Claims:We Claim:

1. A monolithic castable comprising:
a. about 50 to 90% by weight of size graded aggregate selected from process waste of the primary, secondary steelmaking slags and mixtures thereof,
b. about 0% to 20% by weight alumina based fines,
c. about 0% to 20% by weight calcium aluminate cement,
said castable being usable below 7000C and which is settable with less water in the range of 5-20% preferably 8-15% .

2. A monolithic castable as claimed in claim 1 having a bulk density of about 2.3-2.6 g/cc after oven drying at 1100C for 24 hours and a cold crushing strength of about 175-350 kg/cm2.
3. A monolithic castable as claimed in anyone of claims 1 or 2 , the primary, secondary steelmaking slags or mixtures are selected from the group consisting of air dried and/or steam aged BOF slag, EAF slag and ladle slag and wherein the compositions sets on addition of water.
4. A monolithic castable as claimed in anyone of claims 1 to 3 wherein the aggregate includes steelmaking slag containing free lime less than 1 wt%.
5. A monolithic castable as claimed in anyone of claims 1 to 4 , wherein said alumina based fines is selected from the group consisting of bauxite, white tabular alumina, brown fused alumina and white fused alumina and the alumina based powder has a size of – 200 mesh.
6. A monolithic castable as claimed in anyone of claims 1 to 5, wherein the castable has a size analysis of about 1 - 10 % of -5+4 mm, about 25 - 36 % of -4 +2 mm, about 12 - 21 % of -2+1 mm, about 12-26 % of -1+0.05 mm and about 25- 38 % of -0.05 mm and the said castable being usable below 7000C.
7. A monolithic castable as claimed in anyone of claims 1 to 6 , wherein the permanent linear expansion of the material is less than 1.5% to avoid cracking on heating.
8. A monolithic castable as claimed in anyone of claims 1 to 7 comprising an installable lining.
9. A monolithic castable as claimed in anyone of claims 1 to 8 wherein the distribution coefficient (q) of grains is between 0.26 to 0.29.
10. A monolithic castable as claimed in anyone of claims 1 to 9 wherein said slag comprises of :

Slag CaO SiO2 MgO Al2O3 FeO P2O5 MnO
Primary steelmaking 35-45 11-15 5-9 1.5-14 23-28 0.5-1.2 1-2
Secondary steelmaking 50-53 10-12 6-8 20-22 3-4 <0.5 2-3

11. A monolithic castable as claimed in anyone of claims 1 to 10 having physical and chemical indicators including:
compressive strength: 175 to 350 kg/cm2;
bulk density: 2.3 to 2.6 g/cc;
apparent porosity: 15 to 21%; and
permanent linear change on heating (8000C/3h) in the range of -1 to +1.5%

12. A process for manufacture of a monolithic castable comprising:
a) providing a castable composition comprising:
about 50 to 90% by weight of size graded aggregate selected from process waste of the primary, secondary steelmaking slags and mixtures thereof,
about 0% to 20% by weight alumina based fines,
about 0% to 20% by weight calcium aluminate cement,
b) mixing the composition with water 5-20% preferably 8-15 % to thereby obtain the castable therefrom.

13. A process as claimed in claim 12 comprising providing installable lining involving said composition and following technique selected from trowelling, casting, rodding, cast-vibrating with the use of forms, followed by setting and drying.

14. A process as claimed in anyone of claims 12 or 13 comprising: mixing the castable composition according to any one of claims 1-7 with water, forming the mixture into an article, allowing the article to set, drying the article to remove excess water, and optionally firing the article.

Dated this the 12th day of October, 2016
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

, Description:FIELD OF THE INVENTION
The present invention relates to providing monolithic castables using process waste for low temperature applications. More particularly, the present invention is directed to provide a low cost castable composition using selective mix of process wastes comprising steel making slags 50 - 90% by wt, alumina based fine aggregate up to 20% by wt and calcium-aluminate cement binder up to 20% by wt, wherein the distribution coefficient (q) of grains is between 0.26 to 0.29 and can be used up to 7000C. The process requires maintaining moisture content sufficient to achieve the green mix for casting by trowelling, rodding or cast-vibrating with the use of formers. The product (castable) can be used up to a temperature of 7000C in areas not experiencing direct contact with molten metal or slag, hot corrosive gases and mechanical abrasion.

