ISIJ International, Vol. 52 (2012), No. 6, pp. 1101–1108
Influence of Fly Ash and Ground Granulated Blast Furnace Slag on the Mechanical Properties and Reduction Behavior of Cold-Agglomerated Blast Furnace Briquettes Mikko MÄKELÄ,1) Timo PAANANEN,2) Jyrki HEINO,3) Tommi KOKKONEN,3) Satu HUTTUNEN,3) Hannu MAKKONEN3) and Olli DAHL1) 1) Clean Technologies Research Group, Department of Forest Products Technology, Aalto University, School of Chemical Technology, P.O. Box 16400, FI-00076 Aalto, Finland. E-mail:
[email protected] 2) Ruukki Metals, Rautaruukki Oyj, P.O. Box 93, FI-92101 Raahe, Finland. 3) Laboratory of Process Metallurgy, Department of Process and Environmental Engineering, University of Oulu, P.O. Box 4300, FI-90014 University of Oulu, Finland. (Received on November 9, 2011; accepted on February 2, 2012)
The utilization of fly ash and ground granulated blast furnace slag (GGBFS) as supplementary cementing materials in cold-agglomerated blast furnace briquetting was investigated. Sample analysis included chemical and mineralogical composition, particle size, and scanning electron microscopy and the produced briquettes were evaluated for mechanical durability (2, 7, and 28 day tumble strength), mineralogy, thermal decomposition (DSC–TG–MS), and disintegration under reducing conditions at 800°C (LTD). Based on the data, only the use of GGBFS with or without fly ash led to satisfactory 28 day mechanical durability compared to the 28 day reference mean value. The most promising series, where 20% of Portland cement was replaced by a three-fold amount of GGBFS, attested to a 30% strength increase at 28 day compared to the respective reference mean value. However, the 48 hour durability values proved inferior to respective references due to the comparatively larger particle size (one fly ash sample) and slower strength development provided by the supplements. The LTD (800°C) values determined by isothermal reduction at 800°C were strongly correlated (R2 = 0.694) with briquette mechanical durability governed by the dehydration of the C–S–H phase at approximately 320–360°C established by DSC–TG–MS. Subsequent to the dehydration of C–S–H, briquette durability was possibly maintained by the formation of an intermediate carbonated phase prior to final breakdown under the conditions of the LTD (800°C) test. Briquette moisture optimization was encouraged by the variation in detected levels, prospectively emphasized by the ability of industrial-scale briquetting plants to operate on comparatively lower moisture levels. KEY WORDS: briquetting; cement replacement; granulated blast furnace slag; fly ash; tumble strength; isothermal reduction.
To enable the use of alternative or supplementary binder materials, emphasis must be placed on maintaining the mechanical performance of the briquettes. Briquettes are generally used in the BF at an age of approximately 1 month,13) and must thus develop sufficient strength to guarantee stable furnace operation by maintaining a proper gas flow and efficient reduction inside the furnace.14) Additionally, with a briquette input of, e.g., 100 kg/tHM the plant operator has limited possibilities for arranging managed curing conditions for a month’s supply and thus the briquettes are generally stored outdoors after an essential period of curing. This imposes an additional requirement for early strength development to prevent premature breakdown and dramatic increase in fines formation during handling and transport. Quantity and type of binders used, the composition and particle size of secondary raw materials, and briquette curing conditions have been stated as potential controlling parameters.15) The setting and subsequent strength development of Portland cement paste is primarily based on the partial dissolution of tri- and β-dicalcium silicate phases and the pre-
1. Introduction As the implementation of traditional sintering plants is receding, the cold-agglomerated briquetting process is increasingly favored in recycling secondary raw materials to the blast furnace (BF). In cold-agglomerated briquetting various iron-bearing by-products, carbonaceous material, and possible other beneficial ingredients are intermixed with a binder constituent and agglomerated to the form of briquettes.1) However, as the cold-agglomerated briquetting process generally relies on the use of commercial Portland cement,2) increasing environmental pressure and economic viability emphasize the need for alternative or supplementary binder materials.3) By-products, such as ground granulated blast furnace slag (GGBFS), fly ash from coal combustion, and silica fume from ferrosilicon production are already used in commercial blended cements,4) and studies regarding materials such as steel and ladle furnace slags and fly ash from pure biomass combustion or co-combustion with coal are increasingly published in relevant literature.5–12) 1101
