1 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow KEN DAY Consultant Command Alkon Inc.

2 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow The title is not strictly correct, because all the types of control presented are in use today.

3 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow The categories are not separated according to geographical location, per capita income, expenditure on plant, knowledge of concrete properties, or even computer literacy. They are also not necessarily in time sequence. Basic division is on the grounds of philosophical concept.

4 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow The stages of philosophical development are seen as follows: 1) Prescription specification directly supervised by the engineer or owner.

5 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow 2) 2)Strength specification but hedged in by limits on cement content and enforced by minimum strength on an individual truck basis.

6 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow 3) 3) Recognition that, at a given strength, high water content is more deleterious than low cement content, - leading to total abandonment of minimum cement content specification.

7 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow 4) 4) Reluctant permission to use a limited proportion of flyash, slag etc.

8 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow 5) Requirement that pozzolanic materials be used to reduce heat generation.

9 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow 6) Reluctant permission to use admixtures (following decades of successful but unauthorised use).

10 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 7) Requirement that admixtures be used to retard set, reduce water content, shrinkage, heat generation etc.

11 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 8 )Recognition of statistical variation and the importance of low variability, leading to use of a target strength incorporating standard deviation.

12 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 9 ) Recognition that variability cannot be assessed from a very limited number of results.

13 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 10 ) Recognition of testing error, leading to discarding of low result from widely separated pairs rather than penalisation for such a result.

14 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 11) Recognition that it is far more efficient to ensure that no unsatisfactory concrete is produced rather than to try to detect individual unsatisfactory truckloads.

15 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 12) Recognition that the concrete supplier is in a far better position to control his concrete than the purchaser, leading to ISO certification of suppliers instead of control of supplied concrete by purchaser.

16 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 13) Availability of batching equipment and software which can record full details of every truck, and even predict its strength as it leaves the concrete plant, at almost zero cost.

17 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 14) Availability of truck- mounted workability monitoring and control gear (“to close the last loophole”)

18 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 15) Recognition that low variability is an important goal, and that it depends on continuous adjustment of mix proportions as materials properties vary, rather than rigid adherence to approved proportions.

19 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 16) Recognition that mix adjustment based on production test data is much more accurate than trial mixes.

20 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 17) Recognition that cusum (cumulative sum) analysis enables test results (strength, density, slump, temperature and dozens of others) from any number of widely different mixes to be plotted on the same graph, removing the need to concentrate testing on a “control mix” and giving much faster detection of change.

21 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 18) Recognition that pro-active adjustment for material variability can reduce variability, even though less accurate than reactive adjustment and so not replacing the latter.

22 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 19) Availability of software that can instantaneously calculate the revised proportions necessary to compensate for a change of sand or coarse aggregate.

23 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 20) Availability of software that can optimise a whole range of hundreds of mixes in a few minutes

24 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow (optimise meaning automatically select the most economical aggregate proportions which will provide the nominated fresh concrete properties and accompany this with the precise cement content required to achieve the specified strength taking into account current early age test data).

25 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 21) Availability of software that can proportion the next truck of concrete in a few seconds, taking into account desired fresh and hardened properties, current test data, temperature and haulage time/distance.

26 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 22) Availability of software and facilities that will automatically nominated individuals if any truck is dispatched bearing concrete likely to be unsatisfactory for almost any reason.

27 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 23) Availability of hardware and software enabling concrete test specimens to be weighed, measured and compression tested automatically with the results being automatically entered in the control system, assessed, and reported by where appropriate.

28 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow ) 24) Availability of hardware and software enabling the current strength of concrete in any part of a newly cast structural element to be read, and the future strength growth to be predicted.

29 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow We have reached a stage where the production of low variability concrete of almost any reasonably desired strength (ie w/c ratio) can be achieved almost totally automatically.

30 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow The inhibiting factor is that purchasers, structural designers and other specifiers often do not understand the situation or are inhibited by out-of-date regulations, textbooks, or other sources of advice.

31 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow The best control is being achieved where suppliers receive encouragement to control, and are allowed to profit by the attainment of such control.

32 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow Where a supplier is inhibited by minimum cement content specifications or not allowed to design and adjust his mixes freely, he is essentially denied the possibility of making additional profit through using good materials, good plant, or knowing or caring anything about mix design or quality control.

33 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow Under these circumstances the worst suppliers are the most competitive and control technology develops slowly if at all.

34 CONTROLLING CONCRETE QUALITY: Yesterday, Today, and Tomorrow The presented list should enable specifiers, controllers, and producers to see where they are on the time scale of development and to consider where they would like to be.