a) Nature of the hardened material:

• X-ray amorphous at ambient and medium temperatures
• X-ray crystalline at temperatures > 500°C

b) Synthesis Routes:

• alkaline medium (Na, K, Ca) hydroxides and alkali-silicates yielding poly(silicates) – poly(siloxo) type or poly(silico-aluminates) – poly(sialate) type
• acidic medium (Phosphoric acid) yielding poly(phospho-siloxo) and poly(alumino-phospho) types

As an example, one of the geopolymeric precursors, MK-750 (metakaolin) with its alumoxyl group –Si-O-Al=O, reacts in both systems, alkaline and acidic. Same for siloxo-based and organo-siloxo-based geopolymeric species that also react in both alkaline and acidic medium.

Geopolymer Terminology

In the late 1970’s, Joseph Davidovits, the inventor and developer of geopolymerization, coined the term “geopolymer” to classify the newly discovered geosynthesis that produces inorganic polymeric materials now used for a number of industrial applications. He also set a logical scientific terminology based on different chemical units, essentially for silicate and aluminosilicate materials, classified according to the Si:Al atomic ratio:

Si:Al = 0, siloxo
Si:Al = 1, sialate (acronym for silicon-oxo-aluminate of Na, K, Ca, Li)
Si:Al = 2, sialate-siloxo
Si:Al = 3, sialate-disiloxo
Si:Al > 3, sialate link.

This terminology was presented to the scientific community at a IUPAC conference in 1976. See for details in the Library the paper Milestone Paper IUPAC-76

In the introduction of his book on alkali-geopolymer cement, the alkali-cement scientist John Provis, challenged the use of the word ‘sialate’ arguing that “…the term ‘sialate’ was already in use (since the 1950s) to describe any of the salts of organic sialic acid …” He simply forgot to mention that long before 1950 geology has been using extensively the term ‘sialic’, for example in ‘sialic metamorphic rocks‘, or ‘the oceanic crust is mostly basaltic and the continental crust is mostly sialic, meaning the rocks, such as granite, contain high amounts of aluminum and silica‘. Not to forget the fact that fly ashes were and still are commonly classified into three entities: calcic-, ferric- and sialic-groups; the sialic component results from the %weight of (SiO₂ + Al₂O₃ + TiO₂). There exists another example, namely the well known term ‘SIALON’, a specialist class of high temperature refractory materials, acronym of silicon-aluminum-oxo-nitride, i.e. a scientific logical terminology. The geopolymeric ‘sialate‘ term proceeds from the same scientific logic (it is the acronym of silicon-oxo-aluminate), in contrast with the organic molecule ‘sialic acid’ that was derived from an ancient Greek word meaning ‘saliva’, with no scientific association. In fact, for our geopolymer molecules we write poly(sialate) / polysialate or poly(sialate-siloxo), a terminology never used in biochemistry. We shall therefore keep our terminology, use it and promote it without any restriction.

Geopolymers comprise following molecular units (or chemical groups):

-Si-O-Si-O- siloxo, poly(siloxo)
-Si-O-Al-O- sialate, poly(sialate)
-Si-O-Al-O-Si-O- sialate-siloxo, poly(sialate-siloxo)
-Si-O-Al-O-Si-O-Si-O- sialate-disiloxo, poly(sialate-disiloxo)
-P-O-P-O- phosphate, poly(phosphate)
-P-O-Si-O-P-O- phospho-siloxo, poly(phospho-siloxo)
-P-O-Si-O-Al-O-P-O- phospho-sialate, poly(phospho-sialate)
-(R)-Si-O-Si-O-(R) organo-siloxo, poly-silicone
-Al-O-P-O- alumino-phospho, poly(alumino-phospho)
-Fe-O-Si-O-Al-O-Si-O- ferro-sialate, poly(ferro-sialate)

Geopolymers are presently developed and applied in 10 main classes of materials:

