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Definition of "well graded" coarse aggregate?

Definition of "well graded" coarse aggregate?

Definition of "well graded" coarse aggregate?

Hello all,
After reading ACI 325.11R-01 and looking at Figure 4.2, I am led to believe that a well-graded aggregate is pretty important to a pavement mix.  How do I go about mandating this in a project specification? (or do I need to?)
Is the importance of well-graded aggregate over-emphasized in ACI 325.11?
(I'm trying to arrive at a concrete spec for a parking area that sees semi loads and long winters with plenty of salt.  High early strength will be good in order to get the semis back on it quickly.)
Thanks for any comments.

RE: Definition of "well graded" coarse aggregate?

Unless you are in a rural area where the aggregates are not subject to much QC, I would suspect that this is a non-issue from the point-of-view of worry.  However, grading is important for 2 reasons:

1.   A well-graded aggregate (having a reasonable amount of aggregate retained on each sieve) will provide the most economical concrete mix compared to a poorly graded aggregate.  A well-graded aggregate will tend to have the least amount of voids and will require less paste (cement and water).

2.  A concrete containing a well-graded aggregate is easier to place, compact and finish.

With respect to deicing salt and freezing and thawing, refer to the PCA publication Design and Control of Concrete Mixes.  A cementitious content of 575 lb/cy, 6% total air content and a water/cement ratio of no more than 0.45 is recommended, with adequate curing, and a period of air drying prior to application of deicers.  Note that you can get almost the same effect as high-early cement (type 3) by using 10% more type 1.

Also - check with your local ready-mix association for model specifications.

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