United States Department of Transportation
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Reconstruction of railroads and highways with in-situ reclamation materials.
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2011-03-01
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Abstract:The resilient modulus and plastic deformation of recycled roadway materials with and without fly ash stabilization were characterized using a large-scale model experiment (LSME). Stabilization of recycled pavement materials (RPM) and road surface gravel RSG with 10% by weight of Class C fly ash increased the summary resilient modulus (SRM) two to five times. Moreover, the SRM increased with layer thickness in the LSME. The RPM and RSG exhibited the rate of plastic deformation three to four times higher than the Class 5 base. Stabilized RPM and RSG had the lowest plastic deformation. The moduli obtained from the large-scale model experiment (LSME) were used to develop an equivalency-based design for the recycled materials with and without fly ash. Stabilization of the recycled materials by cementitious fly ash reduced the required thickness of a pavement base course up to 30% in accordance with AASHTO-1993 design guide. The SRM and plastic deformation from LSME tests were incorporated in the Mechanistic Empirical Pavement Design Guide (MEPDG) to predict the lifetime expectancy of the recycled materials in a pavement alone and with fly ash stabilization. The results showed that stabilization of recycled materials with fly ash increases the lifetime of pavements constructed with 0.3-m-thick alternative recycled materials from 17 to 21 years.
A testing protocol and guidelines for testing fouled railway ballast was developed due to the lack of consistent and systematic testing guidelines in the literature and in rail engineering practice. The effect of fouling (internally generated mineral fouling, external coal fouling due to surface spillage, and clay fouling due to subgrade intrusion) on the permanent (plastic) deformation of ballast under traffic loading was studied using the developed testing protocol. Two main phases were distinguished in the development of plastic strain (p) with loading cycles in fouled ballast: (1) initial compaction phase (ICP), where the p of ballast steadily increases to a certain point (N < 10,000) and (2) fouling impact phase (FIP), where the p and the rate of plastic strain of ballast increases due to the presence of fouling materials (or remains stable in the absence of fouling). A maintenance planning and scheduling software was developed incorporating the mechanistic based predictive model for railway substructure by limiting the surface deviation of the railway track. Maintenance planning for railway track based on deformation of substructure reveals the need for a mechanistic characterization of ballast. Based on the developed model and a given track condition, ballast with initial fouling of 5% requires four maintenance activities (i.e., tamping events) to level the track surface during six years of evaluation. Based on this model, fouling is expected to increase to 25% after six years.
The fundamental mechanistic data generated provide a basis for assessing pavement or rail behavior for various scenarios of freight transport.
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