Claims:We Claim:

1. A method to manufacture atomized argon oxygen decarburization slag comprising following steps:
providing argon oxygen decarburization slag;
separating metal from argon oxygen decarburization slag;
remelting the argon oxygen decarburization slag, wherein the temperature of remelting is in the range of 1700 to 1750 °C;
atomizing the molten argon oxygen decarburization slag to atomized argon oxygen decarburization slag following quenching the molten slag involving air and mist to form solidified and granular atomized slagsuitable as cement.

2. The method as claimed in claim 1, wherein the metal is separated from argon oxygen decarburization slag by one of the methods selected from the group of gravity separation or magnetic separation.

3. The method as claimed in anyone of claims 1 or 2 , wherein the metal separated from the argon oxygen decarburization slag is iron.

4.The method as claimed in anyone of claims 1 to 3 , wherein the metal is separated from the argon oxygen decarburization slag such that after metal separation the slag contains iron in the range of 0.5-2%.

5. The method as claimed in anyone of claims 1 to 4 , wherein during atomization the air to slag ratio is maintained in the range of 500 Nm3/ton to 1800 Nm3/ton, air velocity is in the range of 50m/s to 100m/s and water flow rate used to generate mist is in the range of 1 lpm to 4 lpm.

6. The method as claimed in anyone of claims 1 to 5 , wherein the amorphousness of the cement is maintained in the range of 25% to 40%.

7. Granular atomized argon oxygen decarburization slag suitable as cement obtained as claimed in anyone of claims 1 to 6 which is granular and sourced from argon oxygen decarburization slag and wherein the glass content of atomized argon oxygen decarburization slag is 30-40% and the rest is crystalline content.

8. The Granular atomized argon oxygen decarburizationslag as claimed in claim 7, wherein the size of atomized argon oxygen decarburization slag granules is in the range of 0.01-3.35mm.

9. The Granular atomized argon oxygen decarburizationslag as claimed in anyone of claims7 or 8 having merwinite percentage in argon oxygen decarburization slag in the range of 15% to 35% preferably about 30%.

10. A Cement composition comprising (a) 5% to 20% of atomized argon oxygen decarburization slag which is having glass content of 30-40% and the rest is crystalline content with respect to (b) granulated blast furnace slag.

11. The cement composition as claimed in claim 10 comprising: said atomized argon oxygen decarburization slag :granulated blast furnace slag : Portland clinker in a mass ratio not more than 13.75 : 41.25 : 45 preferably in the ranges of 10:45:45 to 12:43:45 respectively.

12. The cement as claimed in anyone of claims 10 to 11 having 28 days compressive strength in the range of 51.50 MPa to 52.80 MP.

Dated this the 31st day of March, 2022

Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199
, Description:FIELD OF THE INVENTION

The present invention relates generally to the field of cementing material technology. More specifically, the present invention relates to conversion and activation of a non-reactive Argon Oxygen Decarburization (AOD) slag to a more reactive and amorphous material with enhanced cementitious properties and the method of its conversion through Slag atomising technology.

