Laboratory and computational mechanics-based framework for the analysis and design of cold recycled pavement layers

Cold recycling technologies are becoming increasingly popular for rehabilitation of asphalt pavements. These technologies allow construction of new pavement layers with minimal addition of heat and minimal need for transporting the material. In fact, Cold Recycled Mixtures (CRM) can be prepared in mobile plants or directly in place while using up to 100% of the milled material from an existing asphalt pavement (Reclaimed Asphalt Pavement or RAP) and without the need of heating up the aggregates. The products obtained through the use of cold recycling technologies are also commonly called Bituminous Stabilized Materials (BSM). BSM are considered to be partially-bonded materials since they have mechanical characteristics which are in between fully bonded materials, such as Hot-Mix-Asphalt (HMA) or cemented materials, and unbound materials, such as crushed aggregates. Their mechanical response is simultaneously dependent on testing temperature and three-dimensional stress state (specifically confining pressure) and the main concern related to this class of materials is the accumulation of permanent deformation under traffic loading application. Nonetheless, BSM are usually assumed to give a linear elastic response under traffic loading applications in majority of current pavement design and analysis methods.In this research study, Triaxial Shear Strength (TSS) and Triaxial Resilient Modulus (TMR) tests were performed subjecting the material to different lateral confining pressures and temperature conditions. This approach characterized material response under a three-dimensional stress state and under a wide range of realistic temperature scenarios. Based on these results, a constitutive model for BSM was adopted. Laboratory reaction force-displacement curves from TSS tests were matched with three-dimensional finite element elastic-perfectly plastic model simulations to extract local elastic and yield strength constitutive properties for the material. The calibrated and validated local properties in this stage of research were subsequently used as input parameters in multilayer elastic-perfectly plastic pavement models for pavement structural response evaluation. Different structural solutions with and without BSM as base layer were initially simulated in order to assess the ability of BSM to resist to the accumulation of permanent deformation under traffic loading applications, especially in comparison to traditional granular base layers. Afterwards, simulations were conducted with different pavement layer temperatures and elastic-perfectly plastic analyses results were compared to the traditional layered elastic solution. Number of allowable load repetitions before fatigue and rutting failure were calculated respectively on the basis of horizontal strains at the bottom of HMA and vertical strains on top of subgrade obtained from the model simulation results. The multilayer pavement model was then implemented with the ability to consider a realistic temperature distribution with depth and consequently use temperature dependent material properties. As last step, impact of BSM curing stage on the overall plasticity response of the pavement structure was assessed. The research study indicated the importance of considering plasticity-based models for partially-bonded and unbounded materials in the design and analysis of pavement structures. In addition, it was shown that the effect of temperature on BSM mechanical response cannot be neglected for an accurate pavement evaluation. Overall, this dissertation presents a framework for the analysis and design of BSM based on laboratory tests and computational mechanics analysis, which could be adopted for future studies. In addition, this work gives a contribution for the improvement of current methods for pavement design and analysis including considerations on plasticity, indirect confining pressure effects and realistic temperature distribution with depth