ETHICS LAST CLASS

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GOOD MORNING
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Inspection, Quality, Variation, Statistical
Control and Acceptance Criteria

• Dr. J.SUDHAKUMAR
• Assistant Professor
• Department of Civil Engg.
• NIT, CALICUT

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Inspection, Quality, Variation, Statistical
Control and Acceptance Criteria

• INSPECTION AND QUALITY CHECK
• Need and scope of Inspection
• To ensure that work is done in accordance with
  the plans, specifications and good practice, and
  to prevent mistakes.

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• The other requirements for the same purpose
  include
• Intelligent design
• Adequate specifications
• Reliable construction
• Competent inspection

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• 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

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• 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

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• General observation of contractors plant and
  equipment, weather, working conditions and other
  items affecting the concrete
• Preparation of records and reports

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• Choice of an Inspector
• An ideal inspector should have both technical and
  practical know-how 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

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• Whether the forms are sufficiently tight and
  braced
• Whether the concrete is properly compacted or not
• Whether the forms are removed early or not

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• 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

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• 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

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• Require the removal or repair of faulty
  construction or of construction performed without
  inspection and not accessible to being inspected
  later

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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.

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• 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

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• Table 1
• Daily testing programme
• and composition of team
• ( refer notes )

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• Table 2
• Degree of quality control
• expected under different site
• conditions
• ( refer notes )

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• Measures of Variability of Concrete Mix
• Design
• Factors contributing to Variability
• It is found that strength of concrete varies from
  batch to batch
• The following are the sources of variability

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• 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

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• Quality of supervision and workmanship
• Variation due to sampling and testing of concrete
  specimens
• These variations are inevitable during production
  of concrete

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• 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

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• 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

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• 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)

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• Where
• S S.D. of the test results
• x any value in the test results
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• x arithmetic mean of the results
• n number of test results

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• 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

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• This is obtained by dividing the standard
  deviation by the average value, and is expressed
  as
• V 100 S / -X-

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• 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

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• 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

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• 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

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• 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

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• 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.

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• 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

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• 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

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• Acceptance Criteria
• b) Any individual test result complies with the
  appropriate limits in Table 3.

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• Table 3
• For M15 grade
• Individual test results in N/mm2 must be
  greater than or equal to
• ( fck 3 ) N/mm2

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• Table 3
• For M20 or above grade
• Individual test results in N/mm2 must be
  greater than or equal to
• ( fck 4 ) N/mm2

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• Acceptance Criteria
• Flexural strength
• Both the following conditions must be met

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• The mean strength of any four consecutive test
  results exceeds the specified characteristic
  compressive strength by at least 0.3 N/mm2

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• The strength determined from any test result is
  not less than the specified characteristic
  strength less 0.3 N/mm2

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THANK YOU