Parallels and Nonconformities in Worldwide Fly Ash Classification: The Need for a Robust, Universal Classification System for Fly Ash

Transcription

1 201 World of Coal Ash (WOCA) Conference in Nasvhille, TN - May -7, Parallels and Nonconformities in Worldwide Fly Ash Classification: The Need for a Robust, Universal Classification System for Fly Ash Ross P Kelly 1 1 CTLGroup, 400 Old Orchard Road, Skokie, IL CONFERENCE: 201 World of Coal Ash ( KEYWORDS: Fly Ash, Classification ABSTRACT Management of large volumes of fly ash is a concern for every developed nation in the world, a concern aggravated by the wide range of chemical and physical properties that fly ash exhibits. To facilitate the efficient use and disposal of fly ash, regional authorities across the globe have developed a variety of classification schema. Most fly ash end-users are only concerned with the local specifications selection of fly ash is generally predicated upon the expense of transporting the ash that meets the minimum criteria for the project, a philosophy that is not likely to change in the immediate future. However, the globalization of construction projects, and research into alternate uses of fly ash that depend upon tight control of its chemical and physical properties call for a means to readily translate the specification of fly ash by one nation s standard codes into another s. We propose a simple universal classification scheme for fly ash that expedites that translation. We correlated the fly ash classification standards of the top eight producers of coal combustion products (China, the United States, India, Europe, Russia, Australia, Japan and Canada). This translation tool can, in some instances, allow the end user to avoid costly laboratory testing and re-specification to another country s standards. Cross-border communication and research collaboration is hindered by the different regional vocabularies used to describe varieties of fly ash, and this effort is a small step towards removing some of those barriers. INTRODUCTION Coal-burning power production accounts for approximately 40% of the global total, and that number is not likely to change rapidly. [1] Coal-combustion byproducts (CCBs) are, with good reason, an ongoing and global issue, and effective disposal is a pressing concern. Fly ash, in particular, is the subject of considerable research, and there are an increasing number of options for beneficial re-use, including use in concrete, flowable fill, soil modification, and waste stabilization. [2] Each ton of fly ash that serves such a purpose is one that does not go into a landfill, a relatively expensive, heavily regulated option. Given that suboptimal alternative, barriers to fly ash beneficial use are best minimized or eliminated. Research and product development taking place across the globe is applied to the issue of fly ash re-use; the incorporation of fly ash into concrete is a primary focus of that work. Developing countries, in particular, tend to be dependent on coal power, and also engage in significant infrastructure development that necessitates the widespread use of concrete. China is a perfect case study in that phenomena; China accounts for 49% of global coal consumption [] and has

2 produced more cement in the last three years than the US has in the last hundred. [4] Efficient utilization of fly ash, at such scale, will have a positive impact on both the natural and the built environment. Novel uses for fly ash, no matter where they might have been developed, could contribute towards that goal, and it is important that those innovations be put to use wherever they might have the most impact. The global fly ash industry, as with any industry, benefits from the free flow of knowledge and ideas between business and academia, as well as between countries. Language barriers hinder that dialogue, and not only the language as spoken, but the language and convention of regulations. This paper focuses on those differences as it applies to regulations concerning the use of fly ash in concrete. Those regulations vary widely; some are clearly crafted with an eye towards facilitating concrete mix design, others relate the ash more closely with the type of coal that was burned to produce it. There are no simple ways to translate a grade of ash by one country s code of regulations into another s, as the specifications and test methods are generally unique to their parent countries. However, there are a number of parallels that can be exploited to make that translation process easier, and that is what we focus on in this paper. We describe a system that should allow for ready, informal, definition of fly ash by any of the regulatory systems of the top eight fly ash producers, Australia, Canada, China, Europe, India, Japan, Russia and the United States. [] This system should help describe the criteria by which said countries qualify fly ash for use in concrete, or offer guidance as to how a product will be defined in another market. By no means does this tool guarantee that an ash by one system will qualify for another; the test methods from one country to another are different, and it will always be necessary to re-test by the appropriate test methods. It is fair to say that the majority of users will not need a tool such as this there are very few instances where contractors are transporting fly ash across borders, and in those few instances it s probably fair to assume that they took the time to perform due diligence on the pertinent regulations. Instead, this tool will hopefully facilitate communication between researchers, marketers, or regulators across national boundaries. RESULTS

