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Geopolymers are inorganic, typically ceramic, materials that form long-range, covalently bonded, non-crystalline (amorphous) networks. Geopolymers are a sub-class of alkali-activated cements. They are mainly produced by a chemical reaction between a chemically reactive aluminosilicate powder (e.g. metakaolin or other clay-derived powders, natural pozzolan, or suitable glasses), and an aqueous solution (alkaline or acidic) that causes this powder to react and form into a solid monolith. The most common pathway to produce geopolymers is by the reaction of metakaolin with sodium silicate, which is an alkaline solution, but other processes are also possible.[ citation needed ]
Commercially produced geopolymers may be used for fire- and heat-resistant coatings and adhesives, medicinal applications, high-temperature ceramics, new binders for fire-resistant fiber composites, toxic and radioactive waste encapsulation, and as cementing components in making concrete. The properties and uses of geopolymers are being explored in many scientific and industrial disciplines: modern inorganic chemistry, physical chemistry, colloid chemistry, mineralogy, geology, and in other types of engineering process technologies.
The original raw materials used in the synthesis of geopolymers were mainly rock-forming minerals of geological origin, hence the name: geopolymer was coined by Joseph Davidovits in 1978 [1] These materials and associated terminology were then popularized over the following decades via his work with the Institut Géopolymère (Geopolymer Institute).
One can distinguish between two synthesis routes, respectively:
The alkaline route is the most important in terms of R&D and commercial applications and will be described below. Details on the acidic route have been published by Wagh in 2004, [2] by Perera et al. in 2008, [3] and by Cao et al. in 2005. [4]
In the 1950s, Viktor Glukhovsky developed concrete materials originally known under the names "soil silicate concretes" and "soil cements", [5] but since the introduction of the geopolymer concept by Joseph Davidovits, the terminology and definitions of the word geopolymer have become more diverse and often conflicting. The word geopolymer is sometimes used to refer to naturally occurring organic macromolecules; [6] that sense of the word differs from the now-more-common use of this terminology to discuss inorganic materials which can have either cement-like or ceramic-like character.
In the following presentation, a geopolymer is essentially a mineral chemical compound or mixture of compounds consisting of repeating units, for example silico-oxide (-Si-O-Si-O-), silico-aluminate (-Si-O-Al-O-), ferro-silico-aluminate (-Fe-O-Si-O-Al-O-) or alumino-phosphate (-Al-O-P-O-), created through a process of geopolymerization. [7] This method of describing mineral synthesis (geosynthesis) was first presented by Davidovits at an IUPAC symposium in 1976. [8]
Even within the context of inorganic materials, there exist various definitions of the word geopolymer, which can include (or not) a relatively wide variety of low-temperature synthesized solid materials. [9] The most typical geopolymer is generally described as resulting from the reaction between metakaolin (calcined kaolinitic clay) and a solution of sodium or potassium silicate (waterglass). The chemical reaction of geopolymerization tends to result in a highly-connected, disordered network of tetrahedral oxide units - which are silicate and aluminate tetrahedra in the metakaolin-waterglass example mentioned above - and with the net negative charges that are associated with aluminate tetrahedra being balanced by the sodium or potassium ions.
In the simplest form, an example chemical formula for a geopolymer can be written as Na2O·Al2O3·nSiO2·wH2O, where n is usually between 2 and 4, and w is around 11-15. Geopolymers can be formulated with a wide variety of substitutions in both the framework (Si,Al) and non-framework (Na) sites; most commonly K or Ca take on the non-framework (Na) sites, or Fe or P can in principle replace some of the Al or Si.
Geopolymerization usually occurs at ambient or slightly elevated temperature; the solid aluminosilicate raw materials (e.g. metakaolin) dissolve into the alkaline solution, and then cross-link and polymerize into a growing gel phase, which then continues to set, harden and gain strength.
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 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, [1] 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. [10]
The image shows 5 examples of small oligomeric potassium aluminosilicate species (labelled in the diagram according to the poly(sialate) / poly(sialate-siloxo) nomenclature), which are key intermediates in potassium-based alumino-silicate geopolymerization. The aqueous chemistry of aluminosilicate oligomers is complex, [11] and also plays an important role in the discussion of zeolite synthesis, a process which has many details in common with geopolymerization.
Example of (-Si-O-Al-O-) geopolymerization with metakaolin MK-750 in alkaline medium [12]
It involves four main phases comprising seven chemical reaction steps:
The reaction processes involving other aluminosilicate precursors, e.g. low-calcium fly ash, crushed or synthetic glasses, or natural pozzolans, are broadly similar to the steps described above.
Geopolymerization forms aluminosilicate frameworks that are similar to those of rock-forming minerals. Yet, there are major differences. In 1994, Davidovits [13] 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. [14] [15] 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'. [16] 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.