BACKGROUND OF THE INVENTION

Stainless-steel slag includes Electric Arc Furnace Slag (EAF), Argon Oxygen Decarburization Slag (AOD), and Ladle Metallurgy Slag (LMS) [1]. AOD slag is generated in an AOD furnace in the refining process of stainless-steel. It has a high content of CaO, SiO2, and MgO, as well as some Cr2O3 and fluorine [2]. In its cold state, the crystalline mineral phase composition of AOD slag is mainly ?-dicalcium silicate (?-C2S), ß-dicalcium silicate (ß-C2S), periclase and fluorite, traces of f-CaO, merwinite, and spinel [3]. In the cooling process, C2S transforms from ß-type to ?-type around 490 ?C [4]. This mineral phase transformation causes an increase of about 12% in volume, causing shattering of the crystals and generating the powdery AOD slag [5].
The physicochemical properties of alternative materials determine their potential as cementitious additives in cement-based binders [6,7]. According to the physical and chemical characteristics of AOD slag, it can be classified as a kind of industrial by-product that can be used in cement-based applications [8]. The types and contents of oxides in AOD slag are like Portland cement (PC). Due to the presence of hydratable C2S phases, AOD slag has cementitious properties [9]. It is vital to observe that ?-C2S is the major C2S form in the AOD slag, accounting for approximately 38% of the slag mass [10]. In general, ?-C2S is difficult to hydrate, and its hydration ratio in aqueous media for five years is only 20–25% [11]. ß-C2S is hydraulic, but its content in AOD slag is much lower than that of ?-C2S [12]. Therefore, the application potential of ?-C2S in cement-based materials directly determines the applicability of AOD slag.
?-C2S can be easily carbonated without hydration when in contact with CO2 and water [13]. Using carbonation properties, many researchers have found that ?-C2S can be used as a durability modifier for a cement-based product. Mabudo et al. [14] researched the properties and structure of cement-based mortars and pastes with different ?-C2S supplementary ratios under atmospheric carbonation curing and found that carbonation curing reduced porosity by about 33% and improved the mechanical properties of composite materials from 50 MPa to 70 MPa. For cement-based products with lower initial strength but higher durability requirements, it may be a good choice to use AOD slag as a cementitious substitute.
The literature available on use of AOD slag for various applications including construction industry is very limited. In one of the research work conducted by [1], it was reported that about 14% AOD slag can be utilized in clinker raw mix without affecting the clinker quality. The lower consumption of limestone due to utilization of AOD slag resulted in 12% reduction in CO2 emissions along with savings in fuel cost. The cement produced by utilizing AOD slag in the raw mix showed a better compressive strength against the 42.5 CEM1 cement. The compressive strength after 28 days of curing was found to be 44 MPa.
The use of EAF and AOD slag in concrete applications has also been reported. It is reported in one of the research work conducted by [2], it is reported that AOD and EAF slag can be used as aggregates in concrete in view of their better and dense structure along with higher porosity. The expansive tendency of AOD slag is much lower than other steel making slags and hence a more stable structure. The mechanical properties of concrete obtained by using AOD slag are better than the conventional aggregates. However, a marginal expansion is observed in the concrete.
Argon oxygen decarburization (AOD) slag represents more than 50 wt% of the slag from stainless steel production. Although some applications are available, e.g., as aggregates for road constructions or fertilizers, they are characterized by low economic value and limited applicability. In order to increase the economic value of AOD slag, alternative applications have been proposed, e.g., as partial or full replacement for Ordinary Portland Cement (OPC). The work presented by [5], investigates whether the adaptation of the AOD slag chemistry within a high temperature process leads to an improvement of its hydraulic properties and thereby can demonstrate its potential to be converted into a hydraulic binder suitable for OPC replacement. For this purpose, three synthetic AOD slags with basicities (CaO/SiO2) of 2.0, 2.2, and 2.4 were synthesized, and the effect of the CaO/SiO2 ratio on the material stability, the amount of tricalcium silicate formed, and their hydraulic properties investigated. X-ray diffraction, scanning electron microscope (SEM), and isothermal calorimetry analysis were used to characterize the microstructure and the hydraulic activity. The results show that the proposed method is indeed a promising way to stabilize a stainless steel AOD slag and convert it into a hydraulic binder.
Detailed characterization of calcium aluminate rich secondary steel slag derived from two different refining processes of stainless steel production has been performed in a literature work conducted by [8] . In order to gain generic knowledge about this by-product, and its behaviour as a supplementary cement detailed studies were conducted with this slag. Additionally, slag blended cement composites were investigated and compared to a limestone filler blended cement composites and to a reference cement composites. The results showed that the investigated slag contained several hydraulic phases, mainly in the form of calcium aluminates. In the case of the slag cement composites, a larger proportion of hydration products as observed than in the case of the limestone cement composites, as well as a higher rate of strength increase.
In a research work conducted by [15], the study emphasizes the potential use of Argon Oxygen Decarburization (AOD) steel slag in concrete production. Five mixes along with the control mix were made by partially replacing cement with AOD steel slag varying from 10%, 15%, 20%, and 25%. The different properties of all the concrete mixes were evaluated by assessing slump, compressive strength, flexural strength and other durability properties. The air permeability index and sorptivity index showed positive results with an increased percentage of AOD steel slag in the mixes. From the study, it is concluded that AOD steel slag can easily be replaced by cement in the construction of rigid pavements.
In one of the research work carried out by [16], the authors aim 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, ?-C2S and bredigite, decreased with hydration time. Thermo-gravimetric 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.

