Innovative Hot In-Place Recycling of Hot-Mix Asphalt Pavement in Mississippi

A hot in-place recycling (HIR) project using the MARTEC process was constructed on Interstate 55 in Mississippi from December 1997 to July 1998, the first use of this equipment in the United States. Project size was 180 600 m² (216,000 yd²). This equipment differed from earlier HIR equipment principally in the method of heating the hot-mix asphalt (HMA). Air heated to 600°C (1,100°F) was produced in a diesel-fired furnace and blown onto the pavement through a manifold. An elevated pugmill performed the final mixing after which the recycled mixture dropped into the hopper of an HMA paver. Principal objectives of this project were to evaluate this equipment to satisfactorily recycle to a depth of 50 mm (2 in.) and to evaluate the use of Superpave technology for design of the HIR mixture and quality control during construction. Preliminary testing with a dynamic shear rheometer (DSR) was used to select a rejuvenator and an initial point for mixture design. Quality control testing with a Superpave gyratory compactor at the field laboratory was used to make adjustments in the recycled mixture. Limited DSR data from recovered binder indicate acceptable properties. An asphalt pavement analyzer was used to compare the HIR mixture with HMA by using differing binder grades. Although construction problems were encountered, it has been shown that this equipment can adequately heat an existing HMA pavement to permit hot in-place recycling to a depth of 50 mm. Both acceptable density and ride quality are attainable.