Application of foam bitumen in cold recycling and hydrated lime in airport pavement strengthening

Due to the growth of commercial activities in port of Lengeh in south Iran, it was necessary to rehabilitate and upgrade the existing airport which is almost one hundred years old. Severe distresses that occurred in runway and other aircraft operational areas required that the bearing capacity of the existing pavements should be increased. Limited dimensions of the runway and other operational areas in the airport (i.e. runway, taxiway and apron) required these to be extended and widened. A full recycling program was planned including sub-grade and sub-base stabilization with lime in widening areas and base strengthening with foam bitumen and cement slurry in both existing and new constructed sections. The mix design for the foam bitumen cement bonded mix was performed using both Indirect Tensile (ITS) and Unconfined Compressive Strength (UCS) Testing. To avoid extra stiffening of foam-bitumen cement slurry stabilized layer that could lead to formation of fatigue cracking, Marshall Quotient was established to obtain the optimum cement content. The results showed that CBR values of the sub-grade and sub-base layers were increased appreciably by adding 4% hydrated lime powder, hence the local material was successfully used to construct these layers. In addition, foam-bitumen cement treated base layer was gained ITS and UCS strength values well above the specification requirement. Using the mentioned stabilization and recycling methods resulted in protection of the environment and savings in construction time and virgin materials.