Evaluation of Two Laboratory-Based Design Methods for CIR Mixtures

Abstract

[Abstract] In this laboratory research, two different methods for the design of cold in-place recycled (CIR) asphalt mixtures were compared. By the one hand, the current Spanish design method described in the Circular Order 40/2017 (current PG-4). By the other hand, the former Spanish design method described in the Circular Order 8/2001 (former PG-4). Both design methods specify different compaction mechanisms (static vs gyratory), water sensitivity test (unconfined compression strength ratio vs indirect tensile strength ratio) and different ways to obtain the added water for the samples. In order to compare both design methods, CIR samples were manufactured following both design procedures. A cationic slow setting bitumen emulsion C60B5REC was used as binder. Residual binder contents ranging from 1.5% to 5.25% were tested. Added water contents ranging from 0% to 2.75% were also tested. CIR mixtures manufactured according with the former PG-4 led to an optimum residual binder content of 2.00%. Nevertheless, it was not possible to manufacture a CIR mixture that met all the current PG-4 specifications. In this sense, despite in this last case were used higher residual binder contents, 1% of Portland cement as filler, different water contents and higher compaction energy. In this regard, the indirect tensile strength ratio was achieved, but it was impossible to achieve the dry and wet indirect tensile strength requirements.