Characterizing the Modulus Properties of Texas Perpetual Pavements Based on Laboratory Dynamic Modulus Testing
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Currently, Texas recommends at least a 200 mm thick layer of Stone-Filled Hot-Mix Asphalt (SFHMA) mix as the main structural load-carrying layer in a perpetual pavement (PP) structure. To ensure adequate rutting resistance, the SFHMA mix-design characteristic typically consists of a moderately low asphalt-binder content (about 4.2%) and coarse aggregate gradation with a 25 mm nominal maximum aggregate size. However, perpetual pavements are relatively a new concept to Texas with limited experience or documented literature including the modulus properties and performance history; in particular for the rut-resistant SFHMA mixes. The objective of the work presented in this paper was therefore to evaluate and characterize the modulus properties of the SFHMA layers (mixes) based on laboratory dynamic modulus (DM) testing. Analysis of the results based on eight field in-service PP projects indicated that the SFHMA mixes are generally very stiff mixes with high moduli values averaging 8 000 MPa at 25 C., 10 Hz; which is structurally essential for adequate rutting resistance. The laboratory DM test results were also well corroborated by field falling weight deflectometer (FWD) and multi-depth defiectometer (MDD) surface deflection measurements; which also indicated that the mixes are considerably less temperature sensitive with very marginal pavement surface deflections less than 1 mm even under high summer temperatures of around 42 C. Summarily, the findings of this study indicated that the structural design moduli for the Texas SFHMA mixes (for perpetual pavements) should be in the range of about 6 000 to 8 000 MPa instead of the current specification range of 3 500 to 5 000 MPa, at 25 C. Copyright 2008 ASCE.