Geopolymer

What is a geopolymer?

In the 1950s, Viktor Glukovsky, of Kiev, USSR, developed concrete materials originally known under the names "soil silicate concretes" and "soil cements", but since the introduction of the geopolymer concept by Joseph Davidovits, the terminology and definitions of 'geopolymer' have become more diverse and often conflicting. The examples below were taken from 2011 scientific publications, written by scientists with different backgrounds.

Definitions of the term geopolymer

For chemists

'...Geopolymers consist of a polymeric Si–O–Al framework, similar to zeolites. The main difference to zeolite is geopolymers are amorphous instead of crystalline. The microstructure of geopolymers on a nanometer scale observed by TEM comprises small aluminosilicate clusters with pores dispersed within a highly porous network. The clusters sizes are between 5 and 10 nanometers.'

For geopolymer material chemists

'...The reaction produces SiO₄ and AlO₄, tetrahedral frameworks linked by shared oxygens as poly(sialates) or poly(sialate–siloxo) or poly(sialate–disiloxo) depending on the SiO₂/Al₂O₃ ratio in the system. The connection of the tetrahedral frameworks is occurred via long-range covalent bonds. Thus, geopolymer structure is perceived as dense amorphous phase consisting of semi-crystalline 3-D alumino-silicate microstructure.'

For alkali-cement scientists

'... Geopolymers are framework structures produced by condensation of tetrahedral aluminosilicate units, with alkali metal ions balancing the charge associated with tetrahedral Al. Conventionally, geopolymers are synthesized from a two-part mix, consisting of an alkaline solution (often soluble silicate) and solid aluminosilicate materials. Geopolymerization occurs at ambient or slightly elevated temperature, where the leaching of solid aluminosilicate raw materials in alkaline solutions leads to the transfer of leached species from the solid surfaces into a growing gel phase, followed by nucleation and condensation of the gel phase to form a solid binder.'

For ceramic scientists

'...Geopolymers are a class of totally inorganic, alumino-silicate based ceramics that are charge balanced by group I oxides. They are rigid gels, which are made under relatively ambient conditions of temperature and pressure into near-net dimension bodies, and which can subsequently be converted to crystalline or glass-ceramic materials.'

Covalent bonding

The fundamental unit within a geopolymer structure is a tetrahedral complex consisting of Si or Al coordinated through covalent bonds to four oxygens. The geopolymer framework results from the cross-linking between these tetrahedra, which leads to a 3-dimensional aluminosilicate network, where the negative charge associated with tetrahedral aluminium is balanced by a small cationic species, most commonly an alkali metal cation. These alkali metal cations are often ion-exchangeable, as they are associated with, but only loosely bonded to, the main covalent network, similarly to the non-framework cations present in zeolites.

Geopolymerization starts with oligomers

Geopolymerization is the process of combining many small molecules known as oligomers into a covalently bonded network. The geo-chemical syntheses are carried out through oligomers (dimer, trimer, tetramer, pentamer) which are believed to contribute to the formation of the actual structure of the three-dimensional macromolecular framework, either through direct incorporation or through rearrangement via monomeric species. These oligomers are named by some geopolymer chemists as sialates following the scheme developed by Davidovits, although this terminology is not universally accepted within the research community due in part to confusion with the earlier (1952) use of the same word to refer to the salts of the important biomolecule sialic acid. In 2000, T.W. Swaddle and his team proved the existence of soluble isolated alumino-silicate molecules in solution in relatively high concentrations and high pH, at very low temperatures, as low as −9 °C. Indeed, it was discovered that the polymerization at room temperature of oligo-sialates was taking place on a time scale of around 100 milliseconds, i.e. 100 to 1000 times faster than the polymerization of ortho-silicate, oligo-siloxo units. At room temperature or higher, the reaction is so fast that it cannot be detected with conventional analytical equipment.

