Energetically modified cement
   HOME

TheInfoList



OR:

Energetically modified cements (EMCs) are a class of
cement 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 mix ...
s made from pozzolans (e.g.
fly ash Fly ash, flue ash, coal ash, or pulverised fuel ash (in the UK) plurale tantum: coal combustion residuals (CCRs)is a coal combustion product that is composed of the particulates (fine particles of burned fuel) that are driven out of coal-fired ...
,
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcano, volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used t ...
,
pozzolana Pozzolana or pozzuolana ( , ), also known as pozzolanic ash ( la, pulvis puteolanus), is a natural siliceous or siliceous- aluminous material which reacts with calcium hydroxide in the presence of water at room temperature (cf. pozzolanic reactio ...
), silica sand,
blast furnace slag Ground-granulated blast-furnace slag (GGBS or GGBFS) is obtained by quenching molten iron slag (a by-product of iron and steel-making) from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground int ...
, or
Portland cement 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 c ...
(or blends of these ingredients). 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). This causes, amongst others, a
thermodynamic Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of ther ...
transformation in the material to increase its chemical reactivity. For EMCs, the HEBM process used is a unique form of specialised vibratory
milling Milling may refer to: * Milling (minting), forming narrow ridges around the edge of a coin * Milling (grinding), breaking solid materials into smaller pieces by grinding, crushing, or cutting in a mill * Milling (machining), a process of using rota ...
discovered in
Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
and applied only to cementitious materials, here called "EMC Activation". By improving the reactivity of pozzolans, their strength-development ''rate'' is increased. This allows for compliance with modern product-performance requirements ("
technical standard A technical standard is an established norm or requirement for a repeatable technical task which is applied to a common and repeated use of rules, conditions, guidelines or characteristics for products or related processes and production methods, ...
s") for
concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
s and mortars. In turn, this allows for the replacement of Portland cement in the concrete and mortar mixes. This has a number of benefits to their long-term qualities. Energetically modified cements have a wide range of uses. For example, EMCs have been used in concretes for large
infrastructure Infrastructure is the set of facilities and systems that serve a country, city, or other area, and encompasses the services and facilities necessary for its economy, households and firms to function. Infrastructure is composed of public and priv ...
projects in the United States, meeting U.S. concrete standards.


Justification

The term "energetically modified cement" incorporates a simple thermodynamic descriptor to refer to a class of cements produced using a specialised highly intensive milling process first discovered in 1993 at Luleå University of Technology (LTU) in
Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
. The transformatory process is initiated entirely mechanically as opposed to heating the materials directly. The mechanisms of mechanochemical transformations are often complex and different from "traditional" thermal or photochemical mechanisms. The effects of HEBM-transformation cause a
thermodynamic Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of ther ...
change that resides ultimately in a modified Gibbs Energy. The process increases the binding capacity and chemical reactivity rates of the materials transformed. Continuing academic work and research regarding "self-healing" properties of energetically modified cements is ongoing at LTU. For example, EMCs has received awards from the ''Elsa ō Sven Thysells stiftelse för konstruktionsteknisk forskning'' (Elsa & Sven Thysell Foundation for Construction Engineering Research) of Sweden.


Usage of the "EMC" term

The term "energetically modified cement" was first used in 1992 by Vladimir Ronin, introduced in a paper by Ronin et al. dated 1993 and presented at a formal meeting of the academic Nordic Concrete Research group. The process was refined by Ronin and others, including Lennart Elfgren (now Professor Emeritus of LTU). At the 45th World Exhibition of Invention, Research and Innovation, held in 1996 in
Brussels Brussels (french: Bruxelles or ; nl, Brussel ), officially the Brussels-Capital Region (All text and all but one graphic show the English name as Brussels-Capital Region.) (french: link=no, Région de Bruxelles-Capitale; nl, link=no, Bruss ...
, Belgium, EMC Activation was awarded a gold medal with mention by EUREKA, the European inter-governmental (research and development) organisation, for ''"modification énergique de ciments"''. The term "energetically modified" has been used elsewhere—for example as recently as 2017—although such usage does not denote the method used was EMC Activation as defined here.


