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Energetically modified cement

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

Energetically modified cements (EMCs) 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).[1]. The term "energetically modified" arises by virtue of the mechanochemistry process applied to the raw material, that is more accurately classified as "high energy ball milling" (HEBM). This causes, amongst others, a thermodynamic transformation in the material to increase its chemical reactivity.[2] For EMCs, the HEBM process used is a form of specialised vibratory milling applied only to cementitious materials, here called "EMC Activation".[3]

Justification, Purpose, Usage, Carbon Dioxide Savings ("Low Carbon" Cement)

The term "energetically modified cement" (abbreviated as "EMC" or "EMC cement") refers to a class of cementitious materials that have been produced using a specialised highly-intensive milling process.[4][5] As stated, this transformatory process is initiated entirely mechanically as opposed to heating the materials directly.[5][6] [7] The mechanisms of mechanochemical transformations are often complex and different from "traditional" thermal or photochemical mechanisms.[8][9] The effects of HEBM-transformation cause a thermodynamic change that resides ultimately in a modified Gibbs Energy.[10] The process increases the binding capacity and chemical reactivity rates of the materials transformed.[3][11]

More specifically: [12] [13][14] [15]

  • The purpose of an EMC is to replace the Portland cement requirement in the mortar or concrete being used.
  • There are several types of EMCs, depending on the raw materials transformed. All contain a minority proportion of Portland cement, which may itself undergo EMC Activation.
  • Each type of EMC has its own performance characteristics, including mechanical load and strength development.
  • 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.
  • EMC products have been extensively tested by independent labs and certified for use by several US DOTs including Texas, California and Pennsylvania.
  • EMC Activation is a dry process. EMCs are produced using only a fraction of the energy used in Portland cement production.
  • EMCs require no noxious or toxic chemicals for their thermodynamic transformation—and no noxious fumes are released during production.
  • Unlike Portland Cement, an EMC's production releases no carbon dioxide whatsoever, making EMCs "low carbon cements".[6]

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.[13] [16] From 2011 to 2019, worldwide Portland cement production increased from 3.6 to 4.1 billion tonnes per year.[17][Note 1]

History

The term "energetically modified cement" was first used in Sweden, where the EMC Activation process was discovered in 1992 by Vladimir Ronin at Luleå University of Technology (LTU). The term was introduced in a paper by Ronin et al. dated 1993 and presented at a formal meeting of the academic Nordic Concrete Research group.[18] The process was refined by Ronin and others, including Lennart Elfgren (now Professor Emeritus of LTU).[19] Continuing academic work and research regarding "self-healing" properties of energetically modified cements is ongoing at LTU.[20]

At the 45th World Exhibition of Invention, Research and Innovation, held in 1996 in Brussels, 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".[21]

The research work connected with EMCs has received awards from the Elsa ō Sven Thysells stiftelse för konstruktionsteknisk forskning (Elsa & Sven Thysell Foundation for Construction Engineering Research) of Sweden.[22]

Chemistry of Pozzolanic Reactions

Pictorial insert: Demonstrating an EMC's "self-healing" propensity...[23]

PHOTO A: Cracks had an average width of 150-200 μm.
The photo above depicts a concrete test-beam made from an EMC undergoing RILEM 3-point bending at Luleå University of Technology in Sweden (Feb., 2013). This treatment induces cracks to test for "self-healing" biomimetic propensities.
PHOTO B: Former cracks had undergone a complete "self healing" without any intervention.

Concrete (total cmt: 350 kg/m³) containing 40% Portland cement and 60% EMC made from fly ash was used. Cracks of average width 150-200 μm were induced after circa 3-weeks' water-curing.Without any intervention, the high volume pozzolan concrete exhibited the gradual filling-in of the cracks with newly-synthesized CSH gel (a product of the ongoing pozzolanic reaction). These were completely filled-in after ~4.5 months.[23]

During the observation period, continuous strength-development was also recorded by virtue of the ongoing pozzolanic reaction. This, together with the observed "self healing" properties, have a positive impact on concrete durability.[23]

All photos originally Dr. V. Ronin, now per The Nordic Concrete Federation [23]

EMC Activation is a process that increases a pozzolan's chemical affinity for pozzolanic reactions.[24][25] This leads to faster and greater strength development of the resulting concrete, at higher replacement ratios, than untreated pozzolans.[26] [27] 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 as a postulate that EMC Activation caused "the formation of thin SiO2 layers around C3S [calcium sillicate] crystals", which in turn, "accelerates the pozzolanic reaction and promotes growing of more extensive nets of the hydrated products".[28]

Through the use of 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.[29] Many of the end products of pozzolanic chemistry exhibit a hardness greater than 7.0 on the Mohs scale."Self healing" capabilities may also contribute to enhanced field-application durabilities where mechanical stresses may be present (see picture insert).