The image shows 5 soluble oligomers of the K-poly(sialate) / poly(sialate-siloxo) species, which are the actual starting units of potassium-based alumino-silicate geopolymerization.

Example of (-Si-O-Al-O-) geopolymerization with metakaolin MK-750 in alkaline medium

It involves four main phases comprising seven chemical reaction steps:

Alkaline depolymerization of the layered structure of the calcined kaolinite;

Formation of monomeric and oligomeric species, including the "ortho-sialate" (OH)₃-Si-O-Al-(OH)₃ molecule (#1 in the figure);

In the presence of waterglass (soluble potassium silicate), cyclic Al-Si structures form (e.g. #5 in the figure), whereby the hydroxide is liberated by condensation reactions and can reacts again;

Geopolymerization (polycondensation) into higher oligomers and polymeric 3D-networks.

The geopolymerization kinetics for Na-poly(sialate-siloxo) and K-poly(sialate-siloxo) are slightly different respectively. This is probably due to the different dimensions of the Na⁺ and K⁺ cations, K⁺ being bigger than Na⁺.

Example of zeolitic (Si-O-Al-O-) geopolymerization with fly ash in alkaline medium

It involves 5 main phases

Nucleation stage in which the aluminosilicates from the fly ash particle dissolve in the alkaline medium (Na⁺), releasing aluminates and silicates, probably as monomers.

These monomers inter-react to form dimers, which in turn react with other monomers to form trimers, tetramers and so on.

When the solution reaches saturation, an aluminum-rich gel (denominated Gel 1) precipitates.

As the reaction progresses, more Si-O groups from the initial solid source dissolve, increasing the silicon concentration in the medium and gradually raising the proportion of silicon in the zeolite precursor gel (Gel 2).

Polycondensation into zeolite-like 3D-frameworks.

Geopolymer 3D-frameworks

Geopolymerization forms aluminosilicate frameworks that are similar to those of rock-forming minerals. Yet, there are major differences. In 1994, Davidovits presented a theoretical structure for K-poly(sialate-siloxo) (K)-(Si-O-Al-O-Si-O) that was consistent with the NMR spectra. It does not show the presence of water in the structure because he only focused on the relationship between Si, Al, Na, K, atoms. Water is present only at temperatures below 150 °C – 200 °C, whereas numerous geopolymer industrial and commercial applications work at temperatures above 200 °C, up to 1400 °C, i.e. at temperatures above dehydroxylation. Nevertheless, scientists working on low temperature applications, such as cements and waste management, tried to pinpoint cation hydration and water molecules. This model shows an incompletely reacted geopolymer (left in the figure), which involves free Si-OH groups that will later with time or with temperature polycondense with opposed Al-O-K, into Si-O-Al-O sialate bonds. The water released by this reaction either remains in the pores, is associated with the framework similarly to zeolitic water, or can be released and removed. Several 3D-frameworks are described in the book 'Geopolymer Chemistry and Applications'. After dehydroxylation (and dehydration), generally above 250 °C, geopolymers become more and more crystalline (right in the picture) and above 500-1000 °C (depending on the nature of the alkali cation present) crystallise and have X-ray diffraction patterns and framework structures identical to their geological analogues.

Commercial applications

There exist a wide variety of potential and existing applications. Some of the geopolymer applications are still in development whereas others are already industrialized and commercialized. See the incomplete list provided by the Geopolymer Institute. They are listed in three major categories:

Geopolymer resins and binders

Fire-resistant materials, thermal insulation, foams;

Low-energy ceramic tiles, refractory items, thermal shock refractories;

High-tech resin systems, paints, binders and grouts;

Bio-technologies (materials for medicinal applications);

Foundry industry (resins), tooling for the manufacture of organic fiber composites;

Composites for infrastructures repair and strengthening, fire-resistant and heat-resistant high-tech carbon-fiber composites for aircraft interior and automobile;

Radioactive and toxic waste containment;

Geopolymer cements and concretes

Low-tech building materials (clay bricks),

Low-CO₂ cements and concretes;

Arts and archaeology

Decorative stone artifacts, arts and decoration;

Cultural heritage, archaeology and history of sciences.

