Evaluation of the ASTM Standard Consolidation Requirements for Preparing High-Strength Concrete Cylinders
N. J. Carino, G. M. Mullings and W. F. Guthrie
Appears on pages(s):
Compressive strength; consolidation; cylinders; density; high-strength
concretes; segregation; statistical analysis
An experimental study was designed to accomplish the following: 1) Compare strengths of cylinders prepared by vibration or rodding following current ASTM C 3 1 and C 192 requirements for the number of layers; 2) investigate whether the experience of the operator affects cylinder strength when vibration and rodding are used to consolidate the specimens; and 3) compare the strengths of 100 x 200-mm rodded cylinders prepared by using two or three layers. Two experiments were designed: 1) a half-fraction, factorial design with the following factors: cement content, slump, cylinder size, consolidation method, and operator; and 2) a comparative design to compare the strengths of 100-mm diameter cylinders rodded using two or three layers with the strengths of 150-mm diameter cylinders. The following summarizes the observations from the first experiment: Overall, the 100-mm cylinders (three layers) were 1.5% stronger than the 150-mm cylinders. However, due to a significant interaction effect of size*cement content; there was a 3.4% difference at the high cement content and no statistically significant difference at the low cement content. Overall, the rodded cylinders were 4.2% stronger than the vibrated cylinders. There was a significant interaction effect of method*size; therefore, the rodded 100-mm cylinders were 7.4% stronger than the vibrated 100-mm cylinders, but there was no difference between the 1 50-mm cylinders prepared by the two methods. Also, the rodded 100-m cylinders were 4.6% stronger than the rodded 150-mm cylinders, but the vibrated 150-mm cylinders were 1.6% stronger than the vibrated 100-mm cylinders. The experience of the operator had no effect. There was no significant interaction between slump and method. There was no significant interaction between cement content and method. In the second experiment it was found that the strength differences between 100-mm and 150-mm rodded cylinders were reduced by one-half when two layers, instead of three were, were used to cast the 100-mm cylinders.