Overview

The claims made include: * An EMC is a fine powder (typical of all cements) whose colour depends on the material processed. * EMCs are produced using only a "fraction" of the energy used in Portland cement production (claimed ~120 KWh/tonne, <10% of Portland cement). * No is released by the process. It is "zero emissions". * The purpose of an EMC is to replace the
Portland cement 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 c ...
requirement in the mortar or
concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
being used. More than 70% replacement is claimed. * EMC Activation is a dry process. * No noxious fumes are released. * EMC Activation is a low temperature process, even though temperatures can be "momentarily extreme" at "sub-micron" scales. * EMCs require no chemicals for their thermodynamic transformation. * There are several types of EMCs, depending on the raw materials transformed. * Depending on user-requirements, delivered dry products may comprise also a minority proportion of "high clinker" Portland cement. * Each type of EMC has its own performance characteristics, including mechanical load and strength development. Concretes cast from EMCs may yield significant "self-healing" capabilities. * The most frequently used EMCs are made from fly ash and natural pozzolans. These are relatively abundant materials, and the performance characteristics can exceed those of Portland cement. * Silica sand and granite can also be treated by the process to replace Portland cement. * EMC products have been extensively tested by independent labs and certified for use by several US DOTs including in
Federal Highway Administration The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two programs, the Federal-aid Highway Program a ...
projects. * EMCs comply with respective technical standards, such as ASTM C618-19 (U.S.); EN-197, EN-206 and EN 450-1:2012 ( CEN territories, including EEA); BS 8615‑1:2019 (U.K.). * Compared to using Portland cement, the resulting concrete-mix using EMC does not require a higher "total cementitious content" to meet strength-development requirements. * In testing by BASF, the 28-day strength-development for 55% replacement of Portland cement by a natural pozzolanic EMC was 14,000 psi / 96.5 MPa (i.e. > C95). This comprised a "total cementitious content" of 335 kg/m^3 (564 lbs/CY) concrete mix.


EMCs as "Low Carbon" cements

Unlike Portland Cement, an EMC's production releases no
carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
whatsoever. This makes EMCs " low carbon cements". The first cited claims for EMC's CO2-reduction capabilities were made in 1999, when worldwide Portland cement production stood at 1.6 billion tonnes per year. From 2011 to 2019, worldwide Portland cement production increased from 3.6 to 4.1 billion tonnes per year. Energetically modified cement's potential for contributing to a worldwide reduction of CO2 has been ''externally'' recognised since 2002 and has been ongoing. Recent recognition has included the 2019 Energy Transitions Commission ( Lord Adair Turner and
Lord Stern Nicholas Herbert Stern, Baron Stern of Brentford, (born 22 April 1946 in Hammersmith) is a British economist, banker, and academic. He is the IG Patel Professor of Economics and Government and Chair of the Grantham Research Institute on Cl ...
) report ''Mission Possible sectoral focus: cement'' (2019). Further recognition of the "Zero-Carbon" potential was set out by McKinsey & Co in its 2020 report ''Laying the foundation for zero-carbon cement''.


Production and field-usage


No noxious emissions or toxic chemicals during production

EMC Activation is purely a mechanical process. As such, it does not involve heating or burning or indeed any chemical treatments. This means no fumes at all are produced during an EMC's manufacture.


History of Usage

EMCs have been produced for project usage since 1992 for a wide range of uses. By 2010, the volume of concrete poured containing EMCs was about 4,500,000 cu yd (3,440,496 m3), largely on US DOT projects. To place this into context, that is more than the entire construction of the
Hoover Dam Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on Se ...
, its associated power plants and appurtenant works, where a total of 4,360,000 cu·yds (3,333,459
The cubic metre (in Commonwealth English and international spelling as used by the International Bureau of Weights and Measures) or cubic meter (in American English) is the unit of volume in the International System of Units (SI). Its symbol is m ...
) of concrete was poured—equivalent to a U.S. standard highway from San Francisco to New York City.


Early Usage in Sweden

An early project using EMC made from fly ash was the construction of a road bridge in
Karungi Karungi () is a locality situated in Haparanda Municipality, Norrbotten County, Sweden with 232 inhabitants in 2010. The language most spoken in the village is Meänkieli (literally 'our language') is a group of distinct Finnish dialects or a ...
, Sweden, in 1999, with Swedish construction firm
Skanska Skanska AB () is a multinational construction and development company based in Sweden. Skanska is the fifth-largest construction company in the world according to ''Construction Global'' magazine. Notable Skanska projects include renovation of t ...
. The Karungi road bridge has withstood Karungi's harsh
subarctic climate The subarctic climate (also called subpolar climate, or boreal climate) is a climate with long, cold (often very cold) winters, and short, warm to cool summers. It is found on large landmasses, often away from the moderating effects of an ocean, ge ...
and divergent annual and diurnal temperature ranges.


