Date post: | 20-Jan-2016 |
Category: |
Documents |
Upload: | abigayle-harmon |
View: | 219 times |
Download: | 0 times |
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