The steel slags whether it is BOF slag, EAF slag, LRF slag or AOD slag all have valuable lime content along with other mineralizers that can contribute in clinker making. To overcome the expansion of the direct application, researchers also tried to utilize steel slag in the clinkerization process. The research work conducted by [17], reports that steel slag was used to replace iron ore in raw feed during clinker manufacture. However, only 2% of steel slag can be used as a raw mix component for the correction of iron content in the raw mix.

The steel slags in general are a good source of valuable minerals that can be utilized in many applications. The cementitious product development is one such area where a host of literature is available. European patent EP1741683A2 discloses a major component of cement is cement clinker made from a mixture of raw materials calcium oxide, silica, aluminium, and iron oxide by mixing, milling, and firing. According to the invention, the raw material mixture comprises a lime component and converter slag and/or electro-steelworks slag. The use of steel slag not only saves the virgin limestone and other minerals but also consumes lower energy since it already contains calcined lime. The added advantage is the net reduction in CO2 emissions. It is reported that basic oxygen furnace (BOF) slag was utilized in the proportion of 5-8% with 25-35% of blast furnace slag in the preparation of the cement clinker.

European patent EP0780347B1 discloses the utilization of steel slag as a partial replacement or additive for cement. The present invention provides set retardation and enhanced properties including corrosion inhibiting to the concrete end product.
European patent EP3315471A1 discloses the steel slag was activated to utilize it as a composite material for the cement industry. The slag was modified at a high temperature to achieve the activation of the belitic phase in the slag. However, this activated steel slag was crystalline in nature and had limited applications.
US patent (US20130269573A1) wherein it provided an ultra-rapid hardening hydraulic binder including reduced steel slag powder and a method of preparing the same. The reduced slag powder is prepared by rapidly cooling molten electric arc furnace reduced slag to room temperature not to have free-calcium oxide by scattering the molten electric arc furnace reduced slag into the air using high-pressure gas by dropping the molten electric arc furnace reduced slag through a tundish.
Chinese patent (CN101466650A) wherein, the invention provides a process for conversion of basic oxygen furnace slag into construction materials like a hydraulic binder and other applications. The fluorspar was added to the molten slag to increase its fluidity and then the slag was allowed to cool. However, The reduction process for the separation of metallic and nonmetallic iron was not performed in this method.
Korean patent application no. 10-2010-0111768, wherein method of an ultra rapid-hardening hydraulic binder preparation from reduced steel slag powder is provided. The method comprises the process of scattering electric arc furnace to high pressure in a steel mill; quick freezing at room temperature; pulverizing the reduction slag into a fixed fineness, and mixing gypsum with the pulverized reduction slag was prepared through and a manufacturing method thereof are provided to enhance rapid hardening property and replace normal Portland cement. However, the slag was cooled at room temperature which leads to crystallization of the slag, which is the major drawback of this invention.
Most of the research work available on utilization of AOD slag has focused on as such application of AOD slag either as a blend in portland cement or as an aggregate in construction application. The constraint of using AOD slag as such without any modification is that only a small proportion can be blended with OPC cement due to its non-reactive nature. One of the area of research that has been not touched upon is the modification of AOD slag during the cooling stage itself to make it more suitable and reactive as a supplementary cement.
The cooling of molten AOD slag is mostly carried out in ambient air which results in formation of non reactive phase of belite and other calcium silicate compounds. The research work carried out in this document highlights the innovative steps in cooling that resulted in conversion of AOD slag to a more reactive material. This is due to the slag atomising technology and subsequent improvement in the proportion of glassy phase that resulted due to better and fast cooling of molten AOD slag.
As per IS: 12089-2008. Specification for granulated slag for the manufacture of portland slag cement. Bureau of Indian Standards, New Delhi, India and ASTM (American Society of Testing and Materials). 2017. Standard Specification for Slag Cement for Use in Concrete and Mortars. C989, West Conshohocken, Pennsylvania, USA: ASTM, the glass content or amorphousness in slag should be more than 85% for its gainful utilization in cement. However, the glass content in the original AOD slag is varying from 10% to 20%, which is very low and hence unreactive. The AOD slag is converted into a more reactive material through slag atomising technology. This is an innovative technology that utilizes the mix of mist and air at high velocity to granulate the AOD slag and convert its non-reactive phases to more reactive and stable phases. The modification of AOD slag structure through rapid cooling produces a more amorphous structure with suppression of decomposition of tricalcium silicate phase into dicalcium silicate and lime. At the same time the merwinite phase becomes more stable and hence, the AOD slag produced through faster cooling results in a glassy and stable phase. The slag thus produced is more like granulated blast furnace slag with supplementary cementitious properties making it suitable for blending with ordinary portland cement. Additionally, the increase in glass content that results from SAT further improves the amorphous content thereby resulting in improved cementitious property.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide a method for the modification of the constitutional structure of AOD slag to make it more stable and glassy and hence more reactive as a cement.

