Valorisation of Stainless Steel Slags as a Hydraulic Binder (original) (raw)
Related papers
Effect of mechanical activation on the hydraulic properties of stainless steel slags
Cement and Concrete Research, 2012
This work aims to assess the possibility of using ladle metallurgy and argon oxygen decarburization stainless steel slag as a hydraulic binder after mechanical activation. Prolonged milling in ethanol suspension resulted in 10-fold increase of the surface area and increase of the amorphous phase. Calorimetric analysis of slags mixed with water indicated the occurrence of exothermic reactions. XRD results revealed that periclase, merwinite, γ-C 2 S and bredigite, decreased with hydration time. Thermogravimetric analyses indicated that the main hydration products are most probably C-S-H, CH and MH. The hydrated products in both slags were similar to C-S-H gel. WDS analysis demonstrated Ca and Si to be widespread in the structure. Formation of M-S-H gel or incorporation of Mg in the C-S-H gel remains uncertain. The 90 days compressive strength of mortars prepared from slags reached approximately 20% for LM and 10% for AOD of the compressive strength of mortars prepared from OPC.
Effect of High Cooling Rates on the Mineralogy and Hydraulic Properties of Stainless Steel Slags
Metallurgical and Materials Transactions B, 2013
This article investigates the effect of chemical composition and cooling rate during solidification on the mineralogy and hydraulic properties of synthetic stainless steel slags. Three synthetic slags, covering the range of typical chemical composition in industrial practice, were subjected to high cooling rates, by melt spinning granulation or quenching in water, and to low cooling rates, by cooling inside the furnace. Both methods of rapid cooling led to volumetrically stable slags unlike the slow cooling which resulted in a powder-like material. Stabilized slags consisted predominantly of lamellar b-dicalcium silicate (b-C 2 S) and Mg, Ca-silicates (merwinite and bredigite); the latter form the matrix at low basicity and are segregated along the C 2 S grain boundaries at high basicities. Slowly cooled slags consist of the c-C 2 S polymorph instead of the b-C 2 S and of less Mg, Ca-silicates. Isothermal conduction calorimetry and thermogravimetric analysis indicate the occurrence of hydration reactions in the stabilized slags after mixing with water, while calcium silicate hydrates (C-S-H) of typical acicular morphology are identified by SEM. The present results demonstrate that the application of high cooling rates can result in a stable, environmental-friendly, hydraulic binder from stainless steel slags, rich in b-C 2 S, without the necessity of introducing any additions to arrest the b polymorph.
Cementitious binders from activated stainless steel refining slag and the effect of alkali solutions
Journal of hazardous materials, 2014
With an aim of producing high value cementitious binder, stainless steel refining slag containing a high amount of CaO in γ-dicalcium silicate form was activated with NaOH and Na-silicate as well as KOH and K-silicate solutions, followed by steam curing at 80°C. Higher levels of alkali-silicate in the activating solution resulted in higher cumulative heat suggesting accelerated reaction kinetics. With respect to compressive strength, higher levels of alkali silicate resulted in higher strength and the mortars with Na activator were found to have higher early strength than the ones with K activator. The long term strength was found to be similar, regardless of the alkali metal. Thermogravimetric, QXRD and FTIR analyses showed an increase in the amount of reaction products (CSH type) over time, further confirming the reactivity of the crystalline slag. Batch leaching results showed lower leaching of heavy metals and metalloids with K activator compared to the Na activator. These resul...
On a new hydraulic binder from stainless steel converter slag
Advances in Cement Research, 2013
The aim of this work was to investigate the hydraulic behaviour of a stainless steel converter slag after changing its chemical composition and cooling path. The target slag was designed to resemble ground granulated blastfurnace slag (GGBFS). A synthetic slag with a chemical composition dose to stainless steel converter slags was mixed with 22, 30 and 38 wt% fly ash (FA) from lignite combustion, heated up to 1550°C and then granulated by quenching in water; the solidified new slags were named FA22, FA30 and FA38 respectively. Quantitative X-ray diffraction on FA22 revealed that the amorphous phase was approximately 40 wt%, the rest being bredigite and merwinite. For FA addition of 30 wt% or more, the amorphous phase reached almost 100 wt%. The resulting slags showed significant hydraulic activity when mixed with sodium-based activators, with C-S-H, hydrotalcite and hydrogarnet being the main hydration products formed. The calorimetric behaviour and the mechanical properties of blended cements with 30 wt% FA30 and FA38 were comparable to a blended cement with GGBFS. Assuming that FA addition will take place during the liquid state of the slag, the proposed process can result in a new hydraulic binder.