Geopolymer resins and binders

The class of geopolymer materials is described by Davidovits to comprise:

Metakaolin MK-750-based geopolymer binder

chemical formula (Na,K)-(Si-O-Al-O-Si-O-), ratio Si:Al=2 (range 1.5 to 2.5)

Silica-based geopolymer binder

chemical formula (Na,K)-n(Si-O-)-(Si-O-Al-), ratio Si:Al>20 (range 15 to 40).

Sol-gel-based geopolymer binder (synthetic MK-750)

chemical formula (Na,K)-(Si-O-Al-O-Si-O-), ratio Si:Al=2

The first geopolymer resin was described in a French patent application filed by J. Davidovits in 1979. The American patent, US 4,349,386, was granted on Sept. 14, 1982 with the title Mineral Polymers and methods of making them. It essentially involved the geopolymerization of alkaline soluble silicate [waterglass or (Na,K)-polysiloxonate] with calcined kaolinitic clay (later coined metakaolin MK-750 to highlight the importance of the temperature of calcination, namely 750 °C in this case). In 1985, Kenneth MacKenzie and his team from New-Zealand, discovered the Al(V) coordination of calcined kaolinite (MK-750). This had a great input towards a better understanding of its geopolymeric reactivity.

Since 1979, a variety of resins, binders and grouts were developed by the chemical industry, worldwide.

Potential utilization for geopolymer composites materials

metakaolin MK-750-based and Silica-based geopolymer resins are used to impregnate fibers and fabrics to obtain geopolymer matrix-based fiber composites. These products are fire-resistant; they release no smoke and no toxic fumes. They were tested and recommended by major international institutions such as the American Federal Aviation Administration FAA. FAA selected the carbon-geopolymer composite as the best candidate for the fire-resistant cabin program (1994-1997).

Fire-resistant material

Flashover is a phenomenon unique to compartment fires where incomplete combustion products accumulate at the ceiling and ignite causing total involvement of the compartment materials and signaling the end to human survivability. Consequently, in a compartment fire the time to flashover is the time available for escape and this is the single most important factor in determining the fire hazard of a material or set of materials in a compartment fire. The Federal Aviation Administration has used the time-to-flashover of materials in aircraft cabin tests as the basis for a heat release and heat release rate acceptance criteria for cabin materials for commercial aircraft. The figure shows how the best organic-matrix made of engineering thermoplastics reaches flashover after the 20 minute ignition period and generates appreciable smoke, while the geopolymer-matrix composite will never ignite, reach flashover, or generate any smoke in a compartment fire.

Carbon-geopolymer composite is applied on racing cars around exhaust parts. This technology could be transferred and applied for the mass production of regular automobile parts (corrosion-resistant exhaust pipes and the like) as well as heat shields. A well-known motorcar manufacturer already developed a geopolymer-composite exhaust pipe system.

Geopolymer cements

From a terminological point of view, geopolymer cement is a binding system that hardens at room temperature, like regular Portland cement. If a geopolymer compound requires heat setting it may not be called geopolymer cement but rather geopolymer binder.

Geopolymer cement is being developed and utilised as an alternative to conventional Portland cement for use in transportation, infrastructure, construction and offshore applications. It relies on minimally processed natural materials or industrial byproducts to significantly reduce its carbon footprint, while also being very resistant to many common concrete durability issues.

Production of geopolymer cement requires an aluminosilicate precursor material such as metakaolin or fly ash, a user-friendly alkaline reagent (for example, sodium or potassium soluble silicates with a molar ratio MR SiO₂:M₂O ≥ 1.65, M being Na or K) and water (See the definition for "user-friendly" reagent below). Room temperature hardening is more readily achieved with the addition of a source of calcium cations, often blast furnace slag.

