CONCRETE WORKS IN HIGHWAY ENGINEERING

Er. S. Karthigeyan, Deputy Director – III, HRSEr.P.Elango, Assistant Director, Concrete Lab, HRS

IntroductionConcrete has been used as a construction material in largest quantity for several decades

due to its excellent engineering properties and also due to the economy of this material. Except

for cement all the other ingredients can be used from the locally available resources.

When properly prepared its strength is almost equal to the strength of naturally

occurring hard stone.

The properties of concrete making materials influence the properties of concrete both in

the fresh state as well as in the hardened state. Hence proper care should be taken in selecting

the concrete making materials.

Ingredients of Concrete

The basic ingredients of concrete are cement, fine aggregate (sand), coarse aggregate

and water. Sometimes admixture is also used in order to alter one or more of the specific

properties of concrete such as increasing the workability, reducing the water cement ratio, etc.

Cement 14 - 21 %

Water 7- 15 %

Coarse Aggregate 40 – 50 %Fine

Aggregate 20 – 30 %

1

I. Cement

According to the Strength, cement is classified in to 3 grades namely

(1) 33 Grade.

(2) 43 Grade.

(3) 53 Grade.

33 Grade means strength of 1:3 cement mortar cubes at the end of 28 days is between

33 to 43 N/mm2 (33 Mpa).

43 Grade means strength of mortar cube at the end of 28 days is between 43 and 53 N/

mm2 (43 MPa).

53 Grade means strength of cement mortar cube at the end of 28 days of cement mortar

cube is above 53 N/ mm2 (53 MPa).

Tests on cement

The following are the five basic tests for cement:

1. Consistency test.

2. Initial setting time and final setting time.

3. Soundness test.

4. Fineness test.

5. Compressive strength.

1. Consistency Test

Figure 1: Vicat apparatus with Plunger

2

It is necessary to determine for any cement, the water content which will produce a

paste of standard consistency. This is determined using Vicat's apparatus. For a standard

penetration of 10 mm. diameter plunger under its own weight the water content required is

determined. For a penetration of about 5-7 mm from the bottom of the mould the amount of

water used gives the standard consistency.

2. Initial setting time and final setting time

This is the term used to describe the stiffening of cement paste and it refers to a change

from fluid to a rigid state. It is customary to talk about initial setting which is basically the

beginning of the stiffening and final setting is marked by the disappearance of plasticity. The

setting process should not too early, because of freshly mixed concrete should remain in

plastic condition for a sufficient period to permit satisfactory compaction and finishing after

transporting and placing of concrete. On the other hand too long a setting process is also

undesirable because this will cause a delay in strength development after finishing.

For finding out the initial setting time, the plunger in the Vicat apparatus is replaced by

1 mm diameter needle. The water to be added to the cement is 0.85 times to the standards

consistency. The time when the penetration of the needle is 5 mm from the bottom plate from

the time of addition of water is initial setting time, which shall not be less than 30 minutes.

The needle is replaced by annular arrangement. Initially when the annular arrangement

is getting applied on the surface of the cement paste, a circle and dot is seen on top of the

cement paste in the mould. But later on the circle disappears and only the dot is seen on the

surface and at that stage final setting is said to have occurred. The final setting time is from the

time of water is added to the cement till the appearance of dot only, which shall not be more

than 600 minutes (10 hours).

3

Figure 2: Needle for final Setting time

3. Soundness Test

Unsoundness is the harmful property that occurs when the hardened cement paste

develops and undue expansion that is manifested by cracking of the mass. The usual cause of

unsoundness is the presence of over burned free or uncombined lime and excess quantities of

crystalline magnesia. This may cause disintegration of the hardened paste or concrete.

The apparatus used is Le- Chatlier Apparatus. The water required for this test is 0.78

times of consistency of cement. After filling the Le-Chatlier mould with the cement paste, it

has to be kept in water for 24 hours. Then initial reading between the two needles to be

measured. This arrangement is kept in boiling water for 3 hours. Then the arrangement should

be removed from boiling water and the final reading between the 2 needles to be measured.

The difference between the final and initial reading is the expansion, which shall not be

more than 10 mm.

Figure 3: Le – Chatlier Apparatus

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4. Fineness Test

The term fineness refers to average size of the cement particles. A higher fineness

means a more finely ground cement. The significance of fineness lies in the fact it affects

several technically important properties of cement and concrete. For instance, the higher the

fineness the higher the strengths are developed at earlier ages. Also finer cement bleeds less,

contributes better workability and less expansion.

The apparatus used for this test is Blaine's Air Permeability Apparatus. After

calibrating the permeability cell by mercury displacement method, the weight of the sample

required for this test shall be determined. Using the standard cement of known porosity, the

time taken for the air to push the liquid in the U tube from two levels shall be measured (Ts).

The same weight of the test sample is taken and the test is repeated (T). From the formula

given below this specific surface of the cement can be determined.

S =

Ss T

Ts

Where,

S - Specific surface area in sq.cm per gram of test sample.