Usage in the United States

In the United States, energetically modified cements have been approved for usage by a number of state transportation agencies, including PennDOT,
TxDOT The Texas Department of Transportation (TxDOT ) is a government agency in the United States, American state of Texas. Though the public face of the agency is generally associated with the construction and maintenance of the state's immense state ...
and
CalTrans The California Department of Transportation (Caltrans) is an Executive (government), executive department of the U.S. state of California. The department is part of the Government of California#State agencies, cabinet-level California State Tran ...
. In the United States, highway bridges and hundreds of miles of highway paving have been constructed using concretes made from EMC derived from fly ash. These projects include sections of
Interstate 10 Interstate 10 (I-10) is the southernmost cross-country highway in the American Interstate Highway System. I-10 is the fourth-longest Interstate in the United States at , following I-90, I-80, and I-40. This freeway is part of the originally pl ...
. In these projects, EMC replaced at least 50% of the Portland cement in the concrete poured. This is about 2.5 times more than the typical amount of fly ash in projects where energetic modification is not used. Independent test data showed 28-day strength-development requirements were exceeded in all projects. Another project was the extension of the passenger terminals at the Port of Houston, Texas, where energetically modified cement's ability to yield concretes that exhibit high resistances to
chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
– and sulphate–ion permeability (i.e., increased resistance to sea waters) was a factor.


Properties of concretes and mortars made from EMCs


Custom design for end-usage

The performance of mortars and concretes made from EMCs can be custom-designed. For example, EMC concretes can range from general application (for strength and durability) through to the production of rapid and ultra-rapid hardening high-strength concretes (for example, over 70 MPa / 10,150 psi in 24 hours and over 200 MPa / 29,000 psi in 28 days). This allows energetically modified cements to yield High Performance Concretes.


Durability of EMC concretes and mortars

Any cementitious material undergoing EMC Activation will likely marshal improved durability—including Portland cement treated with EMC Activation. As regards pozzolanic EMCs, concretes made from pozzolanic EMCs are more durable than concretes made from Portland cement. Treating Portland cement with EMC activation will yield high-performance concretes (HPCs). These HPCs will be high strength, highly durable, and exhibiting greater strength-development in contrast to HPCs made from untreated Portland cement. Treating Portland cement with the EMC Activation process may increase the strength development by nearly 50% and also significantly improve the durability, as measured according to generally accepted methods.


Enhanced resistance to salt-water attack

Concrete made from ordinary Portland cement without additives has a relatively impaired resistance to salt waters. In contrast, EMCs exhibit high resistances to
chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
and sulphate ion attack, together with low alkali-silica reactivities (ASR). For example, durability tests have been performed according to the "Bache method" (see diagram). Samples made of HPC having respective compressive strengths of 180.3 and 128.4 MPa (26,150 and 18,622 psi) after 28 days of curing, were then tested using the Bache method. The samples were made of (a) EMC (comprising Portland cement and silica fume both having undergone EMC Activation) and (b) Portland cement. The resulting mass-loss was plotted in order to determine durability. As a comparison, the test results showed: * Whereas, the reference Portland cement concrete had "total destruction after about 16 Bache method cycles, in line with Bache's own observations for high-strength concrete"; * EMC high performance concrete showed a "consistent high-level durability" throughout the entire testing-period of 80 Bache cycles, with for example, "practically no scaling of the concrete has been observed". In other words, treating Portland cement with the EMC Activation process, may increase the strength-development by nearly 50% and also significantly improve the durability, as measured according to generally accepted methods.


Low leachability of EMC Concretes

Leachability tests were performed by LTU in 2001 in Sweden, on behalf of a Swedish power production company, on concrete made from an EMC made from fly ash.  These tests confirmed that the cast concrete "showed a low surface specific leachability" with respect to "all environmentally relevant metals."  


