Download - 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
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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 -
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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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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
July
Jewel
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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