Ss - Specific surface area in sq.cm per gram of standard sample used

in calibration of Apparatus.(3020 sq cm/gm)

T - Measured time interval in second for test sample

Ts - Measured time interval in seconds for standard sample.

The requirement for fineness is not less than 225 sq m /kg.

5

Figure 4: Blaine Air Permeability apparatus

5. Compressive Strength

The Strength developing ability of a cement is its most sought after property because

concrete is a construction material. The hardening of the cement paste is the result of the

cement hydration, the subsequent development of bonds in the hydration process and gradual

reduction of the internal porosity.

The compressive strength of cement is determined by preparing cement mortar cubes

using cement and standard sand (Ennore sand) in the ratio of 1 : 3, ie. 200 gms of cement and

600 gms of standard sand. (l/3 in each size of sand). Water to be calculated from the formula,

P/4+3% (Percentage for total mortar of 800 gms), where P is the consistency of cement

Requirements as per Indian Standards:

Table 1: Compressive Strength of cement

Age33 Grade

IS 269 - 2015

43 Grade

IS 8112 - 2013

53 Grade

IS 12269 - 2013

3 Days 16 MPa 23 MPa 27 MPa

7 Days 22 MPa 33 MPa 37 MPa

28 Days 33 Mpa 43 MPa 53 MPa

6

Figure 5: Compression testing machine

II. Aggregates

Coarse Aggregates

Aggregates out of which 90% retained on IS: 4.75 mm sieve are termed as coarse

aggregates. Generally HBG (Hard Blue Granite) is used as coarse aggregate.

Fine Aggregates

Aggregates out of which 90% is passing through IS: 4.75mm sieve are termed as fine

aggregates. Sand is used as fine aggregate.

According to grading, aggregates are classified into graded aggregate and single size

aggregate. A graded aggregate is one which comprises different fractions of all size ranges.

A single size aggregate is one, which comprises particles falling essentially within a

narrow limit of size fractions.

Fine aggregate should comply with the requirements of any grading zone given in IS:

383 - 2016.

Sieve analysis is done to determine the particle size distribution of the fine and coarse

aggregates (IS: 2386, Part-I). The sample is either prepared by quartering or by using a sample

divider. On completion of sieving the materials retained on each sieve shall be weighed.

7

As per IS: 383 the grading for sand is divided into four zones, zone-I to zone-IV.

Generally Zones-I to III are preferred and aggregate conforming to Grading zone-IV should

not be used in RCC, unless tests have been made to ascertain the suitability of proposed mix

proportions.

Table 2: Fine Aggregate Grading Requirement

Sieve Size Zone – I Zone – II Zone – III Zone – IV

10 mm 100 100 100 100

4.75 mm 90 – 100 90 – 100 90 – 100 95 – 100

2.36 mm 60 – 95 75 – 100 85 – 100 95 – 100

1.18 mm 30 – 70 55 – 90 75 – 100 90 – 100

600 micron 15 – 34 35 – 39 60 – 79 80 – 100

300 micron 5 – 20 8 – 30 12 – 40 15 – 50

150 micron 0 – 10 0 – 10 0 – 10 0 – 15

Size of Coarse Aggregate

The nominal maximum size of coarse aggregate should be as large as possible within

the limits specified but in no case greater than one-fourth of the minimum thickness of the

member. For example, if the thickness of c.c. pavement is 100 mm the maximum size of

aggregate shall be 25 mm.

For heavily reinforced members the maximum size of the aggregate should usually be

restricted to 5 mm less than the minimum clear distance between the main bars or 5 mm less

than the minimum cover to the reinforcement, whichever is smaller.

The grading of coarse aggregate shall be within the limits given in IS: 383-2016.

Table 3: For 40 mm Nominal Size of aggregate

IS Sieve Designation Percentage Passing

80 mm 100

40 mm 90 - 100

20 mm 30 – 70

10 mm 10 – 35

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4.75 mm 0 - 5

Table 4: For 20 mm Nominal Size of aggregate

IS Sieve Designation Percentage Passing

40 mm 100

20 mm 90 - 100

10 mm 25 – 55

4.75 mm 0 – 10

Table 5: For 12.5 mm Nominal Size of aggregate

IS Sieve Designation Percentage Passing

20 mm 100

12.5 mm 90 – 100

10 mm 40 – 85

4.75 mm 0 – 10

Tests on Coarse Aggregate

1. Aggregate Crushing Value: - IS: 2386 (Part-IV)-1963

This test gives a relative measure of the resistance of the aggregate to crushing under

gradually, applied compressive load.

The sample taken shall be 12.5 mm passing and 10 mm retained. The standard cylinder

is filled in three layers with 25 times tamping for each layer. The sample in the cylinder is

weighed. In the compression testing machine the load is applied at the rate of 4 T per minute

and on reaching a maximum load of 40 T the aggregates is removed and sieved in IS: 2.36 mm

sieve. The fraction passing is weighed and it should not be more than 45% for surfaces, other

than wearing surface and not more than 30% for wearing surfaces.

