4 x 8 inch Concrete Cylinders versus 6 x 12 Cylinders

About the report:

Laboratory and field investigations were conducted to compare the compressive strengths obtained for 4 x 8 in. (100 x 200 mm) cylinders with those for standard 6 x 12 in. (150 x 300 mm) cylinders, both made with aggregate having a nominal maximum size of 1 in. (25 mm). In the lab, in addition to the effect of specimen size on strength, other factors as the mold type, aggregate type, and strength level were considered. The results of the laboratory work indicate that the two sizes of cylinders yield equal compressive strength values at a strength level of about 3,200 psi (22.0 MPa). Above this level, the small specimens exhibit higher compressive strengths. The difference in the strength values between the two sizes increases with the strength level. The standard deviation of strength values was higher for the small specimens. For equal precision, more tests are needed for the small specimens than for the larger ones. The field investigation included an examination of the effect of different specimen sizes when different types of mold and capping procedures were used for each size. The results of the field tests comparing specimen sizes were similar to those of the laboratory tests in terms of strength and variability. It is concluded that the results of tests on 3 small cylinders cast in plastic molds and tested with neoprene pads in steel end caps can be used to predict the strengths of A3 and A4 concretes obtained by tests of 2 large cylinders cast in steel molds and tested with sulfur-mortar caps. The variability of small cylinders compared to that of larger ones prepared in the field was slightly higher, even though statistically not significant. Thus, the use of 3 small cylinders rather than 2 larger ones is recommended.

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