Yet another object of the present invention is to provide a method for the bulk use of AOD slag to reduce the content of Portland cement clinker in Portland slag cement.

It is a further object of the present invention to provide a method to develop a more effective slag atomising technology to make the AOD slag glassy and amorphous.

It is yet another object of the present invention to provide a method to develop a more effective slag atomizing technique to make more stable AOD slag by capturing calcium hydroxide and forming merwinite.

It is another object of the present invention to use SAT to modify AOD slag to convert it into a cement to make blended cement much like a Portland slag cement made from granulated blast furnace slag.

It is another object of the present invention to beneficially use waste industrial material like AOD slag in the production of cement/mortar/concrete.

It is a further object of the present invention to reduce the cost of cement products.

It is a yet another object of the present invention to lower the heat of hydration of the cement.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a method of manufacture of supplementary cement from AOD slag. The method comprises of steps of separating metal from AOD slag and re-melting of AOD slag, rapid cooling of molten AOD slag utilizing the Slag atomization technology to modify the structure of AOD slag and render it suitable as a supplementary cement involving: providing batched AOD slag; melting the AOD slag in a furnace at a temperature between 1700 - 1725 °C; providing a suitable air and mist quenching technique to atomize the molten AOD slag ; and thereafter recovery of various size fractions of solidified AOD slag generated after slag atomizing ; and obtaining from said atomized AOD slag the reactive AOD slag which is more like a supplementary cement.

A further aspect of the present invention is directed to said method wherein said step of obtaining from said rapid cooled AOD slag the cement includes granulation using air and mist with required modification such as to obtain desired cement like granulated blast furnace slag matching Indian standard IS:12089 – 1987.

There is further provided said method wherein the AOD slag is selected from the stainless steel slag after separation and recovery of metallic iron from the AOD slag.

There is further provided said method wherein the slag atomizing technique is controlled using variables such as air and slag ratio, air velocity with or without the introduction of mist during the atomizing process.

There is further provided said method wherein prior to said re-melting and slag atomizing the metallic iron is separated from AOD slag, preferably by gravity and magnetic separation process with or without grinding so as to lower the iron content of the AOD slag below 2%.

In accordance with the method of the present invention, the molten slag temperature varies from 1700° C to 1750° C.

In accordance with the method of the present invention, the air to slag ratio maintained during the slag atomizing, ranges from 500 Nm3/ton to 1800 Nm3/ton.

In accordance with the method of the present invention, the air velocity during slag atomizing varies from 50m/s to 100m/s.

In accordance with the method of the present invention, the water flow rate used for generating mist varies from 1 lpm to 4 lpm.

In accordance with the present invention, the amorphousness of the cement is maintained to achieve glass content as high as possible preferably like granulated blast furnace slag that complies with the Indian standard IS:12089 – 1987.

In accordance with the present invention, the amorphousness of the cement is maintained in the range of from 25% to 40%. This amorphousness of modified AOD slag was achieved through maintaining higher air to slag ratio and higher air velocity which resulted in higher glass content and higher proportion of stable merwinite phase. The range of air to slag ratio and the air velocity is indicated in Table 1 along with corresponding glassy content in Table 2.

A further aspect of the present invention is directed to provide granular atomized argon oxygen decarburization slag suitable as cement obtained as stated above which is granular and sourced from argon oxygen decarburization slag and wherein the glass content of atomized argon oxygen decarburization slag is 30-40% and the rest is crystalline content.