2. Aggregate Impact Value: - IS: 2386 (Part-IV) -1963

It gives a relative measure of the resistance of the aggregate to sudden shock or impact.

Aggregate passing through IS: 12.5 mm and retained on 10 mm sieve is taken. The mould of

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the impact testing machine is filled in 3 layers with 25 times tamping for each layer. The test

sample is then subjected to 15 blows with the standard hammer. The aggregate is removed and

sieved through IS: 2.36 mm sieve. The maximum passing shall not be more than 45% for

surfaces other than wearing surfaces and not more than 30 % for wearing surfaces.

3. Los Angeles Abrasion Value: - IS: 2386 (Part-IV) 1963

Abrasion is an important consideration especially for concretes exposed to wearing

actions.

In the Los Angeles Abrasion testing machine the sample is placed and rotated at a speed

of 20 to 33 rev/min with a charge of steel balls (48 mm dia and weighing about 390 to 448 g)

for 500 revolutions. The sample weighing 5 kg is taken in the following manner:-

Table 6: Clause 5.3.2

Passing Retaining

Sample to be taken in grams

A40 mm

B20 mm

40 mm 25 mm 1250 -25 mm 20 mm 1250 -20 mm 12.5 mm 1250 2500

12.5 mm 10 mm 1250 2500

The sample is taken out and sieved through IS: l.7 mm sieve and the amount passing

shall not be more than 30% for wearing surfaces and not more than 50% for surfaces other

than wearing surfaces.

4. Flakiness Index

About 5 kg of the sample is taken and passed through the Flakiness Index Gauge meant

for testing the Flakiness Index. As per MORTH specifications the amount passing through it

should not be more than 35%.

5. Soundness

In this test the aggregates subjected alternatively to immersion in sulphate solution and

to drying. This causes disruption of the particles due to the pressure generated by the

formation of salt crystals. The degree of unsoundness is expressed by the reduction in the

particle size after a specified number of cycles. Other tests include subjecting it to freezing

and thawing.

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However the conditions of all these tests do not really represent those when the

aggregate is influenced by the presence of the surrounding cement paste. Only a service

record can satisfactorily prove the durability of any aggregate.

III. WATER

The quality of the water used for mixing is very important because it may interfere with

the setting time of cement, adversely affect the strength of concrete or may lead to corrosion

of reinforcement.

Most of the specifications say that the quality of water should be of that water which is

fit for drinking. But there is no absolute criterion of portability of water.

As a rule any water with a PH (Degree of acidity) of 6.0 to 8.0 and which does not taste

saline is suitable for use.

Test on Water

Compare setting time of cement and strength of mortar cubes using the water in

question with corresponding results obtained using good or distilled water. If there is no

appreciable difference between the behavior of mortar cubes made using distilled water and

the water in question, then the water can be safely used. A tolerance of 10% for variations in

strength is allowed. If need be, water to be tested for chlorides and sulphates content as per

IS: 3025.

IV. Steel Reinforcement for Concrete Structures

Two types of steel are used in Concrete structures

1. Mild Steel as per IS: 432-Part- l -1982

2. HYSD (High yield strength deformed bars) as per IS: 1786 - 2008.

HYSD bars satisfy the requirements for diameter and percentage elongation as per

Clause-6, 7 of IS - 1786.

Generally Fe 415 is used which has a yield strength of 415 N./mm2

Selection of Test Specimens:

For checking nominal mass, tensile strength, bend test and rebound test, test specimen

of sufficient length shall be cut from each size of the finished bar / wire at random at a

frequency not less than specified in Table-1,2,3,4 0f IS:1786 -2008.

The yield strength of mild steel is only half of that of HYSD bars, hence HYSD bars are

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predominantly used.

It is mandatory to test the steel used for reinforcement. Generally Fe 415 is available in

market but Fe 500 and Fe 550 are also available, to be specially ordered which come with a

single and double star respectively for every metre.

The standard length of the rods purchased from reputed firms like TISCO, ISCO, SAIL

come in 12 m (40') lengths whereas local rolling mills produce in lengths of 11 m (36') only.

The nominal diameter of the bar is to be determined by weighing 1 m cut length of

the bar and finding out the equivalent diameter of a circular bar of same length and not by

using calipers. As per Table-1900-3 of MORTH Specifications for Roads and Bridges,

anticorrosive treatment has to be given for steel reinforcement to be used in coastal areas (15

km from coast line). Adequate extra cover should be given to reinforcement for protection

against corrosion. Cover may be provided as per Clause 25.4 of IS: 456 Pre stressing steel wire

should conform to IS: 1785 (Parts-1 and 11)-1983.

Table 7: Properties of Steel bars

Properties Fe 415 Fe 415 D Fe 500 Fe 500 D

0.2 % Proof Stress Minimum (Mpa) 415 415 500 500

Tensile Strength Minimum (Mpa) 485 500 545 565

Elongation Precentage Minimum (Mpa) 14.5 18 12 16

Admixtures

Admixtures are materials, added to Concrete, to modify the properties; either in the

fresh state immediately after mixing or after the mix has hardened. Admixtures have become

one of the essential components of Concrete in recent years. Admixtures are broadly classified

as Chemical Admixtures and Mineral Admixtures.