Geopolymer cements can be formulated to cure more rapidly than Portland-based cements; some mixes gain most of their ultimate strength within 24 hours. However, they must also set slowly enough that they can be mixed at a batch plant, either for precasting or delivery in a concrete mixer. Geopolymer cement also has the ability to form a strong chemical bond with silicate rock-based aggregates. In March 2010, the US Department of Transportation Federal Highway Administration released a TechBrief titled Geopolymer Concrete that states: The production of versatile, cost-effective geopolymer cements that can be mixed and hardened essentially like Portland cement represents a game changing advancement, revolutionizing the construction of transportation infrastructure and the building industry.

Geopolymer concrete

There is often confusion between the meanings of the terms 'geopolymer cement' and 'geopolymer concrete'. A cement is a binder, whereas concrete is the composite material resulting from the mixing and hardening of cement with water (or an alkaline solution in the case of geopolymer cement), and stone aggregates. Materials of both types (geopolymer cements and geopolymer concretes) are commercially available in various markets internationally

Portland cement chemistry vs Geopolymer cement chemistry

Left: hardening of Portland cement (P.C.) through hydration of calcium silicate into calcium silicate hydrate (C-S-H) and portlandite, Ca(OH)₂.

Right: hardening (setting) of geopolymer cement (GP) through poly-condensation of potassium oligo-(sialate-siloxo) into potassium poly(sialate-siloxo) cross linked network.

Alkali-activated materials vs. geopolymer cements.

Geopolymerization chemistry requires appropriate terminologies and notions that are evidently different from those in use by Portland cement experts. On this matter, the Australian Geopolymer Alliance outlines on its web site the following statement: "Joseph Davidovits developed the notion of a geopolymer (a Si/Al inorganic polymer) to better explain these chemical processes and the resultant material properties. To do so required a major shift in perspective, away from the classical crystalline hydration chemistry of conventional cement chemistry. To date this shift has not been well accepted by practitioners in the field of alkali activated cements who still tend to explain such reaction chemistry in Portland cement terminology.

Indeed, geopolymer cement is sometimes mixed up with alkali-activated cement and concrete, developed more than 50 years ago by V.D. Glukhovsky in Ukraine, the former Soviet Union. They were originally known under the names "soil silicate concretes" and "soil cements". Because Portland cement concretes can be affected by the deleterious Alkali-aggregate reaction, coined AAR or Alkali-silica reaction coined ASR (see for example the RILEM Committee 219-ACS Aggregate Reaction in Concrete Structures ), the wording alkali-activation sometimes has a negative impact on civil engineers. However, geopolymer cements do not in general show these deleterious reactions (see below in Properties), when an appropriate aggregate is selected. Terminology related to alkali-activated materials or alkali-activated geopolymers is also in wide (but debated) use. These cements, sometimes abbreviated AAM, encompass the specific fields of alkali-activated slags, alkali-activated coal fly ashes, and various blended cementing systems (see RILEM Technical committee 247-DTA).

User-friendly alkaline-reagents

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 (named here: hostile) and irritant products (named here: friendly). The two classes are recognizable through their respective logos.

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 alkaline reagents belonging to this class may also be termed as User-friendly, although the irritant nature of the alkaline component and the potential inhalation risk of powders still require the selection and use of appropriate personal protective equipment, as in any situation where chemicals or powders are handled.

The development of so-called alkali-activated-cements or alkali-activated geopolymers (the latter considered by some to be incorrect terminology), as well as several recipes found in the literature and on the Internet, especially those based on fly ashes, use alkali silicates with molar ratios SiO₂:M₂O below 1.20, or systems based on pure NaOH (8M or 12M). These conditions are not user-friendly for the ordinary labor force, and require careful consideration of personal protective equipment if employed in the field. Indeed, laws, regulations, and state directives push to enforce for more health protections and security protocols for workers’ safety.

