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Re: Pea Gravel Concrete

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seaoc(--nospam--at)seaoc.org,Internet writes:
Can anyone tell me if there could be potential problems in approving the
contractor  to use pea gravel rather than 1" rock concrete mix as specified
on
the plans? The concrete is used for a 3,000 psi grade beam in a two-story
type
V residential building.

Paul Willow

Some general ways aggregate size can influence concrete.  Agregate surface
needs to be coated with cement paste.  Smaller aggregate has a greater the
surface area requiring more cement paste (and water as a lubricant) which
increases shrinkage.  You want as much of the volume as possible to be filled
up with aggregate.  By using pea gravel you will need more sand to fill up
the smaller voids, hence more cement paste to coat the surfaces giving lower
strength and higher shrinkage.  "Generally speaking", smaller aggregate size
gives lower strength concrete for a given water/cement ratio.

The next question I would have is "Does this mix design meet requirements if
ACI chapter 5 (UBC 1905)"?  Does this pea gravel mix  design have a
historical record of testing showing it meets the required strength per ACI
code?


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Richard Lewis, P.E.
Missionary TECH Team
rlewis(--nospam--at)techteam.org

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