Geopolymer Presentation

Geopolymers are a rising materials technology with ancient roots that according to some sources go back for 25,000 years. This ancient technology was rediscovered in modern times just over thirty years ago by Prof. Joseph Davidovits of France. He claims that the builders of the Great Pyramid used the technology to cast the stones of the pyramid in place rather then dragging heavy stone blocks up a slippery ramp by hundreds of thousands of slaves. The rediscovery of this ancient technology has opened many doors for new high tech uses today.

High strength geopolymers can be produced from “F” type coal fly ash that exceeds 100 MPa this is a far higher compressive strength then conventional concrete. Type “F” coal fly ash is derived from burning coal that is produced in the eastern US that is rich in calcium. These coals are both anthracite and bituminous varieties.

Type “C” type coal fly ash is derived from burning the coal produced in the western US and lignite. Both ashes are low in calcium content and in order to produce a pozzolan material hydrated lime has to be introduced artificially.

We have found that the flyash produced in making expanded shale (lightweight aggregate) is more effective then coal flyash.

Geopolymers can also be produced from other pozzelanic materials such as metakaolin, powdered ceramics or glass, granulated metallurgical slag and some types of volcanic ash. Metakaolin is produced by heating kaolin clay to a temperature between 700 and 750 degrees C, and holding it that temperature for 30 minutes.

Geopolymer concrete is much stronger and denser then conventional concrete made using Portland cement. Unlike conventional concrete whose binder is an alumino-hydrated lime, the binder in geopolymers is composed of an alumino-silicate amorphous mineral making geopolymers more akin to man made granite.

Even geologists using sophisticated petrological equipment are hard pressed to distinguish geopolymers from natural stone. The instruments available usually are unable to distinguish geopolymers; the only one that can is an instrument not used in petrology. This instrument is a Magnetic Resonance Spectrometer used by chemists.

If subjected to boiling water or steam at over 100o C geopolymers will disintegrate. However, they have a much greater freeze – thaw life then conventional concrete.

Geopolymer concrete is resistant to most corrosive agents like road salt or magnesium sulfate. It will stand up to the action of acids far better then conventional concrete losing 78% of its strength when immersed in an acid bath of 10% sulfuric acid for 24 days whereas conventional concrete is totally destroyed when exposed to acids for a like period. A great deal of money could be saved using geopolymers instead of the usual concrete for building bridges and highways alone.

The resistance to road salts and other ice melting agents make geopolymers especially valuable in building highways and bridges. Under normal conditions conventional concrete has to be replaced every few years.

An analog of geopolymer concrete was laid down by the Romans over 2,000 years ago in the harbor works at Ostia that looks like it was poured yesterday. This specimen of Roman concrete has been submerged in the Mediterrean Sea since the days of Christ.

An even older example of geopolymers is found on the Great Pyramid of Egypt where it is alleged that the great blocks of stone were cast in place rather then dragged into place by thousands of slaves. This theory has caused great controversy in the world of archeology. The stones in the pyramid have been recreated using the same chemistry right down to the enclosed fossil shells. A similar geopolymer concrete was created by Davidovits from local fossiliferous limestone in France.

One of the beauties of geopolymers lies in the fact that they can almost entirely be built from recycled materials except for their activator fluids that are mostly water. The concrete made with geopolymers is handled in exactly the same way as conventional concrete except that the activator fluid has to be mixed on the jobsite as geopolymers set within a time frame from 15 minutes to one half hour.

Unlike conventional concrete that reaches full strength in about 28 days geopolymers gain their full strength in about 48 hours. You can walk on it in an hour, drive a car over it in four hours and land a 747 on it in eight hours.

Geopolymers are a “green” material made largely from recycled materials that are often discarded or landfilled. Today there are vast amounts of these materials that are stockpiled in landfills waiting to be transformed into geopolymers. In many cases these materials are landfilled at great cost to their producers. When is the last time you made concrete and didn’t have to pay for the cement? You might even be paid to haul the stuff away! How’s that for a deal?

One of the greatest problems with Portland cement besides the concrete from it doesn’t last is its carbon footprint. It has been estimated that making a ton of Portland cement produces a ton of carbon dioxide. This has been estimated to amount to the largest man-made source of carbon dioxide easily accounting for more then 12% of all carbon dioxide in the atmosphere. During a recent year it is estimated that the cement producers in the world made over 9,000,000,000 tons of cement. They also produced over 9,000,000,000 tons of carbon dioxide.

Prof. Joseph Davidovits of the Geopolymer Institute in St. Quentin France coined the phrase “Geopolymers” over thirty years ago for a family of alumino-silicate polymers that were formed in an alkaline environment. Since that time the technology has emerged as a new generation of inorganic polymers having many engineering applications.