Conversely, Geopolymer cement recipes employed in the field generally involve alkaline soluble silicates with starting molar ratios ranging from 1.45 to 1.95, particularly 1.60 to 1.85, i.e. user-friendly conditions. It may happen that for research, some laboratory recipes have molar ratios in the 1.20 to 1.45 range.

Geopolymer cement categories

The categories comprise:

Slag-based geopolymer cement.

Rock-based geopolymer cement.

Fly ash-based geopolymer cement

type 1: alkali-activated fly ash geopolymer.

type 2: slag/fly ash-based geopolymer cement.

Ferro-sialate-based geopolymer cement.

Slag-based geopolymer cement

Components: metakaolin (MK-750) + blast furnace slag + alkali silicate (user-friendly).Geopolymeric make-up: Si:Al = 2 in fact solid solution of Si:Al=1, Ca-poly(di-sialate) (anorthite type) + Si:Al =3 , K-poly(sialate-disiloxo) (orthoclase type) and C-S-H Ca-silicate hydrate.

The first geopolymer cement developed in the 1980s was of the type (K,Na,Ca)-poly(sialate) (or slag-based geopolymer cement) and resulted from the research developments carried out by Joseph Davidovits and J.L. Sawyer at Lone Star Industries, USA and yielded the invention of Pyrament® cement. The American patent application was filed in 1984 and the patent US 4,509,985 was granted on April 9, 1985 with the title 'Early high-strength mineral polymer'.

Rock-based geopolymer cement

The replacement of a certain amount of MK-750 with selected volcanic tuffs yields geopolymer cement with better properties and less CO₂ emission than the simple slag-based geopolymer cement.

Manufacture components: metakaolin MK-750, blast furnace slag, volcanic tuffs (calcined or not calcined), mine tailings and alkali silicate (user-friendly).Geopolymeric make-up: Si:Al = 3, in fact solid solution of Si:Al=1 Ca-poly(di-sialate) (anorthite type) + Si:Al =3-5 (Na,K)-poly(silate-multisiloxo) and C-S-H Ca-silicate hydrate. Gravel

Fly ash-based geopolymer cements

Later on, in 1997, building on the works conducted on slag-based geopolymeric cements, on the one hand and on the synthesis of zeolites from fly ashes on the other hand, Silverstrim et al. and van Jaarsveld and van Deventer developed geopolymeric fly ash-based cements. Silverstrim et al. US Patent 5,601,643 was titled 'Fly ash cementitious material and method of making a product'.

Presently two types based on siliceous (EN 197) or Class F (ASTM C618) fly ashes:

Type 1: alkali-activated fly ash geopolymer (user-hostile):

In many cases requires heat curing at 60-80°C; not manufactured separately as a cement, but rather produced directly as a fly-ash based concrete. NaOH (user-hostile) + fly ash: partially-reacted fly ash particles embedded in an alumino-silicate gel with Si:Al= 1 to 2, zeolitic type (chabazite-Na and sodalite)structures.

Type 2: slag/fly ash-based geopolymer cement (user-friendly):

Room-temperature cement hardening. User-friendly silicate solution + blast furnace slag + fly ash: fly ash particles embedded in a geopolymeric matrix with Si:Al= 2, (Ca,K)-poly(sialate-siloxo).

Ferro-sialate-based geopolymer cement

The properties are similar to those of rock-based geopolymer cement but involve geological elements with high iron oxide content. The geopolymeric make up is of the type poly(ferro-sialate) (Ca,K)-(-Fe-O)-(Si-O-Al-O-). This user-friendly geopolymer cement is in the development and commercialization phase.

CO2 emissions during manufacture

According to the Australian concrete expert B. V. Rangan, the growing worldwide demand for concrete is a great opportunity for the development of geopolymer cements of all types, with their much lower tally of carbon dioxide CO₂.

CO2 emission during manufacture of Portland cement clinker

The manufacture of Portland cement clinker involves the calcination of calcium carbonate according to the reactions:

Reactions involving alumina also lead the formation of the aluminate and ferrite components of the clinker.