Said granular atomized argon oxygen decarburization slag having the size of atomized argon oxygen decarburization slag granules in the range of 0.01-3.35mm and wherein merwinite percentage in argon oxygen decarburization slag in the range of 15% To 35% preferably about 30%.

Yet another aspect of the present invention is directed to provide a Cement composition comprising (a) 5% to 20% of atomized argon oxygen decarburization slag which is having glass content of 30-40% and the rest is crystalline content with respect to (b) granulated blast furnace slag.

A further aspect of the present invention is directed to provide said cement comprising the iron separated AOD slag based cement having 28 days compressive strength in the range of 51.50 MPa to 52.80 MPa at a blast furnace slag replacement ratio of 10% - 20% in Portland slag cement.

A still further aspect of the present invention is directed to provide the cement which is comparable with granulated blast furnace slag that complies with the Indian standard IS:12089 – 1987 and includes 10% to 20% of atomized AOD slag with respect to granulated blast furnace slag.

A still further aspect of the present invention is directed to the cement comprising said iron separated and atomized AOD slag based cement, granulated blast furnace slag and Portland clinker in a mass ratio not more than 13.75 : 41.25 : 45preferably in the ranges of 10:45:45 to 12:43:45. respectively.
.

The blast furnace slag replacement ratio of 5% - 20% in Portland slag cement.

The above and other objects and advantages of the present invention are described hereunder in greater detail with reference to the following accompanying non-limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1: illustrates the flow chart of modification of steel through slag atomizing technique and manufacture of granulated blast furnace slag like material with this slag.

FIG. 2: illustrates the image of slag atomizing process carried out with air and mist.

FIG. 3: illustrates the image of different size fractions of AOD slag obtained after modification with slag atomizing technique.

Figure 4: X-Ray diffraction image of non-modified AOD slag.

Figure 5: X-Ray diffraction image of modified AOD slag.

Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity to help to improve understanding of embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS

The accompanying figure together with the detailed description below forms part of the specification and serves to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.

The present invention is now discussed in more detail referring to the drawings that accompany the present application. In the accompanying drawings, like and/or corresponding elements are referred to by like reference numbers.

Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or the like parts.

Before describing in detail embodiments that are in accordance with the invention, it should be observed that the embodiments reside primarily to the modification and conversion of AOD slag to a more reactive form, much similar to Granulated blast furnace slag (GBS). More specifically, the present invention relates to the utilization of AOD slag as a starting material. The AOD slag was re-melted, and modified using slag atomizing technique wherein the slag was atomized by utilizing a mix of air and mist which resulted in a modified AOD slag with supplementary cement like properties due to its increased glassy and amorphous content.

The present invention discloses an invention wherein the non-reactive AOD slag containing a glassy phase of about 10-20% was modified to form cement with increased glass content. The Figure 1 illustrates the various steps that were followed to finally produce a modified and reactive AOD slag. In step 101, the AOD slag is tapped from stainless steel making process. In step 102, AOD slag is subjected to metallic recovery through a combination of physical separation processes deploying gravity and magnetic separation processes to recover the coarse and fine metallic iron and chromium metal. The AOD slag contained about 32% a-belite and 6% ?-belite which is primarily responsible for instable structure of AOD slag. The merwinite phase was also reported to the extent of about 22%. In addition to this minor proportion of ß-belite and about 22% glass content was also observed in the as-received sample of AOD slag.

In step 103, the steel slag is batched from the metal free AOD slag that was subjected for metal separation.

In step 104, the batched AOD slag was re-melted in the furnace at a temperature of 1700-1750 °C.

In step 105, the slag atomizing unit is adjusted for different variables like air velocity, air to slag ratio, water flow rate, water to slag ratio etc. After suitably adjusting the variables as per the desired product specifications the molten slag is allowed to be atomized in presence of air and mist through the specially designed atomizer that rapid cools and forms the granules of AOD slag.
In accordance with the method of the present invention, the air to slag ratio maintained during the slag atomizing, ranges from 500 Nm3/ton to 1800 Nm3/ton.

In accordance with the method of the present invention, the air velocity during slag atomizing varies from 50m/s to 100m/s.