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cipitation of portlandite and calcium silicate hydrate, a rigid nearly amorphous gel-like structure generically referred to as C–S–H.16) Calcium aluminate and calcium aluminate ferrite phases are also present in ordinary Portland cements, but in significantly lower quantities, mainly resulting in the precipitation of calcium aluminium sulphate related phases (AF1-tri and subsequent AF-mono). The hydration of tricalcium silicate is comparatively more rapid than that of βdicalcium silicate, the respective dissolution degrees in ordinary Portland cements approximating 70 and 30% during the first 28 days.16) Although GGBFS exhibits more latent cementitious characteristics compared to Portland cement, the primary reaction products upon hydration are essentially the same.16,17) In addition to the relatively lower generation of portlandite due to GGBFS hydration, possible pozzolanic characteristics in blended cements (i.e., consumption of Ca(OH)2 from cement hydration to produce secondary C–S–H by reaction with soluble SiO2) have been mentioned in relevant literature.17,18) According to Taylor,16) chemical composition, glass content, and particle size are the most import factors in terms of GGBFS reactivity. In the case of fly ash additions strength development relies mainly on the pozzolanic reaction between active SiO2 and available portlandite to produce C–S–H as stated above.19,20) Antiohos et al.21) mentioned the relatively higher reactivity of high-calcium fly ashes compared to those of a low-calcium content, especially if the surplus lime occurs in the glass phase. Based on the requisite to partially replace commercial Portland cement, the use of fly ash and GGBFS as supplementary cementing materials in cold-agglomerated blast furnace briquetting was investigated. This paper reports the results from the experimental period. Sample analysis included chemical and mineralogical composition, particle size, and scanning electron microscopy and the produced briquettes were evaluated in terms of mechanical durability (2, 7, and 28 day tumble strength), mineralogy, thermal decomposition, and disintegration under reducing lowtemperature conditions. An attempt is made to provide a continuum for the preliminary evaluation of fly ash and lime for use in blast furnace briquetting, which was reported in our previous publication.22)
(mainly bark) and 30% commercial peat fuel (steam generation 50–60 kg·s–1). Fly ash sample F2, generated at a different mill, was collected as a combined one-day sample from three collector silos of an electrostatic precipitator (ESP) representing ash produced during the incineration of 50% of clean forest residues (mainly bark with minor quantities of sludge) and 50% of commercial peat fuel (steam generation 30 kg·s–1). In addition to the fly ash samples, GGBFS generated at the integrated iron and steel mill in question was used as received from an external contractor thus representing normal operating procedure. Normally the mill provides granulated blast furnace slag (GBFS) for the contractor responsible of the grinding process of GBFS to generate GGBFS for use in the cement industry. All samples were stored in sealed 5 or 10 dm³ polyethylene containers in room temperature and humidity to avoid responses to atmospheric humidity. In addition to fly ash and GGBFS, commercial rapid-hardening Portland cement (PC), type CEM II/A-LL 42.5R, was used as a base binder in the briquette formulations. 2.2. Sample Analysis All samples used were analyzed in terms of particle size and chemical and mineralogical composition. Additionally, scanning electron microscopy (SEM) was used to provide information on the morphology of the potential supplements. The particle size determinations were performed according to the guidelines of ISO 1332023) with a Mastersizer 2 000 particle size analyzer equipped with a Hydro SM wet-dispersion unit (measurement range 0.02–2 000 μ m). The fly ash and cement samples were dispersed in an ethanol medium and the GGBFS sample in a 2-propanol medium ultrasonically for a time period of 5–20 minutes with 2 400 rpm in order to attain a stable dispersion. Subsequently, the chemical compositions of the samples was determined with the X-ray fluorescence (XRF) method with a Philips PW 2404 sequential X-ray spectrometer equipped with a Rh anode tube. The X-ray spectrometer was operated in an acceleration voltage range of 32–60 kV and a current range of 10–125 mA with a selection of crystals (synthetic, Ge, or LiF) and detectors (flow, scintillator, or combined flow/sealed detector) depending on the individual element. Prior to analysis, the samples were pulverized and agglomerated using a WCo grinder and Herzog-briquetting equipment. The mineralogical compositions of the samples were determined with the powder X-ray diffraction (XRD) method. A Philips PW 3040 X’Pert MPD X-ray diffractometer was used with CoKα radiation (wavelength 1.78897 Å) and an iron filter, operated at an acceleration voltage of 45 kV and a current of 40 mA. A measurement range of 5°–100° (2θ) with 0.04°/1s was used with a goniometric resolution of 0.001°. The duration of each measurement was approximately 43 minutes. Secondary electron images were taken with a LEO 1450 SEM (LEO Electron Microscopy Ltd., Cambridge, United Kingdom) with an acceleration voltage of 15 kV. Prior to analysis, the powdery samples were attached to bilateral carbon tape and gold-plated with ca. 15 nm Au.
