Aggregate Absorbtion

[Timothy]

Hello,<br>
<br>
I would like to know the problems associated with excessive aggregate absorbtion within concrete and the specifications associated with this area.<br>
<br>
Tim

 

[Ron]

Assuming you are referring to sound but absorptive natural coarse aggregate, I offer the following...<br>
<br>
Absorptive aggregates are difficult to maintain in a saturated, surface dry condition (the basis for mix design proportion computations) so the tendency to have difficulty in controlling the workability of the mix is usually greater. Takes a lot of effort on the part of Ready Mix supplier. Slump loss during placement or pumping can be pronounced, leading to excessive retempering, which is not good for the strength or durability of the concrete.<br>
<br>
Absorptive aggregates have less natural resistance to freeze-thaw as their void structure allows water to freeze and deteriorate the aggregate.<br>
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Natural limestone aggregate is a common absorptive aggregate used in Florida and other locations with excellent success, but requires recognition of the quirks of the material.

 

[ckellerman]

In cold areas, absorptive quarried aggregates must be carefully examined for suspectibility for D-cracking if the application is outdoors. Many state DOTs have already set up programs to certify aggregates for D-cracking, but if it is an untested source, the ASTM D666 test is very lengthy and costly. Normally, river rock is not a threat because mother nature has already put the material through enough freezing cycles to break down the bad rocks.<br>
I would echo Ron's comments on the difficulty in maintaining a consistant mix delivery to the job, especially from a nearby plant when minimum allowable mixing takes place. A highly absorptive material can drive a tester mad at the slump cone.