ABSTRACT
Tensile strain at the bottom of the asphalt concrete (AC) layer is an important pavement response and is related to the fatigue life of AC layer. The AC strains can be measured using strain gauges placed at the bottom of the AC layer during construction. In a mechanistic-empirical design framework, the fatigue damage algorithms rely on tensile strains from mechanistic models. In absence of strain gauges, prediction of such strains with mechanistic models and subsequent estimation of fatigue life can be misleading for in-service pavements and overlay designs owing to the unknown extent of damage governed by load and environment-related factors. This paper lays out a simplified method to estimate AC strains using a deflection basin parameter (shape factor) known as Area Under Pavement Profile (AUPP) from heavy/falling weight deflectometer (HWD/FWD) tests. AUPP is calculated from surface deflections obtained from routine HWD/FWD tests. The concept was developed in the early ’80s using ILLI-PAVE (finite element program) and verified/refined using FWD test data from Mn/ROAD project. As part of a research study conducted at FAA’s National Airport Pavement & Materials Research Center (NAPMRC), HWD tests were performed over AC pavements with embedded AC strain gages during Test Cycle 1 (TC-1). The surface layer of test pavements included Hot Mix Asphalt (HMA) and Warm Mix Asphalts (WMA). WMA was produced using a chemical additive Evotherm. The paper will present the relationship developed between AUPP and AC strains.
