JUST IN TIME MIXTURE PROPORTIONING

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JUST IN TIME MIXTURE PROPORTIONING

• Ken W. Day
• Consultant, Australia

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Objectives of the System

• We need more concrete but it is imperative that
  cement usage be minimised.
• This can be achieved in two ways
• Better control, reducing margin between mean and
  minimum
• Cement replacement materials

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Objectives of the System

• Better control can be achieved by the use of my
  multigrade, multivariable, cusum QC system
  (described on a poster presentation at this
  conference) but how to handle cement replacement
  materials in this system?

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Program Requirements

• It is not sufficient to assign a strength
  equivalence factor to these supplementary
  materials because the ratio varies with both the
  replacement and the required strength level

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Program Requirements

• My solution is to regard each combination of
  cementitious or pozzolanic materials as a
  different cement

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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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Concrete Product Screen
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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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To achieve required control

• 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

• Input all material properties
• Decide upon cement groups
• Decide upon range of products to be offered
• 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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Just in Time Proportioning
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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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Mix Variation Print-out Screen
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Plant Setup Screen
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Cement Group Screen
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Gradation Screen