Mechanistic structural properties of foamed asphalt stabilised base materials

Abstract

Foamed asphalt stabilised base (FASB) material is a partially bound material consisting of four phases of aggregate skeleton, air voids, foamed binder and water. Its mechanical properties and behaviour are greatly influenced by field placement and curing conditions. Given appropriate design and application, the structural capacity of FASB lies somewhere between granular aggregate base (GAB) and hot mix asphalt. Therefore, when FASB is used in the place of GAB, the required thickness of the pavement section can be reduced, resulting in cost savings in addition to recycling benefits. The objective of this study was to investigate and explain the distinct mechanical behaviour of this material and address the most important performance-related parameters of FASB – stiffness and permanent deformation resistance. Triaxial dynamic modulus (|E^*|) and repeated load permanent deformation (RLPD) tests were performed on field-cured FASB cores. The influence of confining stress on dynamic modulus was found minor as compared with that of loading rate and temperature. At a 25°C temperature and a 10 Hz loading rate typical for base layer conditions in high-volume highway pavements, the mean value of dynamic modulus of a new FASB was found to be 4310 MPa, much greater than what would be expected from conventional GAB. RLPD test results demonstrated satisfactory resistance to rutting. The in situ long-term stiffness of FASB measured using a Dynatest falling weight deflectometer was of an order of magnitude greater than the stiffness of GAB. A structural layer coefficient of 0.142 cm^− 1 (0.36 in.^− 1) was recommended for this material for use in the empirical 1993 American Association of State Highway and Transportation Officials design procedure.

Keywords::

• foamed asphalt stabilised base
• recycled material
• dynamic modulus
• permanent deformation
• structural layer coefficient

Acknowledgements

This research was sponsored by Maryland State Highway Administration; technical contributions from Dan Sajedi and Nate Moore are gratefully acknowledged. Additional background information, testing devices and suggestions were provided by Harold Green of Global Resource Recyclers, Inc.; Tom Norris of P. Flanigan and Sons, Inc.; Mike Marshall and Rennie Shunmugam of Wirtgen America; Mike Heitzman of the National Center for Asphalt Technology; Kessler Inc.; and Nelson Gibson and Xinjun Li of Turner-Fairbank Highway Research Center at FHWA. The help from coworkers Regis Carvalho, Rui Li, Endri Mustafa, Sarah Fick, Timothy Briner and Daniel Butler during the laboratory and field investigations are greatly appreciated. All of the views and conclusions expressed in this article are exclusively those of the authors.

Notes

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