Forum Message



Name:   
Heading: 1.1.1Concrete Pop outs
Message:
I noticed a problem here in Minnesota of concrete popout's in concrete. It happens after the first winter, when it appears the freeze thaw cycle has an effect on the coarse aggregate. It leaves a smooth rounded stone imprint, which leads me to believe it is a sand and gravel aggregate. I actually found one piece that looks to be a piece of shale disintegrating.

Question 1)

Is there a way to prove that pop outs do not have a detrimental effect on the concrete? I have been told by a group of readymix suppliers, that it does not have an effect on the concrete. I find this hard to believe.

Question 2)

I have been asked to come up with specifications for an international firm who uses concrete to build structures all over the world. What testing specifications should be used to identify aggregates susceptible to freeze - thaw in concrete? Any suggestions as to what specifications should be used?




---------------------------------------------
Jay Lukkarila


Jay,

The freeze-thaw cycle has definitively an effect on the coarse aggregate. You could look at Canadian Standard Association (www.csa.ca) that have both standard for Concrete and coarse aggregate (CSA A23.2-24A) testing. There is other standard like ASTM C666 and ASTM C672 that are used in Canada in order to qualify scaling resistance of concrete.

---------------------------------------------
Daniel Bissonnette


The standard ready mixed concrete testing program to evaluate mineral aggregate quality in the USA is ASTM C 33 along with ASTM C 666 procedure A for US Army Corps of Engineers and FAA Airport projects or procedure B for the Departments of Transportation in the midwestern states to evaluate D-cracking. Alkali reactivity testing is also commonly required with ASTM C 1260 the common screening test (known to produce false positives for many aggregates) or less commonly requested ASTM C 1293, a more reliable indicator of alkali reactivity. C 1293 requires 12 months minimum and usually 24 months, so the test is not well suited to fast track testing. The tendency for developing popouts can be acertained to a large degree by a visual examination of the C 666 beams after the final cycle. I believe C 666 is the most severe test we perform on aggregates.
---------------------------------------------
Jim Fletcher
 
   Click Here to Reply    Areas
Advertise Here