Evaluation of the anti-rutting potential of polymer-modified binders by means of creep-recovery shear tests
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ORIGINAL ARTICLE
Evaluation of the anti-rutting potential of polymer-modified binders by means of creep-recovery shear tests Ezio Santagata • Orazio Baglieri • Davide Dalmazzo • Lucia Tsantilis
Received: 5 July 2012 / Accepted: 21 December 2012 Ó RILEM 2013
Abstract In the experimental study reported in this paper a creep-recovery shear test method was used to evaluate the anti-rutting potential of different polymer-modified bituminous binders. The effects of several factors related to modification were investigated, such as polymer type (SBS, styrene–butadiene– styrene vs. ethylene–vinyl–acetate), composition (styrene content), structure (linear vs. radial SBS) and dosage (3–6 % by weight of the base bitumen). The effect of short-term aging was also considered by comparing binder response before and after treatment with the rolling thin-film oven test. Following previous work on the development of the test protocol, experimental results were analyzed by referring to shear modulus curves G(t) and to permanent compliance (JP), obtained by dividing residual strain at the end of the unloading phase by the stress applied during
E. Santagata (&) O. Baglieri D. Dalmazzo L. Tsantilis Department of Environmental, Land and Infrastructure Engineering, Politecnico di Torino, 24, Corso Duca degli Abruzzi, 10129 Turin, Italy e-mail: [email protected] O. Baglieri e-mail: [email protected] D. Dalmazzo e-mail: [email protected] L. Tsantilis e-mail: [email protected]
creep loading. Results indicated the effectiveness of the proposed method in discriminating between the behavior of the different polymer-modified binders and in capturing the effects caused by the factors considered in the investigation. Reliable rankings of the binders were established and were explained by referring to the specific behavior of employed modifiers. Keywords Polymer-modified bituminous binders Rutting Creep-recovery Permanent compliance Aging
1 Introduction The modification of bitumen by means of polymers may provide a significant enhancement of its viscoelastic properties [1–3]. For this reason, the use of polymer-modified bituminous binders can be suitable for heavy-duty pavements subjected to high traffic volumes with a significant percentage of heavy and slow-moving vehicles. However, since addition of a modifier to a base bitumen can considerably increase its cost, reliable laboratory test methods and ranking criteria are needed to fully appreciate, before use in paving operations, their effective performance-related value. The initial SUPERPAVE grading system [4] developed in the early 90’s, although supported by
Materials and Structures
an experimental database mainly composed of tests performed on un-modified bitumens, was conceived to accommodate binders of all types, without limitations on the possible presence of additives and/or modifiers. However, several investigations carried out after approval of SUPERPAVE specifications showed that they lead to an underestimate of the real field per
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