The production of 1 tonne of Portland clinker directly generates approximately 0.55 tonnes of chemical CO₂, directly as a product of these reactions, and requires the combustion of carbonaceous fuel to yield approximately an additional 0.40 tonnes of carbon dioxide, although this is being reduced through gains in process efficiency and the use of waste as fuels. However, in total, 1 tonne of Portland cement leads to the emission of 0.8-1.0 tonnes of carbon dioxide.

Conversely, Geopolymer cements do not rely on calcium carbonate as a key ingredient, and generate much less CO₂ during manufacture, i.e. a reduction in the range of 40% to 80-90%. Joseph Davidovits delivered the first paper on this subject in March 1993 at a symposium organized by the American Portland Cement Association, Chicago, Illinois.

The Portland cement industry reacted strongly by lobbying the legal institutions so that they delivered CO₂ emission numbers, which did not include the part related to calcium carbonate decomposition, focusing only on combustion emission. An article written in the scientific magazine New Scientist in 1997 stated that: ...estimates for CO₂ emissions from cement production have concentrated only on the former source [fuel combustion]. The UN’s Intergovernmental Panel on Climate Change puts the industry’s total contribution to CO₂ emissions at 2.4 %; the Carbon Dioxide Information Analysis Center at the Oak Ridge National Laboratory in Tennessee quotes 2.6 %. Now Joseph Davidovits of the Geopolymer Institute... has for the first time looked at both sources. He has calculated that world cement production of 1.4 billion tonnes a year produces 7 % of [world] current CO₂ emissions. Fifteen years later (2012), the situation has worsened with Portland cement CO₂ emissions approaching 3 billion tonnes a year.

The fact that the dangers to the world’s ecological system from the manufacture of Portland cement is so little known by politicians and public makes the problem all the more urgent: when nothing is known, nothing is done.

Geopolymer Cements Energy Needs and CO2 emissions

This section compares the energy needs and CO₂ emissions for regular Portland cement, Rock-based Geopolymer Cements and Fly ash-based geopolymer cements. The comparison proceeds between Portland cement and geopolymer cements with similar strength, i.e. average 40 MPa at 28 days. There have been several studies published on the subject that may be summarized in the following way:

Rock-based Geopolymer cement manufacture involves:

70% by weight geological compounds (calcined at 700°C)

blast furnace slag

alkali-silicate solution (industrial chemical, user-friendly).

The presence of blast furnace slag provides room-temperature hardening and increases the mechanical strength.

Energy needs

According to the US Portland Cement Association (2006), energy needs for Portland cement is in the range of 4700 MJ/tonne (average). The calculation for Rock- based geopolymer cement is performed with following parameters:

In the most favorable case — slag availability as by-product — there is a reduction of 59% of the energy needs in the manufacture of Rock-based geopolymer-cement in comparison with Portland cement. In the least favorable case —slag manufacture — the reduction reaches 43%.

CO₂ emissions during manufacture

In the most favorable case — slag availability as by-product — there is a reduction of 80% of the CO₂ emission during manufacture of Rock-based geopolymer cement in comparison with Portland cement. In the least favorable case —slag manufacture — the reduction reaches 70%.

Fly ash-based cements Class F fly ashes

They do not require any further heat treatment. The calculation is therefore easier. One achieves emissions in the range of 0.09 to 0.25 tonnes of CO₂ / 1 tonne of fly ash-based cement, i.e. CO₂ emissions that are reduced in the range of 75 to 90%.

Properties for Rock-based geopolymer cement (Ca,K)-poly(sialate-disiloxo)

See

shrinkage during setting: < 0.05%, not measurable.

compressive strength (uniaxial): > 90 MPa at 28 days (for high early strength formulation, 20 MPa after 4 hours).

flexural strength: 10–15 MPa at 28 days (for high early strength of 10 MPa after 24 hours).

