The project evaluated a concept of a three-dimensional composite layer design for pavement construction for improved performance and service life. The excogitated composite multifunctional (ECM) layer (Figure 1) will satisfy multiple functions in the pavement system by providing for subbase layer-subgrade separation, subbase shear strength, subbase tensile strength, drainage, and protection of the subgrade from surface infiltration.
The work involved material selection and design and fabrication of the composite layer. A number of synthetic and natural materials were evaluated and several performance-related parameters of the layer were measured. The layer strength was increased significantly by changing the polymer blend in the polyethylene structure and by utilizing a stiffer geotextile. The load-deflection relationship and shear stress for this new layer also showed improvements.
The composite layer was evaluated and compared in large-scale laboratory tests. A test cell, 6 ft. by 6 ft. by 40 in., was constructed with an overhead frame for mounting a hydraulic ram to perform dynamic testing of the composite layer. Load deformation tests showed that the composite layer performed far better than the geotextile and geogrid sections and sections with no separation layer. The large-scale laboratory tests were followed by a limited field test of the composite layer with satisfactory performance results.
The composite layer now needs to be tested in a full-scale field setting. The ECM layer can be shipped to the construction site in rolls and can be easily placed by roll-out procedures similar to those used for geotextiles. The investigating team is working with the Illinois Department of Transportation to identify pavement sites during the 1996 construction season. Potential projects for testing include major highway or airport systems, lowvolume roads, thin pavement overlays, and railroad track systems. After field verification experiments, a cost-benefit analysis is planned by the investigator to establish the efficiency of ECM pavement layers. The final report is available from the National Technical Information Service (NTIS # PB96-154414).