• Waterglass-based geopolymer, poly(siloxonate), soluble silicate, Si:Al=1:0
• Kaolinite / Hydrosodalite-based geopolymer, poly(sialate) Si:Al=1:1
• Metakaolin MK-750-based geopolymer, poly(sialate-siloxo) Si:Al=2:1
• Calcium-based geopolymer, (Ca, K, Na)-sialate, Si:Al=1, 2, 3
• Rock-based geopolymer, poly(sialate-multisiloxo) 1< Si:Al<5
• Silica-based geopolymer, sialate link and siloxo link in poly(siloxonate) Si:Al>5
• Fly ash-based geopolymer
• Ferro-sialate-based geopolymer
• Phosphate-based geopolymer, AlPO4-based geopolymer
• Organic-mineral geopolymer

The number of scientific papers dealing with geopolymer science & technology is following an exponential growth. The chart displays the evolution of the number of geopolymer papers published from 1991 onwards (publication of Davidovits’ reference paper in J. Thermal Analysis), up to 2013, referenced in Science Direct + SpringerLink + Wiley + DOAJ + ACS under the keyword “geopolymer”. Other publications, such as conference proceedings are not accounted for in these statistical tools. The exponential growth of published scientific papers is confirmed for 2014.

Not ionic (tetrahedral) but covalent !

In the figure below, six atomic arrangements are used to illustrate the silicate ionic structure on the one hand, and the siloxonate/sialate covalent construction on the other hand.

a) Electrons distribution: in the external layer of the atoms Si, O, Al and Na. The electrovalence rules command the creation of the octet (8 electrons in the external shell) either by donating electrons (donator) or by receiving electrons (receptor), as follows:
– Si has 4 electrons. It is a donator or an acceptor (tetra-valence).
– O has 6 electrons. It is a receptor (di-valence).
– Al has 3 electrons. It is a donator in acidic medium (tri-valence) and a receptor in alkaline solution (tetra-valence).
– Na has 1 electron. It is a donator (mono-valence).

b) Ionic concept tetrahedron, coordination: The ions (Si⁴⁺, 4O^–) build the single tetrahedron. Si donates 4 electrons to the 4 oxygens and turns into a small cation Si⁴⁺. Si is tetracoordinated with the 4 oxygens. To achieve anionic stability, each oxygen needs an eighth electron supplied by a metal (Na, K, Ca, Mg, Fe, etc.) or another Si, not shown on the Figure.

c) Ionic concept: By the mutual sharing of one oxygen anion O^2-, two or more tetrahedra may link to form polyanionic groups.

d) Covalent concept: The molecule (SiO₄) results from the co-sharing of electrons between one Si atom and the four surrounding oxygens yielding Si-O covalent bonds (tetravalence). The ortho-siloxonate molecule (SiO₄)^4- requires additional metallic ion donators (Na, K, Ca, Mg, Fe) not shown on the figure.

e) Covalent concept: The polycondensation into di-siloxonate and higher polymeric siloxonates occurs by additional co-sharing of electrons between Si and O. The di-siloxonate molecule (Si₂O₇)^6- requires additional metallic ion donators (Na, K, Ca, Mg, Fe).

f) Covalent concept: The formation of the ortho-sialate molecule with the covalent bond Si-O-Al- occurs in alkaline medium. The Al atom takes the single electron pertaining to a metalloid (Na for example) and becomes tetra-valent, like Si, with an additional negative electrostatic charge. The Na+ cation is strongly attached to the sialate molecule and balances the negative charge.

The differences between the ionic concept (coordination) and the covalent macromolecular bonding are profound. The double tetrahedron in structure (c) is sharing one oxygen anion O^2-, whereas in the di-siloxonate molecule of structure (e), the covalent bond is achieved through Si and O co-sharing only one electron. This results in stronger bond within the latter structure.

Geopolymerization starts with oligomers

The geo-chemical syntheses are carried out through oligomers (dimer, trimer, tetramer, pentamer) which provide the actual unit structures of the three dimensional macromolecular edifice. See in J. Davidovits’ book, Geopolymer Chemistry & Applications, the Chapters 2, 5, 6, 7 and 8.