Young Modulus: > 2 GPa.

freeze-thaw: mass loss < 0.1% (ASTM D4842), strength loss <5 % after 180 cycles.

wet-dry: mass loss < 0.1% (ASTM D4843).

leaching in water, after 180 days: K₂O < 0.015%.

water absorption: < 3%, not related to permeability.

hydraulic permeability: 10⁻¹⁰ m/s.

sulfuric acid, 10%: mass loss 0.1% per day.

hydrochloric acid, 5%: mass loss 1% per day.

KOH 50%: mass loss 0.02% per day.

ammonia solution: no observed mass loss.

sulfate solution: shrinkage 0.02% at 28 days.

alkali-aggregate reaction: no expansion after 250 days (-0.01%), as shown in the figure, comparison with Portland cement (ASTM C227). These results were published in 1993. Geopolymer binders and cements even with alkali contents as high as 10%, do not generate any dangerous alkali-aggregate reaction when used with an aggregate of normal reactivity.

The need for standards

In June 2012, the institution ASTM International organized a symposium on Geopolymer Binder Systems. The introduction to the symposium states: When performance specifications for Portland cement were written, non-portland binders were uncommon...New binders such as geopolymers are being increasingly researched, marketed as specialty products, and explored for use in structural concrete. This symposium is intended to provide an opportunity for ASTM to consider whether the existing cement standards provide, on the one hand, an effective framework for further exploration of geopolymer binders and, on the other hand, reliable protection for users of these materials.

The existing Portland cement standards are not adapted to geopolymer cements. They must be created by an ad hoc committee. Yet, to do so, requires also the presence of standard geopolymer cements. Presently, every expert is presenting his own recipe based on local raw materials (wastes, by-products or extracted). There is a need for selecting the right geopolymer cement category. The 2012 State of the Geopolymer R&D, suggested to select two categories, namely:

Type 2 slag/fly ash-based geopolymer cement: fly ashes are available in the major emerging countries;

and

Ferro-sialate-based geopolymer cement: this geological iron rich raw material is present in all countries throughout the globe.

and

the appropriate user-friendly geopolymeric reagent.

Geopolymer applications to arts and archaeology

Because geopolymer artifacts look like natural stone, several artists started to cast in silicone rubber molds replications of their sculptures. For example, in the 1980s, the French artist Georges Grimal worked on several geopolymer castable stone formulations.

Egyptian Pyramid stones

With respects to archaeological applications, in the mid-1980s, Joseph Davidovits presented his first analytical results carried out on genuine pyramid stones. He claimed that the ancient Egyptians knew how to generate a geopolymeric reaction in the making of a re-agglomerated limestone blocks. The Ukrainian scientist G.V. Glukhovsky endorsed Davidovits' research in his keynote paper to the First Intern. Conf. on Alkaline Cements and Concretes, Kiev, Ukraine, 1994. Later on, several materials scientists and physicists took over these archaeological studies and are publishing their results, essentially on pyramid stones.

Roman cements

From the digging of ancient Roman ruins, one knows that approximately 95% of the concretes and mortars constituting the Roman buildings consist of a very simple lime cement, which hardened slowly through the precipitating action of carbon dioxide CO₂, from the atmosphere and formation of calcium silicate hydrate (C-S-H). This is a very weak to medium good material that was used essentially in the making of foundations and in buildings for the populace.

But for the building of their "ouvrages d’art", especially works related to water storage (cisterns, aqueducts), the Roman architects did not hesitate to use more sophisticated and expensive ingredients. These outstanding Roman cements are based on the calcic activation of ceramic aggregates (in Latin testa, analogue to our modern metakaolin MK-750) and alkali rich volcanic tuffs (cretoni, zeolitic pozzolan), respectively with lime. MAS-NMR Spectroscopy investigations were carried out on these high-tech Roman cements dating to the 2nd century AD. They show their geopolymeric make-up.