Knowledge Tree July 2012

8/13/2019 Knowledge Tree July 2012

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Contents...

Volume5Issue 7

July 2012

ditors Note 2P osters . 3T opic .5

T echtoon .9P uzzle10W inners11

International

Friendship dayuru Purnima

24th July

Civil Engineering Magazine


2/11

Dear ReadersWe are much obliged withyour responses and happy to be a part ofthis initiative.India is a land of agriculture & the workforce we use in the construction eld most-ly originates from here.

In construction industry we have many is-sues that creates bottle necks in achieving

required productivity & Quality.

Some of them are

Un educated & Un trained work force

Non availability of same person

throughout the duration of the project

We in L&T have taken up major initiatives

in training & developing the rural workers

through Construction skill training insti-

tutes ( CSTI ).

Still there is a large gap in the demand Vs

Supply of the qualied work force.

This gap cannot be fullled easily in thenear future.

Meanwhile our works are suering in Qual-

ity & productivity.

In order to tackle this issue , we have to ana-

lyse the problem & frame a system to tacklethe issue now!

Our problem is in front of us we can ensure

the self regulation.

We don't have trained skilled or experi-

enced skilled work force.

Many sites have taken up the issue & estab-

lished screening , training & encouraging

mechanisms.

Even if the worker is trained at site in par-

ticular activity say concreting or masonry ,

there is no guarantee that he will continue

for considerable amount of time.

Hence the site engineers & supervisors jobis getting compounded day be day and he is

spending major portion of his time in con-

trolling the work force & rectifying the de-

fects they generated through the work.

It is established fact that Awareness is the

key to Improvement .

PT&D ICCivil Engineering departmentbelieves in this concept & had initiated rst

of its kind step to bring in awareness in the

workers on continuous basis.

Series of posters on workmanship require-

ments were prepared in English , Hindi &

other vernacular languages. This eort is

rst of its kind in construction industry .

Several day to day activities are made in to

Posters and simple language is used to ex-

T S R B a n g a r R a j u K.Satish Varma

d i t o r s N o t e


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plain along with appropriate pictures.

As pictures are worth a million words .,

this concept is the foundation for this de-velopment. These posters were deployed in

pilot project sites of PT&D and that the

same was well received by sta and workers.

These posters are displayed at prominent

places especially in the assembly area and

work spots.

Along with this , the eectiveness could bemultifold if PEPTALK is included on the

work methods on daily basis.

Few minutes with the workers in the begin-

ning of every day can bring dramatic

change in their ability to transform to a pro-

ductive workforce.

We have experienced the power of pep talk

in many walks of our life , right from the as-

sembly sessions in our school to safety pep

talks at our work place.

Hence this can bring a change in workers

mindset & prompt them to adhere to our

standards as time passes by.

This brings in a silent revolution on work-

manship improvement , workers develop-

ment & thus Nation building.

Let us join this movement & bring a change

in our work place.

We call this silent transformationbe a

part of it.

The posters are uploaded in the EIP -Vidya

website. Click on the link given on page4

for accessing.

You can download the same & print it to A

Zero size ex Boards and display themwhere needed & easily seen by all.

We invite your suggestions to improve the

content. Please write to us at

[email protected] for improvisation.

In this month, we have detailed on the ac-

ceptance criteria of concrete in its real

sense.

We hope this topic will be of immense use

to Quality Engineers & to all.

We regret for the delay in publishing the

Knowledge TreeJuly Issue.

This month is having few important events.

1st

July is observed as Doctors day in India .24thJulyis observed as Guru Purnima

30th July is observed as International

Friendship Day.

d i t o r s N o t e

Pep Talks

Awareness

generation


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Click Here

to Down load

the posters
https://km.lntecc.com/ocs/epgo/Igp/PTDS/KT/default.aspxhttps://km.lntecc.com/ocs/epgo/Igp/PTDS/KT/default.aspxhttps://km.lntecc.com/ocs/epgo/Igp/PTDS/KT/default.aspxhttps://km.lntecc.com/ocs/epgo/Igp/PTDS/KT/default.aspxhttps://km.lntecc.com/ocs/epgo/Igp/PTDS/KT/default.aspxhttps://km.lntecc.com/ocs/epgo/Igp/PTDS/KT/default.aspxhttps://km.lntecc.com/ocs/epgo/Igp/PTDS/KT/default.aspx


5/11

Concrete is a versatile material of the 21stcentury. It can be molded in to anyshape or size and can be made to suit torequirements.With the same ingredients and varying proportionwe can obtain dierent concrete grades. The grades

of concrete is designated as M 20 or 25 or 30 Etc.