BACKGROUND OF THE INVENTION
Castables are monolithic refractories comprising of coarse and fine aggregates of refractory material and a binder consisting of calcium-aluminate cement and/or hydratable alumina and/or colloidal silica. Castables are mixed with water and then installed either by trowelling, pouring or pumping followed by setting and drying prior to firing. Placement of the material then requires vibration. Green strength of the material is achieved by the binder whereas volatilization or transformation of the binder facilitates the ceramic bond formation at high temperature.

A considerable amount of work has been done in the art to improve the properties of refractory castables. For example, much work has been done to lower the water content required for casting calcium aluminate cement bonded high alumina and fireclay refractory castables in order to achieve higher density and lower porosity for improved performance of the refractory castables.

Various changes in the industry have caused a shift to the use of reclaimed refractory materials for the production of mainly monolithic refractory materials. Global demand for refractories, increase in the cost of raw materials and freight, depletion of natural raw material resources, and environmental pressures have compelled the manufacturers to explore alternative resources for refractory raw materials. Refractory grog i.e. used refractory bricks and monolithics are based on various refractory raw materials and are used in different application areas in the industry. However, developing a monolithic castable using slag is an area yet to be explored.

Additionally, generation of huge quantity of metallurgical industry wastes has posed a major challenge in terms of environmental compliance. Millions of tones of steelmaking slags are generated annually as a process by-product. It is a mixture of oxides of silicon, calcium, magnesium, aluminum and iron and classified as non-hazardous waste. The target in front of the current industries is to recycle and utilize all their by-products, so as to close the sustainable production loop.

Steelmaking slag has been found to be heavier with higher hardness and density, thereby suitable for road and building applications. [1) D.W. Lewis, Properties and Uses of Iron and Steel Slags, National Slag Association, Symposium on Slag National Institute for Transport and Road Research, South Africa, 1982, MF-182-6. 2) H. Motz; J. Geiseler, Products of Steel Slag an Opportunity to Save Natural Resources, Waste Management 21 (2001) 285-293. 3) P. Chaurand; J. Rose; V. Briois; L. Olivi; J-L. Hazemann; O. Proux; J. Domas; J-Y. Bottero, Environmental Impacts of Steel Slag Reused in Road Construction, Journal of Hazardous Materials B139 (2007) 537-542. 4) S. Wu; Y. Xue; Q. Ye; Y. Chen, Utilization of Steel Slag as Aggregates for Stone Mastic Asphalt Mixtures, Building and Environment 42 (2007) 2580-2585.] EAF slag is a hard and dense material, and has lesser amount of free lime compared to converter slag, and hence is considered as an appropriate aggregate in many applications.

Slag is a byproduct of metal extraction process consisting of inorganic oxides (mainly the compounds of silica, calcia, alumina, magnesia and/or iron oxides) and is a suitable alternative material of natural aggregates for road and building construction to avoid the environmental impact of fast depleting natural resources.

In spite of the increasing use of slag in road and building construction, there exists a huge scope of its usage in refractory industries for developing new products for different applications. Some prior works in the related field are summarized below:

US Patent No. 6,491,751 dated 10th Dec 2002 (Texas Industries, Inc.) by Robert C. Watson describes a method wherein finely ground steelmaking slag in combination with other raw materials was used for manufacturing cement. The ingredients were preferably ground to a fine, dry powder and mixed uniformly followed by heating in the kiln.