The basis for 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, 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:[30]

  • Standard notation:  
  • Balanced:  

The underlying hydration reaction forms two products:

  1. 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.[31]
  2. 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).[32] It is also sectile, with flexible cleavage flakes.[33] Portlandite is soluble in water, to yield an alkaline solution which can compromise a concrete's resistance to acidic attack.[34]

Portlandite makes up about 25% of concrete made with Portland cement without pozzolanic cementitious materials.[29] In this type of concrete, carbon dioxide is slowly absorbed to convert the Portlandite into insoluble calcium carbonate (CaCO3), in a process called carbonatation:[29]

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 (of hardness 1.0 on Mohs scale). 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.[29] This results in a denser, less permeable and more durable concrete.[29] This reaction is an acid-base reaction between Portlandite and silicic acid (H4SiO4) that may be represented as follows:[35]

 [Note 2]

Further, many pozzolans contain aluminate (Al(OH)4−) that will react with Portlandite and water to form:

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:[38]

C2AH8  +  2CSH  +  AH3  +  3H    →    C2ASH8    (cement chemist notation) [39]

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).[40] This can be represented per the following equation:

3C2AH8    →    2C3AH6  +  AH3  +  9H    (cement chemist notation) [41]

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.[42] However, adding high-reactivity pozzolans into the concrete mix prevents such a conversion reaction.[43] 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.[26] [44]

Portlandite, when exposed to low temperatures, moist conditions and condensation, can react with sulphate ions to cause efflorescence; pozzolanic chemistry reduces the amount of Portlandite available, to reduce efflorescence.[45]

Self-healing properties of EMCs using Pozzolans such as volcanic materials

Volcanic ash deposits situated in Southern California, USA.

Natural pozzolanic reactions can cause mortars and concretes containing these materials to "self-heal".[46][47][48] The EMC Activation process can increase the likelihood of the occurrence of these pozzolanic reactions.[24] [25] The same tendency been noted and studied in the various supporting structures of Hagia Sophia built for the Byzantine emperor Justinian (now, Istanbul, Turkey).[49] There, in common with most Roman cements, mortars comprising high amounts of pozzolana were used — in order to give what was thought to be an increased resistance to the stress-effects caused by earthquakes.[50]

EMCs made from pozzolanic materials exhibit self-healing capabilities that can be photographed as they develop (see picture insert above). [23]

EMCs using California volcanic ash

Energetically modified cements have been used in large infrastructure projects in the United States.[12] EMCs made by replacing at least 50% of the Portland cement with have yielded consistent field results in high-volume applications.[26] This is also the case for EMC made from natural pozzolans (e.g., volcanic ash).[27]

Volcanic ash deposits from Southern California were independently tested; at 50% Portland cement replacement, the resulting concretes exceeded requirements.[51] 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.[52] 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.[51] The surface smoothness of pozzolans in the concrete was also increased.[51]

Range of characteristics

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).[14] This allows energetically modified cements to yield High Performance Concretes (HPCs - see section below on Durability).

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

Diagram: "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. In detail, the method induces the sequence of saturation by salt water of 7.5% sodium chloride (i.e., greater salt concentration than sea waters), followed by freezing or heating in a 24-hour cycle, to simulate high diurnal temperature ranges. [53]. The chosen cycle is repeated ad nausem in order to determine the mass-loss. Hence, the Bache method is generally accepted as one of the most severe testing procedures for concrete, as an analogue for durability. [53]

All pozzolanic EMCs are highly durable: indeed, any cementitious material undergoing EMC Activation will likely marshal improved durability—including Portland cement treated with EMC Activation.[14]

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.[14] 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.[14] [53]

Concrete made from ordinary Portland cement without additives has a relatively impaired resistance to salt waters.[53] In contrast, EMCs exhibit high resistances to chloride and sulphate ion attack, together with low alkali-silica reactivities (ASR).[26]

In sum, like all concretes comprising pozzolans, concretes made from pozzolanic EMCs are more durable than concretes made from Portland cement.[34] 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. 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.[14]
  • 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." [14] [53]

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.[14]

Less noxious emissions and low leachability of EMCs

The EMC activation of fly ash is a mechanical process, and does not involve heating or burning.[13] 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." [54][55]  

Projects using EMC

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

An early project using EMC made from fly ash was the construction of a road bridge in Karungi, Sweden, in 1999, with Swedish construction firm Skanska. The Karungi road bridge has withstood Karungi's harsh subarctic climate and divergent annual and diurnal temperature ranges.[13]

In the United States, energetically modified cements have been approved for usage by a number of state transportation agencies, including PennDOT, TxDOT and CalTrans.[15]

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.[12] These projects include sections of Interstate 10.[12] In these projects, EMC replaced at least 50% of the Portland cement in the concrete poured.[26] This is about 2.5 times more than the typical amount of fly ash in projects where energetic modification is not used.[56] Independent text data showed acceptable 28-day strength requirements in all projects.[26]

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– and sulphate–ion permeability (i.e., increased resistance to sea waters) was a factor.[12]

Production and Field Usage

EMCs have been in production since 1992 and have seen a wide range of uses.[12] 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.[12] To place this into context, that is more than the entire construction of the Hoover Dam, its associated power plants and appurtenant works, where a total of 4,360,000 cu·yds (3,333,459 m³) of concrete was poured—equivalent to a U.S. standard highway from San Francisco to New York City.[57]

See also

Background science to EMC Activation:

Academic:

Notes

  1. ^  Two aspects: (I)  2011 Global Portland cement production was approximately 3.6 billion 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 was estimated that Global Portland cement production would increase to 3.7 billion tonnes (a 100 million tonne increase, year-on-year), when in fact the actual figure for 2012 was 3.8 billion tonnes.  (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. ^  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.