The

M-stands for Mix & the remaining part

stands for the strength of the concrete in N/mm2.

Concrete is stronger in Compression & weaker in

Tensionit is a known fact to all. But the strength

is obtained in concrete with

Careful selection of ingredients Carrying Mix design for xing the propor-

tions to suit to the sources. Following strict Quality control measures

during production. Ensuring proper sampling techniques

Careful curing of the member

Several Quality control measures have to be takenfor ensuring good Product which satises the stand-

ards or specications of the project.

Dierent countries have dierent criteria's for ac-

cepting concrete.

In India we follow

IS 4562000 with Amendment3 for deciding

the acceptance of concrete.

Where specication demands we may have to

adopt those requirements. For example , for

railways Jobs we use RVNL(Rail Vikas Nigam

Limited ) specication criteria.

For National Highway / Road Jobs we use

MORTH ( Ministry of Road Transport & High-

ways ) specication.

Where as internationally many standard have theirown criteria's for the concrete acceptance.

British standard sets criteria in BS 8110 .

Accep

tancecrit

eriaof

concrete


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These criteria's are important in deciding the ac-

ceptability of concrete grade.

Many people believe & presume that when a cube is

failed the concrete is failed. But it is not so.

Many factors eects the concrete cube casting & the

subsequent test there on.

The following are the general issues that takes place

in concrete cube failure.

Inbuilt factors : ( Factors that aect concrete

quality & strength ) Incorrect selection of material for concrete use

Improper quality control mechanism adopted

for material tests.

Non adherence to Mix design requirements

Improper Batch plant which is out of calibration

& defective.

Un controlled addition of water

Factors that doesn't aect the concrete quality

but reduces the cube strength:

Sampling defects

Curing inadequacy of the cubes

Cube mould disguring / out of size & Shape

Calibration defects of testing machine.

Technicians skill or training inadequacy

Incorrect placement of cubes in the machine &

loading defects

So Standard has set criteria for acceptance of con-

crete taking in to the above possible errors in to

consideration.

The errors that are inbuilt factors produce defective

concrete , where as for the other factors as men-

tioned above the concrete is not defective. But the

sampling , testing mechanism & methods are defec-

tive.

In order to know whether the concrete poured ispassing or failing the required grade we must not

rely on a single cube , rather on set of cubes that

represents the complete pour.

If one cube from a complete set gets less strength

than the required grade we must not label it as fail-

ure.

The following both criteria must be satised to ac-

cept the concrete grade.

Primarily the concrete can be accepted or rejected

based on the grade of it or as per Table2 of IS 456.

However to evaluate the concrete grade statistically

we must satisfy the following criteria from IS 456

2000section 16.1

The individual cube result shall not be less than

fck3 N/mm2.

The average determined from any group of 4

consecutive non overlapping test results shall

not be less than fck+3 N/mm2

To understand better , let us consider the cube test

results of M25 grade concrete cast on a given day .

250 m3 of concrete was cast at a site & 9 samples

were taken ( 3 specimens per sample )the results are

as given in the following table.

First check whether all the samples are having

strength more or equal to FckIn this case two

specimens found to have less than Fckvalue of 25


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N/mm2.

Though the sample strength is less than specied

grade ( 25 N/mm2 ) we cant reject the concrete

right away. But we need to verify the Acceptance

criteria per Section 16.1.

2. Second check whether the individual specimen

diers from average of the 3 specimens in the

sample. If there is a variation more than 15%

then that sample shall be rejected or not to be

taken in to consideration for acceptance criteria.

( it doesn't mean that the concrete representing

the sample is rejected )

3. Check whether any individual specimen is less

than Fck3. In our illustration, none of them are

less than the same.

4. Then arrange the samples ( average of 3 speci-

mens ) in groups of 4 ( with out using the same

sample again ).