2. Materials and Methods 2.1. Sampling Fly ash samples were provided by two pulp and paper mill complexes situated in the Bothnian Arc Region in Northern Finland. The ashes were produced in identical bubbling fluidized bed-boilers (BFB) with a nominal capacity of 246 MW at the power plants of the respective facilities. The sampling represented normal BFB operating conditions, i.e., exhaust O2 -content of 2–5% and bed temperature of ca. 850°C. Fly ash sample F1 was collected from the discharge screw of the fly ash storage silo during a threeday period and represented ash produced during the incineration of approximately 70% of clean forest residues 1
AFt (tri) and AFm (mono) are generic terms used in describing the hydration products of aluminate, ferrite and sulphate phases of Portland cement. As an example in AF-mono, the “mono” denotes the single formula unit of CaX2 in the general constitutional formula C3(A,F)·CaX2·yH2O, where C=CaO, A=Al2O3, F=Fe2O3, y=2(x+3) and X=e.g. OH–, SO42– or CO32–.16) The formation of AF-tri phases [C3(A,F)·3CaX·yH2O, y=x+30] is similar to that of AF-monos, but generally occurs at higher ratios of CaX to C3(A,F).16)
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ISIJ International, Vol. 52 (2012), No. 6 Table 1. Chemical composition (%, XRF) and mass fractions (d.w.) of individual components included in the secondary raw material batch. Parameter
a b
Mill scale
Mixer scrap
Steel scrap
BF dusta
BF dustb
Coke dust
Iron oxide
Undersized limestone
Rolling mill sludge
wt.%
41.2
11.7
11.7
9.5
4.8
6.4
2.8
7.6
4.3
Fetot
73.75
56.76
53.46
42.65
40.46
0.88
69.30
1.54
72.51
CaO
0.61
19.46
17.85
5.10
3.93
1.11
0.05
50.25
0.53
SiO2
0.76
11.48
9.19
17.55
3.93
6.44
0.32
2.34
0.47
Al2O3
0.15
1.33
1.28
2.40
1.10
3.13
0.06
0.96
0.06
MgO
0.05
0.82
1.61
2.40
1.07
0.20
0.08
1.41
0.08
Na2O
0.01
0.82
0.11
0.11
0.47
0.06
-
-
-
K2O
0.01
0.14
0.06
0.15
0.25
0.16
0.00
0.30
0.01
Mn
0.57
0.45
2.37
0.27
0.21
0.01
0.26
0.02
0.38
S
0.01
0.84
0.07
0.31
0.50
0.11
0.01
0.08
0.03
Cl
0.00
0.00
0.00
0.01
0.03
0.04
0.12
-
0.00
P
0.01
0.04
0.21
0.04
0.03
0.04
0.01
-
0.01
BF flue dust. BF dedusting dust (derived from the cast house and the dosing plant). Table 2. Series
Binder mixture (kg)
Raw material batch (kg)
Dry batch bulk density (kg·dm–3)
Dry batch moisture content (%)
Water addition (l)
Slurry moisture content (%)
REF1a
1.0 PC
9.0
1.42 (1.79)
4.4
0.992
13.25
REF2a
1.0 PC
9.0
1.38 (1.85)
4.4
0.959
12.48
a
1.0 PC
9.0
1.30 (1.75)
4.1
1.049
12.90
S1
0.8 PC, 0.6 F1
8.6
1.35 (1.70)
3.9
1.060
12.61
S2
0.8 PC, 0.6 F2
8.6
1.31 (1.64)
3.9
1.183
13.78
S3
0.8 PC, 0.6 GGBFS
8.6
1.37 (1.72)
4.0
0.985
12.95
S4
0.8 PC, 0.3 F1
8.9
1.34 (1.72)
4.1
0.987
13.77
S5
0.8 PC, 0.3 F2
8.9
1.30 (1.70)
3.0
1.000
12.98
REF3
a
Binder mixture and secondary raw material batching with relevant parameters for briquette manufacture.
