Use of Unbonded Caps 2

[BigH]

Just wondering how many out there use unbonded caps as per ASTM C1231? We are crushing upwards to 200 cylinders each day.

 

[Ron]

BigH...Do a correlation between sulfur caps and unbonded caps to satisfy reasonable QA and then use the unbonded caps. They are easier to use, safer, less expensive (long term) and the results are consistent. Can you have problems with them? Sure. When the elastomer gets worn, the results become less consistent and the edges of the cylinder start to ravel. Also, if the cylinders are not plane within reasonable tolerance, I'm not sure if the results are as consistent.

We don't test cylinders in our lab, but did so for over 25 years. Started using unbonded caps in mid-90's, correlating at regular intervals. Government agencies wouldn't always accept the results, so we had to do those tests in conventional manner.

 

[emmgjld]

BigH ... I have been using unbonded almost exclusively for over 12 years. So long that I had a problem with some of my sulfer getting old and not gaining sufficient strength for our CCRL Inspection a couple of years ago. Had to sort through and open our newest bag to actually make strength. EMBARRASSED!!!

Most of the time, minor grinding to take care of the edges. We do have to actually trim about 5% of the specimens with a diamond saw. I consider that a small price.

As Ron stated, the pads get worn, sometimes a little faster than expected, depending on concrete strength and conditions of the cylinder ends. I make sure we have an adequate supply on hand so there is no incentive to overuse them. Some agencies and Engineers have squirmed a little but not much anymore.

I get the most grief from using 4"x 8" cylinders. You know that bigger is always better, I done it this way for 30 years (me too except I am 40 years) and all that.

 

[BigH]

Thanks my friends . . . Contractor has over 200 sets of the neoprene pads. Our concrete is typically less than 35 MPa so not testing high strength - using steel moulds. We have a ready supply of sulphur - client needs it for his smelting ops; but do have probs with local labour getting caps on just right (too many rejects with "hollow" sounds). Cheers.

 

[Ron]

BigH...sounds like a good move to go to the pad caps.