Example of geopolymerization with metakaolin MK-750

Excerpt from Chapter 8 of Geopolymer Chemistry & Applications:
It involves 3 phases:
– alkaline depolymerization of the poly(siloxo) layer of kaolinite
– formation of the ortho-sialate (OH)₃-Si-O-Al-(OH)₃ molecule
– polymerization (polycondensation) into higher oligomers and polymers

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

Chemical mechanism with Al(V) -Al=O alumoxyl (Al V coordination in MK-750 metakaolin)

The chemical mechanism can be interpreted in the following way, with NaOH or KOH (steps 1 to 6-7) :

Step 1: alkalination and formation of tetravalent Al in the side group sialate -Si-O-Al-(OH)₃-Na⁺,

Step 2: alkaline dissolution starts with the attachment of the base OH- to the silicon atom, which is thus able to extend its valence sphere to the penta-covalent state,

Step 3: the subsequent course of the reaction can be explained by the cleavage of the siloxane oxygen in Si-O-Si through transfer of the electron from Si to O, formation of intermediate silanol Si-OH on the one hand, and basic siloxo Si-O- on the other hand.

Step 4: further formation of silanol Si-OH groups and isolation of the ortho-sialate molecule, the primary unit in geopolymerization.

Step 5: reaction of the basic siloxo Si-O- with the sodium cation Na⁺ and formation of Si-O-Na terminal bond.

Step 6a: condensation between ortho-sialate molecules, reactive groups Si-ONa and aluminum hydroxyl OH-Al, with production of NaOH, creation of cyclo-tri-sialate structure, whereby the alkali NaOH is liberated and reacts again and further polycondensation into Na-poly(sialate) nepheline framework.

Step 6b: in the presence of waterglass (soluble Na- polysiloxonate) one gets condensation between di-siloxonate Q₁ and ortho-sialate molecules, reactive groups Si-ONa, Si-OH and aluminum hydroxyl OH-Al-, creation of ortho-sialate-disiloxo cyclic structure, whereby the alkali NaOH is liberated and reacts again.

Step 7: further polycondensation into Na-poly(sialate-disiloxo) albite framework with its typical feldspar crankshaft chain structure.

For more updated information, see in Davidovits’ book, Geopolymer Chemistry & Applications, the Chapter 4. You may also download previous scientific papers #12 J. Thermal Analysis, #3 NASTS award or #8 Alkaline Cements and Concretes. Other scientific means of investigation, including DTA, XRF, ANOVA, liquid NMR, FTIR spectroscopy, SEM, TEM, mechanical resistance, fatigue under stress and cycles, load-deflection, thermal resistance, leaching behavior, hydraulic conductivity, microbial stability, are discussed in the various papers presented at the Geopolymer World Congress and published in the Proceedings of Geopolymer 2005.

Evidence of oligomer units by NMR

Low molecular elements (monomer, dimer, trimer, tetramer, pentamer) are called oligomers. Oligo-sialate designates the monomer ortho-sialate, the dimer is disialate, etc.; same for oligo(sialate-siloxo) and oligo(sialate-disiloxo). At the beginning of geopolymer research, Joseph Davidovits in 1976 and afterwards for at least 25 years, assumed that the geo-chemical syntheses occurred through hypothetical oligomers (dimer, trimer). Further polycondensation of these hypothetical building units provided the actual structures of the three dimensional macromolecular edifice as displayed in the Figure below. Review papers published at the First Geopolymer Conference in 1988, and at the second, 11 years later, in 1999, could not present scientific details describing the actual reaction mechanism.

Reaction mechanism for sialate and sialate-siloxo species, described as hypothetical by Davidovits in 1988.

It has been the merit of T.W. Swaddle and his team (North M.R. and Swaddle T.W., (2000), Kinetics of Silicate Exchange in Alkaline Aluminosilicate Solutions, Inorg. Chem., 39, 2661-2665) to demonstrate the existence of soluble aluminosilicate species in solution in relatively high concentrations and high pH. One major improvement in their research was that their study was carried out at very low temperatures as low as -9°C. Indeed, it was discovered that the polymerization 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 NMR equipment.

Five ortho-sialate solute species isolated in KOH solutions, after North and Swaddle (2000).

The hypothetical oligomers set forth in geopolymer synthesis are no longer virtual molecules. They actually exist in soluble forms in concentrated solutions at high pH. Swaddle’s study confirms the polymerization mechanisms tentatively reported earlier by Davidovits (1976) with linear oligo-sialate, oligo(sialate-disiloxo) and rings or cycles, as starting geopolymer building units.

