Slag as a secondary raw material from metallurgy is most often heaped in slag disposal areas without any profit. This paper deals with alkali activated slag from iron and steel production which can be used in the building industry. Products of alkali slag activation fulfill the role of inorganic binders.Kao sekundarna sirovina, troska od metalurškog procesa najčešće se odlaže na deponije bez ikakve financijske dobiti. Ovaj rad se bavi lužnato aktiviranom troskom iz proizvodnje željeza i čelika, koja kao anorgansko vezivo može biti korištena u građevinskoj industriji

J. Vlček

M. Vavro

P. Babková

V. Tomková

English

Slag as a secondary raw material from metallurgy is most often heaped in slag disposal areas without any profit.
This paper deals with alkali activated slag from iron and steel production which can be used in the building
industry. Products of alkali slag activation fulfil the role of inorganic binders.Kao sekundarna sirovina,
troska od metalurškog procesa najčešće se odlaže na deponije bez ikakve financijske dobiti. Ovaj rad se bavi
lužnato aktiviranom troskom iz proizvodnje željeza i čelika, koja kao anorgansko vezivo može biti korištena u
gradevinskoj industriji

Vlček, Jozef

Tomková, Václava

Bábková, Petra

Vavro, Martin

DSpace at VSB Technical University of Ostrava

Aktivno lužnati kompoziti dobiveni od troske željezne i čelične industrije

Hrčak - Portal of scientific journals of Croatia

J. VL^EK, V. TOMKOVÁ, P. BABKOVÁ, M. VAVROALKALI-ACTIVATED COMPOSITESBASED ON SLAGS FROM IRON AND STEEL METALLURGYReceived – Prispjelo: 2008-02-28Accepted – Prihva}eno: 2009-01-10Original Scientific Paper – Izvorni znanstveni radINTRODUCTIONThe world production of slag from iron and steel in-dustries per year reaches almost 50 000 kt, whereas ap-proximately 12 000 kt per year is produced in Europe1. Czech Republic ranks among the important produc-ers of steel and pig iron in Europe (6,9 million ton ofsteel and 5,2 million ton of pig iron was produced in theyear 2006 2) and thus approximately 1,2 million ton ofsteel slag and 1,9 million ton of blast furnace slag. Ap-proximately 55 % of blast furnace slag production un-dergoes a granulation process and granulated blast fur-nace slag (GBFS) originates. A significant part of blastfurnace slag is utilized for the production of aggregate.GBFS is commonly utilized in the cement industry forpreparation of blended cement CEM II, CEM IIII andCEM V where cement clinker substitution by GBFSranges from 6 to 95 wt % 3. Steel slag is more variablein chemical composition in comparison with granulatedblast furnace slag (see Table 1). From this point of viewthe utilization of steel slag for inorganic binder prepara-tion is more complicated. Slag with a high content ofiron (ladle slag) is returned to the blast or steel furnace inthe form of agglomeration charge. Another part of steelslag is utilized for production of dense synthetic aggre-gate. The majority of ladle slag production is stored inslag disposal areas without any profit 4.SLAG ALKALI ACTIVATIONInduced cementitious properties of slag by suitablealkali activators allow effective usage of this secondarymetallurgical product in the building industry as a valu-able binding system which represents an alternative tocement binders. Apart from the value of slag for thebuilding industry, raw materials and energy savings oc-cur as well as CO2 emission decreases even though themortars range significantly increase 6.The latent hydraulicity of slag as well as certain nat-ural raw materials (tuffs and eruptive products) orantropogenous materials (slags, fly ashes, metakaolineand silica fume) is a property which is developed afteralkali activation causes solidification and hardening ofthe material. For latent hydraulicity activation, solublesolutions of alkaline compounds - carbonates, alumi-nates and silicates can be used 7, 8.METALURGIJA 48 (2009) 4, 223-227 223Slag as a secondary raw material from metallurgy is most often heaped in slag disposal areas without any pro-fit. This paper deals with