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ASTM C780 Mortar Testing

ASTM C780 Mortar Testing

ASTM C780 Mortar Testing

What would an engineer of record want to see when specifying ASTM C780 for CMU construction on a non-load bearing single wyth wall.  The test method calls out several possable tests including compressive strength, splitting tensile strength, air content and board life.

At what stages ie 7 days, 14 days or 28 days after casting should or would the EOR want to see results.

wouldn't treplets of fully grouted and ungrouted prisms tested for strength make for a more confident (competent) test?

RE: ASTM C780 Mortar Testing

rjeffery...the only definitive, quantitative test in C780 that applies to general masonry construction is the compressive strength test.  The other tests, while providing useful information for evaluative purposes, do little to give the engineer of record solace of a good masonry job.  

Further, I'm usually more concerned with consistency than strict numerical values as I often see compressive strengths that don't get anywhere near the compressive strength criteria for, say, a Type S mortar.  For this reason, when in a position to do so, I require strict measurement of proportions of materials (1 pt. pc, 1/2 pt. lime, 3 pts. sand as an example).  This cannot be done properly with the methods commonly employed (a shovel for the sand, bags for the masonry cement).  I require that the contractor build a one cubic foot box to be used for all measurements.  This prevents the problem of oversanding in the morning when the masonry sand is damp and undersanding in the afternoon after drying.

Extracting prisms from completed construction can be done but extra care must be taken so as not to disturb the integrity of the specimen.  You can also specify an in-place load test using a flat jack and jacking upward against completed masonry.  

RE: ASTM C780 Mortar Testing

Thank you Ron,

My question stemmed from a master spec section 04810 in which the boiler plate said to test the mortar in accordance with ASTM C 780, or words to that effect, without specifically calling out tests and ages to be tested like the 03300 does.  I am concerned with giving the engineer of record the information that he/she needs to provide an amount of certitude that the CMU system in place is adequate to the task it was designed for.  In my case the EOR and the designer are NOT the same.

I enforce strict proportion control as the QA rep on site, but I can't direct the QC as they are contracted out to the (Oh, Heavens) contractor.

I would prefer to see that ASTM C 1314 for masonry prisms are done at the begining, middle and close to the end or the project.  Is that an acceptable method of quality control/assurance?

And if mortar and grout are to be tested, is 7 days, 14 days and/or 28 days after casting adequate for the EOR to have results to provide certitude that the system will perform as designed, to allow bracing to be removed, or to receive structural steel loading?

Thank you again for your insights in these forums


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