Investigation of Warm Mix Asphalt Concrete Mixtures with Recycled Asphalt Pavement Material.

摘要

Today's world faces the challenge of sustainability in all facets of existence, production and consumption. Since roads have a large areal as well as carbon footprint, it is imperative that the pavement industry take serious steps to address their impact on the environment. Warm Mix Technology (WMA) and Reclaimed Asphalt Pavement (RAP) material can enable us to "Reduce, Reuse and Recycle" our way to sustainable pavements.;WMA, with its lower production temperatures, can reduce fuel consumption and lower harmful emissions during construction. However, there is a concern that the lower production temperatures can lead to softer mixtures, affecting rutting and moisture susceptibility, especially in those WMA technologies that employ water as a mechanism to lower production temperatures.;RAP material has been used in the pavement industry since decades and is an obvious move towards sustainability. RAP material is stiffer than freshly produced asphalt concrete. This extra stiffness can be beneficial in terms of improving resistance to permanent deformation. However, concerns related to workability and long-term durability, hinder the usage high amounts of RAP in construction.;As the behavior of softer WMA mixtures is converse to that of the stiffer RAP mixtures, it is believed that these technologies in conjunction can complement each other's perceived deficiencies. There is a potential for large environmental and economic gain if this combination of sustainable technologies is successful in addressing material quality concerns. Thus, there is a need to study the compatibility of different types of WMA technologies with the usage of RAP. Material performance characteristics like workability, moisture-susceptibility and stiffness need to be analyzed for WMA--RAP mixtures.;This research study focuses on combining two WMA technologies---Evotherm RTM 3G and The PTI Foamer with two RAP percentages---20% and 40%, along with control HMA and virgin (no RAP) mixtures. The resulting mixture combinations were evaluated for workability and moisture susceptibility, and their pavement performance was predicted based on dynamic moduli.;The evolution of %Gmm during mixture compaction was used to evaluate workability. Even without a change in binder grade, WMA mixtures with 40% RAP exhibited similar %Gmm trends the HMA mixtures with 40% RAP that incorporated a softer binder grade.;Tensile Strength Ratio (TSR) was used to evaluate the moisture susceptibility. TSR values decreased with increase in RAP content in HMA as well as the two WMA mixtures. Dynamic modulus tests were conducted to obtain the E* master curves for all mixtures. They were also used to compute the E* Stiffness Ratio, i.e. the ratio of dynamic modulus values of moisture-conditioned specimens to that of unconditioned specimens, analogous to the Tensile Strength Ratio. The ESR value of HMA mixture with 40% RAP was significantly lower than all the other mixtures. This may be because of the softer binder grade used in this mixture while all other mixtures used standard binder grade.;AASHTOWare Pavement ME software was used to analyze the rutting and fatigue performance of the mixtures for a design life of 20 years. For a typical pavement section, none of the mixtures exceeded the threshold failure criteria. The only difference in production costs amongst the mixtures are the costs of additives and technology installation for WMA mixtures, screening and processing costs of RAP and energy savings from WMA. Despite these initial costs, using WMA and RAP prove to be more economical than HMA.