Chemical Admixtures:

Chemical Admixtures are organic or inorganic compounds in the form of liquid used for

one or more of the following functions:

Accelerate or retard the initial setting time of fresh concrete mix

Increase workability without increasing water content of concrete

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Decrease the water content at the same workability

Reduce the rate of Slump loss

Improve pumpability of the mix

Reduce segregation of constituents of concrete

Inhibit corrosion of embedded steel reinforcement

Based on the usage in concrete, chemical admixtures are classified as :

Accelerators

Retarders

Plasticizers

Super plasticizers

Accelerators:

Accelerating admixtures are added to concrete either to increase the rate of early

strength development or to shorten the time of setting, or both. Chemical composition of

accelerators includes some of inorganic compounds such as soluble chlorides, carbonates and

silicates.

Retarders:

Retarders are admixtures which delay the setting time of concrete. Retarders are useful

for concreting in hot weather, when normal setting time is shortened by the high temperature,

and in preventing the formation of cold joints between successive layers in mass concrete. A

retarder dosage of 0.05 % by weight of cement leads to 4 hours retardation.

Plasticizers:

Plasticizer generally reduces the required water content of a concrete mixture for a

given slump. These admixtures disperse the cement particles in concrete and make more

efficient use of cement. This increases strength or allows the cement content to be reduced

while maintaining the same strength.

Superplasticizers:

Superplasticizers or High range water reducers are most widely used chemical

admixtures in concrete. They allow water reduction in the range of 15 % to 20 % in concrete

mix. They also help in producing high workable concrete and retarding the same for longer

time without affecting the setting time and strength gain process of the concrete.

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Figure 6: Superplasticizers

Mineral Admixtures for Concrete:

Fly ash

Fly ash is a by-product obtained during the combustion of pulverized coal in thermal

power plants. The main constituent of fly ash is silica. Non crystalline forms of silica, alumina

and iron present in the in fly ash are principally responsible for the pozzolanic reaction with

calcium hydroxide which results from the hydration of Portland cement. Fly ash increase long-

term strength, improves durability, decrease permeability and reduce alkali-aggregate

expansion of hardened concrete. Properties of cement blended with Fly ash @ 25% by mass

have already been tested and has been recommended for adoption by Bureau of Indian

Standards.

Ground Granulated Blast furnace Slag (GGBS):

GGBS is produced as a by-product during the manufacture of iron in a blast furnace.

Calcium oxide and Silicon dioxide are the major constituents of GGBS. Concrete with GGBS

gains strength more slowly, tending to have lower strength at early stages and higher strength

at later stages.

Silica Fume:

Silica fume is a very fine non-crystalline powder obtained as a by-product from silicon

metal production industries. Silicon dioxide is the reactive material in Silica Fume. Adding

Silica fume brings millions of very small particles to concrete mixture. Silica fume fill in the

spaces between cement grains similar to fine aggregates fills in the spaces between coarse

aggregates. Even if Silica fume does not react chemically, the micro filler effect would bring

significant improvements in the nature of concrete.

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V. Concrete

Concrete is a versatile materials which is widely used for construction works. As

already described, the ingredients of concrete are cement, sand as fine aggregate and metal as

coarse aggregate mixed uniformly by addition of water. The hardness of concrete is depending

upon hydration process, which starts as soon as water is added to the mixture of cement, sand

and metal. Concrete mixes are produced to have the desired properties in the fresh and

hardened states as the situation demands.

Influences of Materials and mix proportions

Aggregates occupy nearly 70 to 75% of the total volume of concrete. The total surface

area of the aggregate is to be minimized to the extent possible by the proper choice of size,

shape and proportion of fine and coarse aggregate. Different size of fractions is to be so

chosen as to minimize the voids content. To mobilize such mixture water is needed for

lubricating effects. The requirements of workability are such that there should be enough

cement paste to surround the aggregate particles as well as to fill the voids in the aggregates.

The water content of the mix is the primary factor governing the workability of fresh concrete.

The workability increases with the water content.

For the same volume of aggregates in the concrete, use of coarse aggregates of larger

size gives higher workability because of reduction in the total specific surface area. Use of

flaky and elongated aggregates will result in low workability primarily because of increase in

particle interference.

The use of fine sand with corresponding increase in specific surface area increases the

water demand.