2014
The disintegration of stainless steel slags, due to the beta to gamma dicalcium silicate transformation, hinders the valorisation and increases the landfilling cost considerably. In this work, two industrial wastes, namely boron residues from the dressing of boron minerals and fly ash from lignite’s combustion, have been used as additives in order to produce physically stable stainless steel slags. Results indicate that 1 wt % of boron residue is sufficient, however, 22 wt % of fly ash is required for a synthetic slag of basicity (CaO/SiO2) = 2. The practical implications in terms of valorisation of the produced slags are also discussed.
Waste and Biomass Valorization, 2019
Augmenting granulated blast furnace slag (GBFS) content in Portland Slag Cement (PSC) beyond the conventional limit of 70% is the stimulus for this study. Such enhancement other than bringing down the carbon footprint of cement conserves natural resources. However, beyond 70% slag incorporation, early strength gain of PSC is meagre because of its low reactivity. This study explores mechanical activation (MA) of GBFS to alter its reactivity, and thereby raising the possibility of increased slag incorporation in PSC. MA of slag is carried in an eccentric vibration mill. Formulations with different MA slag contents and clinker are studied in terms of heat of hydration (using isothermal conduction calorimetry) and compressive strength (CS). CS of clinker-slag formulations augmented with the extent of MA. Hydration behaviour of these blends i.e. increased heat evolution, accelerated reactions etc. is in agreement with CS values. X-ray diffraction and TG-DTG employed as complimentary tools to comprehend the hydration process corroborate with CS results, and hydration characteristics. Thus, MA can be used to enhance the hydration characteristics (reactivity) of GBFS, and henceforth its content in PSC. Sufficiently activated slag incorporation even up to 90% yields comparable strength than commercial PSC at all ages of curing. Keywords Granulated blast furnace slag • Portland slag cement • Mechanical activation • Compressive strength • Heat of hydration Statement of Novelty This study investigates the effect of clinker replacements with granulated blast furnace slag (GBFS) in Portland Slag Cement (PSC) past the permissible limit of 70%. The study provides a scientific basis for higher volume incorporation of mechanically activated slag in PSC, being as high as up to 90%. Formation of hydrotalcite phase after hydration is an indication of better slag reaction compared to the absence of such phase in the earlier reported attrition milled slag and clinker blends. Processing-reaction-property correlations have been established thereby giving further insight into the work. Since, mechanical activation is carried out in dry mode using a commercially available milling device, possible industrial applications in context of cement can be envisaged.
Mineral Activator And Physical Characteristics Of Slag Cement At Anhydrous And Hydrated States
2009
The setting agent Ca(OH)2 for activation of slag cement is used in the proportions of 0%, 2%, 4%, 6%, 8% and 10% by various methods (substitution and addition by mass of slag cement). The physical properties of slag cement activated by the calcium hydroxide at anhydrous and hydrated states (fineness, particle size distribution, consistency of the cement pastes and setting times) were studied. The activation method by the mineral activator of slag cement (latent hydraulicity) accelerates the hydration process and reduces the setting times of the cement activated.
Hydration Products, Morphology and Microstructure of Activated Slag Cement
International Journal of Concrete Structures and Materials, 2014
This paper reports the physical properties and hydration products of slag cement that was prepared by activating ground granulated blast furnace slag with commercial lime and plaster of Paris (POP) as activators. The consistency, setting times and soundness of various mixes of slag-lime-POP is reported. The hydration products and formation of bonds in the paste during setting were studied with the help of SEM, FTIR and XRD tests and the same are correlated to the hydration process. The setting times of the mixes are found to be lower than that of the value prescribed for ordinary Portland cement (OPC). Borax is used as a setting retarder and a borax content of 0.4 % by mass gives setting times that are normally prescribed for OPC. In the early stages of setting C-AS -H gels are found in this cementing material instead of C-S-H gel, as generally observed in the OPC.
Effect of Temperature on the Alkali Activation of Continuous Casting Stainless Steel Slag
2013
Continuous casting slag from stainless steel production containing non-hydraulic minerals was activated in alkaline solutions at elevated temperature by steam curing. A steam curing cycle of 24 hours including 16 hours of steam curing was used to provide the elevated temperatures of 60 °C, 70 °C, 80 °C, 90 °C, 100 °C and 110 °C. The compressive strength of the mortars prepared using the slag was found to increase steadily with the increase in the steam curing temperature. Na activators generated higher compressive strength than K activator though Na activated mortars showed higher porosity. Presence of CSH as reaction product was evident by thermal and FT-IR analysis.