Energetically modified cement

Energetically modified cements (EMC) are a class of cementitious materials made from pozzolans (e.g. fly ash, volcanic ash, pozzolana), silica sand, blast furnace slag, or Portland cement (or blends of these ingredients).

Classification and field-usage potential

An energetically modified cement is a cementitious material that has been produced using the EMC Activation process. The term "energetically modified cement" (abbreviated as "EMC" or "EMC cement") refers to a distinct class of cementitious materials. There are several different energetically modified cements depending on the raw materials used.

Although the term "energetically modified cement" implies that such compounds are cements, they are more accurately described as "cementitious materials". EMC cannot fully replace conventional Portland cement in concrete unless Portland cement itself is the raw material undergoing EMC Activation. Where raw materials other than Portland cement undergo EMC Activation, the resultant energetically modified cements are called "Alternative Cementitious Materials" or "Supplemental Cementitious Materials". Colloquially, energetically modified cements not made from Portland cement are sometimes described as "Green Cements", because of the significant energy and carbon dioxide savings. As such, EMC may be viewed as a contributor to the emerging field of ecodesign.

The usefulness of energetically modified cement depends on the performance characteristics required, based on the mechanical loads expected and the ambient environment. The most useful EMCs are those made from fly ash and natural pozzolans — on account of their relative abundance, the performance characteristics of the respective EMC, the relatively high Portland cement replacement ratios made available by EMC Activation using these raw materials, together with the associated energy and carbon dioxide savings.

EMC products have been extensively tested by independent labs, including Caltrans and other concrete producers.

History

The main campus of Luleå University of Technology (LTU) in Luleå, Sweden

The term "energetically modified cement" is widely accepted in the academic community. The term was first used in Sweden, where the EMC Activation process was discovered in 1992 by Vladimir Ronin at Luleå University of Technology (LTU). The process was refined there by Dr. Ronin and others, including Lennart Elfgren (now Professor Emeritus of LTU, Division of Structural Engineering, Department of Civil, Mining and Environmental Engineering).

The term "energetically modified cement" was used first in a paper by Ronin et al. in 1993.

At the 45th World Exhibition of Invention, Research and Innovation, held in Brussels, Belgium, EMC Activation was awarded a Gold Medal with mention by EUREKA, the European inter-governmental (research and development) organisation.

Given that the EMC Activation process is entirely mechanical in nature (as opposed to thermal), its potential to cause significant energy savings has been further recognised independently for a number of years. This recognition continues.

Continuing academic work and research with energetically modified cement is ongoing at LTU, including work within the auspices of the Sveriges Bygguniversitet (SBU). The nascent "self-healing" properties of EMCs have some resonance within the emerging field of biomimetics in the advanced material sciences and civil engineering disciplines. In March 2013 Elfgren presented LTU's perspective at the Future Infrastructure Forum (FIF) held at University of Cambridge.

The research work connected with EMCs has received numerous awards from the Elsa ō Sven Thysells stiftelse för konstruktionsteknisk forskning (Elsa & Sven Thysell Foundation for Construction Engineering Research) of Sweden.

Effect of EMCs on a concrete's chemistry and "self-healing"

Using pozzolans in concrete provides many chemical pathways whereby porous (reactive) Portlandite is transformed into several hard and impermeable (relatively non-reactive) compounds, rather than producing the porous and soft relatively reactive calcium carbonate produced using ordinary concrete. Many of the end products of pozzolanic chemistry exhibit a hardness greater than 7.0 on the Mohs scale. By comparison, Tungsten is 7.5 on the scale.

The greater the replacement in the concrete of Portland cement with pozzolanic cementitious materials (of which EMCs are an example), the greater the propensity for the foregoing. EMC Activation is a process which is thought to increase a pozzolan's chemical affinity for such pozzolanic reactions. This is yields a faster and greater strength development of the resulting concrete—at higher replacement ratios—than untreated pozzolans. As such, EMCs may be classified also as "highly reactive pozzolans". Highly reactive pozzolans are thought to yield further stabilisation benefits upon the pozzolanic reaction-pathways.

