Volume 1, Issue 1 (January 1973)
Some Factors Affecting Cement Mortar Strength Results Using ASTM Standard Test Methods C 348 and C 349
The purpose of this study was to determine the effect of certain factors on test results when using ASTM Methods C 348 and C 349. For this purpose, four series of 3 mortar mixes each were made, and companion test specimens were molded using both hand tamping and vibrating methods. The results showed that, (1) Compaction of mortar test prisms by hand tamping produced densities which increased from the center towards both ends of the prism by an average of 2.1 percent; whereas this increase for prisms which were compacted by vibration averaged only 0.3 percent: (2) Compressive strengths by modified cube tests at the end locations averaged 5.6 percent higher than those at the middle of broken halves of the prisms compacted by hand tamping, but there was only 0.7 percent difference in strengths for the prisms compacted by vibration (Series IV): (3) The density of prisms compacted by vibration was, on the average, 3 percent less than that of tamped prisms. However, their flexural strength, on the average, was 8.5 percent higher than that of prisms compacted by tamping. (4) In comparison with standard 2-in. (50 mm) cube strengths, the compressive strengths of modified cube tests at the middle of broken halves and at the end of the prism averaged 96.0 and 101.7 percent, respectively, for tamped or 96.2 and 96.8 percent, respectively, for vibrated test specimens.