This paper describes equipment developed to determine the dynamic properties of paving materials in axial and torsional loading. Dynamic properties were determined by the excitation of hollow cylindrical specimens using two independent sinusoidal loads with frequencies up to 30 Hz.
An IBM PC/AT equipped with a Metrabyte DASH16 Data Acquisition Board was used to directly control two MTS Hydraulic Servorams. Menu-driven software was developed, taking advantage of DMA channels, so that data acquisition, waveform generation, and closed-loop control could simultaneously take place at rates above 5000 samples/s/channel. To convert raw data into graphs and parameters representative of dynamic material properties, a post-processing menu-driven program was also developed.
Dynamic properties for a dense-graded asphalt concrete are presented for a range in temperatures from 11 to 40°C and for a range in frequencies from 0.5 to 20 Hz. Test results include: dynamic moduli in axial loading defined by |E*|, dynamic shear moduli defined by |G*|, internal damping determined in both axial and shear loading, and dynamic Poisson's ratios. Also included are results illustrating the effects of specimen density on these properties.
Comparisons are included of stiffness moduli determined in a repeated pulse load test (resilient moduli) with those determined from the dynamic load equipment. The data also indicate that some care must be taken when comparing stiffness values determined by this type of loading with those determined from sinusoidal loading, particularly at higher temperatures. Differences in the stiffness moduli may result from the influence of the time between load applications (rest periods) on the value of the recoverable strain used to compute the stiffness (resilient modulus) in the repeated load test.