A simplified explanation for the benefits of EMCs (Pozzolanic) chemistry

In common with all pozzolanic cementitious materials, EMCs improve a concrete's overall chemistry when compared with Portland cement. The full extent of the effects is not entirely known. In concrete (including concretes with EMCs), Portland cement reacts with water to produce a stone-like material. The "setting" of cement, when mixed with water and aggregates to form concrete, involves a complex series of chemical reactions, the full mechanics of which are still not fully understood. That chemical process, called mineral hydration, forms two cementing compounds in the concrete: calcium silicate hydrate (C-S-H) and calcium hydroxide (Ca(OH)2). This reaction can be noted in three ways, as follows: Standard notation:  Ca3SiO5  +  H2O   →   (CaO) · (SiO2) · (H2O)(gel)  +  Ca(OH)2 Balanced:  2Ca3SiO5  +  7H2O   →   3CaO · 2SiO2 · 4H2O(gel)  +  3Ca(OH)2 Cement chemist notation (the hyphenation denotes the variable stoichiometry):  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. In comparison to calcium silicate hydrate, Portlandite is relatively porous, permeable and soft (2 to 3, on Mohs scale). It is also sectile, 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 "ordinary" concrete. In such "ordinary" concretes (i.e. made with Portland cement without pozzolanic cementitious materials), 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      (cement chemist notation: CH + C  →  CC + H) In mineral form, calcium carbonate can exhibit a wide range of hardness depending on how it is formed. For example, at its softest, calcium carbonate can form in concrete as chalk (of hardness 1.0 on Mohs scale). Like Portlandite, calcium carbonate in mineral form can also be porous, permeable and with poor resistance to acid attack (whereupon it releases carbon dioxide). By comparison, as a continuing part of the hydration process (and in common with all pozzolanic concretes), concretes comprising EMCs continue to consume the soft and porous Portlandite — instead 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   →   Ca2+  +  H2SiO42−  +   2H2O   →   CaH2SiO4 · 2H2O      (cement chemist notation: CH + SH  →  C-S-H) Further, many pozzolans contain aluminiate (Al(OH)4−) that will react with Portlandite and water to form: calcium aluminiate hydrates, such as calcium aluminium garnet (hydrogrossular: C4AH13 or C3AH6 in cement chemist notation, hardness 7.0 to 7.5 on Mohs scale);  or in combination with silica, to form strätlingite (Ca2Al2SiO7·8H2O or C2ASH8 in cement chemist notation), which geologically can form as xenoliths in basalt as metamorphosed limestone. Pozzolanic cement chemistry (along with high-aluminiate 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 overall role of pozzolans in a concrete's chemistry is not fully understood. For the sake of illustration, only one aspect has been considered, which alone is complex-enough. 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 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 (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. There are many other benefits to pozzolanic chemistry. For example, Portlandite can also react with sulphate ions to cause efflorescence, typically as either: (i) calcium sulphate (in hydrated form as gypsum or, in a sufficiently dry environment, as anhydrite); or (ii) copper sulphate (in hydrated form as a blue crystalline solid that, when exposed to air, dehydrates to form its white anhydrous counterpart). These reactions are induced by low temperatures, moist conditions and condensation. Pozzolanic chemistry reduces the amount of Portlandite available, to reduce efflorescence.

Self-healing (autogenous effects)

It is for the foregoing reasons (and others) that it is thought pozzolanic mortars and concretes have been observed to "self-heal". This effect is considered a natural autogenous property. By virtue that EMC Activation is a process which is thought to increase a pozzolan's affinity for such pozzolanic reactions, concretes made from EMCs are no different in this regard (see major pictorial insert above). The same autogenous tendency been noted and studied in the various supporting structures of Hagia Sophia built for the Byzantine emperor Justinian (now, Istanbul, Turkey). There, in common with most Roman cements, mortars comprising high amounts of pozzolana were used — in order to give what is thought to be an increased resistance to the stress-effects caused by the various earthquakes that have disrupted the region throughout the millennia (see also, below, "Historical context of the EMC California results").

Range of concretes produced

The performance of concretes made from energetically modified cements can be custom-designed. Hence, concretes can range from those exhibiting superior strength and durability that reduce the carbon footprint at up to ~70% as compared to concretes made from Portland cement, 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 (HPCs – see section below, "Durability of concretes produced and High Performance Concretes").

Portland cement replacement-capabilities (and limitation considerations)

Generally, the strength and strength-development of pozzolan concrete depend upon the "pozzolanic" characteristics of the raw material that is employed to make it. For example, fly ash in its natural state is typically more "pozzolanic" than volcanic ash — although care should be taken not to necessarily imply that all fly ashes are per se more "pozzolanic" than all volcanic ashes. In a similar vein, the nascent characteristics of the raw material undergoing EMC Activation may also act as a consideration as to the upper limit of Portland cement replacement by an energetically modified cement.

Moreover, in practical "everyday" terms, the key consideration is a concrete's strength-development within a specified time period. In a project environment, this means a concrete will need to develop a strength within a given time period that either matches or exceeds a project's specifications. For this reason, although the replacement-ratio of an EMC made from fly ash may exceed even 70%, by comparison, the current upper-limit using EMC made from natural pozzolans is 60% for practical large-scale usage.

No noxious emissions and low leachability of EMCs

The EMC activation of fly ash is entirely mechanical in nature and does not involve any heating or burning in the process. Leachability tests were performed by LTU in 2001 in Sweden on behalf of a Swedish power production company.  These tests confirmed that EMC made from fly ash "showed a low surface specific leachability" with respect to "all environmentally relevant metals."   

EMCs using Californian volcanic ash and significance

Natural Pozzolan (volcanic ash) deposits situated in Southern California in the United States.

Energetically modified cements have been used in large infrastructure projects in the United States. When EMC is made from fly ash, high Portland cement replacements (i.e., the replacement of at least 50% Portland cement) yield concretes consistent field results in high-volume applications. This is also the case for EMC made from natural pozzolans (e.g., volcanic ash).