alkali activated slag from iron and steel production which can be used in the buildingindustry. Products of alkali slag activation fulfil the role of inorganic binders.Key words: steel slag, blast furnace slag, alkali activation, binderAktivno lu`nati kompoziti dobiveni od troske `eljezne i ~eli~ne industrije. Kao sekundarna sirovina,troska od metalur{kog procesa naj~e{}e se odla`e na deponije bez ikakve financijske dobiti. Ovaj rad se bavilu`nato aktiviranom troskom iz proizvodnje `eljeza i ~elika, koja kao anorgansko vezivo mo`e biti kori{tena ugra|evinskoj industriji.Klju~ne rije~i: ~eli~na troska, troska iz visoke pe}i, lu`nata aktivacija, vezivoISSN 0543-5846METABK 48(4) 223-227 (2009)UDC - UDK 669.181.28:666.952:691.54:549.26 = 111J. Vl~ek, V. Tomková, P. Babková, Faculty of Metallurgy and MaterialsEngineering, V[B-TU Ostrava,, Czech RepublicM. Vavro, VSB - Technical University of Ostrava, Faculty of Civil Engi-neering, Czech RepublicTable 1. Comparison of composition of GBFS andsteel slag 5SlagoriginComposition / wt %CaO SiO2 Al2O3 MgO MnO FeO+Fe2O3Blastfurnace35-38 34-38 6-9 10-14 0,5-2 0,5-1EAF car-bon steel35-60 9-20 2-9 5-15 3-8 15-30EAF alloysteel39-45 24-32 3-8 8-15 0,4-2 1-6Oxygenconverter30-55 8-20 1-6 5-15 2-8 10-35Ladle 30-60 2-35 5-35 1-10 0-5 0,1-15EAF - Electric arc furnaceDavidovits clears up the theory of geopolymeriza-tion 9. This process represents the controlled synthesisof phases, so-called geopolymers or polysialates, whoseproperties are similar to natural zeolites. From thepolycondensation reaction, unordered systems contain-ing SiO2 and Al2O3 in high alkali environment can re-sult. The chemical name polysialate represents the factthat the 3D sialate network is built up by chains of SiO4and AlO4 tetrahedron linked up by shared oxygen at-oms. The negative charge of Al in IV coordination isbalanced by Na+, K+, Ca2+ ions which are linked in thestructure 9. With the growing content of CaO, the se-quence of origination of new phases is changed duringalkali activation as in the case of slag. Hydrated almostamorphous phases C-S-H (CaO-SiO2-H2O) which origi-nate as a consequence of alkali activation significantlyharden the resulting structure similarly as in the case ofC-S-H Portland cement hydration products. The processof geopolymerization develops as a consequence.The necessary condition for latent hydraulicity ofslag is the occurrence of an amorphous glassy phase.The presence of an activator causes the interruption ofSi-O, Al-O and Ca-O bonds.EXPERIMENTAL PARTThe aim of this paper is to document iron and steelslag binding competence during the preparation ofdense and lightweight (porous) materials.Basic raw materials chosen for alkali activation ex-periments are characterized in Table 2. This table showsmain components in GBFS, power plant fly ash and fourtypes of ladle steel slag (marked as A, B, C, D) obtainedfrom ArcelorMittal Ostrava, a.s. Ladle slag with verydifferent chemical composition in main substances(CaO, SiO2 and Al2O3) were chosen. With respect to ce-ramic convenience, the oxides are indicated by abbrevi-ations C, S, A e.g. C2AS=2CaO·Al2O3·SiO2.The sums of C+S+A content reach values in therange 77  97 % in all studied raw materials - such highamounts of C, S, A as allowed when considering studiedmaterials as ternary systems. From this point of view themeasured amount of C, S and A was recalculated to100 % (Table. 2). The composition of the studied mate-rials is graphically presented in Figure 1. On the basis ofthe simplified content the raw material composition is il-lustrated in constitution ternary diagram C-S-A (Fig-ure 1) [10]. So expressed raw material composition en-ables the determination of a potential equilibrium phaseassociation for individual slag (equilibrium compositionof totally recrystalized systems). The data is summa-rized in Table 2. For comparison of the phase composi-tion of studied materials obtained with the help of X-raypowder diffraction (XRPD), analysis performed ondifractometer INEL is also shown in Table 2.During the