EMCs using Pozzolans such as volcanic materials


Self-healing properties of Pozzolanic EMCs

Natural pozzolanic reactions can cause mortars and concretes containing these materials to "self-heal". The EMC Activation process can increase the likelihood of the occurrence of these pozzolanic reactions. The same tendency been noted and studied in the various supporting structures of
Hagia Sophia Hagia Sophia ( 'Holy Wisdom'; ; ; ), officially the Hagia Sophia Grand Mosque ( tr, Ayasofya-i Kebir Cami-i Şerifi), is a mosque and major cultural and historical site in Istanbul, Turkey. The cathedral was originally built as a Greek Ortho ...
built for the
Byzantine The Byzantine Empire, also referred to as the Eastern Roman Empire or Byzantium, was the continuation of the Roman Empire primarily in its eastern provinces during Late Antiquity and the Middle Ages, when its capital city was Constantinopl ...
emperor
Justinian Justinian I (; la, Iustinianus, ; grc-gre, Ἰουστινιανός ; 48214 November 565), also known as Justinian the Great, was the Byzantine emperor from 527 to 565. His reign is marked by the ambitious but only partly realized ''renovat ...
(now,
Istanbul Istanbul ( , ; tr, İstanbul ), formerly known as Constantinople ( grc-gre, Κωνσταντινούπολις; la, Constantinopolis), is the List of largest cities and towns in Turkey, largest city in Turkey, serving as the country's economic, ...
,
Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a list of transcontinental countries, transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with ...
). There, in common with most Roman cements, mortars comprising high amounts of
pozzolana Pozzolana or pozzuolana ( , ), also known as pozzolanic ash ( la, pulvis puteolanus), is a natural siliceous or siliceous- aluminous material which reacts with calcium hydroxide in the presence of water at room temperature (cf. pozzolanic reactio ...
were used — in order to give what was thought to be an increased resistance to the stress-effects caused by
earthquakes An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
. EMCs made from pozzolanic materials exhibit " biomimetic" self-healing capabilities that can be photographed as they develop ''(see picture insert).''


EMCs using California Pozzolans

Concretes made by replacing at least 50% of the Portland cement with EMCs have yielded consistent field results in high-volume applications. This is also the case for EMC made from natural pozzolans (e.g., volcanic ash). Volcanic ash deposits from Southern California were independently tested; at 50% Portland cement replacement, the resulting concretes exceeded the requirements of the relevant US standard. At 28 days, the
compressive strength In mechanics, compressive strength or compression strength is the capacity of a material or structure to withstand loads tending to reduce size (as opposed to tensile strength which withstands loads tending to elongate). In other words, compre ...
was 4,180
psi Psi, PSI or Ψ may refer to: Alphabetic letters * Psi (Greek) (Ψ, ψ), the 23rd letter of the Greek alphabet * Psi (Cyrillic) (Ѱ, ѱ), letter of the early Cyrillic alphabet, adopted from Greek Arts and entertainment * "Psi" as an abbreviation ...
/ 28.8 MPa ( N/mm²). The 56-day strength exceeded the requirements for 4,500 psi (31.1 MPa) concrete, even taking into account the safety margin as recommended by the American Concrete Institute. The concrete made in this way was workable and sufficiently strong, exceeding the 75% standard of pozzolanic activity at both 7 days and 28 days. The surface smoothness of pozzolans in the concrete was also increased.