Chinese Patent No. 104478448, dated 1st April 2015 provides a blast furnace slag runner castable prepared from ferrotitanium slag, composed of different size fractions of ferrotitanium slag, brown fused alumina, silicon carbide, bauxite powder, calcium aluminate cement, alumina micro-powder, silicon dioxide micro-powder, pelleted pitch and metallic silicon powder to enhance the resource utilization ratio of the ferrotitanium slag and erosion resistance and life of the runner.
Indian Patent Application No. 193/KOL/2014, 17th Feb 2014 relates to an improved process for the production of refractory bricks using ferrochrome slag of size fraction 0-5 mm, dextrin, molasses and water in a mechanical mixer for homogenous mixing for batch preparation; pressing the mixture at a pressure ranging between 1500 to 2200 kg/cm2 in brick shape by known means, drying at temperature ranging between 100 to 140 °C to remove the moisture and firing the dried bricks at a temperature ranging between 1220 to 1350 °C.

Indian Patent Application No. 1423/KOL/2009, 7th Dec 2009 relates to the composition and method of manufacturing of an environmental friendly fire clay refractory brick especially adapted for the use in general purpose refractory applications having 25-40% alumina (Al2O3) content as a replacement of IS:6, IS:8 fire clay refractory bricks. The composition comprises of (i) 60-70 wt% coal fly ash as the main matrix, (ii) blast furnace granulated slag as the groging agent, (iii) recycled fire clay grog and (iv) up to 30 wt% fresh plastic and non plastic/fresh clay (fire clays) where all the components are mixed with 4 to 6 wt% water.

Chinese Patent No. 102731113 A, dated 17th Oct 2012 (Hunan Xinhua) by Guo Rui ball relates to a silicon-magnesium fireproof wear-resistant composite castable, which is prepared from 30-90 wt% of ferrochromium slag, 5-20 wt% cast stone powder, 5-20 wt% china clay, 5-20 wt% agglomerate, 2-15 wt% sodium silicate, and 2-15 wt% water for application in the medium and low-temperature positions of the kiln.

Chinese Patent No. 103396135, 20th Nov 2013 discloses the preparation and application method of a water based castable for a grid wall of a casting residue basin that is composed of 65-85 wt% of steel slag, 3-10 wt% of silica fume and 10-30 wt% of ordinary cement binder. The castable provided by the invention is low in cost and high temperature resistant, cannot burst, and can be widely used in various grid walls of casting residue basins.

Pattem Hemanth Kumar et al (Journal of Asian Ceramic Societies, Vol 2 [4], 2014, pp 371–379) reported a new class of conventional and low-cement castable based on ferrochrome slag 40 wt.% ferrochrome slag, 45 wt.% calcined bauxite and rest fraction varying between high alumina cement (HAC) acting as hydraulic binder and calcined alumina as pore filling additive. The samples were heated at different temperatures up to 13000C and evaluated in terms of their microstructural properties, phases present, crushing and bending strengths, and permanent linear changes.

The present invention, in particular, differs from the prior art by way of developing a process for utilizing the process waste (electric arc furnace slag) to produce the refractory castable for low temperature applications. Recycling of process waste addresses the usage of process waste for developing a low cost product as well as the environmental concerns.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to provide monolithic castables using steel making process waste for low temperature applications and a process for its production.

A further object of the present invention is directed to provide monolithic castables which is low cost refractory castable for low temperature applications utilizing steel making slag in large proportions.

A still further object of the present invention is directed to provide monolithic castables using process waste which would be suitable for application up to a temperature of 7000C in areas not experiencing direct contact with molten metal or slag, hot corrosive gases and mechanical abrasion.

Another object of the present invention is directed to provide monolithic castables using steel making process waste in order to recycle and utilize steel plant by-products, so as to close the sustainable production loop.

Yet another object of the present invention is directed to provide monolithic castables using process waste wherein castable composition comprising selective mix of process waste (steel making slags 50 - 90% by wt), alumina based fine aggregate up to 20% by wt and calcium-aluminate cement binder up to 20% by wt, and the castable composition sets on addition of water (8-15%) and an applicable castable layer is obtained by mixing the castable composition with 5 to 20 % water by weight.

