National Concrete Pavement Technology Center

Project description

With the depletion of natural resources and limited funding for necessary pavement construction and rehabilitation, recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP) are potential alternatives to the virgin granular base (VGB) typically used. The addition of geosynthetics at the interface of base course and subgrade can stabilize base course sections through separation, lateral restraint, and a tensioned membrane effect. This large-scale box study focused on two different granular base options (VGB and RCA) with geosynthetic stabilization for concrete pavement applications. Unpaved road tests under cyclic loading were first conducted on these granular bases over weak subgrade to evaluate the benefits of three types of geosynthetics (nonwoven geotextile, woven geotextile, and triaxial geogrid) and replacement of VGB with RCA in the improved performance (permanent deformation and stress reduction) and properties (resilient modulus and modulus of subgrade reaction). The nonwoven geotextile was selected for three concrete paved roads with VGB and RCA over the same subgrade under cyclic loading. Displacement transducers and earth pressure cells were placed in the test sections to monitor resilient and permanent deformations on the section surface and vertical interface stresses between base course and subgrade. For the unpaved test sections, the measured resilient and permanent deformations and the interface stress reduction were analyzed to evaluate the benefits of geosynthetics and replacement of VGB with RCA. The modified Burmister solution and the stress reduction method were used to back-calculate the resilient moduli (Mr) of the granular bases for all the test sections. Back-calculated resilient moduli were correlated with the accumulated permanent deformations to assess these methods. The American Association of State Highway and Transportation Officials (AASHTO, 1993) design chart was used to estimate the composite subgrade reaction moduli of the unpaved test sections based on the back-calculated resilient moduli (Mr) of the granular bases. The three concrete paved sections and the benefits of the nonwoven geotextile and the replacement of VGB with RCA were evaluated in terms of their total and permanent displacements and base course-subgrade interface stresses. Based on the measured vertical displacements at the loaded corner, Westergaard’s (1926) method was used to back-calculate the subgrade reaction moduli of these sections and estimate the tensile stresses in the concrete slabs. The back-calculated subgrade reaction moduli of these concrete paved sections were compared with those calculated based on the unpaved road sections. The key findings of this study are: (1) geosynthetics were effective in reducing the permanent deformations of both VGB and RCA base courses over the weak subgrade in unpaved and concrete paved roads under cyclic loading; (2) RCA was stronger and stiffer than VGB and replacement of VGB with RCA reduced the permanent deformations in unpaved and concrete paved roads under cyclic loading; (3) the resilient modulus of the base course in an unpaved road section back-calculated by the modified Burmister solution with the mechanistic-empirical damage model was correlated well with the accumulated permanent deformation of the unpaved road section; (4) the modulus of subgrade reaction of a base over a subgrade estimated by the AASHTO design chart with the back-calculated resilient modulus of the base from an unpaved road test was similar to that back-calculated by the Westergaard solution based on the displacement at the loaded corner; (5) the accumulated permanent deformation of an unpaved or concrete paved section increased with the reduction of the subgrade reaction modulus in a semi-logarithmic relationship; and (6) geosynthetic stabilization and/or replacement of VGB with RCA increased the resilient modulus and the subgrade reaction modulus of a test section.