HOT IN-PLACE RECYCLING EXPERIENCE ON MOTORWAY (M-2) IN PAKISTAN

Abstract

Highway agencies are globally facing increasing financial and environmental constraints due to recurring pavement rehabilitation. These limitations are persuading the highway agencies to use HMA recycling technology as an alternative to conventional pavement rehabilitation. Among the recycling techniques, in-situ recycling can be performed by both hot in-place (HIR) and cold in-place (CIR) recycling methods. HIR is carried out to correct surface distresses not caused by structural inadequacy, it has proved to be economical and environment friendly. In Pakistan, HIR technology was introduced for the first time on Lahore-Islamabad Motorway (M-2), between Lahore and Kalashahkaku in March 2006. M-2 became operational in November 1997. Surface recycling technique of HIR was performed on the rutted sections to a depth of 38-50 mm. At few places remixing technique of HIR was also used. Remixing is the HIR process in which virgin aggregate, new asphalt binder, recycling agent, and/or new HMA (as required) is added to the heated, softened, and scarified existing asphalt pavement. The main objective of this research is to study the effects of recycled wearing course on overall pavement performance. This aim was accomplished by evaluating structural and functional adequacy of selected pavement sections both before and after recycling. The selected pavement sections were on Islamabad - Chakri section. Data collection included non-destructive techniques using falling weight deflectometer (FWD), longitudinal and transverse profiles using profilograph and straight edge respectively. The laboratory investigations were carried out using state-of-the-art equipment. Analysis of transverse profile showed that rutting in all three sections is associated with surface HMA layer. Backcalculation analyses of FWD deflection data indicated that selected sections contained aged and hard HMA layers before recycling. However, the stiffness of HMA layer has reduced after HIR process. Dynamic Cone Penetrometer (DCP) and deflection analysis results indicated very strong granular and subgrade materials in all sections. Laboratory testing of HMA mixture before and after recycling indicated that material was very stiff and aged; however, modulus of HMA layer had significantly reduced after recycling due to rejuvenation. Excess asphalt content was observed before recycling which further increased after recycling. The degradation of the aggregates in wearing course was observed due to scarification; however, the overall gradation remained near the limits of NHA’s Class B asphalt wearing course specifications. During HIR process, lower scarifying and compaction temperatures were observed at site; consequently the need of proper supervision is highlighted to ensure proper quality control and quality assurance. HIR has further increased (deteriorated) the roughness indices (IRI and PI0) and reduced (deteriorated) PSI after recycling. Deterioration in pavement performance of test sections was observed over time. The most effected section 3 shows a rapid increase in roughness (PI, IRI and PSI) after 11 months of recycling which has highlighted the importance of proper QC& QA procedures regarding use of this technology on Motorways/Freeways, as longitudinal roughness is the main concern.