C-1107 Brass Molds vs. Plastic Insert Molds 1

[RStrickland]

I am trying to determine if there is a reason I can't use the plastic inserts for C 1107 testing vs. buying several new brass molds. All I can find is that the mold must be made of metal, which the ones that use the plastic inserts are. Can anyone point me in the right direction either for or against the use of the plastic inserts?

Thanks.

 

[Ron]

Since C1107 references ASTM C109 as the method of test, check that standard to see if it allows the inserts. I believe it does, but you need to check.

 

[lokasjoa]

Looks like what i can interpret, is that you can use those inserts as long as they are backed by the brass molds. Just like using a metal plate to cap blocks, so must you use a metal backing to ensure the .002 spec for planeness on the samples

 

[cementguy49]

On a project some time back we found significant discrepancies between cubes cast with plastic inserts vs. cubes cast in a brass "gang" mold. Upon close inspection we found that none of the surfaces of the cubes made with the plastic insert were plane. This causes a point loading and all of those cubes produces failing results. It is very important that your lab tech check the plane of test specimens before testing for compressive strength.

Fred J. Croen
Technical Services Manager
Keystone Cement Company

 

[henri2]

For non-shrink grout, plastic molds will lead to low compressive strength test results. I have witnessed this. Some materials engineer explained the reason to me. Whether he was right or not, I recall what I witnessed with my own eyes.

I am sure studies have been done on this. Anyway here is one of many articles that addresses this.

http://www.lmcc.com/concrete_news/0301/seven_deadly_sins.asp

 

[msucog]

plus plastic molds have to be replaced much more frequently. i suggest going brass.