S6
0.8 PC, 0.3 GGBFS
8.9
1.37 (1.72)
4.2
0.974
12.41
S7
0.8 PC, 0.3 F1, 0.3 GGBFS
8.6
1.35 (1.87)
3.9
1.042
13.17
S8
0.8 PC, 0.3 F2, 0.3 GGBFS
8.6
1.29 (1.70)
4.3
1.000
12.62
Reference series.
2.3. Briquette Manufacture Various dry batches of 10.0 kg were manufactured by mixing a secondary raw material batch, see Table 1, of 8.6– 9.0 kg with 1.0–1.4 kg of binder mixture according to Table 2 in a Hobart mixer for 10 minutes prior to water addition. A target moisture content was set based on prior experiments and a requisite volume of water was admixed to the batch. Subsequent to water addition, the slurry was mixed for a period of 60 seconds before the mixer was temporarily switched off and the walls of the mixing bowl scraped with a spattle to ensure complete homogenization. The slurry was then mixed for a final time period of 120 s. Subsequent to mixing, individual portions of 550 g were distributed to a parallelogram cell comprised of 16 hexagon-shaped molds (approx. dimensions 60 mm · 60 mm) used for producing the briquettes. As the entire cell was filled and the individual molds compacted by hand, the cell was simultaneously pressed (cylinder pressure 10 bar) and vibrated (60 Hz) with a Teksam aps vibrating press for a period of 5 s. Subsequent
to compaction, the surrounding cell was carefully removed and the briquettes placed under a plastic cover for 48 hours to allow sufficient relative moisture for binder hydration and subsequent curing. After 48 hours the cover was removed and the briquettes were stored in room temperature and humidity for further analysis. During manufacture, a sub sample of ca. 10 g was taken from the dry batch and the generated slurry for rapid moisture content determination by a Mettler Toledo Hg53 Halogen Moisture Analyzer. Additionally, the bulk density of the dry batch was roughly measured by volume displacement of water. The measurement was performed in triplicate and the mean value reported. 2.4. Briquette Analysis Mechanical durability of the produced series were measured according to the guidelines of ISO 327124) at time periods of 48 hours, 7 days, and 28 days from manufacture. As opposed to ISO 3271, in which a test portion of 15 kg is 1103
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used, we placed three briquettes of each series in the cylindrical steel drum (dimensions 1 000 mm · 500 mm) and rotated at 25 r/min for 480 s. Additionally, after 480 seconds the contents of the cylinder were emptied on a 6.0 mm sieve as opposed to the 6.3 mm sieve used in ISO 3271 and the overflow weighted to provide a mass fraction of > 6.0 mm representing a total of ca. 200 revolutions. The dimensions and mass of the tested briquettes were recorded prior to tumbling. In addition to mechanical durability, the mineralogy of a pulverized reference briquette was analyzed by XRD. The same Philips PW 3040 X’Pert MPD X-ray diffractometer was used with equivalent parameters as in the analysis of potential binder materials. Hydrate decomposition was assessed by a combination of differential scanning calorimetric, thermogravimetric and mass spectrometric analysis (DSC–TG–MS). The sample briquettes were crushed and pulverized using a ring roll mill. The powdered material was subsequently screened with a 0.5 mm sieve and the underflow recovered. The pulverization and subsequent sieving was repeated with the 0.5 mm overflow and the attained underflows combined and homogenized for analysis. The DSC–TG–MS analyses were performed on approx. 