For example, volcanic ash deposits from Southern California of the United States were independently tested. At 50% Portland cement replacement, the resulting concretes exceeded requirements:

• At 28 days, the compressive strength was 4,180 psi / 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 results demonstrated that:

• EMC Activation "has a sufficiently positive impact on the water requirement to obtain satisfactory workability and strength of concrete, at about 50% replacement of Portland cement."
• the "index of pozzolanic activity at 7 days was 80% and at 28 days was 88%, which exceeded the relevant standard's requirements (75% at both ages)."

The particle-size distribution and morphology of the EMC produced were studied by Luleå University of Technology. Those studies "evidenced the improvement in the surface smoothness of particles of natural pozzolans processed by the proprietary EMC method."

Durability of concretes produced and high-performance concretes (HPCs)

Diagram: The "Bache method" for testing concrete durability, which simulates daily temperature variations in brine. Test 1 or 2 (each 24 h) may be used, or both performed sequentially during 48 hours. The chosen cycle is repeated ad nauseam to determine the mass-loss, as an analogue for durability.

Treating Portland cement with EMC activation will yield high-performance concretes. These HPCs will be high strength, highly durable, and exhibiting greater strength-development in contrast to HPCs made from untreated Portland cement, which can have moderate to challenging durability impairments by comparison.

For example, durability tests have been performed according to the "Bache method" (see diagram). The Bache method induces the sequence of saturation by salt water of 7.5% sodium chloride (i.e., a brine, which by definition is of greater salt concentration than sea waters), followed by freezing or heating in a 24-hour cycle, in order to simulate high diurnal temperature ranges. Concrete made from ordinary Portland cement without additives has a relatively impaired resistance to salt waters. Hence, the Bache method is generally accepted as one of the most severe testing procedures for concrete.

Samples made of high-performance concrete comprising (a) EMC (comprising Portland cement and silica fume both having undergone EMC Activation) and (b) Portland cement, 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 resulting mass-loss was plotted to determine durability. The test results showed:

• EMC high-performance concrete showed a "consistent high-level durability" throughout the entire testing period. For example, "practically no scaling of the concrete has been observed", even after 80 Bache method cycles, whereas the reference Portland cement concrete had undergone "total destruction after about 16 Bache method cycles, in line with Bache's observations for high-strength concrete."

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.

All energetically modified cements also exhibit high resistances to chloride and sulphate ion attack, together with low alkali-silica reactivities (ASR). These features allow concretes made from energetically modified cements to exhibit superior durabilities as compared to concretes made from Portland cement, a feature common to all concretes comprising pozzolans.

An early project using EMC made from fly ash was the construction of a road bridge in Karungi, Sweden, with Swedish construction firm Skanska. The Karungi road bridge has successfully withstood the tests of time, despite Karungi's harsh subarctic climate and extremely divergent annual and diurnal temperature ranges.

Projects using EMC

Application of EMC on IH-10 (Interstate Highway), Texas, United States

In the United States, energetically modified cements have been approved for usage by a number of state transportation agencies, including PennDOT, TxDOT and CalTrans.

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 the paving of sections of Interstate 10, which is the main U.S. Interstate highway linking Jacksonville, Florida, with Los Angeles, California. In these projects, EMC replaced at least 50% of the Portland cement in the concrete poured. This is roughly 2.5 times more than the Portland cement replacement typically offered by untreated fly ash per se. In all projects, the 28-day strength requirements were exceeded. For example, independent test-data records the highest 28-day strength at 8015 psi (55.26 MPa) against a project requirement of 4400 psi (30.34 MPa).

Another notable project is the extension of the passenger terminals at the Port of Houston, Texas. This project fully exploits energetically modified cement's ability to yield concretes that exhibit high resistance to chloride– and sulphate–ion permeability (i.e., increased resistance to sea waters), as compared to concretes made from Portland cement.

Production

As of 2010 the 18 years cumulative volume of concrete produced contain a least partially energetically modified cement was over 4,500,000 cu yd (3,440,496 m³). This 18 year total represents approximately 0.13% of the yearly worldwide concrete production at 3,500,000,000 cubic yards.

See also

Background science to EMC Activation:

• Archard equation
• Asperity
• Contact mechanics
• Crystallinity
• Crystal structure
• Fretting
• Frictional contact mechanics
• Galling
• Hardness
• Lattice constant
• Material mechanics
• Materials science
• Microstructure
• Nanotribology
• Peter Adolf Thiessen
• Surface engineering
• Surface metrology
• Tribology
• X-ray crystallography
• X-ray fluorescence (XRF)

Academic:

• Luleå University of Technology

External links

• Official website for EMC Cement, Sweden – at EMCcement.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
• U.S. Environmental Protection Agency (EPA), Rule Information for Portland Cement Industry – at EPA.gov
• American Concrete Institute – at Concrete.org
• EDGAR – Emission Database for Global Atmospheric Research  – at Edgar.jrc.ec.europa.eu
• Vitruvious: The Ten Books on Architecture online: cross-linked Latin text and English translation
• WBCSD Cement Sustainability Initiative – at Wbcsdcement.org