method for testing in-place masonry grout 2

[whir]

I have a job that has grout tests at 61% of required strength. I need to have a section of the parapet tested to see if this is the strength of the wall above the roof. Does anyone know if there is an ASTM standard that covers this? I have looked at ASTM C1019 and it does not give specific information for an in-place condition. Thanks for the help.

 

[JAE]

You would probably have to cut out a prism specimen and test that for overall f'm

 

[concretemasonry]

ASTM does not have a specific procedure for your needs. Have the previous ASTM 1019 grout tests been in compliance?

Testing based on cut out prism samples is a very tricking and difficult proposition. It is depenadant on the location selected, the sawing, sample handling and testing variables. A masonry prism is a very difficult animal to handle properly. As you see, there are many variables.

Since it is a parapet wall. there is no compressive load, so the only purpose of the grout is to bond the rebar to the masonry units for the cantilever strength. There is no real need to fill the unrefinforced cores, but if there are some grouted unreinforced cores, you could core a sample cylinder, separate it from the masonry units and conduct a compressive strength test of the cylinder.

The the challenge then becomes to determine the adequacy of the grout for bond in case the grout sample does not meet the compressive strength speification requirements. The in-place compressive strength of the grout in a parapet will be lower than the same grout in a full height bearing wall due to the fluid pressures present during the placement/absorption and curing process.

Usually, in-place grout tests much higher than grout samples. Frequently, grout is incorrectly cured in non-absorbant molds, creating low sample strengths similar to the relationship you cited (61%).

Also, grout can be specified with the incorrect "stronger is better" concept and the specification could really be a barrier to address when the suitability/tear-out question comes. For a parapet application, the grout really does not have to be any stronger than the f'm of the hollow masonry units in place, but that is a practical question for the designer and spec writer.

Dick

 

[msucog]

"stronger is better"--i about fell out today when i saw a 7 day break at 7000+psi for a 3000psi mix...glad it wasn't my job to have the headache on.

i agree with concretemasonry (he's usually on target with his comments...unless he's hassling me about something). first, check to see if the grout was batched onsite or at plant. then check the prism casting procedure (non-absorptive part is probably most critical). if batched on site, it's highly likely the proportions are screwed up and the testing may or may not have been regularly checking that...either way, it's the contractor's headache if they messed up the proportions. cutting the prisms out of the wall and getting "reliable" results is tricky so if it's only one set of failing test results, i'd try to get a comfort level through other means. maybe double check the individual block units first then try to cut a core if possible. get input from the testing firm and batch plant on what they think...i'm sure the batch plant will point fingers at the testing firm and the testing firm will defend themselves and kick it back to the contractor/batch plant. try to decipher through all that. if you've got widespread failing tests, the headaches may be multiplied. try to find the simple solutions first and work you way down the pyramid of possibilities. that's my advice. oh, and i also agree with the last line on concretemasonry's last post.