Table 1700-7, MORTH (Fifth Revision)

ComponentsMaximum Nominal Size of

Coarse Aggregates(mm)

1. RCC Well Curb The size (maximum nominal) of coarse

aggregates for concrete to be used in various components

20

2. RCC / PCC Well Steining 40

3. Well Cap or Pile Cap, solid type

Piers and Abutments

40

15

4. RCC work in girders, slabs, wearing coat, kerb, approach

slab, hollow piers, abutments, pier / abutments caps,

piles etc.,

20

5. PSC Work 20

6. Any other items As specified by Engineers.

Workability

The concrete should have workability such that it can be placed in toe formwork and

compacted with minimum effort without causing segregation or bleeding. The choice of

workability depends upon the size of the section and the concentration of reinforcement. The

aim should be to have the minimum possible workability consistent with satisfactory placing

and compaction of concrete. It should be remembered that insufficient workability resulting in

incomplete compaction, will severely affect the strength, durability and surface finish of

concrete.

Compressive Strength

The compressive strength of hardened concrete is considered to be the most important

property and can be measured on standard size cube,

i.e., 150 mm x 150 mm x 150 mm. It can be taken as an index of overall quality of

concrete.

Among the materials and mix variables, water/cement ratio is the most important

parameter governing Compressive strength. Besides water/cement ratio, the following factors

also affect the compressive strength of concrete:

The characteristics of cement

Characteristics and proportions of aggregates.

Degree of compaction

Efficiency of Curing.

Age at the time of testing for mix proportion and placing.

Water/Cement Ratio

Most of the desirable properties of hardened concrete depend primarily upon the quality

of the cement paste. Hence the first step in proportioning mix design should be the selection of

the appropriate water/cement ratio.

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Within the normal range of strengths, compressive strength is nearly inversely related to

the water / cement ratio.

Some of the advantages of reducing the water/ cement ratio

are as follows:-

1. Increased compressive strength / flexural strength.

2. Increased denseness.

3. Reduced porosity.

4. Increased water tightness.

5. Lower absorption.

6. Increased resistance to weathering.

7. Better bond between successive layers.

8. Better bond between concrete and reinforcement.

9. Less volume change from wetting and drying.

Aggregate-Cement Ratio

As long as the workability is maintained at a satisfactory level, the compressive strength of

concrete had been found to increase with the increase in aggregate cement ratio.

Cement Content

Generally, the cement content itself would not have a direct role on the strength of

concrete. If cement content is required to increase the workability of concrete for a given

water/cement ratio, then the compressive strength may increase with the richness of the mix.

However, for a particular water / cement ratio, there would be an optimum cement content

resulting 28 days compressive strength being the highest. Increasing the cement content above

the optimum value may not increase the strength.

Effect of Age of Testing

Concrete is generally tested for its compressive strength at the age of 28 days. Because

of continuing hydration, the later age strength would generally be higher than at 28 days,

however, the exact increase will depend upon the type of cement, mix composition and the

extent of curing. The mix proportions themselves influence the rate of gain of strength, in that

concrete with lower water/cement ratio tends to attain high initial strength and therefore

further gain in strength at later ages is proportionately smaller than with high water / cement

ratio.

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Effect of placing, compaction and curing

The concrete should be placed in its final position in the formwork as early as possible

after the completion of mixing, so that there is no drying out of the mix, and the mix is

workable enough to receive the compaction. Dropping of concrete from great heights may lead

to segregation and entrainment of air bubbles displacement of reinforcement and damage the

already placed concrete. It is preferable to pour the concrete from a height of 1m.

When the fresh concrete is compacted by vibration, the particles are set in motion

reducing inter-particle friction so that concrete is easily placed. Vibration eliminates most air

pockets on the surface of the concrete. The presence of 5% voids in the hardened concrete left

due to incomplete compaction may result in decrease in compressive strength by about 35%.

The hydration of cement can take place only when the capillary Pores remain

saturated. The additional water available from outside is needed to fill the gel-pores which

will otherwise make the capillary empty. The function of curing is to prevent the loss of water

in the concrete from evaporation, normally done by covering with wet gunny bags,

membrane, curing compounds and continuous pounding of water. Concrete will continue to

gain strength with time provided the sufficient moisture is available for hydration of cement

which can be assured by proper moist curing.

Structural Concrete

Structural Concrete is classified based on the grade of concrete as follows

Nominal Mix Concrete:

M15, M20

Standard Concrete:

M15, M20, M25, M30, M35, M40, M45, M50

High Performance Concrete:

M30, M35, M40, M45, M50, M55, M60, M65, M70, M75, M80, M85, M90

Nominal Mix Concrete

Nominal Mix Concrete is made on the basis of nominal mix proportioned by weight of

its main ingredients – cement, coarse aggregate, fine aggregate and water.

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Table 1700-6, MORTH (Fifth Revision)

Proportions for Nominal Mix Concrete

Grade of

Concrete

Total Quality of Dry Aggregate by Mass by 50 kg

of cement to be taken as the sum of individuals

masses of fine and coarse aggregates (kg)

Proportions of fine and

coarse aggregates (By

mass)

M-15 350

Generally 1 : 2

Subject to upper limit 1 : 1.5

and lower limit of

1 : 2.5

M-20 250

Generally 1 : 2

Subject to upper limit 1 : 1.5

and lower limit of

1 : 2.5

Standard Concrete

Standard Concrete is made on the basis of design mix proportioned by weight of its

ingredients, which in addition to cement, aggregates and water, may contain chemical

admixtures to achieve certain target values of various properties in fresh condition,

achievement of which is monitored and controlled during production by suitable tests.

