Unchanging concepts - Concrete Mix Design, Quality Control and Specification - page 254

Parallel tests by two laboratories on the same truck of concrete reveal
useful information and should be arranged from time to time.
The whole question of the reliability of concrete testing results is a matter
that has received far too little attention. However, it is not a valid reason for
failing to institute the type of cash penalty specification advocated here, as
it causes even more trouble under existing types of specification.
No one can afford cheap testing. The best prospect of reducing testing
costs is to reduce the frequency of testing, made possible by better testing,
better specifications, better analysis of results, and a reduction in the vari-
ability of concrete.
Legal enforceability
Extremely crude forms of penalty are sometimes encountered, particularly
on government work. Such penalties are enforced on the basis that future
contracts will be withheld if they are disputed.
In British and Australian law, the key to legal acceptability is to relate
the penalty to the harm suffered. It is assumed that a building owner would
prefer to pay for the grade of concrete specified rather than accept a lower
grade of concrete at lower cost. If the owner is supplied a lower strength
concrete than specified, then he must have suffered harm in excess of the
cost difference (in terms of margin of safety, durability, etc.) between the
two strength levels.
Actually, the penalties considered here are too small to be worth a con-
tractor's expense to legally challenge. However, the penalties are sufficient
to ensure his cooperation in avoiding them. What the law does object to are
penalties specified to scare the contractor into compliance.
Experience in Australia
Although this proposal is now 20 years old, it has been applied to only
one major contract by Ken Day. This was the Victorian Arts Centre (the
Melbourne equivalent of the Sydney Opera House). On only one occasion
did the results actually merit a cash penalty, which was paid.
However, thousands of cubic metres of concrete have been supplied to
dozens of structures using the previously discussed control system, but
without the cash penalty provision. On no occasion has it proved necessary
to actually remove concrete from any of these structures.
Generally, concrete suppliers have been responsive to requests to adjust
cement contents based on early age analysis. However, there have been fre-
quent occasions when the strength provided, assessed as above, has fallen
below that strictly required, for extended periods, by 1 MPa (145 psi) or less.
Such minor deficiencies have no structural significance but do waste time
in repeated requests and reports and arguments with concrete suppliers