Geopolymerization forms aluminosilicate frameworks which are similar to those of rock-forming minerals. Yet there are major differences. We simulated a theoretical structure for K-poly(sialate-siloxo) that was consistent with the NMR spectra. It does not show the presence of water in the structure because we only focused on the relationship between Si, Al, Na, K, atoms. Water is present only at temperatures below 150-200°C, and numerous geopolymer industrial and commercial applications do work at temperatures above 200°C, up to 1400°C. Nevertheless, scientists working on low temperature applications, such as cements and waste management tried to pinpoint cations hydration and water molecules. For example Barbosa et al.(2000) stressed the importance of water for cement applications and their model was modified by Rowles (2004).

This model is only valid for incompletely reacted geopolymer. It involves free Al-OH groups that will later with time or with temperature evidently polycondense with opposed Si-O-Na, into sialate bonds.

Fully geopolymerized models are very close to the original one proposed by Davidovits (1994).
After dehydroxylation (and dehydration), generally above 250°C, geopolymers are becoming more and more crystalline and above 500°C have X-rays diffraction patterns and framework structures identical to their geological analogues.

Technical Data Sheet for Geopolymeric cement type (Potassium, Calcium) – Poly(sialate-siloxo) / (K,Ca) – (Si-O-Al-O-Si-O-), Si:Al=2:1

Further details in Davidovits’ book, GEOPOLYMER Chemistry & Applications, Part III, Properties, Chapters 15 to 18, GEOCISTEM , GLOBAL WARMING, and also previous papers in the Geopolymer Library.

Tested on standard sand mortar prisms:

• setting: 10 hours at -20°C to 7-60 minutes at +20°C.
• 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 10 MPa after 24 hours).
• Young Modulus: > 2 GPa.
• freeze-thaw: mass loss < 0,1% (ASTM 4842), strength loss < 5% after 180 cycles.
• wet-dry: mass loss < 0,1% (ASTM 4843).
• pH: crushed and powdered, 11-11,5 after 5 minutes in deionized water (compared to Portland cement: 12 to 12,5, and granite: 11).
• 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.
• chlorhydric acid 5%: mass loss 1% per day.
• KOH 50%: mass loss 0,02% per day.
• ammoniac solution: no mass loss.
• sulfate solution: shrinkage 0,02% at 28 days.
• alkali-aggregate reaction: no expansion after 250 days, -0,01% (compared to Portland Cement with 1% Na₂O, +1,5%).
• linear expansion: < 5.10-6/K.
• heat conductivity: 0,2 to 0,4 W/Km.
• specific heat: 0,7 to 1,0 kJ/kg.
• electrical conductivity: strongly dependent on humidity.
• thermal stability:
  • mass loss < 5% up to 1000°C.
  • strength loss < 20% at 600°C, < 60% at 1000°C

Other values:

• D.T.A.: endothermic at 250°C (zeolitic water).
• MAS-NMR spectroscopy:
  • 29Si: SiQ₄, major resonance at -94,5 ± 3ppm.
  • 27Al: AlQ(4Si), major narrow resonance at 55 ± 3ppm.
• Energy consumption: SEC for cement 1230-1310 MJ/tonne (compared to Portland clinker 3500 MJ/tonne).
• CO₂ emission during manufacture: 0,180 t/tonne of cement (compared to Portland clinker 1,0 t/tonne).

Left: hardening of Portland cement (P.C.) through simple hydration of Calcium Silicate into Calcium Di-Silicate hydrate and lime Ca(OH)₂.

Right: hardening (setting) of Geopolymer resin (GP) through poly-condensation of Potassium Oligo-(sialate-siloxo) into Potassium Poly(sialate-siloxo) cross linked network.

The Australian Geopolymer Alliance outlines on his web site the following statement:

(…) 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.

In his recent keynote lecture held at the Geopolymer Camp 2012 State of Geopolymer R&D 2012, Prof. J. Davidovits stated that the present situation, which is prevailing among cement scientists, is a major obstacle to any breakthrough and innovation in geopolymer cement/concrete technology and is responsible for the slow implementation of any world-wide industrialization. See also in the LIBRARY the paper #21 Geopolymer cement review 2013.