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. [17] They are listed in three major categories:
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From a terminological point of view, geopolymer cement [18] 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 [19] (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: [20] 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 [21] [22]
Geopolymerization chemistry requires appropriate terminologies and notions that are evidently different from those in use by Portland cement experts. 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, during the period of the former Soviet Union. [5] 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, also known as alkali–silica reaction, coined ASR (internal swelling of siliceous aggregates due to the reaction of amorphous silica with KOH and NaOH (dissolution of SiO2 at high pH and swelling of the hygroscopic silica gel formed), for more details, see for example the RILEM Committee 219-ACS Aggregate Reaction in Concrete Structures [23] ), 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). [24]
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).[ citation needed ] The two classes are recognizable through their respective logos.
The table lists some alkaline chemicals and their corresponding safety label. [25] 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.
The categories comprise:
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'.
In the 1990s, building on the works conducted on geopolymeric cements and on the synthesis of zeolites from fly ashes on the other hand, Wastiels et al. [33] , Silverstrim et al. [34] and van Jaarsveld and van Deventer [35] developed geopolymeric fly ash-based cements.
Presently two types based on siliceous (EN 197) or class F (ASTM C618) fly ashes:
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 (Ca,K)-(Fe-O)-(Si-O-Al-O). This user-friendly geopolymer cement is in the development and commercialization phase.[ citation needed ]
According to Rangan, an Australian concrete expert, 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. [36]
Geopolymer cements do not rely on calcium carbonate as a key ingredient, and generate much less CO2 than Portland cement during manufacture, with claimed reductions in the range of 40% to 80-90% [ citation needed ]. Joseph Davidovits delivered the first paper on this subject in March 1993 at a symposium organized by the American Portland Cement Association, Chicago, Illinois. [37]
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 [38] that may be summarized in the following way:
Rock-based geopolymer cement manufacture involves:
The presence of blast furnace slag provides room-temperature hardening and increases the mechanical strength.
Energy needs (MJ/tonne) | Calcination | Crushing | Silicate Sol. | Total | Reduction |
---|---|---|---|---|---|
Portland Cement | 4270 | 430 | 0 | 4700 | 0 |
GP-cement, slag by-product | 1200 | 390 | 375 | 1965 | 59% |
GP-cement, slag manufacture | 1950 | 390 | 375 | 2715 | 43% |
CO2 emissions (tonne) | |||||
Portland Cement | 1.000 | 0.020 | 1.020 | 0 | |
GP-cement, slag by-product | 0.140 | 0,018 | 0.050 | 0.208 | 80% |
GP-cement, slag manufacture | 0.240 | 0.018 | 0.050 | 0.308 | 70% |
Energy needs
According to the US Portland Cement Association (2006)[ citation needed ], energy needs for Portland cement is commonly in the range of 4700 MJ/tonne. The calculation for rock-based geopolymer cement is performed considering that the blast furnace slags are available as a by-product from the steel industry (no additional energy needed), or must be manufactured (re-smelting from non granulated slag or from geological resources).
In the most favorable case — slag availability as a 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%.[ citation needed ]
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%.
In June 2012, the institution ASTM International organized a symposium on Geopolymer Binder Systems. The introduction to the symposium states:[ citation needed ]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 elaborated 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, [39] suggested to select two categories, namely:
along with the appropriate user-friendly geopolymeric reagent.
Because geopolymer artifacts can 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. [40]
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. [41] 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. [42] Later on, several materials scientists and physicists took over these archaeological studies and are publishing their results, essentially on pyramid stones. [43] [44] [45] [46]
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. [47]
Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures over time. Concrete is the second-most-used substance in the world after water, and is the most widely used building material. Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined.
A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete. Concrete is the most widely used material in existence and is behind only water as the planet's most-consumed resource.
In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula [SiO(4-2x)−
4−x]
n, where 0 ≤ x < 2. The family includes orthosilicate SiO4−4, metasilicate SiO2−3, and pyrosilicate Si2O6−7. The name is also used for any salt of such anions, such as sodium metasilicate; or any ester containing the corresponding chemical group, such as tetramethyl orthosilicate. The name "silicate" is sometimes extended to any anions containing silicon, even if they do not fit the general formula or contain other atoms besides oxygen; such as hexafluorosilicate [SiF6]2−.Most commonly, silicates are encountered as silicate minerals.
Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th century by Joseph Aspdin, and is usually made from limestone. It is a fine powder, produced by heating limestone and clay minerals in a kiln to form clinker, grinding the clinker, and adding 2 to 3 percent of gypsum. Several types of Portland cement are available. The most common, called ordinary Portland cement (OPC), is grey, but white Portland cement is also available. Its name is derived from its resemblance to Portland stone which is quarried on the Isle of Portland in Dorset, England. It was named by Joseph Aspdin who obtained a patent for it in 1824. His son William Aspdin is regarded as the inventor of "modern" Portland cement due to his developments in the 1840s.
Slag is a by-product of smelting (pyrometallurgical) ores and recycled metals. Slag is mainly a mixture of metal oxides and silicon dioxide. Broadly, it can be classified as ferrous, ferroalloy or non-ferrous/base metals. Within these general categories, slags can be further categorized by their precursor and processing conditions.