Generally concrete grades up to M50 are included in this type.

High Performance Concrete

High Performance Concrete is similar to standard concrete but contains additional

one or more mineral admixtures providing binding characteristics and partly acting as inert

filler material which increases strength, reduces its porosity and modifies its other properties

in fresh as well as hardened condition. Concrete of grades up to M90 are included in this

type.

Tests for Concrete

i) Compressive Strength

ii) Workability

iii) Non Destructive Tests

Compressive Strength

Concrete cubes of 15 x 15 x 15 cm to be cast in 3 layers, each to be vibrated thoroughly

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and finished. If it is hand tamping, three layers, each layer to be compacted 35 times and

finished. On surface dry, the specimen to be covered by wet gunny bag. After 24 hours they

are demoulded and cured for 7 days and 28 days and tested. A minimum of 3 Specimen cubes

of one Sample for analysing the test results are required.

The minimum frequency of sampling of concrete of each grade:

Table 1700-9 MORTH (Fifth Revision)

Quantity of Concrete in m3 No. of Samples

1-5 1

6-15 2

16-30 3

31-50 4

51 and above4 plus one additional sample for each

additional 50 m3 or part there of

Acceptance Criteria for compressive Strength:

1. Cubes

The concrete shall be taken as having the specified compressive strength when both the

following conditions are met:

a) The mean strength determined from any group of four consecutive non-overlapping

samples exceeds the specified characteristic compressive strength by 3 MPa

b) Strength of any sample is not less than the specified characteristic compressive

strength minus 3 MPa

2. Cores

When the concrete does not satisfy both the conditions given in (1) above,

representative cores shall be extracted from the hardened concrete for compression test

in accordance with the method described in IS: 1199 and tested as described in IS: 516

to establish whether the concrete satisfies the requirement of compressive strength.

Concrete in the member represented by a core test shall be considered acceptable if the

average equivalent cube strength of the cores is equal to at least 85 percent of the cube

strength of the grade of concrete specified for the corresponding age and no individual

core has strength less than 75 percent of the specified strength.

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Workability of fresh concrete by Slump Test

Standard slump cone size Standard tamping rod

Top dia = l0 cm Length = 0.6 m

Bottom dia = 20 cm Dia = 16 mm

Height = 30 cm

Figure 7: Slump Cone

Test Procedure:

Concrete shall be poured in four layers - each layer 25 blows. On removing the cone

slowly, the slumped concrete height has to be measured. The difference between this reading

and the original height of 30 cm is the slump of concrete.

Table 1700-4, MORTH (Fifth Revision)

Sl.No Type Slump (mm)

1.(a) Structures with exposed inclined surface requiring low

slump concrete to allow proper compaction25

(B) Plain Cement Concrete 25

2.RCC, structures with widely reinforcement eg. solid

column, piers, abutment footing, well steining40 -50

3.

RCC structure with fair degree of congestion of

reinforcement eg.Pier and abutment, Caps, Box culvert

well curb, well cap, walls with thickness greater than 300

mm

50 - 75

4.

RCC PSC structures with highly congested reinforcement

eg. Deck Slab Girders, Box Girders, walls with thickness

less than 300 mm

75 - 125

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5.Under water concreting through tremie eg. Bottom plug,

cast- in-situ Pilling150 - 200

Non Destructive Tests

Non Destructive tests are used to obtain estimation of the properties of

concrete in the structure. Non Destructive tests provide alternative to core tests for

estimating the strength of concrete in a structure, or can supplement the data

obtained from a limited number of core specimens tested. These methods are based

on measuring a concrete property that bears some relationship to strength. The

accuracy of these methods is determined by the degree of correlation between

strength and quality of the concrete and the parameter measured by the non

destructive tests.

The following Non destructive tests are commonly conducted on concrete

structures:

i) Ultrasonic Pulse Velocity Test as per IS : 13311 part 1-1992

Figure 8: Ultrasonic Pulse Velocity Test

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Table 8: Concrete Quality Grading

Pulse Velocity (km/s) Quality

Above 4.5 Excellent

3.5 to 4.5 Good

3.0 to 3.5 Medium

Below 3.0 Doubtful

ii) Rebound Hammer Test as per IS : 13311 part 2-1992

Figure 9: Position of Rebound Hammer - Vertically Downwards

Figure 10: Position of Rebound Hammer - Vertically Upwards

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Prestressed Concrete:

There are two main types of Prestressed Concrete for structural components of

Concrete Bridges

I) Pre-tensioned Concrete

II) Post-tensioned Concrete

Pretensioned Concrete:

Steel tendons are stressed by Jacks anchored to fixed blocks in the casting yard,

Concrete is then placed in moulds or casting beds around these tendons. When the concrete has

hardened sufficiently, the tendons are released. As they try to return to their original length,

large compressive forces are applied to the concrete.

