JUST IN TIME MIXTURE PROPORTIONING

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JUST IN TIME MIXTURE PROPORTIONING

• Ken W. Day
• Consultant, ConAd Australia

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Proportioning/Designing

• Proportioning is evaluating the actual quantities
  of each ingredient for a particular load
• This is what should be done on a Just in Time
  basis - by the computer alone with current data

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Proportioning/Designing

• Designing is deciding what properties a range of
  mixes should have and which materials should be
  used
• Designs are revised periodically by technical
  management, also using part of this program

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Concrete Production Objective

• There are two possible objectives in producing
  successive trucks of concrete for the same
  purpose
• 1) To produce concrete of the same proportions
• 2) To produce concrete of the same fresh and
  hardened properties

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Assuming selection of the 2nd objective

• It will be necessary to know, and to be able to
  compensate for
• Changes in aggregate properties
• Changes in cementitious material and admixture
  properties
• Changes in production, delivery and climatic
  conditions affecting water content

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Changes in cementitious material properties

• Changes in strength properties can be made based
  on cement tests or concrete tests
• Cement test data may enable prior adjustment to
  change but
• Only concrete test data can make fine tuning
  possible

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Changes in aggregate properties

• Grading changes can easily be compensated for
  using authors MSF concept
• (Mix Suitability Factor, based on specific
  surface)

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Changes affecting water content

• Must compensate for change in
• slump
• temperature
• time of haul
• This is a major reason for Just in Time
  proportioning

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Utilization Sequence

1. Input all material properties
2. Decide upon cement groups
3. Decide upon range of products to be offered
4. Bring in test data to establish w/c v strength
   relationship

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Just in Time

• The design process is now complete, actual
  proportions will depend upon JIT entries of
  slump, temperature and expected time of haul

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Approval of Proposals

• Some see difficulty in approving concrete supply
  proposals if proportions are not known in advance
• Actually proportions are precisely known in
  advance if conditions are known

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The Actual System

• It remains only to present such of the actual
  system as time permits

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Plant Setup Screen
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Cement Group Screen
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Strength Formula(Feret)M x 290 x (c / (c w
a))2 Ac cement volw water vola air
volM A two constants to be found
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Cement Group Screen
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Gradation Screen
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Concrete Product Screen
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Just in Time Proportioning
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Mix Variation Print-out Screen
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Summary

1. The concept may be ahead of its time but is
   already viable
2. It offers lower variability concrete of constant
   properties through varying proportions- the
   reason for Just in Time proportioning
3. It offers easier interfacing with all batching
   systems