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System for Calibration of the Marshall Compaction Hammer.


pdf icon System for Calibration of the Marshall Compaction Hammer. (6913 K)
Shenton, H. W., III; Cassidy, M. M.; Spellerberg, P. A.; Savage, D. A.

NISTIR 5338; FHWA-RD-94-002; 149 p. January 1994.

Sponsor:

Federal Highway Administration, Washington, DC

Available from:

National Technical Information Service
Order number: PB94-145661

Keywords:

asphalt; bituminous; building technology; calibration; compaction hammer; Marshall method; pavement design; standards; tests

Abstract:

The Marshall method is used by many state and local highway agencies for the design of hot-mix asphalt pavement. Although the procedure is specified by several industry standards, round-robin programs have confirmed wide variability in Marshall test results. Much of the scatter in the data is attributed to compaction hammer variables, such as: variation in drop weight, drop height, friction, hammer alignment, pedestal support and foundation. With the objective of reducing the variability of Marshall test results, a robust, easy to use and relatively inexpensive test apparatus has been developed for calibration of mechanical Marshall compaction hammers. The system consists of a spring-mass device with force transducer, power supply and data acquisition system. The device replaces the standard specimen mold during calibration. Force time histories from multiple hammer blows are recorded and analyzed to determine average peak force, energy and cumulative impulse. The proposed calibration procedure requires adjusting the number of blows to achieve a "standard" cumulative impulse. A limited laboratory evaluation program has been undertaken to demonstrate the system. The variability of test results for specimens prepared in calibrated machines was reduced by as much as 60%, as measured by the reduction in standard deviation and range of data for 15 specimens. A draft calibration standard has been developed and formatted according to AASHTO standards.