This process is nearly always carried out in a factory environment and is the usual way

of manufacturing precast Prestressed bridge girders.

Post-tensioned Concrete:

For this type of construction, normally associated with in-situ Concrete, the tensioning

forces are applied to the tendons after the concrete is placed and hardened. Ducts are

incorporated into the formwork and the concrete is placed around them. After the concrete has

hardened, the stressing tendons are threaded through the ducts and are stressed using Jacks. A

special grout is injected into the ducts around the tendons to provide bond and protection from

corrosion. Pos-tensioning is mainly carried out on site although it has been used for special

precast girders.

CONCRETE STRUCTURES

INSPECTION OF BRIDGES

There are about 4,000 major and minor bridges in our State apart from culverts.

All the bridges in a division are to be inspected in detail at least once in a year. Bridges

in hilly areas also to be inspected at least twice a year before and after monsoon. Long span

bridges (individual spans greater than 30 m) are also to be inspected by a senior engineer (S.E)

at least once in a year.

The bridges are to be inspected and maintained as per procedures in IRC-SP:18 and

SP:35. Though detailed procedure is given in the above publication the salient points to be

noted during inspection are:-

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Culverts

1. Check whether the vents are choked with debris, vegetable matter, etc., and clear them.

2. Check for cracks, distresses in body wall and correct them.

3. Check whether the roadway is level on the culvert. If there is a depression suspect

failure of pipes, slab, etc., and take action to rectify it.

4. Observe during monsoons whether flow of water is proper or whether there is

overtopping of the culvert/breach of road adjoining the culvert in which case collect

hydraulic particulars, investigate and redesign the culvert for larger discharge.

Minor and Major Bridges

1. Check the backfill at abutments/approaches and if settlement seen correct it to a level

surface.

2. Check abutment, and wing walls for distress.

3. Check the slope projection works at abutment and replace / repack loose stones.

4. The foundation is to be checked before monsoon for erosion of bed exposing footing,

pile cap, pier cap to a larger extent or damage of concrete, abrasion of concrete.

5. Aprons / Bed protection works to be ensured to avoid erosion of footings underneath

piers and abutments.

6. The abutment and piers are to be checked for cracks, if any, at points just below

bearings.

7. The deck slab has to be checked for spalling of concrete/delaminating by visual

observation and by tapping with a hammer for dull hollow sound. Spalling is due to

corrosion of rebars and subsequent pressure caused due to swelling of bars.

8. Arch bridges are to be checked for the following:

a. Cracks across the span (which are dangerous and bridge may fail suddenly) in the

rib.

b. Cracks along the span (rib separating into two or more pieces).Though this is not

severe, action may be taken to repair them by providing, a relieving slab between

piers on the top of deck.

c. Cracks between spandrel wall and arch rib (along the arch) which shows

separation of the components of the bridge have to be repaired.

d. Vertical cracks at the skew back portion just above the pier, which indicates

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deflection of the arch rib.

e. For a detailed information on theoretical assessment of carrying capacity of arch

bridges IRC:SP:37 may be referred.

9. The beams of the deck may be inspected for cracks and the cracks may be identified

whether due to shear, bending or otherwise (shrinkage etc.,).

10. The bearings may be inspected for proper functioning. Especially, Neoprene pads may

be inspected for distresses by way of squeezing out of plates in the bearing, tearing of

the polymer or puncture of beam into the bearing or bearing into the concrete.

Also check for cracks at bearing points in beams in which case one may suspect

malfunctioning of bearings.

11. Vegetation present on the structure at drainage spouts are to be removed.

12. All drainage spouts are to be cleaned regularly.

13. The wearing coat of bridges are to be inspected and all the joints are to be raked,

cleared and joint filler board with joint sealant to be applied. Clogging of joints does

not allow free movement of the slabs and result in cracks.

14. Expansion joints of all bridges are to be checked for proper functioning, cleaned and

filled with bitumen sealants wherever applicable.

15. The deck and beams near expansion joints and drainage spouts are to be checked for

corrosion of bars due to water logging (clogging of debris).

16. All coastal bridges are to be inspected for corrosion of steel, spalling and

delaminating of concrete.

17. The Designs wing, H.R.S., may be contacted for advice on inspection/remedial

measures.

Repairs and Rehabilitation

A number of procedures for repair and rehabilitation are available starting from patch

repairs with epoxy mortar to extensive guniting.

1. Crack Repair

First identify whether cracks are active or inactive.

Active means the crack is live either expanding and contracting or extending in length.

Inactive cracks are dead cracks which do not vary in size for quite a period of time.

a. Inactive cracks may be filled with resins or cement grouts (non-shrink type).

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Filling may be done by simply pounding or pressure injection (pressure

grouting).

Cracks of width > 10 mm. may be filled with single size aggregate and then

with non shrink cement grouts.

b. Active Crack:- Cracks to be cleared properly by water jetting, compressed air,

etc.,

Sealing with a flexible sealant or filling with a resin, providing a chase and

filling it with flexible sealant.