One of these applications alone has a significant effect on the infrastructure because it has the ability of being a permanent patch for crumbling concrete made from Portland cement. In essence geopolymers or geosynthisis mimics the formation of natural rocks, and has their physical characteristics. They have the same building blocks as natural rocks the SiO4 and AlO4 tetrahedra allowing them to meet a wide variety of rock fabrics through cross-linking of the formula, Mn [-(Si-02)z-Al-O]n .wH2O.

Geopolymers enjoy a wide range of applications in diverse disciplines,

Civil Engineering: As a low CO2 emitter, fast setting concrete, precast concrete products and ready mixed concrete.

Building Materials: Such items as bricks, tiles, pavers, acoustic and fireproof panels and pipes.

Archeology: Repairing and the restoration of archeological monuments.

Composite Materials: Tooling for the aerospace industry, composites for structural purposes, carbon fiber composite materials. Virtually anything organic or inorganic can be embedded in a geopolymer matrix.

Refractory Applications: Moulds for casting of aerospace metals, as a refractory adhesive.

Recycling Industrial Waste: Fly ash, slag from smelters, mine tailings, volcanic ash.

Environmental Uses: Encapsulation of domestic, hazardous and radioactive waste.

Other: Adhesives, paint

Geopolymers are not meant to replace most modern construction practices, but rather supplement them with a far superior material when applicable. They also enjoy the capability of being able to be made of almost 100% waste products.

References:

Geopolymers and Roman Cement, John Carter, http://www.geopolymersandromanconcrete.blogspot.com

Geopolymers – Aiding the Pursuit of Sustainability in Minerals Sector (and Beyond)
http://www.mineralstrategies.com.au/Images/GeopolymerPaper.pdf

Hydration Process of Potassium Polysialite (K-PSDS) Geopolymer Cement, Y. S. Yang, W. Sun, Z. J. Li, http://www.thomastelford.com/journals/DocumentLibrary/ADCR170103.pdf

Geopolymers and Roman Concrete are Two Ancient Technologies that have been Rediscovered

Geopolymers and Roman Concrete are two ancient technologies that have been rediscovered in recent times. Roman Concrete is something that has lasted for over two thousand years ever since the time when Jesus Christ walked the earth. Geopolymers have been around even longer since it is claimed the Ancient Egyptians used the technology to cast the stones used to build the Pyramids. Both civilizations had the materials and the skills to use either technology.

These technologies share some common materials, and practices, but widely differ in the materials they use. Roman Cement and Concrete are actually derived from the ancient practice of whitewashing rammed earth structures to protect them from the rain. The hydrated lime in the whitewash combined with the materials found in the rammed earth wall. The Egyptian invention depended on their use of Natron, sodium carbonate to preserve their dead.

Roman Concrete structures have lasted for over 2,000 years whereas modern concrete structures are falling apart in as little as 50 years. What is the difference between the two concretes, and why has the Roman concrete lasted so long? Chemically their compositions are quite similar yet they are so different in quality. Once again we have to ask why?

To make cement the Romans combined two simple ingredients; hydrated lime that was made by burning lime leaving behind calcium oxide or quicklime that has been slacked in water. To this they added volcanic ash of which they had in plenty. Red ash came from near Rome, and a more yellowish/gray ash came from near Naples.

If you mix there two ingredients together with additional aggregate you form concrete. The Romans didn’t have cement mixers like we do today, but they knew how to mix their concrete in mortar tubs.

The concrete was mixed using very little water so it was delivered to the jobsite as a non-slumping concrete that was rammed in place using several different tools to assure that all the spaces in the concrete were filled in, and the concrete was compacted. This technique left no open spaces in their concrete that allowed it to be penetrated by water or salt.

Geopolymers are another matter and here they deviate from Roman Cement in their choice of materials. The active ingredient in Geopolymers was sodium silicate that can be made from natron by heating it to drive off the carbon dioxide leaving behind sodium oxide that if it is added to water forms a solution of sodium hydroxide and gives off a lot of heat. By adding quartz sand to this solution the sand is dissolved by the sodium hydroxide leaving a solution of sodium silicate.

If you add finely ground alumino-silicate minerals like those found in granite you wind up with a superior material with cement like characteristics. You can use volcanic ash as well to form Geopolymers. If you fill the Geopolymer with a suitable aggregate filler it will set like regular concrete.

Both of these materials use a special material that is called pozzelanic that is an alumino-silicate that has been affected by high heat. One example of this is volcanic ash, but other pozzelanic materials are found in finely ground glass or ceramics including bricks.