There is often confusion between the meaning of the terms “cement” and “concrete”. A cement is a binder whereas concrete is the composite material resulting from the addition of cement to stone aggregates. Cement is sold to companies that make concrete.
Geopolymer cement is often mixed up with alkali-activated slag developed since 1956 in Eastern Europe by G.V. Glukhovsky. Alkali-activation, which is generally performed with corrosive chemicals (see below User-friendly), is used for the making of concretes exclusively. The alkali-activated materials are not manufactured separately and not sold to third parties as commercial cements. On the opposite, geopolymer technology was from the start aimed at manufacturing binders and cements for various types of applications.
In this section we are developing:
a) Pyrament® cement developed in the 1980-1990 at Lone Star Industries, USA, see below;
b) The User-friendly geopolymer cement concept, see next page.
At the Geopolymer Camp 2009 at Saint-Quentin, France, Prof. Joseph Davidovits presented a keynote on “Practical Problems on Mass Produced Geopolymer Cement”. What are the key issues and what are the dead ends? What to do to make a cement that reduces the CO2 emission by 60 up to 80%?
Mass Production of Geopolymer Cement
J. Davidovits’ Keynotes at Geopolymer Camp 2010, 2011 and 2012 contain additional information. Go to Keynotes GPCamp
Geopolymer cement Pyrament®
In 1991, the world was impressed on how fast the US Air Force managed to build and equip temporary military airports in the wilderness of Saudi Arabia during the Gulf War. One of the reasons for this efficiency might result from the application by the US Air Force Engineering of a very new rapid high strength and high performance cement, the Pyrament®. Sources: US Air Force Command report and Pyrament brochure.
The American Cement Company, Lone Star Industries, introduced this exceptional cement in 1988. It was the result of an unique collaboration that started in 1983 between the Lone Star Industries Research Center in Houston, Texas, and the Geopolymer Institute. Geopolymer chemistry, in particular the Poly(sialate-siloxo) based system, improves the properties of Portland cement and regular concrete. In the recently updated book Geopolymer Chemistry & Applications several chapters are dedicated to geopolymer , metakaolin-based, rock-based and fly ash-based cements and concretes, see in Chapters 8, 9, 10, 11, 12, 24 and 25. You may also go to the Geopolymer Library and download several papers.
The Pyrament® blended-cement is the ideal material for repairing runways made of concrete, industrial pavements, and highway roads. In the case of a runway, a 4-6 hours hardening is enough to allow the landing of an Airbus or a Boeing. The geopolymeric cement reaches a compression strength of 20 Mpa after 4 hours, whereas plain concrete gets to this strength after several days.
The Pyrament® blended cement was recognized in the construction industry for its ability to gain very high early strength quite rapidly. As of fall 1993, Pyrament concrete was listed for over 50 industrial facilities in the USA, 57 military installations in the USA, and 7 in other countries, and for nonmilitary airports. In 1994 the US Army Corps of Engineers released a well documented study on the properties of PYRAMENT Blended Cements based concretes, which are performing better than had ever been expected for high-quality concretes (Performance of Concretes Proportioned with Pyrament Blended Cement, by Tony B. Husbands, Philip. G. Malone, Lilian D. Wakeley, US Army Corps of Engineers, Final Report CPAR-SL-94-2, April 1994).
If we compare in a microscope the structure of mortar made of regular cement with another sample made of geopolymer, we notice that the regular cement is a coarse stacking of grains of matter. This causes cracks and weaknesses. On the opposite, geopolymer cement (in black) is smooth and homogeneous. This provides, in fact, superior assets.
Plain concrete (left) / Geopolymer concrete (right)
In 1996, Lone Star Industries definitively stopped marketing Pyrament, not for technical reason, rather because Lone Star has been faced with a severe financial and corporate crisis, which had nothing to do with the development of the innovative Pyrament business.
User-friendly geopolymer cements
Although geopolymerization does not rely on toxic organic solvents but only on water, it needs chemical ingredients that may be dangerous and therefore requires some safety procedures. Material Safety rules classify the alkaline products in two categories:
- corrosive products
- irritant products
The two classes are recognizable through their respective logos displayed below.
The Table lists some alkaline chemicals and their corresponding safety label. The corrosive products must be handled with gloves, glasses and masks. They are User-hostile and cannot be implemented in mass applications without the appropriate safety procedures. In the second category one finds Portland cement or hydrated lime, typical mass products. Geopolymeric mixes belonging to this class may also be termed as User-friendly.
Note: The limit for “user-friendly” ratio is now 1.6 instead of 1.45.
When we started the research on geopolymer cements, we decided to select alkaline conditions that are User-friendly. (Na,K,Ca)-Poly(sialate-siloxo) and K-Poly(sialate) products (resins, binders and cements) have starting molar ratio SiO2:M2O ranging from 1.45 to 1.85. Unfortunately, this is not followed by other scientists and technicians involved in the development of so-called alkali-activated-cements, especially those based on fly ashes, with molar ratio in average below 1.0. Looking only at low-costs consideration, not at safety and User-friendly issues, they propose systems based on pure NaOH (8M or 12M). For example in a “State of the Art” on alkali-activated fly-ash cements, wrongly named geopolymer technology, published in 2007, several scientists claimed that the pure NaOH system should be considered as the reference for fly-ash-based cements (see: Duxson P., Fernandez-Jimenez A., Provis J.L., Lukey G.C., Palomo A. and van Deventer J.S.J., Geopolymer technology: the current state of the art, J. Mater. Sci., 42, 2917-2933, 2007). These are User-hostile conditions for the ordinary labor force employed in the field.
Finally, companies refuse to support the liability and pay high insurance fees based on such out-of-date processes. Indeed, laws, regulations, and state directives push to enforce for more health protections and security protocols for workers’ safety. Further details on fly-ash-based geopolymer cement in the page GEOASH, a project aimed to develop a real industrial process driven by these constraints.