Prof. Joseph Davidovits presents the road map for the next couple of years on geopolymer science innovation and research, at the 2^nd International Congress on Ceramics, Verona, Italy, July 4th, 2008.

There is a great need for innovation and therefore further research must be carried out. We have listed below the topics that deserve further involvement in the field of chemistry, physical-chemistry, materials science, and others. These needs are outlined in Davidovits’ book Geopolymer Chemistry & Applications, generally at the end of the chapter dedicated to the topic, and are given in the list.

We hope that this initiative will minimize the number of scientific papers and conference communications that are simply re-inventing the wheel, i.e. replicate studies and research already performed by others, sometimes several decades ago, and outlined in the reference book Geopolymer Chemistry & Applications.

The GeopolymerCamp is the opportunity to prepare the new edition of the book Geopolymer Chemistry & Applications. Indeed, the Geopolymer Institute wishes to publish every year a new revised edition with the most up to date information. During this session, participants will propose subjects or issues that are worthwhile to be edited or added, and the assembly will discuss about it. Prepare your arguments if you want to see your last research, data, applications be added to this reference book.

Research topics:

Chapter 2: Polymeric character of geopolymers: geopolymeric micelle
“Further research is needed to provide scientific tools for the determination of several physical parameters such as overall dimension and molecular weight.”

Let physicochemical research institutions confirm covalent bonding system. Determine the molecular weight of the geopolymer micelle, a nanosized particulate detected by W. Kriven in 2003.

Chapter 5: Poly(siloxonate), soluble silicate (waterglass)
“The standard industrial silicates are mixtures of several silicate species (…) Any changes in the industrial fabrication parameters will strongly affect the nominal mixture composition and the geopolymeric properties of the soluble silicates obtained with these glasses (…) Nevertheless, researchers in geopolymer science should always keep in mind these data when developing tailored industrial geopolymer applications (…) Further research on this important topic will probably provide additional 3-D structures connected with the solid rings and polygons disclosed in Figure 5.9. (…) Further research is needed on this crucial technology.”

Let modify and master the manufacture process in order to get uniformity and quality control on the molecular sizes of Na-poly(siloxonate), K-poly(siloxonate) (soluble silicate).

Chapter 8: Metakaolin MK-750-based geopolymer
“In general, (Na,K)–poly(sialate-siloxo) is not made of single polymeric macromolecules but consists of a mixture, a solid solution, of at least two well defined geopolymers with different Si:Al ratios. The standardized methods of investigation, like ²⁹Si and ²⁷Al NMR spectroscopy, are not sophisticated enough for the detection and separation of these different macromolecules. Future research is necessary. (…) The identification of Al-O-Al bonding in geopolymers has been confirmed by ¹⁷O MAS-NMR spectroscopy as the one displayed in Figure 8.24… The effect seems to diminish with the increase of the Si:Al ratio, when oligo-siloxonate molecules, Q₀ , Q₁ and Q₂ types are added to the geopolymeric reactant mixture. Further research is needed.”

Chapter 9: Calcium-based geopolymer
“There is production of two geopolymers: hydrated gehlenite and (Na,K)–poly(sialate-siloxo), and in addition calcium di-siloxonate hydrate (CSH cement type). Further research is needed on this very interesting topic of ancient Roman technology. (…) We could also assume that, in the hydrated state, our geopolymeric structures are more flexible than the rigid anhydrous chains. Their molecular arrangement might comply with the replacement of K⁺ with Ca⁺⁺. Further research is needed to clarify this important issue.”

Chapter 10: Rock-based geopolymer
“The extrapolation from the solid solution structures set forth in Chapter 9 would probably focus on the Ca-siloxonate-hydrate, and its resonance at -78 ppm for Q₁ structure in the ²⁹Si spectrum of Figure 10.5. However, in addition to the dimer Ca-di-siloxonate hydrate molecule, one could get higher oligomers: trimer, tetramer, pentamer, hexamer, with cyclic structures similar to those depicted for soluble silicates in Figure 5.13 of Chapter 5 as well as in Figure 2.8 of Chapter 2. Further research is needed.”