A further object of the present invention is directed to provide monolithic castables using steel plant process waste which can be used for manufacturing of pre-shaped articles, in whole or part; for example, bricks and blocks.

A still further object of the present invention is directed to provide monolithic castables using process waste e.g. steel making slag wherein the set and dried castable articles with optional firing meet the property requirements e.g. CCS, bulk density, porosity or permanent linear change on heating to suit the intended application.

A still further object of the present invention is directed to provide monolithic castables using process waste including steel making slag comprising the primary, secondary steel making slags or mixtures thereof are selected from the group consisting of air dried and/or steam aged BOF slag, EAF slag and ladle slag.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to provide a monolithic castable comprising:
a. about 50 to 90% by weight of size graded aggregate selected from process waste of the primary, secondary steelmaking slags and mixtures thereof,
b. about 0% to 20% by weight alumina based fines,
c. about 0% to 20% by weight calcium aluminate cement,
said castable being usable below 7000C and which is settable with less water in the range of 5-20% preferably 8-15%.

A further aspect of the present invention is directed to a monolithic castable having a bulk density of about 2.3-2.6 g/cc after oven drying at 1100C for 24 hours and a cold crushing strength of about 175-350 kg/cm2.

A still further aspect of the present invention is directed to a monolithic castable wherein the primary, secondary steelmaking slags or mixtures are selected from the group consisting of air dried and/or steam aged BOF slag, EAF slag and ladle slag and wherein the compositions sets on addition of water.

Another aspect of the present invention is directed to said monolithic castable wherein the aggregate includes steelmaking slag containing free lime less than 1 wt%.

A still further aspect of the present invention is directed to a monolithic castable wherein said alumina based fines is selected from the group consisting of bauxite, white tabular alumina, brown fused alumina and white fused alumina and the alumina based powder has a size of – 200 mesh.

Another aspect of the present invention is directed to a monolithic castable wherein the castable has a size analysis of about 1 - 10 % of -5+4 mm, about 25 - 36 % of -4 +2 mm, about 12 - 21 % of -2+1 mm, about 12-26 % of -1+0.05 mm and about 25- 38 % of -0.05 mm and the said castable being usable below 7000C.

Yet another aspect of the present invention is directed to a monolithic castable wherein the permanent linear expansion of the material is less than 1.5% to avoid cracking on heating.

According to a further aspect of the present invention said monolithic castable comprising an installable lining.

A further aspect of the present invention is directed to a monolithic castable wherein the distribution coefficient (q) of grains is between 0.26 to 0.29 so that it can be used as trowelling or vibro casting.

A still further aspect of the present invention is directed to a monolithic castable wherein said slag comprises of:
Slag CaO SiO2 MgO Al2O3 FeO P2O5 MnO
Primary steelmaking 35-45 11-15 5-9 1.5-14 23-28 0.5-1.2 1-2
Secondary steelmaking 50-53 10-12 6-8 20-22 3-4 <0.5 2-3

A still further aspect of the present invention is directed to a monolithic castable having physical and chemical indicators including:
compressive strength: 175 to 350 kg/cm2;
bulk density: 2.3 to 2.6 g/cc;
apparent porosity: 15 to 21%; and
permanent linear change on heating (8000C/3h): -1 to +1.5%

Yet another aspect of the present invention is directed to a process for manufacture of a monolithic castable comprising:
a) providing a castable composition comprising:
about 50 to 90% by weight of size graded aggregate selected from process waste of the primary, secondary steelmaking slags and mixtures thereof,
about 0% to 20% by weight alumina based fines,
about 0% to 20% by weight calcium aluminate cement,
b) mixing the composition with water 5-20% preferably 8-15 % to thereby obtain the castable therefrom.

A further aspect of the present invention is directed to said process comprising providing installable lining involving said composition and following technique selected from trowelling, casting, rodding, cast-vibrating with the use of forms, followed by setting and drying.