selection of raw materials (mentioned inTable 2) for experiments, the main emphasis was placedon their glassy character which is assured mainly bytheir quick cooling. The high amount of glassy phase is anecessary condition for the successful alkali activationprocess and optimal phase composition for the develop-ment of hydrated systems. Comparing the amounts ofthe main components (C, S, A) in studied materials (Ta-ble 2), it is evident that initial phase composition will bedifferent to what was also approved by XRPD and thecourse of the hydration process will be different for eachgiven raw material. Differences in the hydration pro-cesses cause changes in phase composition, microstru-cture and functional parameters of hardened binders.All used raw materials were milled to achieve thespecific surface area of 320 ± 20 m2/kg according to the‘Blaine’ method. Sodium metasilicate solutions (waterglass) from different commercial sources were used foralkali activation. After the initial measurement of den-sity and silicate module Ms (equation 1), the activatorquality was subsequently changed using NaOH solution(50 %) to reach Ms in the range 1,35 – 2,00.MnnSSiONa O 22(1)The modified water glass solution with the requiredamount of Na2O was added to the prepared mixtures.For dense materials the content of Na2O reached3,1 – 5,0 wt% and the water ratio (solid to liquid ratio)was set to give the value 0,33±0,02. In the case of light-weight materials, the optimization of the alkali activatoramount was one of the goals of the presented work.224 METALURGIJA 48 (2009) 4, 223-227J. VL^EK et al.: ALKALI-ACTIVATED COMPOSITES BASED ON SLAGS FROM IRON AND STEEL METALLURGYTable 2. Chemical and phase composition of usedraw material and composition calculated onmacrocomponentsGBFS Slag A Slag B Slag C Slag D Fly ash/ wt %CaO 37,65 37,52 46,10 51,84 57,74 3,40SiO2 38,07 31,93 23,80 17,30 3,50 50,39Al2O3 5,87 7,24 11,80 18,85 35,76 27,85MgO 10,61 7,10 11,40 7,44 2,10 3,00FeO/Fe2O3 0,28 8,16 1,38 3,88 0,66 7,90C+S+A 81,59 76,69 81,70 87,99 97,00 81,60C 46,15 48,92 56,43 58,92 59,53 4,16S 46,66 41,64 29,13 19,66 3,61 61,72A 7,19 9,44 14,44 21,88 36,86 34,12Equilibri-um phaseasoc.CS-C2AS-CAS2C3S2-CS-C2ASC2S-CA-C2ASC2S-C3A-C12A7C2S-C3A-C12A7A3S2-S- CAS2Phasecomposi-tion.XRPDglass,(me-li-liteCAS2)glass,C3S2,CS,C2ASglass,C3A,-C2S,-C2S-C2S, -C2S,C3A,(glass)C3A,-C2S,(- C2S)glass,A3S2,-cri-sto-ba-lite-quartzPreparationand characteristic of dense samplesIn the case of dense samples, initial substances(given latent hydraulic material, alkali activator and wa-ter) were homogenized and cast into laboratory moulds(mould dimensions are 20×20×20 mm). The hydrationof samples proceeded in a moist environment (relativehumidity 99 % and laboratory temperature) until astrength test was performed. The strength test was real-ized after 2, 7, 28 and 50 days. In the same time intervalsthe bulk densities (without drying) were measured.The measured values of strength for a single alkaliactivated ladle slag (A, B, C, D) and these alkali acti-vated ladle slags in combination with GBFS and fly ashare shown in Table 3. The combination of ladle slag withGBFS and fly ash were prepared with the aim to changechemical composition of initial mixtures resulting in thedifferent hardening processes and different strengths ofprepared samples.Excellent strength values after 28 days hydrationshow samples prepared from GBFS and water glass in abroad range of quality and dosage. Strength values of70 MPa reached samples using water glass with 3,1 wt%of Na2O and Ms=2,0 after 28 days of hydration. By in-creasing the dosage of Na2O up to 5,0 wt %, the strengthvalues reached 115 MPa. Using the water glass with Ms= 1,35 and 5,0 wt% of Na2O, the prepared samplesreached a compressive strength of 90 MPa, with pro-longed setting time. The achieved values of compres-sive strength exceeded the strength of samples preparedfrom ordinary Portland cement CEM I 42,5R (Figure 2).The samples prepared only from GBFS and the mix-tures of GBFS with fly ash showed also excellentstrength