Chapter 11: Silica-based geopolymer
“The geopolymer composite has a high potential for fire-heat resistant coatings as well as corrosion resistant paint for steel. With tailored ceramic fillers one obtains heat stable materials with remarkable heat resistance. Further research is needed. (…) These results highlight the need for caution during the use and disposal of these manufactured nanomaterials to prevent unintended environmental impacts, as well as the importance of further research on tailored formulations aimed at preventing any risk.”

Chapter 12: Fly ash-based geopolymer
“Overall, the geopolymer matrix gives a Si:Al molar ratio ranging from 1.56–2.14 corresponding to a poly(sialate-siloxo) with inclusions of siloxonate-hydrate molecules consisting of higher oligomers: trimer, tetramer, pentamer, hexamer, with cyclic structures similar to those depicted for soluble silicates in Figure 5.13 of Chapter 5 as well as in Figure 2.8 of Chapter 2. Further research is needed. (…) Gasifier slag consists of four main components: silica, alumina, iron oxide and calcium oxide, mainly added as a flux in the gasification process. The gasifier slag composition is similar to that of iron blast-furnace slag (Sullivan and Hill, 2001). In other words, a possible shortage of iron blast-furnace slag would be easily compensated by the production of gasifier slag, opening new perspectives for the industrial implementation of geopolymers issuing from coal combustion in electrical power plants. Further research is needed.”

Chapter 13: Phosphate-based geopolymer
“Several laboratories are working on the inclusion of PO₄ units into sialate and sialate-siloxo sequences. Data have not been published, so far. Further research is needed on these materials that show promising potential applications.”

Chapter 14: Organic-mineral geopolymer
“Further research is needed in order to take advantage of the chemical compatibility of poly-organo-siloxane and mineral geopolymers. (…) Further research is needed on the geopolymerization mechanism in acid medium. (…) The previous examples show the potentiality of organo-mineral geopolymer compounds. Further research is needed.”

Chapter 17: Long-term durability
“As for technological applications of geopolymeric materials in waste management, any risk assessment must contain input from geological and geochemical analogues. The problem is the very low amount of available data on this topic. Further research is needed.

Chapter 21: Geopolymer-fiber composites
“In this Chapter, the best results involved the use of carbon or SiC fibers that are more expensive than E-glass. Future research will therefore take advantage of the geopolymeric systems outlined in Chapter 13 with phosphate based acidic matrix. This chemistry is not as aggressive to E-glass as the alkali driven poly(sialate) medium.”

The introduction of composites on a large scale in aircraft manufacture by Boeing and Airbus highlights the demand for fire- as well as heat-resistant geopolymer matrices.

Chapter 23: Geopolymer in ceramic processing
Introduce and develop LTGS for the production of low-cost building materials in developing countries with user-friendly geopolymeric ingredients.

Chapter 24: The manufacture of geopolymer cements
“We have learned in Chapter 19 that these dry mixes based on dry NaOH/KOH are corrosive in nature and may not be used (see in section 19.2, The need for user-friendly systems ). Research and development should therefore focus on innovative solutions involving the manufacture of ready to use, user-friendly, geopolymeric precursors. (…) Further research and development is needed on this very important technology.”

The major obstacle to the mass application of geopolymer cements comes from the chemical industry that is unable to manufacture the estimated 250-300 millions tonnes / year of alkali-silicates poly(siloxonates) needed for mass production of geopolymer cements, world-wide (presently ca. 15 millions tonnes / year). One must invent new methods of manufacture for poly(siloxonate) glasses, from geological raw-materials rich in K₂O and Na₂O, as in the European Research project GEOCISTEM (Brite-Euram 1994-1997).

Chapter 25: Geopolymer concrete
“When one adds together the properties described in this Chapter 25, and the chemical and physical parameters of geopolymer cements outlined in previous chapters, it becomes evident that geopolymer concrete is better than Portland cement concrete. Yet, further research is needed to apply and generalize to all geopolymer concrete types the results obtained by B.V. Rangan and his team.”