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RE: Spec needed for 3000 psi concrete

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I agree with Bill (talk about a shocker!).  The enigneer does have the
responsibility to clearly "specify" what must be used.

This does not mean that what Dennis did may or may not meet that "level".
If Dennis only cares that it is a 3000 psi mix, but does not care what the
about the specifics what is used to get to that strength value (i.e. w/c
ratio, aggregate size, amount (if any) of fly ash to be allowed, etc),
then a very limited spec might be OK.

The problem is that a mix that a supplier may use might easily meet the
3000 psi strength requirement in a "controlled" environment (i.e. cylinder
testing) but the in the field other factors could cause it to no longer
meet the strength requirements in the end for example because the mix
design and envrionmental conditions are such that the heat of hydration
rate causes signigicant shrinkage and cracking and overall deterioration
of the concrete.

In otherwords, it is the engineer's responsibility to look at "situation"
that the concrete will be placed and ultimately "live" and determine what
requirements might be necessary to achieve a quality concrete by making
sure that there is a proper mix design AND proper handling during place,
finishing, and curing.

After all, your typical concrete spec calls out more than just the mix
design.  It should address what curing methods (if any) are required; what
finishing requirements are required; any special requirements such as hot
weather concreting (likely in Dennis' case as he is out in a desert area)
or cold weather concrete; etc.

Bill is on point in suggesting ACI 301 as a good basis.  That is precisely
what it is "made" for.


Adrian, MI

On Fri, 8 Oct 2004, Bill Polhemus wrote:

> I disagree. ACI 318/315/301 give the "division of labor" between engineer
> and constructor. We engineers DO have a responsibility to be precise in our
> specification of material requirements.
>   _____
> From: David Maynard [mailto:davemaynard(--nospam--at)]
> Sent: Friday, October 08, 2004 12:57 PM
> To: seaint(--nospam--at)
> Subject: RE: Spec needed for 3000 psi concrete
> Dennis,
> I tend to agree with Joe on this one.  Really let your contractor do the
> work.  The more guidance you give him, the more liability you accept on the
> project.

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