Pozzolana or pozzuolana, also known as pozzolanic ash, is a natural siliceous or siliceous-aluminous material which reacts with calcium hydroxide in the presence of water at room temperature. In this reaction insoluble calcium silicate hydrate and calcium aluminate hydrate compounds are formed possessing cementitious properties. The designation pozzolana is derived from one of the primary deposits of volcanic ash used by the Romans in Italy, at Pozzuoli. The modern definition of pozzolana encompasses any volcanic material, predominantly composed of fine volcanic glass, that is used as a pozzolan. Note the difference with the term pozzolan, which exerts no bearing on the specific origin of the material, as opposed to pozzolana, which can only be used for pozzolans of volcanic origin, primarily composed of volcanic glass.
Silica fume, also known as microsilica, is an amorphous (non-crystalline) polymorph of silicon dioxide, silica. It is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production and consists of spherical particles with an average particle diameter of 150 nm. The main field of application is as pozzolanic material for high performance concrete.
Concrete recycling is the use of rubble from demolished concrete structures. Recycling is cheaper and more ecological than trucking rubble to a landfill. Crushed rubble can be used for road gravel, revetments, retaining walls, landscaping gravel, or raw material for new concrete. Large pieces can be used as bricks or slabs, or incorporated with new concrete into structures, a material called urbanite.
Joseph Davidovits is a French materials scientist. He posited that the blocks of the Great Pyramid are not carved stone but mostly a form of limestone concrete or man-made stone.
Metakaolin is the anhydrous calcined form of the clay mineral kaolinite. Rocks that are rich in kaolinite are known as china clay or kaolin, traditionally used in the manufacture of porcelain. The particle size of metakaolin is smaller than cement particles, but not as fine as silica fume.
Ground granulated blast-furnace slag is obtained by quenching molten iron slag from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder. Ground granulated blast furnace slag is a latent hydraulic binder forming calcium silicate hydrates (C-S-H) after contact with water. It is a strength-enhancing compound improving the durability of concrete. It is a component of metallurgic cement. Its main advantage is its slow release of hydration heat, allowing limitation of the temperature increase in massive concrete components and structures during cement setting and concrete curing, or to cast concrete during hot summer.
Pozzolans are a broad class of siliceous and aluminous materials which, in themselves, possess little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically with calcium hydroxide (Ca(OH)2) at ordinary temperature to form compounds possessing cementitious properties. The quantification of the capacity of a pozzolan to react with calcium hydroxide and water is given by measuring its pozzolanic activity. Pozzolana are naturally occurring pozzolans of volcanic origin.
Coal combustion products (CCPs), also called coal combustion wastes (CCWs) or coal combustion residuals (CCRs), are categorized in four groups, each based on physical and chemical forms derived from coal combustion methods and emission controls:
The alkali–silica reaction (ASR), also commonly known as concrete cancer, is a deleterious internal swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive amorphous silica found in many common aggregates, given sufficient moisture.
Calcium silicate hydrates are the main products of the hydration of Portland cement and are primarily responsible for the strength of cement-based materials. They are the main binding phase in most concrete. Only well defined and rare natural crystalline minerals can be abbreviated as CSH while extremely variable and poorly ordered phases without well defined stoichiometry, as it is commonly observed in hardened cement paste (HCP), are denoted C-S-H.
The pozzolanic activity is a measure for the degree of reaction over time or the reaction rate between a pozzolan and Ca2+ or calcium hydroxide (Ca(OH)2) in the presence of water. The rate of the pozzolanic reaction is dependent on the intrinsic characteristics of the pozzolan such as the specific surface area, the chemical composition and the active phase content.
Energetically modified cements (EMCs) are a class of cements made from pozzolans, silica sand, blast furnace slag, or Portland cement. The term "energetically modified" arises by virtue of the mechanochemistry process applied to the raw material, more accurately classified as "high energy ball milling" (HEBM). At its simplest this means a milling method that invokes high kinetics by subjecting "powders to the repeated action of hitting balls" as compared to (say) the low kinetics of rotating ball mills. This causes, amongst others, a thermodynamic transformation in the material to increase its chemical reactivity. For EMCs, the HEBM process used is a unique form of specialised vibratory milling discovered in Sweden and applied only to cementitious materials, here called "EMC Activation".
Polymer soil stabilization refers to the addition of polymers to improve the physical properties of soils, most often for geotechnical engineering, construction, or agricultural projects. Even at very small concentrations within soils, various polymers have been shown to increase water retention and reduce erosion, increase soil shear strength, and support soil structure. A wide range of polymers have been used to address problems ranging from the prevention of desertification to the reinforcement of roadbeds.
Geopolymer bonded wood composite (GWC) are similar and a green alternatives to cement bonded wood composites. These products are composed of geopolymer binder, wood fibers/ wood particles. Depending on the wood and geopolymer ratio in the material, the properties of the wood-geopolymer composite material vary. The main functions of wood in the composite material are weight reduction, reduction of thermal conductivity and the fixture function whereas the main functions of geopolymer are bonding of wood particles, improvement of fire resistance, providing mechanical strength, improvement of humidity resistance and protection against fungal and insect damages.
Susan Andrea Bernal López is a Colombian materials scientist who is Professor of Structural Materials at the University of Leeds. Her research considers design, development and characterisation of novel cements. She was awarded the 2020 Institute of Materials, Minerals and Mining Rosenhain Medal and Prize.