Field Testing of Masonry Mortar and Grout: Consistency, Water Content, and Strength Specimens
Consistency, water content, and specimens
Field mortar testing under ASTM C780 typically includes consistency, water content, and compressive strength. Consistency may be measured by cone penetration or by flow table (ASTM C1437); these are different methods and are not interchangeable. Water content is determined by drying a representative mortar sample-oven or microwave-and calculating water as a percentage of the dry mass. Compressive strength specimens are molded from field mortar, usually as 2-in. cubes, consolidated, moist-cured, and tested at the specified age. Grout specimens under C1019 are sampled and molded separately; grout strength is not inferred from mortar cubes.
The controlling variables are time, water, and specimen preparation. Adding water in the field to restore workability raises the water-cementitious ratio and lowers strength; a technician must record any water added and must not test a sample that has been retempered. Mold specimens with the specified number of layers and rodding or tamping, strike off the top, and cure under the standard's moisture and temperature conditions. Identify each specimen and record the mold, curing history, and test age.
Trap: reporting flow as a penetration value, or treating a single cube as the test result; the result is normally the average of a set, with individual values reported. Another trap is computing water content on the wet mass rather than the dry mass. Worked example: wet mortar 500 g, oven-dry 435 g. Water = 65 g; water content = 65/435 × 100 = 14.9% of dry mass. If the specification limit is 15%, the sample passes narrowly.