In accordance with the method of the present invention, the water flow rate used for generating mist varies from 1 lpm to 4 lpm.

In accordance with the present invention, the amorphousness of the cement is maintained to achieve glass content as high as possible preferably like granulated blast furnace slag that complies with the Indian standard IS:12089 – 1987.

In accordance with the present invention, the amorphousness of the cement is maintained in the range of from 25% to 40%.

In step 106, the modified AOD slag is blended with other cement like portland clinker and granulated blast furnace slag in a certain proportion to manufacture portland slag cement.

The cement includes 8.25% to 13.75% of AOD slag, 41.25% to 46.75% of granulated blast furnace slag and 45% of ordinary portland clinker. The amorphousness of the AOD slag cement is like granulated blast furnace slag that complies with the Indian standard IS:12089 – 1987. The amorphousness of the cement varies from 20% to 140%. The modified AOD slag, granulated blast furnace slag and the portland clinker cement is mixed with Portland clinker and in a mass ratio as stated above. The resulting cement was tested for cementitious properties. Hence prepared cementitious binder has performed better than the cement prepared with blending of GBS and Portland cement in terms of compressive strength properties. The cement prepared with steel slags has a compressive strength in the range of 51.50 MPa to 52.80 MPa.

In step 107, the AOD slag modification was done through addition of mist along with high air to slag ratio and high air velocity. It was found that the addition of mist did not improve the glass content of the modified AOD slag. Also the merwinite phase was found to be lower than the AOD slag modified without mist.

Hence the AOD slag could be effectively utilized in the manufacturing of cement. This will not only save natural resources but also help in reducing land filling issues and encouraging cleaner production. The sustainable use of slags will also contribute towards environment friendly, economical, and energy-efficient construction. It works as an efficient metal recovery process. It provides the cement industry with alternative cement. It also provides protection for natural resources and reserves. The products are cost-effective as well as eco-friendly as waste materials from the steel industry were valorised.

In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or composition that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article or composition. An element proceeded by "comprises...a" does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or composition that comprises the element.

In the present specification, when a part “includes” a certain component, it means that the component may further include other components, not to exclude other components, unless specifically stated otherwise.

Although not defined differently, all terms including technical terms and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention pertains. Commonly used dictionary-defined terms are additionally interpreted as having meanings consistent with related technical documents and currently disclosed content and are not interpreted as ideal or very formal meanings unless defined.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

In addition, unless otherwise specified, % means weight%.

The advantages and features of the present invention and methods for achieving them will be clarified with reference to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms, and only the embodiments allow the disclosure of the present invention to be complete, and are conventional in the art to which the present invention pertains. It is provided to fully inform the knowledgeable person of the scope of the invention, and the invention is only defined by the scope of the claims. The same reference numerals refer to the same components throughout the specification.

Thus, in some embodiments, well-known techniques are not specifically described to avoid obscuring the present invention. Unless otherwise defined, all terms (including technical and scientific terms) used in the present specification may be used as meanings commonly understood by those skilled in the art to which the present invention pertains.

The present invention is described further hereinafter by reference to a series of accompanying examples.

Experiments that were actually performed are now described by way of the following examples.

Examples

The AOD slag obtained after metal separation (without modification) and the AOD that was modified using re-melting and rapid cooling were studied for changes in mineralogical characteristics and the cementitious behaviour to understand the effect of rapid cooling that was carried out through slag atomizing technology. The following examples will be helpful in demonstrating the change in phases and the cementitious behaviour of modified and non-modified AOD slag.

Example 1: Phase transformation and validation through X-ray diffraction
The non-modified AOD slag and the AOD slag modified through slag atomizing technology were characterized for phase changes using X-ray diffraction technique. The phase changes primarily occur due to either the change in chemistry of the slag or the cooling pattern of the molten slag. In this innovative work the slag atomizing technology was deployed by varying the independent variables such as air-slag ratio, air velocity and the water flow rate. The effect of cooling rate on X-ray diffraction pattern and the associated phase changes in shown in Figure 4 and Figure 5 for non-modified AOD slag and modified AOD slag respectively.

