JUST IN TIME MIXTURE PROPORTIONING Ken 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 2 nd objective: It will be necessary to know, and to be able to compensate for: 1.Changes in aggregate properties 2.Changes in cementitious material and admixture properties 3.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 haul This is a major reason for Just in Time proportioning

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

Just in Time The 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 vol w = 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

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