"Chert Free" Concrete

[jheidt2543]

Back in the 1970's we had a ready-mix supplier in our area that produced a "Chert Free" concrete mix. In reality, it wasn't 100% chert free, but did have a significantly reduced chert content. In our area we have a lot of naturally occuring sand and gravel aggregate that is used for concrete. I believe the supplier had some type of vibrating screening system that either bounced the lightweight chert out or floated it out in a water blast.

The concrete using this processed aggregate cost $2-3 per yard more (at that time), but we used it for architectural concrete because it would produce fewer surface popouts.

My question is, has anyone heard of this and is this type of "Chert Free" aggregate still in use or available? Our supplier has changed ownership and the equipment is not used anymore.

 

[Ron]

jheidt2543...that was also before litigious paranoia set in. I doubt that any supplier these days would certify a "chert free" aggregate in an area where calcedony chert was known to exist as a contaminant/reactant.

I worked on one about 15 years ago that cost the supplier over a million bucks in a small shopping center because of popouts.

 

[jheidt2543]

Thanks Ron for the note, I guess I was showing my age. The process did make a difference, although as noted, it was not 100% Chert Free.

I guess I was just curious about the process itself.

 

[Ron]

The process is a relatively good one, but expensive as an aggregate beneficiation these days. Even in areas of aggregate scarcity, lenses or seams of chert contamination are usually excluded as viable concrete aggregates unless performance has shown there to be innocuous results in their use.