Mechanistic-Empirical Evaluation of Pavement containing Cold Central Plant Recycling Layer

Abstract: Cold Central Plant Recycling (CCPR) technology allows 100% utilization of recycled asphalt pavement (RAP) materials in the reconstruction or new construction of flexible pavements. However, it is still uncertain whether CCPR materials exhibit characteristics as a bound or unbound material, or somewhere in between. This presents a challenge on how to design pavements with CCPR layers. Consequently, the overall goal of this study is to determine the most appropriate usage of the CCPR material in the pavement. The objectives formulated to achieve this goal are to identify the performance of CCPR layers when used as either an aggregate base or an asphalt base in pavement structures, and to compare the predicted performance of a pavement containing a CCPR layer with a traditional pavement structure (without CCPR). Foamed PG 64-22 asphalt binder and CSS-1h emulsion were used as recycling agents to produce the CCPR mixtures. Mixture dynamic modulus (|E*|) of the full-size (100 mm diameter and 150 mm height) samples at five temperatures (-10,4.4,21.1,37.8, and 54.4℃) and six frequencies (25, 10, 5, 1, 0.5, and 0.1 Hz) were determined in the laboratory. Level 1 inputs for the traffic, climate, and pavement structure were used in the AASHTOWare software for the analysis. To determine the pavement performance, the pavement sections were analyzed by designing CCPR layer i) an asphalt base layer and ii) an aggregate base layer. The structures were 22 inches thick and consisted of a 5-inch hot mix asphalt layer, a 5-inch CCPR layer, a 12-inch dense graded aggregate base course, and A-5 subgrade soil. The design was intended to withstand a traffic load equivalent to 13 million equivalent single axle loads (ESALs). The global calibration coefficients and the New Jersey criteria for the dense graded unmodified hot mix asphalt mixture were used to finalize the sections. The optimized design showed that the CCPR layer reduced the total pavement rutting by approximately 16% (as an asphalt base layer) and 8% (as an aggregate base layer) compared to the conventional asphalt base layer. There were no significant changes in the terminal IRI, AC thermal cracking and the AC top-down fatigue cracking performance. AC rutting showed a reduction of approximately 74% and 67% respectively for the CCPR asphalt base layer and the CCPR aggregate base layer. However, the bottom-up fatigue cracking increased 73% for the CCPR asphalt base layer and decrease 32% for the CCPR aggregate base layer. This implies that the pavement containing the CCPR layer as an enhanced aggregate base layer, will produce the same pavement performance with improved rut resistance, despite the absence of the conventional asphalt base layer. Once the current version of AASHTOWare software has been updated to incorporate the precise properties of CCPR material, the design can be reevaluated to verify the findings of this investigation. Apart from the several environmental benefits, the outcome of this study will help reduce pavement construction costs by reducing the structure thickness, utilizing the stockpiled RAP materials, and saving non-renewable resources like virgin binder and aggregates.