A still further aspect of the present invention is directed to said process comprising: mixing the castable composition according to any one of claims 1-7 with water, forming the mixture into an article, allowing the article to set, drying the article to remove excess water, and optionally firing the article.

The above and other objects and advantages of the present invention are described hereunder in greater details with reference to following accompanying figures and examples.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE

Figure 1: show the Castable blocks produced according to the invention after heating at 1100C and 8000C and their stickability test.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURE AND EXAMPLES

The present invention is directed to provide monolithic castables using steel making process waste for low temperature applications such as a low cost castable composition using selective mix of process wastes comprising steel making slags 50 - 90% by wt, alumina based fine aggregate up to 20% by wt and calcium-aluminate cement binder up to 20% by wt, wherein the distribution coefficient (q) of grains is between 0.26 to 0.29 and can be used up to 7000C. The product (castable) can be used up to a temperature of 7000C in areas not experiencing direct contact with molten metal or slag, hot corrosive gases, and mechanical abrasion.

The castable composition is produced involving steelmaking slags 50 - 90% by wt, alumina based fine aggregate up to 20% by wt, and calcium-aluminate cement binder up to 20% by wt. The castable composition is formable into a joint-less or unshaped product upon addition of water, setting and drying to remove excess water. In the castable composition comprising said steel making slag wherein about 50-90 % by weight of size-graded primary steelmaking slag, secondary steelmaking slag, or mixtures thereof are used, based on the total dry weight of the castable composition. The best result was obtained with castable composition of 70-80 % EAF slag by weight.

During development of the castable composition following stages were traversed to reach the desired composition and properties.

During development of the castable, initially, 20% steel ladle slag was used in the castable batch. In the process of castable preparation, an excessive heat generation was observed and the prepared castable was found to exhibit rapid setting (less setting time) during moulding. In order to overcome these issues, the steel ladle slag was reduced in steps from 20% to 15% and 10% with addition of more water resulting in reduced heat generation and relatively more setting time. However, the porosity and high temperature strength were found to be affected.

Subsequently, in further trials, the steel ladle slag was completely eliminated and calcium aluminate cement was used up to 20% during batch preparation. The heat generation and early setting issues were resolved.

Use of steam aged BOF slag exhibited higher expansion in the castable upon heat treatment at temperatures 8000, 10000 and 1200 0C which can be attributed to formation of hydroxides of CaO and MgO and generation of stress leading to cracking of castable. To overcome the expansion, the BOF slag grains were treated prior to batch preparation by heating at a temperature of 6000C followed by normal cooling. This treated BOF slag grains were used as the aggregate in the castable recipe. This helped in reduced expansion of the castable upon heating. However, the castable was still found to exhibit > 0.8% expansion upon heating.

In order to achieve the desired properties in the final castable, EAF slag characteristics were studied and found to be suitable ingredient for castable production. Lower amount of free lime and absence of free MgO in EAF slag helped in achieving the required properties.

The primary steelmaking slag, secondary steelmaking slag, or mixtures thereof may comprise a material selected from weathered or steam aged BOF slag, EAF slag, ladle slag having a free lime content < 1% by weight.

Thus according to the present invention the castable composition comprises of;
a) 50 to 90% by weight of slags of primary steelmaking process, secondary steelmaking process or their mixtures. Chemical analyses and phases of the slags are shown in Table 1 and Table 2 respectively,
b) 0 to 20% by weight alumina based fines,
c) 0 to 20% by weight calcium aluminate cement binder,
d) wherein the said castable being usable below 7000C (as shown in Table 3),
e) wherein the said castable contains alumina based fines of -200 mesh size,
f) wherein the castable composition sets on addition of water (8-15%).

