Field Validation of Using Warm Mix Asphalt at Reduced Production Temperatures to Achieve Balanced Mix Design

Abstract

Under the Balanced Mix Design (BMD) framework, several mix design strategies, such as increasing asphalt content, using softer binders, and reducing reclaimed asphalt pavement (RAP), have been adopted to improve rutting and cracking resistance and enhance pavement durability. Among these strategies is the use of warm mix asphalt (WMA), which enables production at reduced temperatures. This study presents field validation of asphalt mixtures from two projects in Virginia and Missouri, designed to achieve balanced rutting and cracking resistance using WMA at reduced production temperatures. Each project evaluated a volumetric control hot mix asphalt (HMA), a BMD HMA mixture, and a BMD WMA mixture at reduced production temperatures. The plant-produced mixtures were sampled and later reheated to prepare plant-mixed, lab-compacted (PMLC) specimens, while component materials were used to prepare lab-mixed, lab-compacted (LMLC) specimens according to the job mix formula (JMF). Fuel consumption and emissions were recorded during production to assess the environmental benefits of lower-temperature WMA. Performance testing for the Virginia mixtures included the Asphalt Pavement Analyzer (APA), High-Temperature Indirect Tensile Strength Test (HT-IDT), Cantabro, and Indirect Tensile Asphalt Cracking Test (IDEAL-CT). Additional testing on plant-produced mixtures using Dynamic Modulus (E*), Direct Tension Cyclic Fatigue (DTCF), and Overlay Test (OT) tests was conducted after 8 hours of loose mix aging at 135°C. The IDEAL CT was performed on both reheated and long-term aged (LTA) specimens. For the Missouri mixtures, rutting and cracking evaluation using the Hamburg Wheel Tracking Test (HWTT) and IDEAL-CT. The IDEAL CT and OT were conducted on LTA specimens after 5 days of loose mix aging at 95°C. Mechanistic empirical (M E) performance predictions were conducted using the Flexible Pavement Analysis and Design Software (FlexPAVE) for the Virginia plant-produced mixtures and the Texas Asphalt Concrete Overlay Design System (TxACOL) for both projects. Lowering production temperatures using WMA resulted in notable fuel savings and emissions reductions for both Virginia and Missouri projects. In the Virginia project, the BMD WMA mixture showed significantly improved cracking resistance compared to the two HMA mixtures and achieved balanced performance without compromising rutting resistance both in mix design and during production. The E* and OT results indicated similar or improved cracking resistance for the BMD WMA mixture relative to the HMA mixtures, although DTCF results showed reduced fatigue resistance. The FlexPAVE simulations indicated that the BMD WMA mixture did not improve fatigue damage resistance when used as the asphalt layer for a new construction pavement. The TxACOL simulations showed that the BMD WMA mixture significantly improved reflective cracking performance, extending overlay life by approximately 1 to 4 years. In the Missouri project, the BMD mixtures significantly outperformed the Control HMA mixture in cracking resistance for mix design but showed similar cracking resistance during production. All three mixtures achieved balanced performance. The OT results indicated comparable cracking resistance across the plant-produced mixtures. The TxACOL simulations showed that the Control HMA mixture provided better reflective cracking performance and longer overlay life than the BMD mixtures. Overall, the findings suggest that using lower-temperature WMA is a promising approach for achieving balanced mixture performance during mix design. However, the performance benefits observed in the laboratory may not always fully translate to production due to increased variability in plant operations compared to controlled laboratory settings.