Table of Contents

Appendix D 1 Introduction

The Australian Standard test for the determination of the resilient modulus of asphalt (AS 2891.13.1) is based upon an indirect tensile measurement. A repeated vertical compressive force is applied acting parallel to and along the vertical diametrical plane and the horizontal displacements are measured mid-height through the horizontal diameter (Figure D 1).

Figure D 1: Indirect tensile test

The resilient modulus is calculated using the relationship shown in Equation A13.

  \[\mathrm{E}\mathrm{ }\mathrm{=}\frac{\mathrm{P}\mathrm{ }\mathrm{*}\mathrm{ }\left( \mathrm{\vartheta}\mathrm{ }\mathrm{+}\mathrm{ }\mathrm{0.27} \right)}{\mathrm{h}_{\mathrm{c}}\mathrm{ }\mathrm{*}\mathrm{ }\mathrm{H}}\]A13
where    
 \[\mathrm{E}\]=estimated resilient modulus (MPa) 
 \[\mathrm{P}\]=peak load (N) 
 \[\mathrm{\vartheta}\]=Poisson’s ratio (0.4, unless more precise information is available) 
 \[\mathrm{h}_{\mathrm{c}}\]=average height of specimen (mm) 
 \[\mathrm{H}\]=recovered horizontal deformation (mm) 

The standard requires that a total horizontal strain of between 30 and 70 microstrain be achieved in the sample to ensure that there is sufficient deformation for the linear variable displacement transducers (LVDTs) to measure accurately and that the response of the specimen remains elastic. The load capacity of the testing device specified in AS 2891.13.1 (approximately 4.5 kN) allows specimens with resilient moduli between 600 to 28 500 MPa to be tested, but in practice the pneumatic loading response limits the upper resilient modulus to around 16 000 and 5500 MPa for 100 and 150 mm diameter specimens respectively. (These values are calculated on a sample thickness range of between 35 to 90 mm and a rise time of 40 ms.)

The loading and response of a specimen is shown in Figure D 2. A pulsed load, essentially triangular in shape, is applied to the specimen. The strain (deformation divided by thickness) is measured on the unloading portion of the curve. The total recoverable (defined here as the resilient) strain is calculated as the peak strain minus the strain immediately prior to the application of the next load pulse.

Figure D 2: Force pulse and displacement timing diagram for resilient modulus test

The rise time is defined as the time required to increase the load from 10% of the peak load to 90% of the peak load.

To compare the resilient modulus determined using the Australian Standard with a modulus determined by another method, it is necessary to understand the definitions related to the stresses and strains of the resilient modulus test.