Table 1: Chemical Analysis of Slags, %
Slag CaO SiO2 MgO Al2O3 FeO P2O5 MnO
Primary steelmaking 35-45 11-15 5-9 1.5-14 23-28 0.5-1.2 1-2
Secondary steelmaking 50-53 10-12 6-8 20-22 3-4 <0.5 2-3

Table 2: Phases present in slags
Slag Phases
Primary steelmaking Calcium-alumino ferrite, Calcium ferrite, Wustite, Calcium silicates, Gehlinite
Secondary steelmaking Calcium aluminate, Calcium silicates, Free lime

Table 3: Free Lime and Melting range of Slags
Slag Free Lime (wt%) Melting Range (0C)
Primary steelmaking < 1 1330-1370
Secondary steelmaking 3-5 1300-1320

The primary steelmaking slag, secondary steelmaking slag, or mixtures thereof may comprise of particles up to about 10 mm in size as determined by an appropriately sized sieve. The composition also includes about 0 to 20% by weight alumina based fines which may comprise a material selected from brown fused alumina, sintered alumina, white fused alumina, calcined alumina, reactive or semi-reactive alumina, and bauxite having a size of -200 mesh. The composition also includes about 0 to 20% by weight calcium aluminate cement. Such cements are available commercially. Generally, the cement is used in a size that passes a 100 mesh with over 50% of it being finer than 200 mesh.

The castable composition sets upon addition of an appropriate amount of 8-15% water. The appropriate amount of water will vary depending on the precise composition of the castable, its intended use and the method by which it is installed.

The castable has size analysis of about 1 - 10 % of -5+4 mm, about 25 - 36 % of -4 +2 mm, about 12 - 21 % of -2+1 mm, about 12-26 % of -1+0.05 mm and about 25- 38 % of -0.05 mm.

In accordance with an aspect of the present invention, the same is directed to a method of installing the lining using a technique selected from trowelling, casting, rodding, cast-vibrating, followed by setting and drying. These techniques are well known to persons of ordinary skill in the art.

In accordance with another aspect, the present invention is directed to a method of installing the castable by mixing the castable composition with water in proportion as stated above, forming the mixture into an article, allowing the article to set, drying the article to remove excess water, and optionally firing the article at an elevated temperature, as described above.

The castable composition and the method of producing the same according to the present invention are described in further details with the help of following specific embodiments:

Example 1 : A castable composition comprising of 70% primary steelmaking slag, 20% secondary steelmaking slag, 10% alumina based fines and devoid of calcium aluminate cement, and having grain size in the range of 0-4 mm.
A method for the preparation of the castable composition, comprising the steps of dry mixing of the ingredients for 2 minutes followed by addition of 10.75% water and mixing for 3 minutes. The physical and chemical indicators: compressive strength (110°C/24h) 351 kg/cm2, compressive strength (800°C/3h) 138 kg/cm2; bulk density (110°C/24h) 2.51 g/cm3, bulk density (8000C/3h) 2.35 g/cm3, apparent porosity (110°C/24h) 20.2%, apparent porosity (8000C/3h) 22.3%, permanent linear change on heating (8000C/3h) was +2.04%.

Example 2 : A castable composition comprising of 75% primary steelmaking slag, 5% secondary steelmaking slag, 10% alumina based fines, 10% calcium aluminate cement, and having grain size in the range of 0-5 mm.
A method for the preparation of the castable composition, comprising the steps of dry mixing of the ingredients for 2 minutes followed by addition of 9.75% water and mixing for 3 minutes. The physical and chemical indicators: compressive strength (110°C/24h) 364 kg/cm2, compressive strength (800°C/3h) 153 kg/cm2; bulk density (110°C/24h) 2.59 g/cm3, bulk density (8000C/3h) 2.48 g/cm3, apparent porosity (110°C/24h) 19.2%, apparent porosity (8000C/3h) 21%, permanent linear change on heating (8000C/3h) was +1.61%.

Example 3 : A castable composition comprising of 70% primary steelmaking slag, 10% alumina based fines, 20% calcium aluminate cement and devoid of secondary steelmaking slag, and having grain size in the range of 0-5mm.
A method for the preparation of the castable composition, comprising the steps of dry mixing of the ingredients for 2 minutes followed by addition of 9.75% water and mixing for 3 minutes. The physical and chemical indicators: compressive strength (110°C/24h) 352 kg/cm2, compressive strength (800°C/3h) 149 kg/cm2; bulk density (110°C/24h) 2.55 g/cm3, bulk density (8000C/3h) 2.4 g/cm3, apparent porosity (110°C/24h) 17.2%, apparent porosity (8000C/3h) 19.1%, permanent linear change on heating (8000C/3h) was +1.58%.