Effect on Pozzolanic reactions

EMC Activation is a process that increases a pozzolan's chemical affinity for pozzolanic reactions.Patent abstract for granted patent "Process for Producing Blended Cements with Reduced Carbon Dioxide Emissions" (Pub. No.:WO/2004/041746; International Application No.: PCT/SE2003001009; Pub. Date: 21.05.2004; International Filing Date: 16.06.2003) This leads to faster and greater strength development of the resulting concrete, at higher replacement ratios, than untreated pozzolans. These transformed (now highly reactive pozzolans) demonstrate further benefits using known pozzolanic reaction-pathways that typically see as their end-goal a range of hydrated products. An NMR study on EMCs concluded that EMC Activation caused "the formation of thin SiO2 layers around C3S crystals", which in turn, "accelerates the pozzolanic reaction and promotes growing of more extensive nets of the hydrated products". In simple terms, by using pozzolans in concrete, porous (reactive) Portlandite can be transformed into hard and impermeable (relatively non-reactive) compounds, rather than the porous and soft relatively reactive calcium carbonate produced using ordinary cement. Many of the end products of pozzolanic chemistry exhibit a hardness greater than 7.0 on the
Mohs scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...
."Self healing" capabilities may also contribute to enhanced field-application durabilities where mechanical stresses may be present. In greater detail, the benefits of pozzolanic concrete, starts with an understanding that in concrete (including concretes with EMCs), Portland cement combines with water to produce a stone-like material through a complex series of chemical reactions, whose mechanisms are still not fully understood. That chemical process, called
mineral hydration In chemistry, mineral hydration is an inorganic chemical reaction which adds water to the crystal structure of a mineral, usually creating a new mineral, usually called a ''hydrate''. In geological terms, the process of mineral hydration is know ...
, forms two cementing compounds in the concrete: calcium silicate hydrate (C-S-H) and
calcium hydroxide Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed or slaked with water. It has m ...
(Ca(OH)2). This reaction can be noted in three ways, as follows: :* Standard notation:  Ca3SiO5 + H2O -> (CaO) * (SiO2) * (H2O) + Ca(OH)2 :* Balanced:  2Ca3SiO5 + 7H2O -> 3CaO * 2SiO2 * 4H2O + 3Ca(OH)2 :* Cement chemist notation (the hyphenation denotes the variable
stoichiometry Stoichiometry refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equal ...
):  C3S  +  H   →   C-S-H  +  CH The underlying hydration reaction forms two products: # Calcium silicate hydrate (C-S-H), which gives concrete its strength and dimensional stability. The crystal structure of C-S-H in cement paste has not been fully resolved yet and there is still ongoing debate over its nanostructure. # Calcium hydroxide (Ca(OH)2), which in concrete chemistry is known also as
Portlandite Portlandite is a hydroxide-bearing mineral typically included in the oxide mineral class. It is the naturally occurring form of calcium hydroxide (Ca(OH)2) and the calcium analogue of brucite (Mg(OH)2). Occurrence Portlandite occurs in a variety ...
. In comparison to calcium silicate hydrate, Portlandite is relatively porous, permeable and soft (2 to 3, on
Mohs scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...
). It is also
sectile Sectility is the ability of a mineral to be cut into thin pieces with a knife. Minerals that are not sectile will be broken into rougher pieces when cut. Metals and paper are sectile. Sectility can be used to distinguish minerals of similar appea ...
, with flexible cleavage flakes. Portlandite is soluble in water, to yield an alkaline solution which can compromise a concrete's resistance to acidic attack. Portlandite makes up about 25% of concrete made with Portland cement without pozzolanic cementitious materials. In this type of concrete, carbon dioxide is slowly absorbed to convert the Portlandite into insoluble calcium carbonate (CaCO3), in a process called carbonatation: ::Ca(OH)2 + CO2 -> CaCO3 + H2O In mineral form, calcium carbonate can exhibit a wide range of hardness depending on how it is formed. At its softest, calcium carbonate can form in concrete as
chalk Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Chalk ...
(of hardness 1.0 on
Mohs scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...
). Like Portlandite, calcium carbonate in mineral form can also be porous, permeable and with a poor resistance to acid attack, which causes it to release carbon dioxide. Pozzolanic concretes, including EMCs, however, continue to consume the soft and porous Portlandite as the hydration process continues, turning it into additional hardened concrete as calcium silicate hydrate (C-S-H) rather than calcium carbonate. This results in a denser, less permeable and more durable concrete. This reaction is an acid-base reaction between Portlandite and silicic acid (H4SiO4) that may be represented as follows: ::Ca(OH)2 + H4SiO4 -> Ca^2+ + H2SiO4^2- + 2H2O -> CaH2SiO4 * 2H2O  Further, many pozzolans contain
aluminate In chemistry, an aluminate is a compound containing an oxyanion of aluminium, such as sodium aluminate. In the naming of inorganic compounds, it is a suffix that indicates a polyatomic ion, polyatomic anion with a central aluminum atom. Aluminate ...
(Al(OH)4) that will react with Portlandite and water to form: :*calcium aluminate hydrates, such as calcium aluminium garnet (
hydrogrossular Hydrogrossular is a calcium aluminium garnet series (formula: Ca3Al2(SiO4)3−''x''(OH)4''x'', with hydroxide (OH) partially replacing silica (SiO4)). The endmembers of the hydrogarnet family (grossular, hibschite, and katoite) depend on the deg ...
: C4AH13 or C3AH6 in cement chemist notation, hardness 7.0 to 7.5 on
Mohs scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...
);  or :*in combination with silica, to form strätlingite (Ca2Al2SiO7·8H2O or C2ASH8 in cement chemist notation), which geologically can form as
xenolith A xenolith ("foreign rock") is a rock fragment (country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusively used to describe inclusions in igne ...
s in
basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
as metamorphosed
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
. Pozzolanic cement chemistry (along with high-aluminate cement chemistry) is complex and per se is not constrained by the foregoing pathways. For example, strätlingite can be formed in a number of ways, including per the following equation which can add to a concrete's strength: ::C2AH8  +  2CSH  +  AH3  +  3H    →    C2ASH8    (cement chemist notation) The role of pozzolans in a concrete's chemistry is not fully understood. For example, strätlingite is metastable, which in a high temperature and water-content environment (that can be generated during the early curing stages of concrete) may of itself yield stable calcium aluminium garnet (see first bullet point above). This can be represented per the following equation: ::3C2AH8    →    2C3AH6  +  AH3  +  9H    (cement chemist notation) Per the first bullet point, although the inclusion of calcium aluminium garnet per se is not problematic, if it is instead produced by the foregoing pathway, then micro-cracking and strength-loss can occur in the concrete. However, adding high-reactivity pozzolans into the concrete mix prevents such a conversion reaction. In sum, whereas pozzolans provide a number of chemical pathways to form hardened materials, "high-reactivity" pozzolans such as
blast furnace slag Ground-granulated blast-furnace slag (GGBS or GGBFS) is obtained by quenching molten iron slag (a by-product of iron and steel-making) from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground int ...
(GGBFS) can also stabilise certain pathways. In this context, EMCs made from fly ash have been demonstrated to produce concretes that meet the same characteristics as concretes comprising "120 Slag" (i.e., GGBFS) according to U.S. standard ASTM C989. Portlandite, when exposed to low temperatures, moist conditions and condensation, can react with sulphate ions to cause
efflorescence In chemistry, efflorescence (which means "to flower out" in French) is the migration of a salt to the surface of a porous material, where it forms a coating. The essential process involves the dissolving of an internally held salt in water, or ...
. In contrast, pozzolanic chemistry reduces the amount of Portlandite available, to reduce the proliferation of efflorescence.


