Click for next page ( 8


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 7
7 A few processes that rely on chemical additives have been the rate of 1.5 to 2.5 percent by weight of the asphalt binder. developed in the United States and Europe. The manufactur- The pellets can be added to the binder at the asphalt terminal ers do not disclose specific information on the chemicals used or in the plant supply tank, or they can be added to the mix- in these processes. The first chemical additive process used in ture by blowing them into the drum in a manner similar to the United States was the Evotherm process developed by the addition of fibers to SMA. MeadWestvaco and introduced in 2005. The active ingredients in Evotherm are chemical additives that reportedly improve 1.2 Problem Statement coating, workability, and adhesion at lower temperatures. Ini- and Objective tially, Evotherm was supplied as a high residue emulsion, cur- rently referred to as Evotherm ET (Emulsion Technology). The NAPA has been instrumental in bringing WMA technolo- emulsion contained approximately 70-percent asphalt binder gies into practice in the United States. Numerous demonstra- by weight. The water in the emulsion vaporizes when mixed tion projects have been constructed since 2004. These projects with hot aggregates leaving the residual asphalt and chemical have demonstrated the feasibility of using warm mix processes additives. A number of projects were constructed in the United in the United States. Pavements have been successfully con- States using the Evotherm ET process. MeadWestvaco then structed using various warm mix processes with only minimal introduced a process where the chemical additives are injected changes to equipment and quality control practices. These proj- as a solution directly into the asphalt line at the plant. This ects have served the important functions of introducing WMA process is referred to as Evotherm DAT (Dispersed Addi- to agency and contractor personnel; demonstrating the con- tive Technology). It has the advantage that much less water structability of WMA; and providing initial data on energy is added to the mixture compared to the emulsion process. usage, emissions, and pavement performance. The success of MeadWestvaco has recently introduced a third-generation these demonstration projects has led some state highway agen- process referred as Evotherm 3G, which is a water-free warm cies to allow WMA to be used routinely on paving projects. mix technology developed jointly by Ergon Asphalt and Emul- One of the critical issues facing WMA is the lack of a formal sions, Inc., and Mathy Construction Company. This process mixture design procedure. For most WMA projects con- allows the additive to be mixed with the binder at a terminal and structed in the United States, WMA has been substituted into distributed to asphalt plants using the normal binder distribu- a mixture designed as HMA with no change to the job mix for- tion process. Because of their improved convenience, Evotherm mula. If warm mix is to replace hot mix in the future, a labora- DAT and Evotherm 3G have largely replaced Evotherm ET. tory mixture design procedure for WMA must be established. Rediset WMX is a chemical process that was introduced in The objective of NCHRP Project 09-43 was to develop mixture the United States in 2007. Rediset WMX is produced by Akzo design and analysis procedures that can be used with the wide Nobel and is marketed as a warm mix additive with adhesion- range of warm mix processes that are currently available or promoting properties. It is supplied as a pellet and added at may likely become available in the future.