3 Before describing the translation rubric we will briefly go through the classification schemes for fly ash in the eight countries of interest. It is possible to read a great deal about the priorities of the standard-writing bodies into the content of the standards, but it may be equally informative to note how recently the standards have been updated, and how many substantive edits were made. The science of fly ash application is developing rapidly, and the lack of a regulatory response to advances in technology may hinder adoption of those technologies. Australia Relevant Standard: AS [6] This standard has the fewest qualification criteria, at only five. It does not take into account coal-type in fly ash classification, and specifies only one grade by its potential to affect cement/fly ash mixes (grade F). Table 1 Australian Fly Ash Standards AS Grade Fine Fine Medium Coarse (Special) SO (Ash) Moisture LOI Fineness 4 μm Retained (% maximum) (Ash + Cement) Strength Activity Index at 28 days (% minimum) Canada Relevant Standard: CSA A000-1 [7]

4 Much like the Australian requirements for fly ash, the Canadian criteria are minimal, and do not specify fly ash based upon coal-type. Table 2 Canadian Fly Ash Standards CSA A000-1 Type F Cl CH SO Calcium Oxide, CaO (%) 1 >1, LOI (Ash) Fineness 4 μm Retained (% maximum) (Ash + Cement) Autoclave Expansion or Contraction (%) China Relevant Standard: GB/T [8]

5 Chinese fly ash standards do take into account coal type, defined (simply) as low ash and high ash (F and C), with the latter possessing % CaO. The grade for fly ash defines 4.0% free CaO as the limit for type C and 1.0% for F. There are significant economic barriers to the widespread use of fly ash, and CCPs in general. They mainly stem from the intransigence of less environmentally sound industries that compete with CCP-derived products, [9] and the high cost of transporting concrete-viable fly ash to construction sites. [9] Table Chinese Fly Ash Standards GB/T Grade I II III SO Free Calcium Oxide, fcao (Type F, max % / Type C, max %) 1.0 / / / 4.0 Moisture LOI (Ash) Fineness 4 μm Retained (% maximum) (Ash + Cement) Water Requirement Le-Chatelier Autoclave Expansion (mm) Europe Relevant Standard: BS EN 40-1:2012 []

6 The European Union standard for fly ash in concrete in unique in so far that it makes considerable accommodations for ash derived from coal burning with up to 0% of selected cocombustion materials. Those ashes are subjected to additional mandatory testing. The EU re-uses more than 90% of the fly ash it produces, [11] and if it can be shown that the regulatory system facilitates that high rate of re-use then it may be worth replicating in other countries. Table 4 European Fly Ash Standards BS EN 40-1:2012 Category A B C SO Free Calcium Oxide, fcao Reactive Calcium Oxide Total Chloride LOI (Ash) Fineness 4 μm Retained (Type N max % / Type S, max %) 40 / / / 12 (Ash + Cement) Water Requirement (Type N max % / Type S, max %) -- / 9 -- / 9 -- / 9 Strength Activity Index at 28 days (% minimum) Strength Activity Index at 90 days (% minimum) India [12] [1] Relevant Standard: IS 812: 201

7 This standard splits fly ash into use as either cement replacement or admixture, with a minimum strength activity index requirement for the former, as well as more stringent sulfate and loss-onignition specifications. Overall, however, Indian fly ash specifications mandate more chemical testing than most; including routine testing of magnesium oxide, total alkalis, and total chloride. Table Indian Fly Ash Standards IS 812 : 201 Use Cement Replacement Admixture Type Siliceous Calcareous Siliceous Calcareous SiO2 + Al2O + Fe2O (% minimum) SO SiO2 (% minimum) 2 2 MgO Alkalis as Na2O Total Chloride (maximum %) Moisture LOI (Ash) Fineness by Blaine's Permeability (m2/kg minimum) (Ash + Cement) Autoclave Expansion (%) Strength Activity Index at 28 days (minimum %) Japan Relevant Standard: JIS A 6201: 1999 [14]

