Fundamental characterization of asphalt mixtures: warm mix asphalt technologies in flexible pavement systems

Abstract

Increasing concerns on environment and greenhouse effect, coupled with increased construction prices led to the development of new technologies by the Asphalt industry to produce Asphalt Concrete (AC) pavements. Extensive research is being done to evaluate the impact and performance of these new technologies. Warm Mix Asphalt (WMA) is one of these technologies that allow mixing, production, placing and compaction of asphalt mixes at significantly lower temperatures as compared to the traditional Hot Mix Asphalt (HMA) practice. Lower temperatures result in reduced fuel usage, fume exhausts, greenhouse gas emissions, wear and tear at plants; while enhancing worker health and safety conditions. The performance characteristics of asphalt mixtures containing WMA technologies may be affected and should be quantified. A detailed laboratory study has been conducted to evaluate and quantify the performance of different WMA technologies. Eleven mixes from three overlay field projects across Louisiana were taken into consideration. Evotherm, Rediset, Foaming and Latex were different warm mix technologies used. Each project included a companion HMA mixture section to allow comparison of WMA to conventional HMA. Mechanistic tests were conducted on plant produced–lab compacted (PL) specimens to evaluate Rutting (permanent deformation), Fatigue/Fracture and Low temperature cracking performance of the mixtures at high, intermediate and low temperatures respectively. The testing factorial included Dynamic Modulus, Indirect Tensile Strength (ITS), Flow Number (FN), Loaded Wheel Tester (LWT), Beam Fatigue, Semi-Circular Bend (SCB), Dissipated Creep Strain Energy (DCSE), Thermal Stress Restrained Specimen Test (TSRST) and Modified Lottman Test. A Life Cycle Assessment (LCA) has been performed to evaluate the economic and environmental benefits of WMA. Overall, the WMA mixtures showed similar performance compared to that of control HMA mixtures. Asphalt mixtures with Rediset and Latex showed better performance than conventional mixtures with respect to fatigue and permanent deformation. The use of WMA technologies resulted in lesser aging of the binder. Energy assessment has shown a 12-15 % energy savings. On average, $1.61 of cost savings per ton of produced asphalt was observed along with a considerable reduction in air pollutants without any reduction in the mechanistic performance of these mixtures.