Mix Design
The two key components of pavement design are mix design and structural design. This section deals with HMA and PCC mix design. The goal of mix design is to determine the optimum mixture of component materials for a given application. This includes detailed evaluations of aggregate, asphalt and portland cement as well as a determination of their optimum blending ratios.
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Asphalt mixes
HMA Mix Design Fundamentals
HMA mix design is the process of determining what aggregate to use, what asphalt binder to use and the optimum combination of the two.
HMA Weight-Volume Terms and Relationships
Basic HMA weight-volume relationships are important to understand for both mix design and construction purposes.
Superpave Overview
"Superpave" is an overarching term for the results of the asphalt research portion of the 1987 - 1993 Strategic Highway Research Program (SHRP).
Superpave Mix Design
The Superpave mix design method, a principal result of the Strategic Highway Research Program (SHRP), designed to replace the Hveem and Marshall methods.
Superpave Gradation Requirements
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.
Marshall Mix Design
The Marshall mix design method, developed by Bruce Marshall of the Mississippi Highway Department around 1939 and refined by the U.S. Army.
Hveem Mix Design
The Hveem mix design method, developed by Francis Hveem of the California Division of Highways in the late 1920s and 1930s.
Job Mix Formula
The end result of a successful mix design is a recommended mixture of aggregate and asphalt binder.
Laboratory vs. Field Conditions
This table (taken largely from TRB, 2000) gives a brief outline of some of the major differences between mix design laboratory conditions and actual field conditions.
Batch Plant & Mix Design
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.
Mix Selection Guidance
The National Asphalt Pavement Association (NAPA) has published some general rules Based for HMA mix type use, which are summarized in Table 1.
Mix Type Selection Example
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.
Concrete mixes
PCC Mix Design Fundamentals
PCC consists of three basic ingredients: aggregate, water and portland cement. According to the Portland Cement Association (PCA, 1988):
ACI Mix Design
The American Concrete Institute (ACI) mix design method is but one of many basic concrete mix design methods available today. This section summarizes the ACI absolute volume method because it is widely accepted in the U.S.
ACI Mix Design Example
A concrete mix is to be designed for use in a 250 mm (10 inch) thick JPCP pavement. The desired properties are:
PCC Mix Design Testing
When aggregate, water and portland cement paste are combined to produce a homogeneous substance, that substance takes on new physical properties that are related to but not identical to the physical properties of its components.
PCC Admixtures
Admixtures are the ingredients in PCC other than aggregate, portland cement and water. Typically, an admixture is added to alter a specific PCC property such as workability, setting time, strength or durability.