The results of resilient modulus (MR) testing at North Carolina State University as a part of the Strategic Highway Research Program (SHRP) asphalt concrete core proficiency testing program are presented. As a requirement of participating in this proficiency testing, thorough calibration was conducted on the MR test system at NCSU before the commencement of any testing. Then four synthetic specimens were tested within the framework of ASTM D4123-82. After the MR values of the synthetic specimens were verified to be within the acceptable range, the MR testing was performed on field cores supplied by the proficiency testing program. The MTS Systems Corp MR testing fixture was used with the MTS servohydraulic closed-loop loading system. The mountable measurement device consisting of two extensometers with springs was used in measuring the horizontal deformation. Load and deformation data were acquired by a 12-bit data acquisition board and the LabWindows data acquisition program. A computer program that automatically calculates the instantaneous and total deformation values from the raw data was developed on the basis of regression analysis. The MR testing of field cores was performed in accordance with the SHRP P07 protocol (September 1990 version). The test results indicated that the effects of testing axis and rest period are relatively small compared with the influence of Poisson's ratio. The MR values from the assumed Poisson's ratio were as much as five times larger than those calculated by using Poisson's ratio calculated from the vertical and horizontal deformations. (Author/publisher)
Samenvatting