EMC Activation

EMC Activation's purpose is to cause a fundamental destruction to the
crystalline structure In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns th ...
of the material processed, to render it
amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek ''a'' ("wi ...
. Although this change increases the processed material's chemical reactivity, no chemical reaction is caused ''during'' the EMC Activation process. Mechanochemistry itself can be defined as a branch of chemistry which is concerned with the "chemical and physico-chemical transformation of substances in all states of aggregation produced by the effect of mechanical energy."
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
carries no standard definition of the term ''mechanochemistry'', instead defining a "mechanochemical ''reaction''" as a chemical reaction "induced by the direct absorption of mechanical energy", while noting, "shearing, stretching, and grinding are typical methods for the mechano-chemical generation of reactive sites". More narrowly, "mechanical activation" was a term first defined in 1942 as a process "involving an increase in reaction ability of a substance ''which remains chemically unchanged''." Even more narrowly, EMC Activation is a specialised form of mechanical activation limited to the application of high energy ball milling (HEBM) to cementitious materials. More narrowly than that, EMC Activation uses vibratory milling, and even then, only by using its own ''grinding media''.


Thermodynamic Justification

More particularly, HEBM can be described as increasing the chemical reactivity of a material by increasing its chemical ''potential'' energy. In EMC Activation, transferred mechanical energy is stored in the material as lattice defects caused by destroying the material's crystalline structure. Hence, the process transforms solid substances into thermodynamically and structurally more ''unstable'' states, allowing an explanation for that increased reactivity as an increase in Gibbs energy: :: \Delta G = G_T^* - G_T  ''where,'' for temperature T, the terms G_T^* and G_T are the respective Gibbs values in the processed and unprocessed material. At its simplest, HEBM causes the destruction of crystalline bonds, to increase a material's reactivity. From the thermodynamic perspective, any subsequent chemical reaction can decrease the excess energy level in the activated-material (i.e. as a reactant) to produce new components comprising both a lower chemical energy and a more stable physical structure. Conversely, to render the pre-processed material into a more reactive physical state, the disordering process during the HEBM process can be justified as being equivalent to a ''decrystallisation'' (and hence an entropy increase) that in part yields a volume increase (decrease of bulk density). A reverse process, sometimes called "relaxation", can be almost immediate (10−7 to 10−3 seconds) or take much longer (e.g. 106 seconds). Ultimately, any overall ''retained'' thermodynamic effect can be justified on the basis that any such ''reverse'' process is incapable of reaching an ideal thermodynamic end-state of its own accord. As a result, in the course of the mechanical activation of minerals, reverse "relaxation" processes cannot completely decrease the Gibbs free energy that has been created. Hence, energy remains in the material, which is stored in the crystal-lattice ''defects'' created.


Net Thermodynamic Effect of HEBM

Overall, HEBM renders a net thermodynamic effect: * The structural disordering implies an increase of both entropy and enthalpy and thus stimulates the crystal properties according to the thermodynamic modifications. Only a small fraction (approximately 10%) of the excess enthalpy of the activated product may be accounted-for as surface-area enlargement. * Instead, the main part of the excess enthalpy and modified properties can mostly be assigned to the development of thermodynamically unstable states in the material's lattice (and not as a reduction of particle size). * Since the activated system is unstable, the process of activation is reversible—resulting in deactivation, re-crystallization, entropy loss and energy output of system. That reverse ("relaxation") process continues to a thermodynamic equilibrium, but ultimately can never reach an ideal structure (i.e. one free of defects). * A more complete description of such an "activation" process factors-in enthalpy also, by which according to the Gibbs-Helmholtz equation, the Gibbs free energy between activated and non-activated solid state can be represented: ::\Delta G = \Delta H - T \Delta S   ''where'', \Delta H is the change in enthalpy and \Delta S the change in entropy.


