JUST IN TIME MIXTURE PROPORTIONING

1. JUST IN TIME MIXTURE PROPORTIONING Ken W. Day Consultant, Australia

2. 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

3. 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?

4. 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

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

6. 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

7. Cement Group Screen

8. Concrete Product Screen

9. 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

10. 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

11. 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

12. 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

13. Changes in aggregate properties : Grading changes can easily be compensated for using author’s MSF concept (Mix Suitability Factor, based on specific surface)

14. Changes affecting water content Must compensate for change in • slump • temperature • time of haul This is a major reason for Just in Time proportioning

15. 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

16. Just in Time The design process is now complete, actual proportions will depend upon JIT entries of slump, temperature and expected time of haul

17. Just in Time Proportioning

18. 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

19. Mix Variation Print-out Screen

20. Plant Setup Screen

21. Cement Group Screen

22. Gradation Screen