There are several methods for determining the stiffness of asphalt concrete in an existing pavement. The three primary methods are: dynamic modulus testing in the laboratory, predictive equations, and falling weight deflectometer (FWD) testing. Asphalt over asphalt (AC/AC) overlay design procedures allow the use of multiple methods to characterize fatigue damage in the existing asphalt concrete. Therefore, understanding the difference between these methods is critical for AC/AC overlay design. The differences between the methods for determining asphalt concrete stiffness and how these differences are related to FWD load magnitude and asphalt temperature are examined. Data from the Federal Highway Administration’s Long-Term Pavement Performance Program (LTPP) are used in this investigation. It is found that the stiffness determined through FWD testing and backcalculation is generally less than that estimated using the Witczak predictive equation and binder aging models. Furthermore, it is found that both FWD load magnitude and asphalt temperature have a significant effect on the difference between backcalculated and estimated stiffness of asphalt concrete. Backcalculated stiffness increases relative to estimated stiffness as FWD load and temperature increase. These effects must be considered when multiple methods of determining asphalt concrete stiffness are used interchangeably for overlay design.

有几种方法可以确定现有路面中沥青混凝土的刚度。三种主要方法是：实验室中的动态模量测试，预测方程式和落锤挠度计（FWD）测试。沥青沥青覆盖（AC / AC）覆盖设计程序允许使用多种方法来表征现有沥青混凝土的疲劳损伤。因此，了解这些方法之间的差异对于AC / AC覆盖设计至关重要。研究了确定沥青混凝土刚度的方法之间的差异以及这些差异与FWD荷载大小和沥青温度之间的关系。本次调查使用了来自联邦公路管理局的长期路面性能计划（LTPP）的数据。发现通过FWD测试和反算确​​定的刚度通常小于使用Witczak预测方程和粘结剂老化模型估算的刚度。此外，发现FWD载荷大小和沥青温度均对沥青混凝土的反算刚度和估算刚度之间的差异产生重大影响。随着FWD负载和温度的增加，相对于估计的刚度，反算的刚度增加。当多种确定沥青混凝土刚度的方法交替用于覆盖设计时，必须考虑这些影响。结果发现，FWD的载荷大小和沥青温度都对沥青混凝土的反算刚度和估计刚度之间的差异有显着影响。随着FWD负载和温度的增加，相对于估计的刚度，反算的刚度增加。当多种确定沥青混凝土刚度的方法交替用于覆盖设计时，必须考虑这些影响。结果发现，FWD的载荷大小和沥青温度都对沥青混凝土的反算刚度和估计刚度之间的差异有显着影响。随着FWD负载和温度的增加，相对于估计的刚度，反算的刚度增加。当多种确定沥青混凝土刚度的方法交替用于覆盖设计时，必须考虑这些影响。