JUST IN TIME MIXTURE

PROPORTIONINGKen W. Day

Consultant, Australia

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

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?

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

Program Requirements

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

Strength Formula(Feret)

M x 290 x (c / (c + w + a))2 + A

c = cement volw = water vol

a = air vol

M & A two constants to be found

Cement Group Screen

Concrete Product Screen

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

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

To achieve required control

It will be necessary to know, and to be able to compensate for:

1. Changes in aggregate properties2. Changes in cementitious material

and admixture properties3. Changes in production, delivery

and climatic conditions affecting water content

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

Changes in aggregate properties :

Grading changes can easily be compensated for using author’s MSF concept

(Mix Suitability Factor, based on specific surface)

Changes affecting water content

Must compensate for change in • slump• temperature• time of haulThis is a major reason for Just in

Time proportioning

Utilization Sequence

1. Input all material properties2. Decide upon cement groups3. Decide upon range of

products to be offered4. Bring in test data to establish

w/c v strength relationship

Just in TimeThe design process is now

complete, actual proportions will depend upon JIT entries of slump, temperature and expected time of haul

Just in Time Proportioning

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

Mix Variation Print-out Screen

Plant Setup Screen

Cement Group Screen

Gradation Screen