ORIGINAL ARTICLE Complex shear modulus and phase angle of crumb rubber modified binders containing organic warm mix asphalt additives Ana Marı ´a Rodrı ´guez-Alloza . Juan Gallego . Felice Giuliani Received: 31 March 2016 / Accepted: 15 September 2016 Ó RILEM 2016 Abstract Pavements containing crumb-rubber modi- fied (CRM) binders present one major drawback: larger amounts of greenhouse gas emissions are produced as there is an increase in the energy consumption at the asphalt plant due to the greater viscosity of these type of binders compared with a conventional mixture. One possible solution to this problem could be the Warm Mix Asphalt (WMA) technology, which has been developed recently to reduce the manufacturing and paving temperatures of asphalt mixtures. The WMA additives may improve the mixture’s workability without significantly affecting the mechanical properties of the pavement materials. However, most of the existing research has been focused on conventional asphalt pavements while asphalt rubber mixtures with WMA additives have yet to be studied in detail. The present study includes the results of tests performed using a dynamic shear rheometer of 15 and 20 % CRM binders that incorporate two different types of organic WMA additives (waxes) to provide information about the trend of the complex modulus and the phase angle in function of frequency sweeps. The master curves have highlighted the significant change produced by the additives regarding their rheological behaviour and the non-applicability of the time–temperature superposition principle. The results suggest that these binders might be appropriate for countries with warm climates although further tests should be made to evaluate the behaviour of the mixtures that contain these binders at low temperatures. Keywords Crumb rubber Á Warm mix asphalt Á Wax Á Dynamic shear rheometer (DSR) Á Complex modulus Á Phase angle 1 Introduction Waste management has become a critical problem for sustainable development as well as causing eco- nomic, security and social problems. Tyres in particular have a huge environmental cost. In Europe alone during 2011, approximately 3.27 million tons of used tyres were managed in an environmentally sound manner. After resolving the data of those tyres going for retreading, an estimated 2.3 million tons of end-of-life tyres (ELTs) were left to be treated [1]. A. M. Rodrı ´guez-Alloza (&) Department of Civil Engineering: Construction, Infrastructure and Transport, Universidad Polite ´cnica de Madrid (UPM), C/Alfonso XII 3, 28014 Madrid, Spain e-mail: anamaria.rodriguez.alloza@upm.es J. Gallego Department of Civil Engineering: Transport and Territory, Universidad Polite ´cnica de Madrid (UPM), C/Profesor Aranguren 3, 28040 Madrid, Spain F. Giuliani Department of Civil and Environmental Engineering and Architecture, Universita ` degli Studi di Parma, Parco Area delle Scienze, 181/A, 43124 Parma, Italy Materials and Structures (2017)50:77 DOI 10.1617/s11527-016-0950-1