19-07-2012, 03:30 PM
Geopolymer Concrete
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Introduction
Geopolymer materials represent an innovative technology that is generating considerable interest in the construction industry, particularly in light of the ongoing emphasis on sustainability. In contrast to portland cement, most geopolymer systems rely on minimally processed natural materials or industrial byproducts to provide the binding agents. Since portland cement is responsible for upward of 85 percent of the energy and 90 percent of the carbon dioxide attributed to a typical ready-mixed concrete (Marceau et al. 2007), the potential energy and carbon dioxide savings through the use of geopolymers can be considerable. Consequently, there is growing interest in geopolymer applications in transportation infrastructure.
What Is a Geopolymer?
The term geopolymer was coined by Davidovits in 1978 to represent a broad range of materials characterized by chains or networks of inorganic molecules (Geopolymer Institute 2010). There are nine different classes of geopolymers, but the classes of greatest potential application for transportation infrastructure are comprised of aluminosilicate materials that may be used to completely replace portland cement in concrete construction (Davidovits 2008). These geopolymers rely on thermally activated natural materials (e.g., kaolinite clay) or industrial byproducts (e.g., fly ash or slag) to provide a source of silicon (Si) and aluminum (Al), which is dissolved in an alkaline activating solution and subsequently polymerizes into molecular
Existing Applications
To date, there are no widespread applications of
geopolymer concrete in transportation infrastructure,
although the technology is rapidly advancing
in Europe and Australia. One North American
geopolymer application is a blended portlandgeopolymer
cement known as Pyrament® (patented
in 1984), variations of which continue to be
successfully used for rapid pavement repair. Other
portland-geopolymer cement systems may soon
emerge. In addition to Pyrament®, the U.S. military
is using geopolymer pavement coatings designed
to resist the heat generated by vertical takeoff and
landing aircraft (Hambling 2009).
Future Developments
User-friendly geopolymer cements
that can be used under
conditions similar to those suitable
for portland cement are the
current focus of extensive worldwide
research efforts. These cements
must be capable of being
mixed with a relatively low-alkali
activating solution and must cure
in a reasonable time under ambient conditions (Davidovits
2008). Until such cements are developed,
geopolymer applications in transportation infrastructure
will be limited.