This paper presents a characterization analysis of alkali-activated steel slag. The effect ratio of steel slag and ferronickel slag which are the precursor materials on the compressive strength of the alkali-activated materials was investigated. The combination of sodium hydroxide solution of 15 moles concentration and sodium silicate was used as an alkaline activator. The ratio between steel slag and alkaline liquid was fixed at 3.31 for all mixtures. Ambient curing (20℃ - 25℃) are used throughout the experiment. Compressive strength shows the alkali-activated steel slag presented high strength at 14 days curing which is 21. 56 MPa. In comparison, the alkali activated steel slag had better strength than 50/50 Fe/SS alkali-activated slag which only achieved 16.75 MPa. Result obtained shows that alkali-activated steel slag had better water absorption than 50/50 Fe/SS alkali-activated slag at 7 days curing. Furthermore, the activation of steel slag was contributed to the presences of gehlenite, larnite, akermanite and magnetite. Lastly, the alkali-activated steel slag presents the vibration of the Si-O bonds at wave number 970.46 cm ﹣1 contributed by the calcium silicate hydrate.
Since the early of 1990s [
Alkali aluminosilicates mechanism appears to have main role in waste disposal. It could reduce permeability of the matrix and fixes certain ions in the structure of the phase formed [
The potential of slag from the production of ferronickel in steel industry has been extensively investigated. Annual production of crude steel was estimated about 1.4 billion metric tonnes produced all over the world [
On the basis, there are two main models of alkali-activated binding systems. It can be classified as calcium-dominated (alkali-activated slag) and aluminosilicate-dominated (geopolymer) systems. In present study, a particular discussion on the chemistry of alkali activated binder dominated by high calcium allows it to function like OPC. Theoretically, the high calcium binder can be defined as a binder that have Ca/(Si + Al) ratio of approximately to 1, from the activation of blast furnace slag with alkaline solution. Alkaline activator act as the accelerator in this reaction as they assist the almost instantaneous hardening compared to the reaction with water which then leads to longer setting time and slow hardening [
In succession, because of their properties and sustainability awareness in the industry majority of the Europe country including Spain has been adapting the potential use of slag in construction [
Moreover, extensive research have been carried out in order to study into deep the main factor apart of type of activators used that could affect the development of mechanical strength of AAS mortars and concretes [
Thus, this paper provides information on the characterizations of steel slag which presence high amount of calcium and the comparison of blended steel slag and ferronickel slag. The main objectives of the study include the in- vestigation to know the compressive strength, setting time, mineralogical cha- racteristics and the properties obtained by the alkaline activation of the slag mixtures.
Steel slag and ferronickel slag was used as the aluminosilicate source in this alkali- activated synthesis. The slag is siliceous materials that primarily consist of CaO, MgO, SiO2 and FeO. The chemical compositions are highly variable and change depending on the raw materials, type of steel made and furnace condition. The slag used originated from the metallurgical plant of the Greek company LARCO G.M.M.S.A that treats laterites. The chemical analysis composition of the slag performed by XEPOS X-ray Fluorescene diffractometer utilizing X-LAB software is given in
An adequate quantity of granulated slag was grinded to −500 um and the resulted powder has a mean particle size (d50) of 15.05 um, measured on a MALVERN Laser Particle Size Analyzer. The mineralogical analysis confirmed that steel slag used contains some trace amount minerals such as merwinite, gehlenite, akerminite and larnite.
In order to synthesize alkaline activated material, steel slag and ferronickel slag was mixed with the alkaline activator in a mixer for 5 minutes until a homogeneous mixture was obtained. Then the mixture was molded in 50 mm open plastic (ERTASETAL) moulds. The resulted paste and its setting time was determined by a MATEST Vicat apparatus according to the EN 196-3:2005. The viscosity of the homogenous pastes was measured instantly subsequent their preparation by Brookfield Viscometer LV+. The sample was cured at ambient temperature until the day of testing.
The formulation of Fe-Ni slag and Steel slag (Fe/SS) has been designed as
Chemical Composition | Steel Slag (wt%) | FeNi Slag (wt%) |
---|---|---|
SiO2 | 13.65 | 41.14 |
Al2O3 | 10.26 | 13.79 |
FeO | 32.20 | 34.74 |
MgO | 2.782 | 3.59 |
CaO | 32.06 | 0.71 |
Ni | 0.007 | 0.14 |
Sample | Steel Slag | FeNi Slag |
---|---|---|
AAS1 | 100 | 0 |
AAS2 | 70 | 30 |
AAS3 | 50 | 50 |
AAS4 | 30 | 70 |
shown in
The comparison of phase characterization between AAS1, AAS2, AAS3, and AAS4 has been performed by using X-ray diffractometry (XRD) in order to detect the amorphous material The compressive strength were measured and comprised the average value of 3 samples according to ASTM C109 using the specimen of 50 mm edge. The mechanical properties performed on a testing machine of the Structural Behavior Engineering Laboratories Inc. (PTL-10 model) were measured at 1 day, 7 days, and 14 days after curing period.