It is observed from the XRD image in Figure 4 that the non-modified AOD contains phases ?-belite, periclase, merwinite, calcium carbonate, magnesium silicate and magnesium aluminate. The ?-belite is non-reactive and is prone to disintegration during cooling. The periclase phase present in the slag has a tendency to expand slowly over a long time period thereby causing delayed expansion and cracking of concrete structure.
The Figure 5 is the XRD image of modified AOD slag. It is observed from this image the merwinite content has increased in the total structure. The periclase phase is not observed in the structure of modified slag, while the total proportion of ?-belite has also decreased. This change in proportion of phases results in a more stable structure which has lower tendency to disintegrate into powder. The absence of periclase results in a sounder microstructure of slag which results in a lower delayed expansion and cracking tendency of the slag.
Slow cooling of slag results in:
Formation of dicalcium silicate from tricalcium silicate and free lime.
C3S = C2S + Free Lime (CaO) ………… (1)
Free lime, upon subsequent hydration, undergoes volume expansion resulting into disintegration of material:
CaO + H2O = Ca(OH)2 ………………… (2)
Also, during slow cooling, a- phase of C2S undergoes a polymorphic solid phase transition to ß-phase of C2S subsequently transforms fully or partially into ?-phase leading to high internal stress due to change in crystal structure and density causing disintegration of slag into powder.
Rapid cooling of slag results in:
? C3S gets bonded in Merwinite phase (3CaO.MgO.2SiO2).
? No major transformation from C3S to C2S. Hence, No Free lime.
? Skips the formation of ?-C2S phase even for transformed C2S phase

Example 2: Effect of various atomising parameters on qualitative and quantitative phase analysis of AOD slag
The molten slag quenching was done bu varying the parameters such as water flow rate, air velocity and air:slag ratio. The objective of slag atomising and rapid cooling was to convert the phases present in normal AOD slag to more reactive phases and also to avoid the formation of certain phases which are responsible for disintegration and volume instability of AOD slag upon cooling.
The Design of experiments plan of the three parameters is shown in Table 1.
The data presented in Table 2 shows the results obtained through XRD analysis for various present in slag modified through slag atomizing technology. The semi-quantitative analysis obtained through XRD is carried out to estimate the effect of various parameters together and also to understand the effect of each parameter in individuality.
The phase changes were recorded for phases such as a-C2S, ß-C2S, ?-C2S and merwinite phase and other minor phases. The total amorphousness was obtained after subtracting the crystallinity of structure from the total sum which is hundred.

Table 1: Design of experiments for atomization of AOD slag
Test No. Air Velocity
(m/s) Nozzle area
(m2) Total tilting time
(sec) Air:Slag

(Nm3/ton) Water flow rate
(lpm) Water:Slag

(l/ton) Slag temp
(°C)
1 50 0.008 28 1252 0.0 0.0 1699
2 50 0.008 15 658 0.0 0.0 1704
3 50 0.008 14 606 0.0 0.0 1711
4 50 0.008 13 568 0.0 0.0 1698
5 100 0.008 18 1581 0.0 0.0 1727
6 100 0.008 16 1413 0.0 0.0 1686
7-1 100 0.008 19 1709 0.0 0.0 1700
7-2 100 0.008 16 1466 0.0 0.0 1697
8 100 0.008 7 610 0.0 0.0 1725
9 50 0.008 26 1175 1.0 48.93 1702
10 50 0.008 14 613 2.0 51.07 1715
11 100 0.008 19 1591 2.0 66.31 1694
12 100 0.008 10 862 4.0 71.80 1707

Table 2: Phase distribution of various phases present in modified AOD slag
Test No. Total semi-quantitaive weight % Crystallinity
% Glass Content
%
a-Ca2SiO4 ß-Ca2SiO4 ?-Ca2SiO4 Ca3Mg(SiO4)2 Others
1 20.45 8.02 3.73 23.47 16.43 72.10 27.90
2 23.14 7.79 4.30 26.26 14.11 75.60 24.40
3 20.10 9.18 5.40 28.45 2.78 65.90 34.10
4 23.78 10.01 4.97 30.63 3.40 72.80 27.20
5 21.71 7.67 3.90 34.50 6.72 74.50 25.50
6 17.42 5.23 2.55 15.43 20.27 60.90 39.10
7-1 19.09 8.43 3.67 34.86 3.35 69.40 30.60
7-2 15.34 5.57 3.63 36.62 15.93 77.10 22.90
8 11.18 7.70 3.55 34.47 18.71 75.60 24.40
9 17.16 5.50 3.63 30.81 20.60 77.70 22.30
10 14.98 6.08 3.14 27.41 20.89 72.50 27.50
11 15.86 5.89 4.19 30.08 17.49 73.50 26.50
12 20.98 7.08 3.72 26.81 17.01 75.60 24.40
Raw 32.31 9.20 6.18 22.16 7.86 77.70 22.30

