when

exposed to the elements.

• It should rest on a firm base.

Types of Formwork (Shuttering)

1. Timber FormworkTimber for formwork should satisfy the following requirement:

It should be:

• Well-seasoned

• Light in weight

• Easily workable with nails without splitting

• Free from loose knots

Timber used for shuttering for exposed concrete work should have smooth and even surface on all faces which come in contact with

concrete.

2. Plywood Formwork

Resin-bonded plywood sheets are attached to timber frames to make up panels of the required sizes. The cost of plywood formwork

compares favorably with that of timber shuttering, and it may even prove cheaper in some instances given the following

considerations:

• It is possible to have a smooth finish in which case on cost in surface finishing is there.

• By the use of large-size panels, it is possible to affect saving in the labor cost of fixing and dismantling.

• The number of reuses are more as compared with timber shuttering. For estimation purposes, the number of reuses can be taken

as 20 to 25.

3. Steel Formwork

• This consists of panels fabricated out of thin steel plates stiffened along the edges by small steel angles. The panel units can be

held together through the use of suitable clamps or bolts and nuts.

• The panels can be fabricated in large numbers in any desired modular shape or size. Steel forms are largely used in large projects

or in a situation where large number reuses of the shuttering is possible. This type of shutter is considered most suitable for circular

or curved structures.

Walls, columns and vertical sides of beams

1 to 2 days

1)

Slabs (props left under) 3 days

2)

Beam soffits (props left under) 7 days

3)

Removal of props to slabs

(a) For slabs spanning upto 4.5 m

7 days

(b) For slabs spanning over 4.5 m

14 days

4Walls, columns and vertical sides of beams

1 to 2 days

THANK YOU

16

Unit-5Extreme weather concreting &

chemical Admixture in concrete

Hot Weather Concreting

As per BUREAU OF INDIAN STANDARDS IS:7861(Part I), “ Any operation of concreting done at atmospheric temperatures above 40 degree Celsius or any operation of concreting ( other than steam curing) where the temperature of concrete at time of its placement is expected to be beyond 40 degree Celsius is termed as HOT WEATHER CONCRETING”.

Cold Weather Concreting

“Cold weather” as a period of three or more successive days during which the average daily outdoor temperature drops below 40 degrees F (4 degrees C).

Problems associated with cold-weather concreting are freezing of concrete at an early age; lack of required strength; improper curing procedures; rapid temperature changes; and improper protection of the structure consistent with its serviceability.

Admixture

Chemical admixtures are the ingredients in concrete other than portland cement, water, and aggregate

that are added to the mix immediately before or during mixing

admixtures primarily used to reduce the cost of concrete construction; to modify the properties of

hardened concrete; to ensure the quality of concrete during mixing, transporting, placing, and curing;

and to overcome certain emergencies during concrete operations.

There are five distinct classes of chemical admixtures: air-entraining, water-reducing, retarding,

accelerating, and plasticizers (superplasticizers).

1) Water-reducing admixtures –

usually reduce the required water content for a concrete mixture by about 5 to 10 percent.

Consequently, concrete containing a water-reducing admixture needs less water to reach a required

slump than untreated concrete.

The treated concrete can have a lower water-cement ratio. This usually indicates that a higher strength

concrete can be produced without increasing the amount of cement.

2) Retarding admixtures –

It slow the setting rate of concrete, are used to counteract the accelerating

effect of hot weather on concrete setting.

High temperatures often cause an increased rate of hardening which

makes placing and finishing difficult. Retarders keep concrete workable

during placement and delay the initial set of concrete.

Most retarders also function as water reducers and may entrain some air in

concrete.

3) Accelerating admixtures

It increase the rate of early strength development, reduce the time required

for proper curing and protection, and speed up the start of finishing

operations.

Accelerating admixtures are especially useful for modifying the properties

of concrete in cold weather.

4) Superplasticizers –

It is also known as plasticizers or high-range water reducers (HRWR), reduce

water content by 12 to 30 percent and can be added to concrete with a low-to-

normal slump and water-cement ratio to make high-slump flowing concrete.

Flowing concrete is a highly fluid but workable concrete that can be placed with

little or no vibration or compaction. The effect of superplasticizers lasts only 30

to 60 minutes, depending on the brand and dosage rate, and is followed by a

rapid loss in workability. As a result of the slump loss, superplasticizers are

usually added to concrete at the jobsite.

Unit-6

Properties of Special Concrete

1) Ready Mix Concrete

• Ready Mixed Concrete also is known as RMC, is the concrete which is delivered in a ready-to-use manner.

• Ready Mixed Concrete is a tailor – made concrete that is manufactured in a factory or within a batching plant based on the

standard required specifications. The prepared concrete mix is then taken to the work site within transit mixers mounted over a truck.

Advantages of Ready-Mix Concrete

• Better quality concrete is produced as it is made from consistent methods and in advanced equipment.

• No need to store construction materials at the site.

• Labour associated with the production of concrete is eliminated, thereby reducing labour cost.

• Air and Noise pollution at the job site is reduced.

• Wastage of basic materials at the site is avoided.

• Reduce the time required for construction.

• No delays in completing major projects like constructing dams, roads, bridges, tunnels, etc.

• Economy in the use of raw materials results in conservation of natural resources.

Disadvantages of Ready-Mix Concrete

• Requires huge initial investment.

• Not suitable for small projects (less quantity of concrete is required).

• Need an effective transportation system from the batching plant to the job site.

• Labour should be ready at the site to cast the concrete in position without any delay to avoid slumps in the mixture.

• Concrete has limited time and should be used within 210 minutes of batching the plant. Traffic jam or breakdown of

the vehicle can create a problem.

