CAL/APT Program: Test Results from Accelerated Pavement Test on Pavement Structure Containing Asphalt Treated Permeable Base (ATPB) Section 500RF

This report is the second in a series which describe the results of tests on full-scale pavements constructed at the Richmond Field Station (RFS) which have been designed and constructed according to Caltrans procedures. It contains a summary of the results and their interpretation of the Heavy Vehicle Simulator (HVS) tests on the first of four pavement test sections, an asphalt-concrete section containing an asphalt-treated permeable base (ATPB), designated section SOORF. The tests on the four test sections have been performed as part of Goal 1 of the CALIAPT Strategic Plan. Results of the test and their analysis indicate the following: (1) the HVS testing environment at the Richmond Field Station with respect to fatigue performance is more benign relative to moisture effects but provides a slightly more severe temperature environment than that which might be expected in natural California settings, (2) the importance of mix compaction on pavement performance has been conclusively demonstrated and the current Caltrans mix compaction specification has been shown to permit excessive air-void contents. Improved pavement performance that could result from tightening the specification has been demonstrated by the results obtained from Section 500RF, and such a change in the specification has the potential to result in large (and quantifiable) savings to the state, (3) the fatigue analysis and design system developed during the SHRP program and refined within the CALIAPT program has been used to explain the difference between the design estimate for Section SOORF of approximately I x106 ESALs and the HVS measurement of approximately 112x I06 ESALs; although some of the discrepancy remains unaccounted for (possibly as a result of difficulties in modeling the bonding between the two lifts of asphalt concrete), the overall agreement helps to validate both the analysis and design system as a mechanism for structural design and the current Caltrans design methodology, (4) the weak bond observed between asphalt-concrete lifts in Section 500RF has been found to significantly degrade pavement performance; while the extent to which weak bonding may be prevalent in California pavements is unknown, the fact that the HVS test pavement was constructed according to standard Caltrans procedures suggests possible problems within pavements in service; if additional investigations confirm such possible problems, remedial action such as the application of suitable tack coats will result in significant improvements in pavement performance, (5) the Asphalt Institute's subgrade strain criterion for controlling subgrade rutting has been confirmed by the SOORF test; while additional validation is necessary, this criterion enables a mechanistic/empirical analysis of subgrade rutting to supplement routine Caltrans design procedures in special investigations, and (6) results of the 500RF test suggest that the Caltrans structural design procedure is conservative, presumably because it must accommodate a wide variety of mixes, climates, and construction practices; the likely result in many instances is overdesign; the economic consequences of this overdesign can, conceptually at least, be evaluated by life-cycle cost models; the analysis and design system, being developed and refined in part within the CALIAPT program, will provide a basis for more accurate structural designs compatible with acceptable levels of reliability.