Behavior of the Expanded Polystyrene Elastic Inclusion at Integral Abutments

About the report:

This report presents the findings of a laboratory study conducted by the Sustainable Geotransportation/Geoenvironmental Infrastructure (SGI) Research Group at George Mason University. The research focused on investigating the ability of standard (S) and elasticized (E) expanded polystyrene (EPS) to provide elastic inclusion in integral abutments. EPS materials in this study were selected based on input from the Technical Review Panel of this research. The laboratory tests were divided into the following three tasks.

Task 1 focused on quantifying the behavior of EPS when the material is loaded under uniform uniaxial compression (not cyclic loading) at a 10% per minute strain rate per the current ASTM D1621 (2016) standard. The findings showed that the behavior of E-EPS differs when loaded in the elasticized versus non-elasticized directions. The direction of loading did not affect the behavior of S-EPS. Specimen shape did not significantly influence stress-strain behavior, but specimen size affected the stress-strain behavior of both EPS types. In all testing conditions, both EPS types exhibited elastic behavior only when the applied load induced no more than 2 to 3% strain on EPS.

Task 2 focused on developing a specific testing protocol to evaluate the cyclic behavior of EPS that simulates the thermally induced movement of the bridge. In these tests, the findings showed that the elastic range of both EPS types may be increased as long as EPS is confined and imposed to a constant minimum 3% strain. Under these conditions, both EPS types stayed elastic as long as the cyclic-induced strains stayed within the 4.6% range (e.g., EPS is strained to 7.6%). The results also showed that if the immediately expected behavior of the bridge after installation becomes in the direction of expansion, the minimum constant strain imposed on EPS has to be increased from 3 to 7.6%. The constant strain condition is envisioned to be achieved in the field by controlling the compaction efforts of the aggregate surrounding EPS at the time of installation (not investigated as part of this research).

Task 3 focused on evaluating EPS behavior under cyclic traffic loading without a concrete approach slab. The magnitude of traffic-induced stresses on EPS was calculated as 1.6 psi using the KENPAVE software model and based on 18 inches of pavement layers (imposing a constant 2 psi stress) on top of EPS. However, for conservatism, laboratory tests were conducted with a 5 psi vertical stress (traffic-induced stress plus overburden). Due to test setup limitations, traffic loading tests in the laboratory were conducted without confinement pressure. Based on the traffic loading test results, S-EPS and E-EPS experienced approximately 0.9% strain.

Based on the overall findings, researchers suggest a new equation (with a step-by-step decision tree) to calculate the required thickness of both types of EPS. The results indicate that both EPS types appear to satisfy Virginia Department of Transportation’s (VDOT) Kp limiting value for abutment design. This study also proposes recommendations for revising the current VDOT SP404-000130-00 Special Provision for Elastic Inclusion.

Supplemental files can be found at https://library.vdot.virginia.gov/vtrc/supplements

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