Influence of specimen geometry on the complex modulus of cold recycled material mixtures

Cold recycling of bituminous pavements is becoming increasingly important because it leads to the reduction of costs of pavement maintenance and to lower pollutant emissions with respect to hot recycling. The stiffness characterization of cold recycled material (CRM) mixtures is essential to predict the stress-strain behaviour of the pavement structure. The present paper describes a laboratory experiment for evaluating the effects of specimen geometry on the complex modulus of CRM mixtures manufactured with bitumen emulsion and cement. In particular, the focus was on cylindrical specimens with diameter of 38 mm, adopted to improve the efficiency of laboratory specimen fabrication. Specimens with three different diameters (100 mm, 75 mm and 38 mm) were obtained by coring samples compacted using a gyratory compactor. Their complex modulus was measured by means of cyclic compression tests, using the Asphalt Mixture Performance Tester. The testing temperatures were 5, 15, 25, 35, 45 and 55 °C and the testing frequencies were 20, 10, 5, 1, 0.5, 0.1 Hz. The tests were carried out after long-term curing in a climate chamber. Results showed that the complex modulus measured on 38 mm specimens, although with a greater dispersion, is comparable to that measured on 100 mm and 75 mm specimens, thus it can be used for evaluating the mechanical behaviour of CRM mixture.