Resulting Crystalline Disorder

Where the crystal disordering is low, \Delta S is very small (if not negligible). In contrast, in highly deformed and disordered crystals, the values of \Delta S can have a significant impact on the rendered Gibbs free energy. Leaving aside the heat generated during the process on account of friction etc. occasioned during the activation process, the excess Gibbs free energy retained in the activated material can be justified as being due to two changes, namely an increase in (\Iota) specific surface area; and (\Iota\Iota) defect structure. In successful HEBM processes such as EMC Activation: ::* as to (\Iota), only about 10% of the excess energy of such an activated product may be accounted-for as a change in surface area. ::* as to (\Iota\Iota), almost all the imparted energy is contained in the actual structural defects in the material processed.


An approximation for EMC Activation

The relatively low value of (\Iota) as against the high value of (\Iota\Iota) serves to further distinguish HEBM from general grinding or "milling" (where instead the only aim there is to increase the surface area of the materials processed), thereby accounting for an explanation for the change in entropy S of the rendered material in the form of elastic energy (stored in lattice defects that can take years to "relax" ) that is the "source of excess Gibbs energy and enthalpy". As for enthalpy H, four descriptors can be derived to provide an overview as to the total change during such an activation process:
:: \Delta H_T = \Delta H_d + \Delta H_S + \Delta H_A + \Delta H_p  ''where'': ::* \Delta H_d  is a measure of the ''dislocation density''; ::* \Delta H_p  is a measure of new phases (polymorphic transformation); ::* \Delta H_A  is a measure of the formation of amorphous material; ::* \Delta H_S  is a measure of specific surface area. Because the majority of the work exacted during the EMC Activation process goes to aspect (\Iota\Iota) above, \Delta H_S is trivial. Hence the major functions for the change in enthalpy approximate to:
::\Delta H _ \approxeq \Delta H_d + \Delta H_A + \Delta H_p In EMC Activation, the foregoing terms \Delta H_d and \Delta H_A are seen as being particularly prominent because of the nature of the changes in the physical structure observed. Hence, the change in enthalpy H occasioned during EMC Activation can be approximated to: ::\Delta H _ \thickapprox \Delta H_d + \Delta H_A      ''i.e,''   \Delta H_ \thickapprox (\rho M_V) \frac\ln \left ( \frac \right ) + C_AE_A ::''where'': ::*M_V, b, \mu_s and \rho correspond respectively to the molar volume of the material, Burgers vector, shear modulus and
dislocation density In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to sl ...
; ::* C_A and E_A are respectively the concentration of the amorphous phase and molar amorphisation energy.


Low temperature reactivity

From the above thermodynamic construct, EMC Activation results in a highly ''amorphous'' phase that can be justified as a large \Delta H_A and also a large \Delta H_d increase. The benefits of the EMC Activation being large in H means that an EMC's reactivity is less temperature dependent. In terms of any reaction's thermodynamic impetus, a reactant's overall H is not T dependent, meaning that a material having undergone HEBM with a corresponding elevation of H can react at a lower temperature (as the "activated" reactant is rendered less reliant on the temperature-dependent function T \Delta S for its onward progression). Further, an EMC's reaction can exhibit physical mechanisms at extremely small scales "with the formation of thin SiO2 layers" to aid a reaction's pathway—with the suggestion that EMC Activation increases the ratio of favourable reaction sites. Studies elsewhere have determined that HEBM can significantly lower the temperature required for a subsequent reaction to proceed (up to a three-fold reduction), whereby a major component of the overall reaction-dynamics is initiated at a "nanocrystalline or amorphous phase" to exhibit "unusually low or even negative values of the apparent activation energy" required to cause a chemical reaction to occur. Overall, EMCs are likely less temperature dependent for a chemical pathway's onward progression (see section above on Pozzolanic reactions), which may explain why EMCs provide ''self-healing'' benefits even at low arctic temperatures.


Physical Justification (Amorphisation)

Large changes in \Delta G, more particularly in the resultant values of \Delta H_A and \Delta H_d provide an insight into EMC Activation's efficacy. The amorphisation of crystalline material at high-pressure conditions "is a rather unusual phenomenon" for the simple reason that "most materials actually experience the reverse transformation from amorphous to crystalline at high-pressure conditions". Amorphisation represents a highly distorted "periodicity" of a material's lattice element, comprising a relatively high Gibbs free energy. Indeed, amorphisation may be compared to a ''quasi-molten'' state. All told, in common with other HEBM processes, EMC Activation causes crystalline destruction because of extremely violent and disruptive factors that are occasioned at the nanoscale of the material being processed. Although over in short duration and highly focal, the processes are repeated at a high frequency: hence those factors are thought to mimic pressures and temperatures found deep inside the Earth to cause the required phase change. For example, Peter Thiessen developed the ''magma-plasma model'' that assumes localised temperatures—higher than 103 Kelvin—can be generated at the various impact points to induce a momentary excited
plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...
state in the material, characterized by the ejection of
electrons The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...
and
photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...
s together with the formation of excited fragments (see diagram above). Experimental data gathered from localised crack-generation, itself an important component of EMC Activation, has confirmed temperatures in this region as long ago as 1975.