35 mg samples of the attained underflows at 28 days from briquette manufacture with a Netzsch STA 409 PC Luxx thermal analyzer with a Pt-crucible integrated to a Netzsch QMS 403 Aëolos quadrupole mass spectrometer. The temperature program ranged from 30°C to 1 000°C with 20°C/min in a He atmosphere with a He flow rate of 60 ml/min. During the analysis, multiple ion detection (MID) was used for H2O+ and CO2+ (mass-charge ratios 18 and 44, respectively) to determine the decomposition of relevant phases. Prior to analysis, vacuum degassing of the equipment was performed in triplicate to ensure He atmosphere conditions. Finally, briquette disintegration under reducing lowtemperature conditions was assessed with a low-temperature disintegration (LTD) test built upon the guidelines of ISO 13930.25) The standard ISO 13930 test exposes the sample to isothermal reduction at a temperature of 500°C with the following gas composition: CO, 20%; CO2, 20%; H2, 2%; and N2, 58% thus corresponding to the hematite-magnetite reduction phase. However, we used an increased temperature of 800°C corresponding to wüstite equilibrium conditions with the equivalent gas composition as sufficient disintegration of the briquette samples was not attained at lower temperatures. Additionally, only the most promising briquette formulations in terms of mechanical durability were analyzed for LTD (800°C) after approximately 120 days from manufacture (see discussion in Section 3.2). Normal sieving procedure according to ISO 13930 was applied to attain the > 6.3 mm mass fraction subsequent to reduction and tumbling.
content exceeds 10%. The high CaO contents were also reflected in the X-ray diffractograms, which indicated the existence of lime [CaO], gehlenite [Ca2Al2SiO7], and srebrodolskite [Ca2Fe2O5] in the case of F1, and lime and anhydrite [CaSO4] in the case of F2. In addition, the high total Fe content in the form of maghemite [Fe2O3] and srebrodolskite or as magnetite [Fe3O4] is also worth noting with F1 Table 3. Chemical composition (%, XRF) of fly ashes (F1, F2), GGBFS, and rapid-hardening Portland cement (PC). Parameter
F1
Fetot
11.5
F2
GGBFS
PC
9.62
0.54
1.9
CaO
30.2
23.2
39.4
58.8
SiO2
27.6
34.8
34.5
19.5
Al2O3
9.8
12.9
8.9
4.9
MgO
3
2.8
12.1
3.3
Na2O
2
1.7
0.49
0.78
K2 O
1.9
1.9
0.47
0.95
Mn
0.52
0.4
0.24
0.03
S
1.3
1.4
1.7
1.4
Cl
0.21
0.17
6.3 mm) was strongly correlated (R2 = 0.694, see Fig. 7) with mechanical durability, i.e., tumble strength values. The most promising result was again attained with the S3 sample which, unlike the other samples, did not fully disintegrate but remained in compact form. In support of the ability of briquettes to resist disintegration under reducing conditions, Singh and Björkman1) proposed a model accord-
Fig. 6.
ing to which the dehydration of generic C–S–H at above 600°C coupled with respective decomposition into CaO and 2CaO·SiO2 is followed by reactions with hematite or wüstite depending on dominant equilibrium conditions. However, as the dehydration of the C–S–H phase was in our case attested to occur at a temperature range of approx. 320–360°C, briquette durability until final breakdown under the conditions of the LTD test at 800°C could possibly be explained by the formation of an intermediate carbonated phase. Although performing investigations at 20 and 65°C, Hyvert et al.40) concluded that the carbonation rate of undehydrated C–S–H was directly dependent on the partial pressure of CO2 while that of calcium from, e.g., portlandite was more susceptible to carbonation even at atmospheric CO2 pressures. Finally, the compressibility of the produced briquettes was evaluated by plotting briquette height (mm) at 48 hours from manufacture as a function of produced slurry moisture (%) during manufacture and is respectively illustrated in Fig. 8. The rapid Hg53 Halogen Moisture Analyzer was used in attaining moisture data on produced slurries to decrease the effect of binder hydration on the respective results. However, as can be seen from Fig. 8, no clear trend was detected regarding the compressibility of briquettes on specific moisture levels. Additionally, the variation in the determined moisture levels (i.e., 12.4–13.8%) indicates that maintaining predetermined slurry moistures should be emphasized in future experiments to improve comparability between different formulations and thus enable optimization of briquette strength. Even though the inclusion of supple-
Reference DSC–TG–MS pattern with peak temperatures for detected H2O+ and CO2+.
