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RE: Concrete Mix Design

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James,

I will reply below.

Regards,
Harold O. Sprague

> -----Original Message-----
> From:	James Lin [SMTP:se3949(--nospam--at)yahoo.com]
> Sent:	Monday, October 01, 2001 6:39 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Concrete Mix Design
> 
> Hi everyone,
> 
> There are 3 concrete mix design samples, all have same
> AMOUNT of cement, water, fine aggregate (in VOLUME),
> coarse aggregate (in VOLUME), etc., except that
> SAMPLE A: well-graded combination of max. 1" crushed
> rock coarse aggregate
> SAMPLE B: well-graded combination of max. 3/8" crushed
> rock coarse aggregate
> SAMPLE c: max. 3/8" pea gravel coarse aggregate
> 
> Question:
> 1. Which one is cheapest in cost? 
	It depends on the operations of local aggregate suppliers.  If they
have computerized screens they tend not to stock pile.  They can basically
dial in the aggregate gradation that they want for no real additional cost.
If they stock pile canned fixed gradations (like the LA Green Book) there
would be more of a handling cost and Sample C (which is a standard) would be
the least expensive.
> 2. Which one is strongest (in compression)?
	Sample B would probably be the strongest.  Although for strength I
prefer to go up to 1/2" max aggregate.
> 3. Which one will shrink least? 
	Sample A would shrink the least because it minimizes the paste.  It
is the paste that shrinks.
> 4. Which one is the structural engineer's best choice?
	It depends on the application.  For slab on grade minimize the
shrinkage.  For structural work maximize the strength, but don't ignore
shrinkage.  For heavily congested rebar areas go to the pea gravel.  

	Don't pay too much attention to the cost per yard of the concrete.
You want to consider more what it costs in place and serviceability.

> Thanks for your opinion,
> 
> James Lin
> IDS, Inc.
> 
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