Potential of RAP as Aggregate Base and Subbase in the Context of Bangladesh

Road agencies of Bangladesh rely mostly on imported bitumen and stone aggregates for construction, maintenance, and rehabilitation of flexible pavements. Expenses for importing materials are one of the reasons for the higher construction cost in Bangladesh. The study attempts to investigate the recycling prospects of RAP in base and subbase layers in accordance with existing construction practices. RAP is collected from the roadside stockpile of Tongi-Ashulia-Zerabo-EPZ Road a national highway in Bangladesh (N302). Series of laboratory tests are performed on RAP to determine the bitumen content and physical properties of milled RAP aggregates. The study reports the laboratory test results of soaked CBR tests for the specimens prepared with 100%, 70%, 60%, and 50% RAP and remaining virgin aggregates. Since gradation affects the strength properties of aggregate, it is kept fixed for all the cases. The study finds that with 100% of RAP aggregates CBR value is 15 and observed a slight increase in CBR values when RAP is replaced with virgin aggregates. However, when RAP, and virgin aggregate combinations are treated with a binder, it shows a significant improvement in CBR values. Maximum CBR value 47 is found for 50% replacement of RAP and treated with 5% cement. However, CBR value rises to 52 if only RAP is treated with 1% bitumen.