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Fig. 7.
Attained LTD (800°C) values (% > 6.3 mm) as a function of tumble strength (% > 6.0 mm), i.e., briquette mechanical durability with respective regressional data.
Fig. 8.
Briquette heigth (mm) at 48 hours from manufacture as a function of briquette slurry moisture (%) during briquetting.
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ISIJ International, Vol. 52 (2012), No. 6
mentary fly ashes and GGBFS affected the particle size distribution and thus the compressibility of the produced series S1-S8, moisture variation was notable (i.e., 12.5–13.3%) also in the case of the reference series REF1-REF3 in which the particle size distributions should have been comparable. Briquette compressibility can be considered analogous to the consistency, i.e., slump parameter (e.g., EN 12350-241)) used in concrete applications to describe the ease by which a certain mold can be filled with freshly mixed concrete. Respectively, requisite moisture levels are also mandatory in briquetting to allow sufficient compression of a certain slurry in the briquette mold. However, excessive moisture should be minimized for the optimization of subsequent strength development which is further corroborated by the ability of industrial-scale briquetting plants to operate on lower briquette moisture contents.
analyses and D.Sc. Erkki Heikinheimo from the Department of Materials Science and Engineering (Aalto University, School of Chemical Technology) in SEM imaging are deeply appreciated. REFERENCES 1) M. Singh and B. Björkman: Ironmaking Steelmaking, 34 (2007), 41. 2) M. Singh and B. Björkman: ISIJ Int., 44 (2004), 59. 3) M. C. G. Juenger, F. Winnefeld, J. L. Provis and J. H. Ideker: Cem. Concr. Res., 41 (2011), 1232. 4) S. Korounis, T. Tsivilis, P. E. Tsakiridis, G. D. Papadimitriou and Z. Tsibouki: Cem. Concr. Res., 37 (2007), 815. 5) C. Shi: J. Mater. Civ. Eng., 16 (2004), 230. 6) C. Shi: Cem. Concr. Res., 32 (2002), 459. 7) C. Shi and S. Hu: Cem. Concr. Res., 33 (2003), 1851. 8) J. M. Manso, M. Losañez, J. A. Polanco and J. J. Gonzalez: J. Mater. Civ. Eng., 17 (2005), 513. 9) J. Setien, D. Hernández and J. J. González: Constr. Build. Mater., 23 (2009), 1788. 10) D. Adolfsson, R. Robinson, F. Engström and B. Björkman: Cem. Concr. Res., 41 (2011), 865. 11) R. Rajamma, R. J. Ball, L. A. C. Tarelho, G. C. Allen, J. A. Labrincha and V. M. Ferreira: J. Hazard. Mater., 172 (2009), 1049. 12) S. Wang, A. Miller, E. Llamazos, F. Fonseca and L. Baxter: Fuel, 87 (2008), 365. 13) M. Singh and B. Björkman: Ironmaking Steelmaking, 34 (2007), 30. 14) H. K. Tripathy, B. V. R. Murthy, Y. V. Swamy, J. N. Mohanty and A. K. Tripathy: J. Mine. Met. Fuel., 56 (2008), 28. 15) M. Singh and B. Björkman: Miner. Metall. Process., 23 (2006), 203. 16) H. F. W. Taylor: Cement Chemistry (2nd ed.), Thomas Telford Publishing, London, (1997), 459. 17) S. Kumar, R. Kumar, A. Bandopadhyay, T. C. Alex, B. Ravi Kumar, S. K. Das and S. P. Mehrotra: Cem. Concr. Comp., 30 (2008), 679. 18) B. Samet and M. Chaabouni: Cem. Concr. Res., 34 (2004), 1153. 19) S. Wang, L. Baxter and F. Fonseca: Fuel, 87 (2008), 372. 20) A. Johnson, L. J. J. Catalan and S. D. Kinrade: Fuel, 89 (2010), 3042. 21) S. Antiohos, K. Maganari and S. Tsimas: Cem. Concr. Comp., 27 (2005), 349. 22) M. Mäkelä, T. Paananen, T. Kokkonen, H. Makkonen and J. Heino: ISIJ Int., 51 (2011), 776. 23) International Standardization Organization (ISO): Particle Size Analysis – Laser Diffraction Methods, ISO, Geneve, (2009), 51. 