We have done correlation studies of the pad caps and sulphur caps on many cylinders with strengths ranging from 2000 psi to over 8000 psi.  We use pad caps routinely for anything up to about 8000 psi.  Anything higher, we use conventional sulphur caps.

The pad caps work fine.  The break patterns are a bit different but the strength values correlate favorably with conventional caps.

I have already tedested it.The fracture  is entirely different.What we get A farcture for a cylinder we r getting D fracture.The ASTM also says that it will damage the compression machine.Also the cylinders r to be tested for perpedicularity.In that way it is not working fine.I want Ron to reply to this.

Most often, the fracture pattern is a center shear break with small "raveling" on the top or bottom edges of the cylinder.  You will not likely see the typical shear-cone failure pattern.

What are your strengths and how many times have the caps been used?  Are you testing the cap liners for durometer hardness?  Why are the cylinders not perpendicular to the platen of the machine?

The pad caps should not cause significantly more damage to the machine than a full break with the sulphur caps.  The difference is that we know when the sulphur capped concrete has reached ultimate and can stop the machine, though we shouldn't if we follow ASTM procedures.  With the pad caps, there is no pre-fail warning so you have to break them to ultimate and shatter the specimen.

Ron

Ron
We have started testing it initially for 10 cylinders.It showed D fracture even when the cylinder is perpendicular to the plane.I wanted to know that whether the fracture is important or not.And what is the comparison in rates with reference to capping and neoprene caps.W have used neoperene with 70 durometer hardness and we have cylinders that break between 3000psi to 5500psi.I want Ron to reply to this.

msharief...The break pattern is irrelevant as long as the correlation is good.  For our studies, using many cylinders, we found the correlation to be good even when the break pattern was not conventional.

Plot your sulphur cap results against your pad cap results and the bias will be immediately apparent if you have one.

Ron

msharief
        My office has used the pad caps for over 2000 breaks, virtually all concrete was less than 5500 psi. Our corrolations with sulfer caps, taken at random and as part of our ASTM & CCRL required comparisons have been good, AS LONG AS THE CYLINDER ENDS ARE IN GOOD CONDITION. Up until about a year ago we were corrolating at the rate of 5 pad caps to 1 sulfer cap. The sulfer has the advantage of taking care of minor to moderate end problems.  Of course, all problem cylinder ends should be cut or ground, but this doen't always occur.
        As far as damage to the machine, we have not observed any problems. The technician does have to exhibit a bit more care on the higher strength (more brittle) tests.