8 The JIS standard is unique in that it includes a minimum percentage Flow Value Ratio (the ratio of flow of a fly ash mixture relative to a Portland cement control), furthermore, elemental analysis is limited to total silica testing, making the Japanese standard the only to neglect sulfate testing. Table 6 Japanese Fly Ash Standards JIS A 6201 : 1999 Type I II III IV (Ash) (Ash + Cement) SiO2 (% minimum) Moisture Fineness 4 μm Retained (% maximum) Fineness by Blaine's Permeability (m 2 /kg minimum) Density (minimum g/cm ) Strength Activity Index at 28 days (minimum %) Strength Activity Index at 91 days (minimum %) Flow Value Ratio (minimum %) Russia Relevant Standard: ГОСТ [1]

9 Russian standards for fly ash are heavily tied to coal types; anthracite/bituminous coals, semibituminous coals and lignite. Standards, furthermore, specify the CaO content of the burned coal at >% for type O and <% for type K. The former is generally associated with lignite coals, and standards are generally more stringent. The standard is proscriptive in that the fly ash types are designated for the following uses: I - For use in regular and light weight concrete II - For use in regular and light weight concrete and mortars III - For use in cellular concrete IV - For use in special construction projects such as dams, pavements, and airstrips There are no specifications in the relevant table that apply directly to the use of fly ash in concrete (no call for soundness or strength activity index testing), but it is permissible to exceed CaO, MgO, SO, and fineness limits given additional concrete testing, such as autoclave or durability testing. Nonetheless, there has been some criticism of the standards as being outdated and unhelpful for the concrete producer. [16] Table 7 Russian Fly Ash Standards ГОСТ Coal Classification Fly Ash Type Coal Type I II III IV Calcium Oxide, CaO (maximum %) All Types Free Calcium Oxide, fcao (maximum %) All Types MgO Alkalis as Na2O All Types All Types -- 6 LOI Anthracite Semi-Bituminous (Ash) Fineness by Blaine's Permeability (m2/kg minimum) Fineness 4 μm Retained All Types All Types United States Relevant Standard: ASTM C618-12a [17]

10 The American standard for coal fly ash, ASTM C618-12a, classifies fly ash into types F and C, each pozzolanic, the latter being potentially cementitious as well. Nominally, F ashes are produced from burning anthracite and bituminous coal, and C ash is produced by burning lignite or semi-bituminous coal, and has higher CaO content than F ash (these differences are not specified, however). The American standard specifies three ash/cement tests; strength activity index, water requirement, and autoclave expansion. That burden of testing is unique to the US. Table 8 SiO2 + Al2O + Fe2O (% minimum) American Fly Ash Standards ASTM C618-12a Type F C SO.0.0 Moisture.0.0 LOI (Ash) Fineness 4 μm Retained (% maximum) 4 4 (Ash + Cement) Strength Activity Index at 7 days (minimum %) Strength Activity Index at 28 days (minimum %) Water Requirement Autoclave Expansion or Contraction (%) Proposed System Generic Universal Fly Ash Standard: 201 Finally, over the course of devising a translation tool that applied to these eight classification schemes, it was possible to build an intermediate classification system. Each physical or chemical criterion was given a point for every classification system that included it in its fly ash standard. For instance, seven out of eight systems include a specification for loss on ignition (LOI), so that criterion scored a seven. Only one system includes seven day strength activity index (the US), so that scored a one. The new system takes into account every criterion that scored a three or more. This restricted the acceptance criteria to a manageable eight. The

11 three grades were defined by the minimum, average, and maximum (excepting a few outlier values) defined in the eight standard codes. Hopefully those criteria will prove of utility in designing applications for fly ash, and that will be a focus of further work. The concentration of calcium (CaO) in a fly ash is of considerable interest to a concrete producer, and its measurement is either directly or indirectly specified in every standard (calcium effectively balances the SiO2 + Al2O + Fe2O equation called for in American and India standards). That measurement is not correlated with the quality of fly ash under specification. Instead, it can be correlated with the cementitious character of that ash, and that may or may not be optimal for the producer. So, this standard calls for characterization of the Calcium, but does not tie that measurement to any of the specified grades. Table 9 Global System (Proposed) Generic Universal Fly Ash Standard : 201 Grade 1 2 SO Moisture LOI (Ash) Fineness 4 μm Retained (% maximum) 2 40 (Ash + Concrete) Strength Activity Index at 28 days (minimum %) Water Requirement Autoclave Expansion or Contraction (%) A B C Calcium Oxide, CaO (%) < 20 >20 The translation tool (available at CTLGroup.com) will accept input in the form of a fly ash type designation, prompt for a goal classification scheme, and then output the types of ash the FA will qualify as, given additional testing as noted. The tool does not include various caveats and

