JUST IN TIME MIXTURE

PROPORTIONINGKen W. Day

Consultant, ConAd Australia

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

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

Assuming selection of the 2nd objective:

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

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

The Actual System

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

Plant Setup Screen

Cement Group Screen

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

Gradation Screen

Concrete Product Screen

Just in Time Proportioning

Mix Variation Print-out Screen

Summary1. The concept may be ahead of its

time but is already viable2. 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