2. Repair of Spalled concrete

Corrosion is the process. of rusting of steel due to action of saline water (chlorides) .

Structures near the coast (upto15 kms from sea or creek) and those on backwaters are prone to

corrosion.

The corrosion product (rust or iron oxide) is larger in volume and creates great pressure

on the concrete (cover concrete) and concrete ultimately cracks. This cover concrete separates,

(called delaminating) and falls from the structure (called spalling of concrete).

Repair:

All loose concrete should be chipped off and the spalled area should be cleaned by

water jetting. Any damaged reinforcement to be replaced with new piece of bar by welding

and placing in position. The reinforcement may be protected by applying zinc rich coating.

Then a bonding agent may be applied, to ensure proper bond between old and new concrete.

The epoxy mortar, either ready-to-use or prepared by adding admixtures to normal cement

mortar may then be applied layer by layer up to a maximum thickness of 1 inch at a time,

(which may be allowed to cure and then next layer applied) Polymer based mortar or concrete

can also be used for repair.

3. Guniting

(Application of concrete by spraying) Guniting is used for large scale repairing of

structures (such as decks of bridges, columns, beams etc.,) which have damaged

extensively.

Here mortar is applied over the area to be required by pressure from a gun. A guniting

machine with compressor is required for the above work. It has to be done by skilled

workmen as loss of mortar (rebound) will be high.

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For large repairs proper temporary supports, frameworks are to be provided.

4. Bridge Wearing coats

When the wearing coat of bridges is extensively damaged, they may be replaced by a

new wearing coat.

The cracks on the wearing coat may be repaired by filling with non-shrink cement

based grouts or by filling with sand mastic (a mix of bitumen and sand).

IMPORTANT INDIAN STANDARDS PERTAINING TO

CONCRETE AND STRUCTURES

I. Cement

1. IS : 4031-1988 Methods of Physical Tests for Hydraulic Cement (Part - I to 13)

2. IS : 4032-1985 Methods of Chemical Analysis of Hydraulic Cement

3. IS : 3535-1986 Methods of Sampling Hydraulic Cement

4. IS : 269-2015 Specification for 33 Grade ordinary Portland cement

5. IS : 8112-2013 Specification for 43 Grade ordinary Portland cement

6. IS : 12269-2013 Specification for 53 Grade ordinary Portland cement

7. IS : 12330-1988 Specification for Sulphate resisting Portland cement.

II. Aggregates - Metal and Sand (Coarse Aggregate and Fine Aggregate)

1.IS : 2386 - 1963

(Part - I to 8)Methods of tests for Aggregates for Concrete.

2. IS: 383 - 2016.Specification for coarse and fine aggregates from Natural sources

for concrete.

III. Steel

1. IS : 1786-2008High Strength deformed steel bars and wires for Concrete

reinforcements.

2. IS : 2751-1979Code of Practice for welding of mild steel, plain and deformed

Bars for reinforced concrete construction

3. IS : 1139-1966Hot rolled mild steel, medium tensile steel and high yield strength

steel and deformed bars for concrete reinforcement.

4. IS : 432-1982 Specification for mild steel and medium tensile steel bars.

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IV. Concrete

1. IS : 10262-2009 Concrete Mix Proportioning-Guidelines

2. IS : 456 - 2000 Code of practice for plain and reinforcement concrete.

3. IS : 1343 - 1980 Code of practice for Prestressed concrete

4. IS : 516 - 1959 Method of test for strength of Concrete.

5. IS : 1199 - 1959 Method of sampling and Analysis of fresh concrete.

6. IS : 9013 -1978Methods of making, curing and determining compressive strength

of accelerated cured concrete test specimen.

7. IS : 6509- 1985 Code of practice for installation of joints in concrete pavement.

V. Bricks

1. IS : 1077 - 1992 Specification for common burnt clay building bricks.

2. IS : 2180 - 1988 Heavy duty burnt clay building bricks.

3. IS : 3102 - 1971 Classification of burnt clay solid bricks.

4. IS : 5454 - 1978 Methods of sampling of clay building bricks.

5. IS : 3583 - 1988 Specification for paving bricks

6. IS : 2212 - 1991 Code of practice for brick works.

I.S. Special Publications

1. SP - 11Hand Book for Quality Control for construction of Roads and

Runways.

2. SP - 23 Hand Book on concrete mixes.

3. SP - 24 Code of practice for plain and reinforced concrete.

4. SP - 34 Concrete reinforcement

5. SP - 35 Guidelines for Inspection and Maintenance of Bridges.

I.R.C.

1. I.R.C. - 15Standard Specification and code of practice for construction of

concrete Roads.

2. I.R.C. - 112 Code of practice for Concrete Road Bridges

3. I.R.C. -44 Method of concrete mix design for Concrete pavement.

4. I.R.C. - 58 Guidelines for the design of ridge pavement for Highways.

5. I.R.C. - 84 Code of practice for curing of C.C. pavement.

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6. I.R.C. - 77Tentative guideline for repairing concrete pavement using

Synthetic Resins.

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