List of Unbound Materials

Unbound materials include the following types:

•AB: aggregate base,

•AS: aggregate subbase,

•Subgrade

•FDR-N: full depth recycled material with no stabilization

•ATPB: asphalt treated permeable base

Consideration for FDR-N

The UCPRC has conducted extensive research on FDR-N (also known as pulverized) material (Jeon, 2009). Comprehensive laboratory and field tests of the pulverized materials were conducted and the results were compared with those of typical aggregate materials. It was concluded that the pulverized material is stiffer than typical aggregate base material and the permanent deformation resistance of the pulverized material was worse than that of the typical aggregate base material in California at low stress levels but better at higher stress levels. CalME simulations suggested that the difference in accumulated permanent deformation in the aggregate base layer after 20 years of trafficking were minimal between the pavements using pulverized material and the ones using typical aggregate material.

It was decided to consider FDR-N material as typical aggregate base, i.e., AB-Class 2.

Consideration for ATPB

Caltrans has only one generic classification for asphalt-treated permeable base (ATPB) (Section 29, Caltrans Standard Specifications). It is produced the same way as hot mix asphalt except with lower binder content that has a default value of 2.5 percent by weight of aggregate. It has historically been used almost exclusively as a 75 mm (0.25 ft) thick drainage layer directly below the dense-graded asphalt concrete layers.

Research (Bejarano et al., 2004) has shown that ATPB layer is prone to stripping in accelerated pavement testing. ATPB layer stiffness was found to decrease from around 1,500 MPa before HVS trafficking to between 200 and 400 MPa after HVS trafficking. This significant reduction in the stiffness of the ATPB was due to stripping resulting from loading and the intrusion of fines from the aggregate base, regardless of the presence of water. Caltrans and UCPRC researchers have noted that ATPB has about a 50 percent chance of stripping in the field within 10 years of construction.

It was decided to use ATPB in its stripped condition. Specifically, ATPB is treated as an unbound material with stiffness similar to a Class 2 aggregate base.

Bejarano, M.O., J.T. Harvey, A. Ali, M. Russo, D. Mahama, D. Hung, and P. Preedonant. Performance of Drained and Undrained Flexible Pavement Structures under Wet Conditions Test Data from Accelerated Pavement Test Section 543-Drained. 2004. Prepared by University of California Pavement Research Center, Institute of Transportation Studies, University of California, Berkeley

Jeon, E.J., PhD Thesis. Comprehensive Performance Evaluation of In-place Recycled Hot Mix Asphalt as Unbound Granular Material. University of California, Davis, 2009