Experimental Study on Geocell-Reinforced Flexible Pavements with Recycled Asphalt Pavement (RAP) Bases under Cyclic Loading

ABSTRACT The reprocessed old hot mix asphalt (HMA) concrete also called "Recycled Asphalt Pavement (RAP)", if used to build new roads or to maintain existing roads, would have several benefits, such as preservation of natural resources for future generation, protection of environment, and conservation of energy, etc. To use RAP as a granular base in pavement construction as a sustainable solution, it must have enough strength and stiffness to ensure the performance of the pavement. Geocells are three-dimensional honeycombed cellular structures which can provide confinement to compacted infill soil. The literature review of past studies indicated that geocell-reinforced bases provide better lateral and vertical confinement, distribute the load over a wider area, increase the bearing capacity, and reduce the settlement. Use of RAP as a base material with geocell as reinforcement in the HMA pavement can have the combined advantages and can create an attractive solution to pavement reconstruction or rehabilitation. In this research, the behavior of HMA pavements constructed over unreinforced and geocell-reinforced RAP bases was studied in the geotechnical testing box at the University of Kansas. Pavement sections consisting of subgrade, base, and HMA surface were constructed in the geotechnical testing box and tested under cyclic loading. The subgrade was composed of a mixture of 75% Kansas river sand and 25% Kaolin at 10.4% optimum moisture content, which corresponds to 5% CBR. The RAP base was constructed without or with geocell at 6.6% optimum moisture content to achieve the density requirement. The base thicknesses varied from 15 to 30 cm. The HMA surface above the base was 5 cm thick. Extensive QC/QA tests and instrumentation were included. The test sections were evaluated by vane shear test, light weight deflectometer test, and dynamic cone penetration test for consistency. Earth pressure cells were placed at the interface between subgrade and base to measure the vertical stresses applied on the subgrade. Tell tales were placed at the interface of subgrade and base and the interface of base and HMA surface to measure their corresponding compression. Strain gauges were placed on geocells and at the bottom of the HMA layer to measure the strains. Large-scale plate load tests with a cyclic load up to 40 kN was applied to the failure criterion of 25 mm permanent deformation. Six cyclic plate load tests were conducted on unreinforced and geocell-reinforced test sections by varying the thickness of the RAP base. The performance of each test section under cyclic loading was evaluated for a number of passes or number of loading cycles up to the failure of the test section. The test results show better performance of the geocell-reinforced section than the unreinforced section at the same base thickness. The higher stress distribution angle, higher percentage of elastic deformation, lower compression of HMA surface, and lower compression of RAP base were observed in the geocell-reinforced test section as compared with those in the unreinforced test section. The compression of subgrade was high compared to that of RAP base and HMA layers. The geocell-reinforced section with higher stiffness resulted in better compaction of the HMA layer as well. The subgrade and/or RAP base layer with a higher CBR value improved the performance of the pavement section. To obtain consistent test results, it is also important to follow the same procedure to prepare and test the pavement sections.