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RE: Grout in lieu of conc.

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I agree with the cautions about the contractor's solution.  Another consideration should be reactive aggregate.  Gravels in particular are very often reactive.  Was ASR checked?

Regards, Harold Sprague


From: thorm(--nospam--at)
To: seaint(--nospam--at)
Subject: RE: Grout in lieu of conc.
Date: Tue, 12 Oct 2010 13:03:29 -0700

It's not really "grout" unless you're using it for masonry, in which case it would need a slump of about 9 inches or more.  But what you describe is pretty lousy concrete.
Shrinkage will be a big issue, and is really unavoidable because of the extra water needed to coat the increased surface area of smaller aggregate (much larger surface area for same mass of pea-gravel vs. 3/4" or 1-inch rock).   Pea-gravel mixes are usually about 55% sand, 45% gravel.  Best mixes that can be 'tail-gated' or pumped with boom-pumps are 65% rock and 35% sand.
I really dislike pea-gravel concrete that I've seen;   furthermore I question the economics of using a pump.  While placing concrete for one phase of my own recently-completed basement project, I hired a "rock-pump" that could hande 1-inch aggregate.  It took 3 or 4 guys to haul the pump hose around, the line clogged once or twice because the overkill engineer (moi) wouldn't add water to the mix, and the pump guy dumped a big pile of waste concrete next to my driveway.  For the next phase *I* was the "pump."  I wheel-barrowed about 6 CY of concrete into place (spent about $30 extra on 'stand-by' time for the concrete truck, but saved $200 on the cost of a pump--not to mention the 3 guys to drag the pump hose around).   Most recently I was one of 3 guys who carried concrete in 5-gallon buckets to dump into the top of the last section of wall forms.
Unless you have to work off of a scaffold, I'd bet that moving mud by wheel-barrow is as fast as, and cheaper than, a pump--and you get much better concrete.  But what do I know, I'm only a structural engineer and builder....
Thor Matteson
From: "Joseph R. Grill" <vveng(--nospam--at)>
To: <seaint(--nospam--at)>
Subject: grout in lieu of conc.

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I have a contractor that wants to use a pea gravel grout in lieu of regular
aggregate concrete due to pumping reasons.  In all my years I have never
been asked this.  At first thought I can't think of a reason why not. Any
reasons why not or anything else I should watch for?




Joseph R. Grill, PE

Verde Valley Engineering, PLLC

email: VVEng(--nospam--at)