Masonry Magazine August 2000 Page. 13
Mortar-Aggregate Ratio
Repeated testing for mortar aggregate ratio can indicate a mixer operator's ability to properly and consistently add the cementitious materials and sand to the mixer and can determine batch-to-batch variations in mortar composition. The method for determining mortar-aggregate ratio is indicated in ASTM C 780 Annex A.4. The test is performed by obtaining a representative dry sample of mortar mix from the job site and performing a series of calculated measurements in the laboratory. However, the sieving operation utilized during this test is not capable of separating an individual cementitious material when more than one material is used.
Compressive Strength
Compressive strength tests of mortar prepared in the field reflect approximate mortar strengths. Samples of field mortar are retrieved in molded cylinders or cubes and delivered to the laboratory for testing. The methods for compressive strength tests are indicated in ASTM C 780 Annex A.7. The values obtained from testing are not to be compared with strength requirements listed in ASTM C 270 or with compressive values obtained from preconstruction testing.
SUMMARY
Establishing a quality control program for mortars by requiring field tests in conformance with ASTM C 780 can be beneficial. Field testing mortar can provide valuable information of properties and characteristics of mortar prepared at the job site. However, the information obtained through this testing should be used to modify the consistency of mortar mixed in the field and not to condemn a mortar based on previously obtained results.
NOTE FROM EDITOR: For more on mortar testing, see accompanying article "A Misunderstanding or Mortar Failure" on page 14.
Robert L. Nelson is the President of Robert L. Nelson & Associates, Inc. in Schaumburg, IL. He also sits on the CAA Editorial Advisory Board.
Photos taken on-site at the BAPS Cultural Center in Bartlett, Minos.
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MASONRY-JULY/AUGUST, 2000 13