Transcript ethics last class

Inspection, Quality,
Variation, Statistical Control
and Acceptance Criteria
Dr. J.SUDHAKUMAR
Assistant Professor
Department of Civil Engg.
NIT, CALICUT
Inspection, Quality, Variation, Statistical Control and
Acceptance Criteria

INSPECTION AND QUALITY CHECK
 Need
 To
and scope of Inspection
ensure that work is done in
accordance with the plans,
specifications and good practice,
and to prevent mistakes.

The other requirements for the
same purpose include
 Intelligent
design
 Adequate specifications
 Reliable construction
 Competent inspection

The following items are covered by
the inspection of concrete
construction at various stages:
 Sampling,
Identification, Examination,
and any field testing of materials
 Control of concrete proportioning and
the measurement of materials
 Examination of the foundation, forms
and other work preparatory to
concreting
 Continuous
inspection of the
batching, mixing, conveying,
placing, compacting, finishing
and curing of concrete
 Testing
for consistency of
concrete, and preparation of
any concrete specimens
required for laboratory testing
 General
observation of
contractor’s plant and
equipment, weather, working
conditions and other items
affecting the concrete
 Preparation
reports
of records and
Choice
of an Inspector
 An
ideal inspector should have
both technical and practical knowhow of the subject. He should
essentially understand the
following:
 Bulking
of fine aggregate (sand)
 Well proportioned mix or not
 Whether the mix has desired slump
 Whether
the forms are sufficiently
tight and braced
 Whether
the concrete is properly
compacted or not
 Whether
the forms are removed
early or not
 Authority of the Inspector
 An authority should be given to the
inspector to :
 Prohibit
concreting until all
preliminary conditions (such
as completion of forms) have
been fulfilled and inspection
report for concreting has been
provided
 Stop
the use of materials and
equipment, which do not
comply with the specifications
 Stop
any work which is not
being done in conformity with
the plans and specifications
 Require
the removal or repair
of faulty construction or of
construction performed
without inspection and not
accessible to being inspected
later
 Normally,
the inspector is
authorised to take direct action in
the first three cases above
 He should report the matter
immediately to his superior
 He should stop the work only as a
last resort, when it is clear that
unsatisfactory concrete will result
from the continuing operations
 Quality check on concrete
 Before concrete is placed, the
specification requirements in all
aspects must be fulfilled
 Forms
should be of proper size
and strength and in their correct
location
 Cement, aggregates, water and any
other ingredients should be
inspected
 Batching
of materials, time of
mixing, possibility of segregation,
proper curing etc., as this will
influence the properties of
hardened concrete
 Preparation of test specimens
 At least 3 specimens for each 200
m3 of concrete
 Each sample should be from
different points of the structure
 Sampling
should not be from the
conveying device
 Taken at irregular times and
without prolonged preparations
 Sample should be placed in a
water-tight non-absorbent
container
 Remixed fast enough to make it
uniform, and then moulded into
specimens
 For
compression test, 150 mm
cube moulds are used
 Moulds are filled in 3 layers
 Each layer is compacted with 25
strokes of a 16 mm diameter and
600 mm long, round bullet pointed
steel rod
 After the top surface has been
levelled, the specimen is covered
to prevent evaporation
Flexure
specimens are 150 mm
x 150 mm in section. Moulds
are placed with their long axis
horizontal and are filled in 2
layers, each layer being rodded
50 times.
 Quality
check on Personnel and
Equipment
 Should have a well trained team,
conversant with different quality
control procedure of inspection,
testing and data analysis
 An adequately equipped field
laboratory for carrying out
routine control tests
 Table
1:
Daily testing programme
and composition of team
( refer notes )
 Table
2:
Degree of quality control
expected under different site
conditions
( refer notes )

Measures of Variability of Concrete Mix
Design
 Factors
 It
contributing to Variability
is found that strength of concrete
varies from batch to batch
 The following are the sources of
variability
 Variation
in the quality of
constituent materials used
 Variation
in the mix proportions
due to batching processes
 Variations
in the quality of
batching and mixing equipment
available
 Quality
of supervision and
workmanship
 Variation due to sampling and
testing of concrete specimens
 These
variations are inevitable
during production of concrete
 The
purpose of quality control
using statistical means is to
produce concrete of uniform
quality
 If
a large number of cube strength
test results are plotted on a
histogram, the results are found to
follow a bell-shaped curve termed
as “Normal Distribution Curve”
 The
arithmetic mean of a number
of test results gives no indication
of the extent of variation of
strength
 However, this can be ascertained
by relating the individual strength
to the mean strength and
determining the variation from the
mean, with the help of the
characteristics of the N.D.curve
 Standard
Deviation
 The
root mean square deviation of
the whole consignment is termed
as the ‘standard Deviation”. It can
be defined numerically as:
S =  (x – -x-)2/(n-1)

Where
S = S.D. of the test results
x = any value in the test results
_
x = arithmetic mean of the results
n = number of test results

Coefficient of Variation
 An
alternate method of expressing
the variation of results about the
mean is by coefficient of variation
 This
is a non-dimensional measure
of variation
 This
is obtained by dividing the
standard deviation by the average
value, and is expressed as
V = 100 S / -X-
where
 V = coefficient of variation
S = S.D. in strength
-X- = Mean value in strength

 When
the C.V. is constant, S.D.
increases with the increase in
strength of concrete

STATISTICAL CONCEPTS OF
MIX DESIGN
 Characteristic
strength
This means that value of
the strength of concrete below
which, not more than 5 percent of
the test results are expected to fall
 Target
mean strength
ft = fck + K.s
where
ft = target mean strength
fck = characteristic strength
K = a statistical constant, depending on
the definition of fck and is derived
from the mathematics of Normal
Distribution
s = standard deviation
 The
value of K is equal to 1.65
where not more than 5% of test
results are expected to fall below
the characteristic strength
ft = fck + 1.65 s
1.
Acceptance Criteria
(IS 456 : 2000)
Compressive strength
Both the following conditions
must be met :
a) The mean strength of any four
consecutive test results compiles
with the appropriate limits in
Table 3.
Table 3
For M15 grade
Mean of 4 consecutive results in
N/mm2 must be greater than or
equal to
fck + 0.825 x SD
or
fck + 3 N/mm2 , whichever is greater
Table 3
For M20 or above grade
Mean of the group of 4 consecutive
results in N/mm2 must be greater
than or equal to
fck + 0.825 x SD
or
fck + 4 N/mm2 , whichever is greater
Acceptance Criteria
b) Any individual test result
complies with the appropriate
limits in Table 3.
Table 3
For M15 grade
Individual test results in N/mm2
must be greater than or equal to
( fck – 3 ) N/mm2
Table 3
For M20 or above grade
Individual test results in N/mm2
must be greater than or equal to
( fck – 4 ) N/mm2
Acceptance Criteria
1.
Flexural strength
Both the following conditions
must be met :
a)
The mean strength of any four
consecutive test results exceeds
the specified characteristic
compressive strength by at least
0.3 N/mm2
b)
The strength determined from
any test result is not less than
the specified characteristic
strength less 0.3 N/mm2
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