Masonry Magazine April 1997 Page. 39
ASTM C 780 outlines procedures for determining properties of freshly mixed mortar, such as mortar consistency, board life, and air content. It also outlines procedures for determining the aggregate ratio and water content of freshly mixed mortar, a procedure that can be used to confirm accuracy of site proportioning of mortars. Finally, it defines procedures for measuring properties of the hardened mortar such as compressive strength and splitting tensile strength. If ASTM C 780 compressive strength tests are to be conducted during construction, preconstruction tests need to be performed to establish baseline values that can be expected during construction when using the approved mortar mix design. Field test results of mortar conducted according to ASTM C 780 are not required to meet the minimum compressive strengths of the property specifications of ASTM C 270. Field test measurements of the compressive strength of mortar can be expected to be lower and more variable than laboratory test results, and do not correlate well with the structural properties of the in-place masonry. Since a significant time interval is required between sampling of mortar and obtaining results, compressive strength tests are not an effective means of establishing control of mortar proportions. Observation or utilization of the aggregate ratio test provides more timely information with respect to proportioning. Additional information on field testing of mortars and on the relationship between mortar compressive strength and the compressive strength of masonry is contained in PCA publications IS 242, Trowel Tips: Field Testing Masonry Mortar, and IS 276, Compressive Strength of Masonry.
The Quality Perspective.
Good information, effective management systems, and quality conscious personnel will minimize the occurrence of mistakes and problems. However, if something does go wrong, the mason contractor should look at that situation as an opportunity to communicate to customers and employees his commitment to providing quality masonry. The steps required to do this are: define the problem, determine the cause, decide on appropriate corrective action, and take that corrective action. Corrective action includes correcting existing errors and modifying or implementing procedures to prevent reoccurrence of the problem. The knowing and doing are driven by a commitment on the part of the mason contractor to provide quality masonry. The mason contractor needs to communicate that commitment to customers and employees both through words and action.
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Editor's Note: John Melander is Program Manager, Masonry in the Department of Engineering Services, Codes and Standards for the Portland Cement Association and a member of MASONRY'S Editorial Advisory Board.