Masonry Magazine August 2000 Page. 11
OF MORTAR
pling mortar at various stages of construction, and by performing tests on mortar in plastic and hardened states. The test results could verify data derived from preconstruction testing and could reflect variations in mortar performance characteristics resulting from batching during mortar production and use at the job site. If inconsistencies between preconstruction mortar composition and on-site mortar composition exist, immediate corrective action to modify mortar batching and mixing can be introduced.
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INTERPRETING FIELD TEST METHODS
ASTM C 780 outlines procedures for measuring physical properties of plastic mortar such as consistency, air content, water retention and board life. It also defines methods for obtaining the aggregate ratio and water content of freshly mixed mortar, a procedure that can be used to verify the accuracy of site proportioning of mortars. Procedures for measuring properties of hardened mortars, such as compressive strength, are also defined.
Consistency
The consistency of field mortars is an indicator of batch-to-batch variations in mix materials and mixing time. Large variation in consistency readings is an indicator of poor control during mortar batching and mixing. However, erratic consistency does not indicate whether mortar materials are improper. The consistency of field mortars can be measured using a cone penetrometer as referenced in ASTM C 780. This device measures the depth of mortar penetration in millimeters. The values obtained can be used to verify that the consistency of each batch of mortar is the same. A consistency measurement of 55 millimeters is good for low-to-moderate suction masonry units, while a measurement of 65 to 70 millimeters is required for high suction masonry units.
Air Content
Repetitive testing to determine mortar air content indicates changes caused by variations in mixing consistency and in mixing time. The air content of field mortars can be measured by using a pressure meter or by using a "roll-o-meter" as indicated in ASTM C 780 Annex A.6. The pressure meter is easier to use in the field, but the "roll-o-meter is more accurate.
Water Retention
Water retention measures the plastic life and workability of mortar. Mortars with sufficient water retention allow the mason time to set and adjust the mortar and masonry unit before the mortar begins to harden. A water retention test indicates a mortar's ability to retain mixing water after being exposed to suction from a masonry unit. Water retention tests must be performed in the laboratory.
Board Life
Board life is the time frame in which a masonry mortar can be used after it is removed from the mixer and placed on the mason's mortar board. Once mortar is placed on a board, it begins to stiffen through loss of water and harden through normal setting of cement. If mortar begins to stiffen before it is placed in usage, bonding will be negatively affected. The method for measuring board life is indicated in ASEM C780 Annex A.3. This method is useful for determining whether a mortar is acceptable or unacceptable due to stiffness.
prepares a mortar sample at the BAPS Cultural Center.
Coutimaal ott per 12
MASONRY-JULY/AUGUST, 2011