Vibratory Ball Mills (VBMs)

For EMC activation, the HEBM method used is a vibratory ball mill (VBM). A VBM uses a vertical eccentric drive-mechanism to vibrate an enclosed chamber up to many hundreds of cycles per minute. The chamber is filled with the material being processed together with specialised objects called ''grinding media''. In their most simple format, such media can be simple balls made from specialised ceramics. In practical terms, EMC Activation deploys a range of grinding media of different sizes, shapes and composites to achieve the required mechanochemical transformation. It has been suggested that a VBM will grind at 20 to 30 times the rate of a rotary ball mill, reflecting that a VBM's mechanism is especially rapacious.


VBM Kinetics

In simple terms, the compressive force F acting between two ''identical'' colliding balls in a VBM can be expressed:

::F =\left \left ( \frac \right ) ^ \left ( \frac \right )^ \right ^     ''where,'' k = \frac ::where, m is the mass of both balls, r the radius, v the absolute velocity of impact and E the
Young's modulus Young's modulus E, the Young modulus, or the modulus of elasticity in tension or compression (i.e., negative tension), is a mechanical property that measures the tensile or compressive stiffness of a solid material when the force is applied leng ...
of the balls' material.
As can be seen, an increase in velocity of impact increases F. The size and mass of the grinding media also contribute. F's denominator term k incorporates E meaning that the nature of the material used for the grinding media is an important factor (k is ultimately squared in F, so its negative value is of no consequence). More fundamentally, due to the rapid vibration a high acceleration is imparted to the grinding media, whereupon the continuous, short, sharp impacts on the load result in rapid particle-size reduction. In addition, high pressures and
shear stress Shear stress, often denoted by (Greek: tau), is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. ''Normal stress'', on the ot ...
es facilitate the required phase transition to an amorphous state both at the point of impact and also during the transmission of shock-waves that can yield even greater pressures than the impact itself. For example, the contact time of a two-ball collision can be as short as 20μs, generating a pressure of 3.3
GPa Grading in education is the process of applying standardized measurements for varying levels of achievements in a course. Grades can be assigned as letters (usually A through F), as a range (for example, 1 to 6), as a percentage, or as a numbe ...
upwards and with an associated ambient temperature increase of 20
Kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phys ...
. Because of the short duration of the impact, the rate of change in
momentum In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass an ...
is significant—generating a shock wave of duration only 1-100μs but with an associated pressure of 10 GPa upwards and a highly localised and focal temperature (i.e., at the nanoscale) up to several thousands of degrees Kelvin. To place this into context, a pressure of 10GPa is equivalent to about 1,000 kilometers of sea water. As a further example, the impact of two identical steel balls of 2.5 cm diameter of velocity 1 m/s will generate a collision
energy density In physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It is sometimes confused with energy per unit mass which is properly called specific energy or . Often only the ''useful'' or extract ...
of over 109
joule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
s/m2, with alumina balls of the same 2.5 cm diameter and velocity of 1 m/s generating an even greater energy density. The collisions occur in a very short timescale and hence the "rate of energy release over the relatively small contact area can be very high".


See also

Background science to EMC Activation: * * * * * * * * * * * * Academic: *


Notes


References


External links

*, Sweden at lowcarboncement.com
Luleå University of Technology
Sweden at LTU.se
Future Infrastructure Forum
University of Cambridge, United Kingdom at Fif.construction.cam.ac.uk
U.S. Geological Survey (USGS) Cement Statistics and Information
at Minerals.usgs.gov

at EPA.gov * ttps://web.archive.org/web/20130510160418/http://www.concrete.org/general/home.asp American Concrete Instituteat Concrete.org
EDGAR – Emission Database for Global Atmospheric Research
at Edgar.jrc.ec.europa.eu

online: cross-linked Latin text and English translation
WBCSD Cement Sustainability Initiative
at Wbcsdcement.org {{DEFAULTSORT:EMC Cement Cement Swedish inventions Science and technology in Sweden Environmental design Building materials