Abstract: Deep cold recycling with foamed bitumen (FB-RCM) is currently one of the most widely used road rehabilitation methods. As the percentage of reclaimed asphalt pavement (RAP) in the base mixture may vary with the thickness of recycled bituminous layers, it is vital that the rheological characteristics of the recycled base are evaluated within the linear viscoelastic (LVE) region of response. Calculating complex modulus as a function of loading time and temperature enables the acurate determination of stress and strain distributions for individual conditions. These parameters are of most relevance in the case of a base layer, especially of a recycled base layer, as they provide information needed to determine the limit state in the subgrade and the probability of creep occurring in the recycled base. An increase in the viscous part (E2) of the complex modulus (E*) is an indication of a possible creep growth. A higher RAP content in the recycled base layer is likely to increase creep in this layer, thereby reducing the load bearing capacity of the entire pavement layer system.
The primary aim of this study was to assess the effect of RAP quantity on the change of complex modulus (E*) of the recycled mineral-cement mixture with foamed bitumen (FB-RCM) in terms of the time of loading and temperature. The rheological characteristics of the FB-RCM mixtures can be used for predicting the load bearing capacity in individual cases, depending on RAP availability.
The rheological properties of the FB-RCM mixture were measured within the RAP percentage range 20% to 80% with a step of 20%. Complex modulus was investigated at five temperatures (-7ºC, 5ºC, 13ºC, 25ºC, and 40ºC) and six loading times (0.1 Hz, 0.3 Hz, 1 Hz, 3 Hz, 10 Hz, and 20 Hz) in the direct tension-compresion test on cylindrical specimens (DTC-CY) according to EN 12697-26. The output variables of the test were the complex modulus (E*), the phase angle (φ) and complex modulus components (E1) and (E2). Results showed that the complex modulus decreased as the the RAP content increased. Irrespective of the mixture type used and the test conditions, the modulus values were from E*=1497 MPa to E*=13 797 MPa, whereas the phase angle was between 4º and 15º. It was also demonstrated that the highest complex modulus obtained for the mixtures at short loading times did not quarantee the same values at long loading times. But lead to structural deformations due to a rapid decrease in stiffness modulus at high temperatures and exceeded the limit state in the subgrade. The rapid drop in complex modulus value decreases the durability of the entire pavement layer system.
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DOI 
Web of Science