Raw has 22% merwinite, and atomized slag averages 30.4% (excluding exp. 6)
? Raw has 6.2% ?-C2S, and atomized slag averages 4% (excluding exp. 6 at low T)
? Raw has 32.3% a-C2S, and atomized slag averages 18.7% (excluding exp. 6)
? There is a decrease in minerals that cause decrepitation, and an increase in minerals with improved stability

Example 3: Compressive strength of Portland slag cement made by blending modified AOD slag and granulated BF slag
The modification of AOD slag through slag atomising technique and the subsequent conversion of phases resulted in a higher percentage of glass content compared to the AOD slag that was not modified.
The glass content of the slag determines the reactivity of any slag with respect to its cementitious nature. The granulated blast furnace slag which is categorized as Supplementary cement contains about 90%-95% glass content when observed under microscope. This glassy material when blended with portland cement(OPC) forms a stable gel upon hydration. The free lime present in OPC forms Ca(OH)2 and reacts with calcium silicate of granulated blast furnace slag to form stable C-S-H (calcium silicate-hydrate gel).
Therefore any inert calcium silicate bearing material if converted to a more amorphous and glassy form will behave like supplementary cement. In the case of AOD slag the air cooled AOD (non modified slag) contains only about 15%-20% reactive glassy phase while the same AOD slag when atomized results in a comparatively higher glass content of about 35%-40%. When atomized through high air to slag ratio maintained in the range of 1250 to 1600 Nm3/ton of slag.
However, the actual behaviour of modified AOD slag can be validated only through mortar and concrete tests wherein the mortar or concrete cubes are casted and tested for compressive strength at 1, 3, 7 and 28 days. The slag activity index which is a measure of reactivity of any slag for its cementitious properties should be minimum 75% of the control (The control test specimen is casted with 100% OPC cement and the strength ratio of blended to control gives the slag activity index).
The Table 3 presented below shows the data that was obtained with modified AOD slag by replacing certain proportion of granulated blast furnace slag in the portland slag cement.

Table 3: Compressive strength and other physical testing parameters of non-modified and modified AOD slag
Tests OPC: BF OPC:BF:AOD OPC:BF:AOD(m)
45 : 55 45 : 44 : 11 45:41.25:13.75 45:46.75:8.25 45 : 44 : 11 45:41.25:13.75
Normal Consistency % 30.75 30.75 30.0 30.75 31.25 31.50
Blaine no.(m2/kg) 352 346 348 357 355 356
Autoclave Expansion % 0.013 0.011 0.015 0.023 0.067 0.049
Initial setting time (min)

Final setting time (min) 145

240 160

250 155

245 160

255 135

260 145

290
Compressive strength (MPa)
1 Day 12.85 11.75 11.95 12.30 12.55 11.95
3 Days 23.35 23.05 22.45 21.45 20.60 19.95
7 Days 37.10 33.60 30.65 36.90 36.35 32.55
28 Days 52.65 46.95 44.80 52.80 52.45 51.45

It is thus possible by way of the present invention to providemore reactive and amorphous material with enhanced cementitious properties, the amorphousness of the cement is maintained in the range of from 25% to 40%. The cement that is manufactured include the iron separated and atomized AOD slag based cement along with blast furnace granulated slag and Portland clinker. The blended cement thus produced has a 28 days compressive strength in the range of 51.50 MPa to 52.80 MPa at a blast furnace slag replacement ratio of 10% - 20% in Portland slag cement. The recommended ratio of various slags in the portland slag cement thus produced include the atomized AOD slag based cement, granulated blast furnace slag and Portland clinker in a mass ratio not more than 13.75 : 41.25 : 45.