2) Reinforced Concrete

• Reinforced concrete, concrete in which steel is embedded in such a manner that the two materials act together in resisting forces. The reinforcing steel—rods, bars, or mesh—absorbs the tensile, shear, and sometimes the compressive stresses in a concrete structure. Plain concrete does not easily withstand tensile and shear stresses caused by wind, earthquakes, vibrations, and other forces and is therefore unsuitable in most structural applications. In reinforced concrete, the tensile strength of steel and the compressive strength of concrete work together to allow the member to sustain these stresses over considerable spans.

Advantages of Reinforced Concrete

• Reinforced concrete has a high compressive strength compared to other building materials.

• Due to the provided reinforcement, reinforced concrete can also withstand a good amount tensile stress.

• Fire and weather resistance of reinforced concrete is fair.

• The reinforced concrete building system is more durable than any other building system.

• Reinforced concrete, as a fluid material, in the beginning, can be economically molded into a nearly limitless range of shapes.

• The maintenance cost of reinforced concrete is very low.

Disadvantages of Reinforced Concrete

• The tensile strength of reinforced concrete is about one-tenth of its compressive strength.

• No Scrap Value.

• The cost of the forms used for casting is relatively higher.

• Shrinkage causes crack development and strength loss.

3) Prestressed Concrete

• Pre-stressed concrete is a form of concrete where initial compression is given in the concrete before applying the

external load so that stress from external loads are

counteracted in the desired way during the service period.

This initial compression is introduced by high strength

steel wire or alloys (called ‘tendon’) located in the concrete section.

Advantages of Prestressed Concrete

• Longer span length increases untroubled floor space and parking facilities.

• Thinner slabs, that are important for high rise building as with the same amount of cost, it can construct more slabs than traditional thicker slabs.

• As the span length is larger, fewer joints are needed than traditional RC structures.

• Because of fewer joints, maintenance cost also becomes reduced during the design life as joints are the major locus of weakness in a concrete building.

• Long-term Durability.

• Better finishing of placed concrete.

• It requires a smaller amount of construction materials.

• It resists stresses are higher than normal RCC structures and is free from cracks.

https://civiltoday.com/civil-engineering-materials/concrete/270-concrete-definition-components-types

Disadvantages of Prestressed Concrete

Followings are the disadvantages of prestressed

concrete:

• It requires high strength concrete and high tensile strength steel wires.

• The main disadvantage is construction requires additional special equipment like jacks, anchorage, etc.

• It requires highly skilled workers under skilled supervision.

• Construction cost is little higher than RCC structures.

https://civiltoday.com/civil-engineering-materials/steel

4) Precast Concrete• The form of construction where concrete is casted in a re-usable mould and then cured in a controlled environment

(precast plant) is called precast concrete. The casted structural member is then transported to the construction site and then erected.

Advantages of Precast Concrete

• Saves Construction Time: Precast Concrete construction saves time, the risk of project delay is also less. The precast concrete casting can be carried on simultaneously with other works on site such as earthwork, survey, etc. and thus saves time.

• Quality Assurance: The key factors which regulate the quality of construction such as curing, temperature, mix design, formwork, etc. can be monitored for Precast Concrete. So, improved quality construction can be performed.

• Usage of Prestressed Concrete: By using pre-stressed precast, structural materials of high strength and load-bearing capacity can be achieved, which can result in greater clear span, reduced size of the cross-section of structural members, etc.

• Cost-effective: The simplified construction process reduces the time, increases the productivity, quality and safety and thus the cost is reduced.

• Durability: Precast Concrete structure has a longer service time period and minimal maintenance. The high-density Precast Concrete is more durable to acid attack, corrosion, impact, reduces surface voids and resists the accumulation of dust.

• Aesthetics: As the structures are prefabricated in a controlled factory environment, several combinations of colors and textures can be used. A wide range of shapes and sizes are available to choose from with smooth finishing and thus the aesthetical value of products are increased.

https://civiltoday.com/surveying/13-definition-and-importance-of-surveyinghttps://civiltoday.com/civil-engineering-materials/concrete/270-concrete-definition-components-types

Disadvantages of Precast Concrete

• There are some disadvantages to precast concrete.They are discussed below.

• High Initial Investment: For installing a Precast Concrete plant, heavy and sophisticated machines are necessary which requires a high initial investment. A large scale of precast construction projects must be available to ensure sufficient profit.

• Transportation Issue: The construction site can be at a distant location from the Precast Concrete plant. In that case, the precast members must be carried to the site using trailers. In many cases, the reduced costs of Precast Concrete is compensated by the transportation cost.

• Handling Difficulties: Proper care and precaution have to be taken for handling precast concrete. Usually, precast members are heavy and large which makes it difficult to handle without damage. Generally, portable or tower cranes are used to handle precast members.

• Modification: Limitation In case of precast structures, it is difficult to modify the structure. For example, if a structural wall is to be dismantled for modification it will impact the overall stability of the structure.

5) High performance Concrete

• High performance concrete is defined as “A concrete which meets special performance and uniformity requirements that cannot a lways be achieved routinely by using only conventional materials and normal mixing, placing and curing practices”.

Advantages of High Performance Concrete

• Ease of placement and consolidation without influencing strength.

• Reduce the size of structural members which lead to the increase of usable area. Consequently, concrete volume is cut.

• The size of structural members like beams and columns are reduced since smaller sections are enough to carry high loads.

• Reduction in the thickness of floor slabs and supporting beam sections which are a major component of the weight and cost of the majority of structures.

• Increase life span of the structure in severe environments

• Superior long-term service performance under static, dynamic and fatigue loading.

• Low creep and shrinkage.

• Greater stiffness as a result of a higher modulus.

• High resistance to freezing and thawing, chemical attack, significantly improve long-term durability, and crack propagation.

• Reduced maintenance and repairs.