The mineralogical characterization of alkali-activated slag (AAS) after the compressive test was performed by means of X-ray diffractometry (XRD) on a SIEMENS D58000 diffractometer. The FTIR measurement has been proposed to observe the movement of band that can present as well as the appearance of new band attributable to the formation of new chemical compounds. The infrared spectra were recorded in the region of 4000 - 800 cm−1 and collected using the Perkin Elmer 2000 analyser.
1) FTIR Analysis
FTIR analysis was performed in order to see the potentially band forms through the alkali activation process of steel slag.
The activation of slag with sodium silicate generated the formations of C-(A)-S-H gel and hydrotalcite-like phase (co-existing with C-S-H depending on the MgO content of the slag) as the major reaction products [
2) XRD Analysis
XRD analysis of steel slag incorporating with ferronickel slag is investigated with the different ratio of the material (AAS1-AAS4) in order to produce the amorphous geopolymer material. The AAS1 results mainly constituted of merwinite (Ca3Mg(SiO4)2), akermanite (Ca2.Mg∙Si2O7), and larnite (β-2CaO∙SiO2, β-Ca2SiO4). The XRD analysis obtained that alkali-activated steel slag mainly consisted of the metal oxides, silicates and aluminate forms that contributed to gehlenite and magnetite as the main reaction products. In addition, the activating steel slag in alkali solution exhibited the non-amorphous phase due to the presence of short range order of CaO-FeO-SiO2-Al2O3 structure within the materials.
The introduction of ferronickel slag in the alkali-activated slag modifies the XRD pattern which the characteristic of crystalline phases changes to low
amorphous phases due to higher content of ferronickel slag in the mixture. Indeed, the CaO-Al2O3-SiO2 system as crystalline phases corresponds to larnite and gehlenite. Gehlenite is one of the principal crystalline silica-containing phases in normal aluminous cements [
Furthermore, it represents low amorphous material from a mixture of oxides of a relatively complex chemical composition. Such an example, wustite (FeO), larnite (β-2CaO⋅SiO2, β-Ca2SiO4) and fayalite (Fe2SiO4) are the most represented mineral phases detected in cement hydration mechanism [
1) Setting time
Setting time was performed to determine the effect of ferronickel slag with alkali-activated steel slag. As shown in
According to
2) Water absorption properties
Water absorption properties are important criteria in the application of the binders in construction. AAS1 and AAS3 exhibited comparable water absorption values at different curing period are presented as in
Alkali-activated slag | Binder content (kg/m3) | Period of curing (day) | ||
---|---|---|---|---|
Water absorption (wt%) | ||||
1 | 3 | 7 | ||
AAS1 | 235.73 | 4.2 | 3.8 | 3.7 |
AAS3 | 242.14 | 5.1 | 4.9 | 4.8 |
does not readily penetrate, and also the ongoing formation of reaction products at advanced ages of curing [
3) Compressive strength
X-ray diffraction phase analysis confirms that alkali-activated steel slag produced the non-amorphous material. Meanwhile, the incorporating of ferronickel slag in the alkali-activated steel slag exhibited low amorphous material.
The compressive strength of the AAS1 achieved the highest strength at 21.56 MPa, showed that steel slag are preferable use as cement concrete material than AAS2, AAS3, and AAS4. Besides, it setting time of 30 min fully harden and excellent water absorption (3.7 weight%) at 7 days curing. The FTIR and XRD analysis obtained the producing of CSH which influenced the properties of AAS1.
In this study, it was proved that AAS1 was preferable used as concrete material due to excellent characterization and mechanical properties. Others, with some improvement and further study, AAS1 can be produced as lightweight or foam concrete material.
The authors gratefully acknowledge Center of Excellence Geopolymer and Green Technology (CEGeoGTech), School of Materials Engineering, UniMAP and National Technical University of Athens, Greece for their expertise and support. The authors would also like to thank for the funding support from the Fundamental Research Grant Scheme (FRGS-9003-00540) under Ministry of Education Malaysia (MOE) and support from “Partnership for Research in Geopolymer Concrete” (PRIGeoC-689857) sponsored by the European Union.
Aziz, I.H., Zulkifly, K., Sakkas, K., Panias, D., Tsaousi, G.M., Al Bakri, M.M.A. and Yong, H.C. (2017) The Characterization of Steel Slag by Alkali Activation. Open Access Library Journal, 4: e3816. https://doi.org/10.4236/oalib.1103816