P2P WHAT DOES IT MEAN

1
P2PWHAT DOES IT MEAN?

• Ken W. Day
• Consultant, Australia

2
Two Alternatives

• PRESCRIPTION TO PERFORMANCE
• (true meaning, as intended by USA initiators)
• PURCHASER TO PRODUCER
• (my interpretation of significance as to who
  designs and controls)

3
The Current Situation

• USA is almost the last major country where
  specifiers/purchasers of concrete nominate actual
  mix details rather than the properties required
  of the concrete.
• As a consequence of this there is no financial
  incentive for producers to acquire expertise in
  mix design or quality control

4
The Current Situation

• So any producer who spends money on better plant
  and materials than he can get away with, or
  employs more or more expensive staff, prejudices
  his chances of obtaining a contract under
  competitive tendering.

5
Difficulties to be Overcome

• Specifiers and producers eye the overseas
  situation enviously
• Specifiers would like to allow more freedom to
  producers if only the producers were more expert
• Producers would like to develop more expertise if
  enabled to profit by it

6
Difficulties to be Overcome

• The real difficulty seen by US specifiers is how
  to ensure durability as opposed to strength.
• They are leaning towards RCP tests (Rapid
  Chloride Permeability) but this is both too
  delayed and has too high variability for use as a
  primary acceptance test.

7
Difficulties to be Overcome

• My solution to this is to use strength for
  primary acceptance and to insert a bonus/penalty
  clause based on several RCP results over a period.

8
Standard Mixes

• A major benefit of a performance specification is
  that it permits a producer to develop and control
  a range of standard mixes of which a range of
  properties have been established in advance of a
  particular contract.

9
Reaction to Change

• A quick reaction to any change in concrete
  quality is very important.
• A purchaser cannot demand a reaction until there
  is clear evidence (usually taking weeks) but a
  producer can take action at the first sign of
  change.

10
Costs of Inaction on P2P

• A prescription specification must necessarily be
  more conservative and allow for greater
  variability.
• It is likely also to increase the producers
  costs by requiring him to use or not use
  particular materials.

11
Costs of Inaction on P2P

• A prescription specification would also increase
  the purchasers costs substantially if he really
  exercised control over his concrete.
• However few specifiers have the expertise to do
  more than pick on isolated items in a submission
  and react to an unfavourable report from a
  commercial testing lab.

12
Costs of Inaction on P2P

• Other substantial worries are that few specifiers
  have the expertise to know what really matters,
  particularly in respect of supplementary
  materials such as fly ash, silica fume,
  metakaolin, limestone fines and high fines
  contents in crusher fines used as fine aggregate.

13
Inept Specifications

• Favourite items to specify are minimum cement
  contents and/or water/cement ratios.
• W/C ratio is an important factor but is very
  difficult to measure and enforce.
• Excess water is more deleterious than less cement
  at a given W/C, so, at a given strength, the mix
  with the lowest cement content is the best mix.

14
Benefits of Producer Control

• Under producer control, any substantial producer
  finds it worth while to operate his own high
  standard laboratory
• A good specification clause, after specifying
  required properties, would be the producer shall
  operate an approved effective QC system