Performance of geocell-reinforced recycled asphalt pavement (RAP) bases over weak subgrade under cyclic plate loading

Abstract

Recycled Asphalt Pavement (RAP) is the most reused and recycled material in the United States. It has been included at percentage of 15–50% in new hot mix asphalt (HMA) concrete and used as a base course material up to 100% for pavement construction. Due to the existence of asphalt in RAP, RAP base courses may have increased or excessive permanent deformation under traffic loading. To minimize such deformation, use of geocell was proposed by authors to confine RAP. To verify the performance of geocell-reinforced RAP bases and the benefit of geocell reinforcement, an experimental study was conducted on geocell-reinforced RAP bases over a weak subgrade under cyclic plate loading. A large geotechnical test box was used for the cyclic plate loading tests. The subgrade was a mixture of sand and kaolin and compacted at the moisture content corresponding to a California Bearing Ratio (CBR) value of 2%. The fractionated RAP was compacted at the moisture content close to the optimum value. A total of four sections with three base thicknesses (0.15, 0.23, and 0.30 m) were prepared and tested, which included one 0.30 m thick unreinforced section and three geocell-reinforced sections. During the testing, surface deformations and vertical stresses at the interface of base and subgrade and strains in geocell walls were monitored. Test results show that the geocell-reinforced RAP bases had much smaller permanent deformations than the unreinforced RAP bases. The geocell-reinforced bases reduced the vertical stresses at the interface between base and subgrade as compared with the unreinforced base. The strain measurements demonstrated that the thicker geocell-reinforced RAP base behaved as a slab while the thinner base behaved as a tensioned membrane. The experimental results indicated that novel polymeric alloy (NPA) geocell reinforcement improved the life of 0.15, 0.23, and 0.30 m thick reinforced RAP base sections by factors of 6.4, 3.6, and 19.4 at a permanent deformation of 75 mm as compared with the 0.30 m thick unreinforced section at the same permanent deformation, respectively. Geocell reinforcement increased the minimum stress distribution angle by 2°, 3.5°, and 7° for the 0.15, 0.23, and 0.30 m thick reinforced RAP base sections as compared with the unreinforced section.