Marshall Method

Although HDOT does not use the Marshall method, it accepts Marshall mix designs. Most private laboratories use the Marshall method because it is a proven method and requires relatively light, portable and inexpensive equipment. Like the Hveem and Superpave methods, the Marshall method has been proven to produce quality HMA from which long-lasting pavements can be constructed. This section briefly discusses the Marshall mix design method.


Figure 1: Marshall Hammer.	Figure 2: Marshall Stability and Flow device.	Figure 3: Marshall samples.

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.

HAPI Pavement Note on Marshall Mix Design

The Marshall method is the most popular in Hawai'i because of its relative simplicity, economical equipment and proven record.

Typically, the Marshall mix design method consists of three basic steps:

Aggregate selection. Different agencies/owners specify different methods of aggregate acceptance. Private labs may or may not run periodic aggregate physical tests on a particular aggregate source. For each mix design, gradation and size requirements are checked. Often, aggregate from more than one source is required to meet gradation requirements.
Asphalt binder selection. HDOT uses the the Superpave PG system. Hawai'i's common asphalt binder grade is a PG 64-16.
Optimum asphalt binder content determination. In the Marshall method, this step can be broken up into 5 substeps:

Prepare a series of initial samples, each at a different asphalt binder content. For instance, two to three samples each might be made at 4.5, 5.0, 5.5, 6.0 and 6.5 percent asphalt by dry weight for a total of 10 to 15 samples. There should be at least two samples above and two below the estimated optimum asphalt content.
Compact these trial mixes using the Marshall drop hammer (see Figure 1). This hammer is specific to the Marshall mix design method.
Test the samples in the Marshall testing machine (see Figure 2) for stability and flow. This testing machine is specific to the Marshall mix design method. Passing values of stability and flow depend upon the mix class being evaluated.
Determine the density and other volumetric properties of the samples.
Select the optimum asphalt binder content. The asphalt binder content corresponding to 4 percent air voids is selected as long as this binder content passes stability and flow requirements.

Basic HDOT Marshall mix design specifications from the HDOT 1994 Standard Specifications for Road, Bridge and Public Works Construction are shown in Tables 1 and 2 below. These tables do not list all specifications.

Table 1: Basic HDOT Marshall Mix Design Specifications

Item	Specification
Compaction (number of blows for each side)	75
Minimum Stability	1,800 lbs.
Flow (in units of 0.01 inch)	8 - 16
Air Voids	3 - 5%

Table 2: Basic HDOT VMA Specifications for Marshall Mix Designs

Nominal Maximum Aggregate Size (inches)	1.5	1.0	0.75	0.50	0.375
VMA (percent)	12	13	14	15	16