values (Figure 3) if water glass with 3,5 wt % ofNa2O and Ms = 2,0 was used.The highest values of compressive strength wereachieved in the samples containing GBFS. The mainreason for the high values of compressive strength ofthese samples is the significant amount of SiO2 whichassured a high content of amorphous glassy phase.Glassy slag is an optimal starting material for alkali acti-vation and together with sufficient amounts of CaO inthis slag is responsible for the C-S-H phase formationwhich guarantees high initial strength values.Ladle slag A shows similar properties to GBFS –high amount of glassy phase, CaO, SiO2 and Al2O3which assure origination of suitable hydration products.The chemical composition of slag B showed a sufficientamount of SiO2 and low amount of Al2O3. Overall thehydration process of slag B probably consists of alkaliactivation of a glassy phase together with direct hydra-tion of -C2S with water. Slag A and B in mixtures withGBFS or fly ash show also favourable mechanical prop-erties (see Table 3). Two areas representing suitable andunsuitable phase compositions of raw materials for al-kali activation are depicted on ternary diagram pre-sented in Figure 1. Both slag A and B lie in the area des-METALURGIJA 48 (2009) 4, 223-227 225J. VL^EK et al.: ALKALI-ACTIVATED COMPOSITES BASED ON SLAGS FROM IRON AND STEEL METALLURGYFigure 1. Occurrence range of used slags marked in equili-brium phase diagram CaO – Al2O3 – SiO2Table 3. Compressive strength values of prepared sam-ples using water glass with 4,5 wt % of Na2Oand Ms = 2,0LadleslagMixture composition / % Compressive strength / MPaSlag GBFS Fly ash 2 days 7 days 28days50daysA 100 0 0 20,8 41,3 51,3 68,050 50 0 33,8 47,5 55,0 76,050 25 25 25,4 46,3 54,9 77,3B 100 0 0 27,6 54,2 73,4 76,050 50 0 29,6 45,8 60,0 72,350 25 25 16,8 46,2 53,4 57,1C 100 0 0 21,3 33,0 41,3 45,750 50 0 23,8 37,5 45,0 51,250 25 25 8,8 20,0 27,5 34,6D 100 0 0 - 17,8 20,0 27,850 50 0 12,6 28,4 36,3 47,750 25 25 10,5 15,9 24,7 33,6Figure 2. Compressive strength of alkali activated granu-lated blast furnace slag and CEMI/42,5 Rignated as the area with suitable slag composition for al-kali activation and thus suitable for alternative inorganicbinder preparation.On the other hand slag C and D lie in the area desig-nated as an area with unsuitable slag composition for al-kali activation. The amount of SiO2 is lower for this slagwhich is not favourable for the formation of a glassyphase. For this reason slag D doesn’t contain a glassyphase, also CaO and Al2O3 content is high and the maincrystalline phases are calciumaluminates (C3A, C12A7).Mixtures containing these slags (C and D) harden morerapidly but resulting values of compressive strength arelower. This trend is evident for slag D which has a nega-tive influence on compressive strength values in its mix-tures with GBFS.Preparation andcharacteristic of lightweight samplesOn the basis of the previously mentioned results, thepresumption that GBFS could be a suitable componentfor preparation of lightweight materials, similar to po-rous concrete, can be made. The porous structure is ac-quired by the addition of Al powder which in an alkalimedium undergoes a chemical reaction (2) during whichhydrogen is released and a lightened porous structureoriginates. The character of the porous structure is de-pendent on the hydrogen evolution rate 11.2Al+2NaOH+2H2O=2NaAlO2+3H2 (2)In this part of research we focused on the determina-tion of the optimal amount of Al powder and amount ofalkali activator (water glass).Prepared mixtures of selected substances were ho-mogenized by milling. The Al powder was added to thehomogenized mixtures just before forming, whichavoids the development of hydrogen too early. The pre-pared homogenized mixtures were cast into tubularmoulds. Hydration of samples proceeded in a moist en-vironment (relative humidity 99 % and laboratory tem-perature) until the strength test was performed. After 28days of hydration, compressive strengths and bulk den-sities were determined. The composition