12 substitutes for the described tests, nor does it provide guidance as to what test methods are applicable, and it is recommended that the user perform laboratory testing or obtain certification that the FA conforms to the relevant specifications. More functionality and specificity will be included in subsequent iterations of the online translation tool. Conclusion The diversity of classification schemes for fly ash is at odds with the nature of fly ash as a global concern. Widespread beneficial re-use has the potential to decrease landfill growth, moderate greenhouse gas emissions, improve structural durability, and benefit commercial and environmental stakeholders in many other ways. Facilitating communication between those stakeholders is critical to spreading best practices and overcoming outdated regulations. As such, while universal acceptance of one fly ash classification system might come far into the future if it is even necessary at all instruments that make it easier to share knowledge across borders and language barriers fulfill a current and pressing need. BIBLIOGRAPHY [1] Coal Industry Advisory Board, "Power Generation from Coal Measuring and Reporting Efficiency Performance and CO2 Emissions," International Energy Agency, Paris, 20. [2] T. H. Adams, "Coal Ash Production and Use Survey 201," in News Conference, Washington DC, [] J. Ayoub, "China produces and consumes almost as much coal as the rest of the world combined," US Energy Information Administration, 14 May [Online]. Available: [Accessed 16 March 201]. [4] B. Gates, "Have You Hugged a Concrete Pillar Today?," 12 June [Online]. Available: [Accessed 16 March 201]. [] C. Heidrich, "Coal Combustion Products: A Global Perspective," in 201 World of Coal Ash Conference, Lexington, 201. [6] Standards Australia, "AS , "Supplementary cementitious materials for use with portland and blended cement Part 1: Fly ash"," Standards Australia, Homebush, [7] CSA Group, "A000-1, "Cementitious materials compendium"," CSA Group, Mississauga, [8] Standardization Administration of China, "GB/T , "Fly ash used for cement and concrete"," Standardization Administration of China, Beijing, 200. [9] J. Fu, Challenges to Increased Use of Coal Combustion Products in China, Linköping: Linköping University, 20. [] EUROPEAN COMMITTEE FOR STANDARDIZATION, "BS EN 40-1:2012, "Fly ash for concrete Part 1: Definition, specifications and conformity criteria"," EUROPEAN COMMITTEE FOR STANDARDIZATION, Brussels, 2012.

13 [11] H.-J. Feuerborn, "Coal Combustion Products in Europe- an update on Production and Utilisation, Standardisation and Regulation -," in World of Coal Ash 2011, Denver, [12] Bureau of Indian Standards, "IS 812 (Part 1) : 201, "PULVERIZED FUEL ASH SPECIFICATION PART 1 FOR USE AS POZZOLANA IN CEMENT, CEMENT MORTAR AND CONCRETE"," Bureau of Indian Standards, New Delhi, 201. [1] Bureau of Indian Standards, "IS 812 (Part 2) : 201, "PULVERIZED FUEL ASH SPECIFICATION PART 2 FOR USE AS ADMIXTURE IN CEMENT MORTAR AND CONCRETE"," Bureau of Indian Standards, New Delhi, 201. [14] Japanese Standards Association, "JIS A 6201:1999, "Fly Ash for Use in Concrete"," Japanese Standards Association, Tokyo, [1] Euro-Asian Council for Standardization, Metrology and Certification, "ГОСТ , "Thermal plant fly-ashes for concretes. Specifications"," Euro-Asian Council for Standardization, Metrology and Certification, Moscow, [16] A. Ukhanov, "Experience and regulatory framework for the use of dry fly ash from Russian TPPs for producing concrete, mortar and dry construction mixes," in Ashes from TPPs: removal, transport, processing, storage, Moscow, [17] ASTM International, "ASTM Standard C618: 2012, "Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete"," ASTM International, West Conshohocken, 201.