Void Parameters of 24 Cores of Concrete Removed From a Consolidation Test Study Section of I-64

About the report:

During the construction of I-64 near Charlottesville, Virginia, the Ballenger Paving Company chose to set up a limited experiment to investigate various factors affecting the consolidation of concrete by vibration. The test design varied the speed of the paver and used vibrations at several frequencies. Speeds of 3, 4, 25, 5.5, 11, 12, and 14 feet per minute and frequencies ranging from 7, 800 to 10,100 revolutions per minute were used in 6 test sections. When the experiment was initiated it was anticipated that differences in the concrete which were related to the variations in vibration would be reflected in the results of conventional measurements of density and void content made on cores removed from each of the test sections. The unit weights determined on the cores indicated large variations in void content across the width of the pavement at a given station. In the hope of determining whether the variations in unit weight were due to variations in the air void system or to segregation of the aggregate, the Research Council was asked to make micrometric air void and aggregate analyses on 24 core samples. The analyses showed that for any particular concrete the faster the motion of the vibrators through the concrete and the greater the spacing the less will be the consolidation. Between batches, it was found that the greater the slump or workability, the greater the consolidation achieved by a set of vibrator conditions. The frequencies of the vibrators used covered such a narrow range that no correlation between frequency and consolidation was possible. Insufficient sampling precluded the determination of aggregate segregation. Although the numerical results of the void determinations and correlations with vibration parameters are not statistically defensible, the trends obtained appear reasonable and valid and should be helpful in establishing general relationships. The results are presented in numerical form to provide data as to the order of magnitude of the interactions of the factors involved in the consolidation process. For the type of concrete and kind of vibrators used, the data seem to indicate that if the slump approaches l-inch then the forward speed of the vibrator screed should be no more than 6 feet per minute when the spacing of the vibrators is about 2 feet. Higher speeds will probably produce high void, less abrasion resistant areas of pavement.

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