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  42. ^ Matusinović, T; Šipušić, J; Vrbos, N (November 2003). "Porosity–strength relation in calcium aluminate cement pastes". Cement and Concrete Research. 33 (11): 1801–1806. doi:10.1016/S0008-8846(03)00201-1. ISSN 0008-8846.
  43. ^ See, for ex., Majumdar, A.J.; Singh, B. (November 1992). "Properties of some blended high-alumina cements". Cement and Concrete Research. 22 (6): 1101–1114. doi:10.1016/0008-8846(92)90040-3. ISSN 0008-8846.
  44. ^ ASTM International (2010). "ASTM C989: Standard Specification for Slag Cement for Use in Concrete and Mortars". Book of Standards Volume. 4 (2). doi:10.1520/c0989-10.
  45. ^ Nhar, H.; Watanabe, T.; Hashimoto, C.; Nagao, S. (2007). Efflorescence of Concrete Products for Interlocking Block Pavements (Ninth CANMET/ACI International Conference on Recent Advances in Concrete Technology: Editor, Malhotra, V., M., 1st ed.). Farmington Hills, Mich.: American Concrete Institute. pp. 19–34. ISBN 9780870312359. {{cite book}}: Unknown parameter |last-author-amp= ignored (|name-list-style= suggested) (help)
  46. ^ Yang, Y; Lepech, M. D.; Yang, E.; Li, V. C. (2009). "Autogenous healing of engineered cementitious composites under wet-dry cycles". Cement and Concrete Research. 39 (5): 382–390. doi:10.1016/j.cemconres.2009.01.013. ISSN 0008-8846.
  47. ^ Li, V., C.; Herbert, E. (2012). "Robust Self-Healing Concrete for Sustainable Infrastructure" (PDF). Journal of Advanced Concrete Technology. 10 (6). Japan Concrete Institute: 207–218. doi:10.3151/jact.10.207.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  48. ^ Van Tittelboom, K.; De Belie, N. (2013). "Self-Healing in Cementitious Materials—A Review". Materials. 6 (6): 2182–2217. Bibcode:2013Mate....6.2182V. doi:10.3390/ma6062182. ISSN 1996-1944. PMC 5458958. PMID 28809268.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  49. ^ Moropoulou, A.; Cakmak, A.; Labropoulos, K.C.; Van Grieken, R.; Torfs, K. (January 2004). "Accelerated microstructural evolution of a calcium-silicate-hydrate (C-S-H) phase in pozzolanic pastes using fine siliceous sources: Comparison with historic pozzolanic mortars". Cement and Concrete Research. 34 (1): 1–6. doi:10.1016/S0008-8846(03)00187-X.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  50. ^ Moropoulou, A; Cakmak, A., S., Biscontin, G., Bakolas, A., Zendri, E.; Biscontin, G.; Bakolas, A.; Zendri, E. (December 2002). "Advanced Byzantine cement based composites resisting earthquake stresses: the crushed brick/lime mortars of Justinian's Hagia Sophia". Construction and Building Materials. 16 (8): 543. doi:10.1016/S0950-0618(02)00005-3. ISSN 0950-0618.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  51. ^ a b c Stein, B (2012). A Summary of Technical Evaluations & Analytical Studies of Cempozz® Derived from Californian Natural Pozzolans (PDF). San Francisco, United States: Construction Materials Technology Research Associates, LLC.
  52. ^ ACI 318 "Building Code Requirements for Structural Concrete and Commentary"
  53. ^ a b c d e Bache, M (1983). "Densified cement/ultra fine particle-based materials". Proceedings of the Second International Conference on Superplasticizers in Concrete.
  54. ^ Private study, Luleå University of Technology (2001) "Diffusionstest för cementstabiliserad flygaska", LTU Rapport AT0134:01, 2001-09-03
  55. ^ Ronin, V; Jonasson, J-E; Hedlund, H (1999). "Ecologically effective performance Portland cement-based binders", proceedings in Sandefjord, Norway 20–24 June 1999. Norway: Norsk Betongforening. pp. 1144–1153.
  56. ^ Schneider, M.; Romer M., Tschudin M. Bolio C.; Tschudin, M.; Bolio, H. (2011). "Sustainable cement production – present and future". Cement and Concrete Research. 41 (7): 642–650. doi:10.1016/j.cemconres.2011.03.019.
  57. ^ USBR. "Hoover Dam Frequently Asked Questions and Answers". U.S. Bureau of Reclamation. Retrieved 10 August 2020.
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