of preparedsamples and measured parameters are shown in Table 4.The alkali activator increases pH values of preparedmixtures and is responsible for the disruption of disor-dered structures of latent hydraulic materials. Thehydration products are calciumsilicate hydrates (C-S-Hphases) and zeolites.Present experience with the preparation of light-weight materials clearly shows that the main problem isone of proper timing of the addition of both the Al pow-der as well as of the alkali activator. The reaction (2) isprobably the fastest one which occurs during the light-weight samples preparation and must follow the appro-priate stage of other processes.The lower amount of Na2O (3,5 and 4,0 wt %) andcurrently higher amount of Al powder (0,26 and0,35 wt %) in the mixtures cause hydrogen evolutionwhereas the creation of suitable hydration products dur-ing alkali activation doesn’t occur. This causes the for-mation of big non-uniformely distributed pores, whichare responsible for the fragmentation of prepared sam-ples. A high amount of Na2O and also an increasingamount of Al powder causes the bulk densities and com-pressive strength values to decrease as is shown in Ta-ble 4.Table 4. Compressive strength and bulk density valu-es of prepared samplesLightweightsamplesNa 2O/wt%Compressivestrength after 28days of hydration /MPaBulk density after 28days / kg/m3Al /wt .% Al /wt .%0,130,190,260,350,130,190,260,35E 3,5 5,1 2,1 - - 867 708 - -F 4,0 2,8 3,0 - - 849 732 - -G 4,5 3,5 3,2 2,7 2,1 1030 885 802 793H 5,0 2,8 2,5 2,0 2,0 835 731 564 634I 5,5 2,4 2,0 1,8 1,9 696 551 520 534CONCLUSIONThis paper summarizes the experimental results ob-tained for the alkali activated technogenous puzzola-na-granulated blast furnace slag, steel slag and fly ashfrom power plants. The prepared materials, both denseand lightweight, displayed good product manufacturingqualities while their preparation is economically accept-able as well as being environmentally friendly.Authors acknowledge for the financial support re-ceived from Czech science foundation (project - Devel-opment of Light-weight Materials Based on the Waste226 METALURGIJA 48 (2009) 4, 223-227J. VL^EK et al.: ALKALI-ACTIVATED COMPOSITES BASED ON SLAGS FROM IRON AND STEEL METALLURGYFigure 3. Compressive strength of alkali activated mixtu-res granulated blast furnace slag (GBFS) and flyash (FA)from Metallurgy, No. GACR 106/07/P301 and begin-ning project - Influence of Phase Composition andMicrostructure on Function Properties of GeopolymerSystems from Industry Pozzolans, No. GACR106/09/0588) and Ministry of Industry and Trade of theCzech Republic (project - Material Utilization of Slagsfrom Secondary Metallurgy, No. MPO CR FI-IM5/133).REFERENCES1 S. Kourounis, et al., Cement and Concrete Research, 37(2007), 815 – 822.2 International Steel and Iron Institute, on line Search stati-stics archive org Available from http://www.worldsteel.org3 CSN EN 197 - 1 Cement - Part 1: Composition, Specifica-tions and Conformity Criteria for Common Cements. Praha:^eský normaliza~ní institut, 2001.4 B. Gajdzik, Metalurgija, 48, (2009) 1, 63 – 67.5 C. Shi, P. Krivenko, D. Roy, Alkali-Activated Cement andConcretes, Taylor & Francis, London, 2006, 100 – 101.6 V. Tomková, J. Vl~ek, et al., 11th Conference on Environ-ment and Mineral Processing, V[B-TU, Ostrava, 2007,61-64.7 V. Gluchovskij, A. Pachomov, [lako{~olo~nyje cementy ibetony, Budivelnik, 1978, Kijev.8 J. Brand{tetr, Stavivo, 62 (1984), 110 – 114.9 J. Davidovits, Journal of Thermal Analysis, 37 (1991),1633 – 1656.10 E. F. Osborn, Phase Equilibria Diagrams. Am. CeramicsSociety, 1960.11 R. Drochytka, Pórobeton, VUTIUM, Brno, 1999.Note: The responsible translators for English language is Petra Babková,Czech Republic.METALURGIJA 48 (2009) 4, 223-227 227J. VL^EK et al.: ALKALI-ACTIVATED COMPOSITES BASED ON SLAGS FROM IRON AND STEEL METALLURGY

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Aktivno lužnati kompoziti dobiveni od troske željezne i čelične industrije

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