5. Take the average of the 4 samples. (consecutive

non overlapping sample results ). Out of the ver-

ication , even if any one sample passes the Fck

+3 requirement along with check on step4 ,

the concrete grade is accepted.

Final Result : As both the criteria's are met , the

grade is accepted.

For all the above purposes the frequency of concrete

cube casting as mentioned in IS 456Section 15.2.2

must be followed.

In case the frequency of sampling is not mentioned

in the specication or in tender , then the maxi-

mum concrete that 4 consecutive test results repre-

sents must be limited to 60m3.

This means when concrete is carried in small batch-

es , then to evaluate the grade of concrete , the total

quantity of all such concretes must not exceed

60m3. ( this concrete may be carried in same day or

in 2 or 3 days ).

In order to ensure that such low strength doesn'tarise , we need to check the sampling methods

adopted & correct them where necessary.

If the result doesn't satisfy the above requirements

27 4%

Sample -1 28 26.00 8%

23 -12%

29 1%

Sample -2 27 28.67 -6%

30 5%

28.42

29 -1%

Sample -3 30 29.33 2%

29 -1%

28 -6%

Sample -4 29 29.67 -2%

32 8%

30 7%

Sample -5 29 28.00 4%

25 -11%

25 -7%

Sample -6 29 27.00 7%

27 0%

28.83

29 -1%Sample -7 29 29.33 -1%

30 2%

31 0%

Sample -8 33 31.00 6%

29 -6%

22 -21%

Sample -9 30 28.00 7%

32 14%

This result is higher

than 15% hence

invalid

Criteria -1

Mean of 4

consecutiv

e non

overlappin

g test

results >

25 + 3 =

28

No

individual

test

specimen

shall be

less than

25 - 3 = 22

Deviation

from MeanAverage

Mean of 4

consecutive

samples

Strength

in N/mm2

Sample results Evaluationfor Concrete


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then further investigation need to be carried using

NDT techniques .

For the railway projects in India the acceptance

criteria is applied as below:For the rst 5 sets

The average strength determined from any

group of the three consecutive test cubes ex-

ceeds the specied characteristic strength +o.6X

current margin

Only one individual test cube in any set may be

below 0.95X specied characteristic strength

After 5 sets

The average strength of any 15 consecutive cubes

exceeds the specic characteristic cube strength +0.9 X current margin

All the subsequent results are accepted if

The average strength of any group of three con-

secutive test cubes exceeds the specied charac-

teristic strength + 0.6 X current margin.

Only one individual cube test result in any set

may fail below the specied characteristic

strength provided that his value is not less than

0.9 X characteristic strength.

Current margin for all grades is 9.

As per MORTH specication , concrete grade is

accepted only when both the conditions are

met. The mean strength determined from any group

of four consecutive samples exceed specied

characteristic strength

Strength of any sample is not less than the speci-

ed characteristic compressive strength3 N/

mm2.


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10/11

Across

3. CARRIED TO PROMOTE HYDRATION OF

CEMENT

5. VERSATILE MATERIAL IN CONSTRUC-

TION

8. ENSURES REPRESENTETIVE IS EQUAL

TO BULK

9. LOSING SHAPE OR SIZE

10. STANDS FOR M IN GRADE OF CON-CRETE

Down

1. INHERENT CHARECTER OF THE MATE-

RIAL

2. ONE OF THE INGREDIENT IN CON-

CRETE THAT IS NON REACTIVE

4. NEEDED TO USE A MACHINE OR CARRY

A TEST

5. BINDING MATERIAL IN CONCRETE

6. NATIONAL HIGHWAY AUTHORITY OFINDIA

7. CARRIED TO CHECK EQUIPMENTS AC-

CURACY/ DEPENDENCY

Find the

words

Mail to

[email protected]

July

Jewel


11/11

Disclaimer :No part of this publication shall be reproduced without the written permission from the Editors. The views

expressed here need not be the views of the L&T Construction L&T doesn't take any responsibility of what so ever for the views expressed by the Editors / Authors This is for the

S.Manikandan

S Ramya Sri

Sankaran

Roshan

G Anitha Nivashini

D Pavan

Choudary K

Rajith Kumar

K Praveen

Bharat T

Ujwal Kumar

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