24) International Standardization Organization (ISO): Iron Ores – Determination of Tumble Strength, ISO, Geneve, (1995), 7. 25) International Standardization Organization (ISO): Iron Ores – Dynamic Test for Low-Temperature Reduction-Disintegration, ISO, Geneve, (1998), 10. 26) European Committee for Standardization (CEN): Cement – Part 1: Composition, Specifications and Conformity Criteria for Common Cements, CEN, Brussels, (2004), 26. 27) B. Samet and M. Chaabouni: Cem. Concr. Res., 34 (2004), 1153. 28) K.-S. You, J.-S. Cho, J.-W. Ahn and G.-C. Han: Resour. Process., 53 (2006), 23. 29) O. Dahl, H. Nurmesniemi, R. Pöykiö and G. Watkins: Fuel Process. Tech., 90 (2009), 871. 30) M. Cruz-Yusta, I. Màrmol, J. Morales and L. Sánchez: Environ. Sci. Tech., 45 (2011), 6991. 31) S. Wang, L. Baxter and F. Fonseca: Fuel, 87 (2008), 372. 32) V. G. Papadakis: Cem. Concr. Res., 29 (1999), 1727. 33) F. M. Lea: The Chemistry of Cement and Concrete (3rd ed.), Edward Arnold (Publishers) Ltd., London, (1980), 727. 34) I. G. Richardson: Cem. Concr. Res., 29 (1999), 1131. 35) L. Alarcon-Ruiz, G. Platret, E. Massieu and A. Ehrlacher: Cem. Concr. Res., 35 (2005), 609. 36) I. Pane and W. Hansen: Cem. Concr. Res., 35 (2005), 1155. 37) M. J. DeJong and F.-J. Ulm: Cem. Concr. Res., 37 (2007), 1. 38) R. Gabrovšek, T. Vuk and V. Kaučič: Acta Chim. Slov., 53 (2006), 159. 39) I. F. Kurunov, T. Y. Malysheva and O. G. Bol’shakova: Metallurgist, 51 (2007), 548. 40) N. Hyvert, A. Sellier, F. Duprat, P. Rougeau and P. Francisco: Cem. Concr. Res., 40 (2010), 1582. 41) European Committee for Standardization (CEN): Testing Fresh Concrete – Part 2: Slump-test, CEN, Brussels, (2009), 9.
4. Conclusions According to the attained data, the use of fly ash and GGBFS as supplementary cementing materials in coldagglomerated BF briquetting led to satisfactory 28 day mechanical durability values only when GGBFS was used with or without fly ashes F1 or F2. The most promising series, where 20% of the Portland cement content was replaced with a three-fold amount of GGBFS, attested to a 30% strength increase compared to the 28 day mean value of produced reference series. However, the 48 hour durability values which were used in describing the end of the managed curing period in industrial-scale proved inferior compared to the 48 hour reference mean value due to the comparatively larger particle size (F1) and slower strength development provided by the supplements. The LTD (800°C) values determined by isothermal reduction at 800°C were strongly correlated (R2 = 0.694) with briquette mechanical durability, which was mainly governed by the dehydration of the C–S–H phase at approximately 320– 360°C established by DSC–TG–MS. Subsequent to the dehydration of the C–S–H phase, briquette durability was possibly maintained by the formation of an intermediate carbonated phase prior to final breakdown under the conditions of the LTD (800°C) test. The need for the optimization of briquette moisture contents was supported by the variation in detected moisture levels, which will be emphasized by the ability of industrial-scale briquetting plants to operate on comparatively lower moisture levels. Acknowledgements The Finnish Funding Agency for Technology and Innovation (Tekes) is kindly acknowledged for providing financial support for the Finnish Metals and Engineering Competence Cluster (FIMECC) in launching the ELEMET plan and the Material Efficient Blast Furnace (MEBF) project. Additionally, the contributions of the Ruukki Raahe laboratory personnel in briquette manufacture and respective
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