Flexible Pavement Mix Design

One of the principal results from the Strategic Highway Research Program (SHRP) was the Superpave mix design method. The Superpave mix design method was designed to replace the Hveem and Marshall methods. The volumetric analysis common to the Hveem and Marshall methods provides the basis for the Superpave mix design method. The Superpave system ties … Read more »

Basic HMA weight-volume relationships are important to understand for both mix design and construction purposes.  Fundamentally, mix design is meant to determine the volume of asphalt binder and aggregates necessary to produce a mixture with the desired properties (Roberts et al., 1996[1]).  However, since weight measurements are typically much easier, they are typically taken then … Read more »

HMA consists of two basic ingredients: aggregate and asphalt binder.  HMA mix design is the process of determining what aggregate to use, what asphalt binder to use and what the optimum combination of these two ingredients ought to be. When aggregate and asphalt binder are combined to produce a homogenous substance, that substance, HMA, takes … Read more »

The basic concepts of the Marshall mix design method were originally developed by Bruce Marshall of the Mississippi Highway Department around 1939 and then refined by the U.S. Army. Currently, the Marshall method is used in some capacity by about 38 states. The Marshall method seeks to select the asphalt binder content at a desired … Read more »

“Superpave” is an overarching term for the results of the asphalt research portion of the 1987 – 1993 Strategic Highway Research Program (SHRP). Superpave consists of (1) an asphalt binder specification, (2) an HMA mix design method and (3) HMA tests and performance prediction models. Each one of these components is referred to by the … Read more »

Batch Plant The asphalt originated from Lakeside Industries’ drum plant (see Figure 1) in Issaquah, WA which is approximately 20 miles from the project site. This counter flow drum plant uses natural gas or diesel fuel to dry/heat the aggregate. The fuel source can be changed as necessary to use the least expensive fuel available. … Read more »

Superpave mix design specifies aggregate gradation control points through which aggregate gradations must pass. These control points are very general and are a starting point for a job mix formula. These tables (data taken from AASHTO MP 2, Standard Specification for Superpave Volumetric Mix Design) show typical Superpave aggregate specifications for 37.5 mm (1.5 inch) … Read more »

This example is taken from Example 3 of the NAPA HMA Pavement Mix Type Selection Guide.  It shows how two different representative States would select mixes for a specific situation.  The idea is to show the basic rationale for mix type selection and to show that there are most likely several alternatives that will work … Read more »

This table (taken largely from TRB, 2000[1]) gives a brief outline of some of the major differences between mix design laboratory conditions and actual field conditions.  NAPA’s The Effect of Testing and Production Procedures on Mix Design Results, Information Series 112 is an excellent resource.   Laboratory Conditions Field Conditions Asphalt Binder Aging is simulated … Read more »

The end result of a successful mix design is a recommended mixture of aggregate and asphalt binder. This recommended mixture, which also includes aggregate gradation and asphalt binder type is often referred to as the job mix formula (JMF) or recipe. For HMA manufacturing, target values of gradation and asphalt binder content are specified based … Read more »