Energetically modified cement

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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.[1][2] 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, are more accurately be 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 describes as "Green Cements", because of the significant energy and carbon dioxide savings[clarification needed].[3] As such, EMC may be viewed as a contributor to the emerging field of ecodesign.[4]

The usefulness of energetically modified cements 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. [Note 1]

EMC products have been extensively tested by independent labs, including Caltrans and other concrete producers[clarification needed].[5][6]

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).[7]

The term "energetically modified cement" was used first in a paper by Ronin et al. in 1993.[8]

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.[9]

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.[10][4] This recognition continues.[2]

Continuing academic work and research with energetically modified cements 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.[11]

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.[12]

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

Using pozzolans in concrete provides a number of chemical pathways whereby porous (reactive) Portlandite is transformed into a number of hard and impermeable (relatively non-reactive) compounds, rather than producing the porous and soft relatively reactive calcium carbonate produced using ordinary concrete.[13] 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.[14]

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.[13] EMC Activation is a process which is thought to increase a pozzolan's chemical affinity for such pozzolanic reactions.[15][16] This is yields a faster and greater strength development of the resulting concrete—at higher replacement ratios—than untreated pozzolans.[17][18] 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.

"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".[35][36] This effect is considered a natural autogenous property.[37] 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).[15][16] 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).[38] 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").[39]

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).[40] This allows energetically modified cements to yield High Performance Concretes (HPCs – see section below, "Durability of concretes produced and High Performance Concretes").[41]

Portland cement replacement-capabilities (and limitation considerations)

Generally, the strength and strength-development of pozzolan concretes 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.[5]

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.[3] Leachability tests were performed by LTU in 2001 in Sweden on behalf of a Swedish power production company.[42]  These tests confirmed that EMC made from fly ash "showed a low surface specific leachability" with respect to "all environmentally relevant metals." [43][44]  

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.[5] 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.[17] This is also the case for EMC made from natural pozzolans (e.g., volcanic ash).[18]

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:[45]

The results demonstrated that:

  • EMC Activation "has a sufficient 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)." [45]

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." [45]

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 a 48-hour period. The chosen cycle is repeated ad nauseam in order 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.[40]

For example, durability tests have been performed according to the "Bache method" (see diagram).[40] 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.[47] Concrete made from ordinary Portland cement without additives has a relatively impaired resistance to salt waters.[47] Hence, the Bache method is generally accepted as one of the most severe testing procedures for concrete.[40]

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.[40] The resulting mass-loss was plotted in order 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 was been observed", even after 80 Bache method cycles,[40] whereas the reference Portland cement concrete had undergone "total destruction after about 16 Bache method cycles, in line with Bache's own observations for high-strength concrete." [40][47]

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).[17] 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.[23]

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.[3][48]

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.[5][6]

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.[5] 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.[5] In these projects, EMC replaced at least 50% of the Portland cement in the concrete poured.[17] This is roughly 2.5 times more than the Portland cement replacement typically offered by untreated fly ash per se.[49] 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).[17]

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 resistances to chloride– and sulphate–ion permeability (i.e., increased resistance to sea waters), as compared to concretes made from Portland cement.[5]

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.[50]

See also

Background science to EMC Activation:

Academic:

Notes

  1. ^  Two aspects: (I)  2011 Global Portland cement production was approximately 3.6 million tonnes per United States Geological Survey (USGS) (2013) data, and is binding as a reasonably accurate assimilation, rather than an estimate per se. Note also, that by the same report, for 2012 it is estimated that Global Portland cement production increased to 3.7 billion tonnes (a 100 million tonne increase, year-on-year).  (II)  2011 Estimate of Global total CO2 production: 33.376 billion tonnes (without international transport). Source: E.U. European Commission, Joint Research Centre (JRC)/PBL Netherlands Environmental Assessment Agency. Emission Database for Global Atmospheric Research (EDGAR), release version 4.2. The 2009–2011 trends were estimated for energy-related sectors based on fossil fuel consumption for 2009–2011 from the BP Review of World Energy 2011 (BP, 2012), for cement production based on preliminary data from USGS (2012), except for China for which use was made of National Bureau of Statistics of China (NBS) (2009, 2010, 2011).   [As of May 2013. See, EDGAR, external link section].
  2. ^ a b  Further notes on pozzolanic chemistry: (A) The ratio Ca/Si (or C/S) and the number of water molecules can vary, to vary C-S-H stoichiometry. (B) Often, crystalline hydrates are formed for example when tricalcium aluminiate reacts with dissolved calcium sulphate to form crystalline hydrates (3CaO·(Al,Fe)2O3·CaSO4·nH2O, general simplified formula). This is called an AFm ("alumina, ferric oxide, monosulphate") phase. (C) The AFm phase per se is not exclusive. On the one hand while sulphates, together with other anions such as carbonates or chlorides can add to the AFm phase, they can also cause an AFt phase where ettringite is formed (6CaO·Al2O3·3SO3·32H2O or C6S3H32). (D) Generally, the AFm phase is important in the further hydration process, whereas the AFt phase can be the cause of concrete failure known as DEF. DEF can be a particular problem in non-pozzolanic concretes (see, for ex., Folliard, K., et al., Preventing ASR/DEF in New Concrete: Final Report, TXDOT & U.S. FHWA:Doc. FHWA/TX-06/0-4085-5, Rev. 06/2006). (E) It is thought that pozzolanic chemical pathways utilising Ca2+ ions cause the AFt route to be relatively suppressed.

References

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  41. ^ United States Federal Highway Administration (FHWA). What is High Performance Concrete. Washington, DC. 
  42. ^ See, also, NEN 7345:1995, "Leaching Characteristics Of Solid Earthy And Stony Building And Waste Materials – Leaching Tests – Determination Of The Leaching Of Inorganic Components From Buildings And Monolithic Waste Materials With The Diffusion Test".
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  46. ^ ACI 318 "Building Code Requirements for Structural Concrete and Commentary"
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