Laboratory investigations on Reclaimed Asphalt Pavement (RAP) for using it as base course of flexible pavement

During Capacity augmentation of existing National Highway (NH) Projects, grade separated structures in terms of Flyovers, Vehicular underpass (VUP), Pedestrian underpass (PUP), Cattle underpasses (CUP) are proposed at regular intervals. Accordingly, existing road levels at approaches of these structures are required to be raised making the existing pavement materials redundant. Existing pavement materials are also obtained due to milling of existing pavement surface before laying overlay for strengthening. The present study is to assess the suitability of using these redundant pavement materials also called Reclaimed Asphalt Pavement (RAP) as potential subbase / base course materials for flexible pavement. It was observed from literature survey of various past studies that California bearing ratio (CBR) of 100% RAP is not suitable for its use as base of flexible pavement as per Indian Standards (IRC). Accordingly, attempts were made to improve strength of RAP in terms of CBR by mixing it with crushed stone aggregates, stabilizing it with cement and combination of both. In the present study, laboratory CBR tests have been conducted on RAP, mixture of RAP and crushed stone aggregates and also on mixture of RAP and crushed stone aggregates stabilized with various percentages of cement. It was observed that though un soaked CBR values of RAP were not influenced much due to its mixing with crushed stone aggregates and/or stabilization with cement, soaked CBR values increased substantially due to both mixing with crushed stone aggregates and stabilizing with cement. The soaked CBR value of RAP increases from 20% to in excess of 100% when it is mixed with crushed stone aggregates in various proportions and stabilized with small percentages of cement and thereby making it suitable for using it as subbase/base of flexible pavement. Modified proctor compaction tests were conducted on both RAP and mixture of RAP and crushed stone aggregates to established optimum moisture content for the preparation of CBR moulds for testings.