Example 4 : A castable composition comprising of 72% primary steelmaking slag, 10% alumina based fines, 18% calcium aluminate cement and having grain size in the range of 0-4.75mm.
A method for the preparation of the castable composition, comprising the steps of dry mixing of the ingredients for 2 minutes followed by addition of 10% water and mixing for 3 minutes. The physical and chemical indicators: compressive strength (110°C/24h) 363 kg/cm2, compressive strength (800°C/3h) 155 kg/cm2; bulk density (110°C/24h) 2.61 g/cm3, bulk density (8000C/3h) 2.45 g/cm3, apparent porosity (110°C/24h) 17.9%, apparent porosity (8000C/3h) 19.4%, permanent linear change on heating (8000C/3h) was +0.78%.

Example 5 : A castable composition comprising of 75% primary steelmaking slag, 10% alumina based fines, 15% calcium aluminate cement and devoid of secondary steelmaking slag, and having grain size in the range of 0-4.75mm.

A method for the preparation of the castable composition, comprising the steps of dry mixing of the ingredients for 2 minutes followed by addition of 9.25% water and mixing for 3 minutes. The physical and chemical indicators: compressive strength (110°C/24h) 382 kg/cm2, compressive strength (800°C/3h) 168 kg/cm2; bulk density (110°C/24h) 2.63 g/cm3, bulk density (8000C/3h) 2.52 g/cm3, apparent porosity (110°C/24h) 18.2%, apparent porosity (8000C/3h) 20.1%, permanent linear change on heating (8000C/3h) was +0.55%.

Compressive strength of the castable at 1100C is achieved by the cement added. Secondary steelmaking slag, which is a Calcium-Alumino-Silicate based one, also exhibits some cementitious properties when added with water. It would be evident from the above results that the castables of the invention have significantly improved physical properties and strength for non-critical applications.

Typical properties of the developed castable are shown in Table 4.

Table 4: Typical properties of developed castable
Parameter Developed Castable
Casting water (%) 9.25
Bulk Density (g/cc) at 1100C 2.67
Apparent Porosity (%) at 1100C 19
CCS (kg/cm2) at 1100C 392
CCS (kg/cm2) at 8000C/3h 174
PLC (%) at 8000C/3h + 0.52

Accompanying Figure 1 shows (a) Castable Block using BOF slag after heating at 8000C / 3h, (b) Castable Block using EAF slag after oven drying at 1100C / 24h, (c) Castable Block using EAF slag after heating at 8000C / 3h and (d) result of stickability property test of castable composition.

As such no standard testing methodology exists or is in practice to assess the sticking property of a castable by conventional manual trowelling. The gross estimation of sticking of castable may be representated in the form of rebound loss. Let us assume that W2 quantity of castable falls during trowelling out of the initial quantity of castable W1. Therefore, the rebound loss may be representated as [(W2/W1)*100]. The lower the rebound loss, the better is the stickability.

It is thus possible by way of the present invention to provide monolithic castables using steel making process waste for low temperature applications such as a low cost castable composition using selective mix of process wastes comprising steel making slags 50 - 90% by wt, alumina based fine aggregate up to 20% by wt and calcium-aluminate cement binder up to 20% by wt, wherein the distribution coefficient (q) of grains is between 0.26 to 0.29 and can be used up to 7000C. The product obtained comprising castable lining installed in situ or pre shaped articles such as bricks or blocks, having a bulk density of about 2.3-2.6 g/cc after oven drying at 1100C for 24 hours, a cold crushing strength of about 175-350 kg/cm2, and permanent linear expansion of less than 1.5%, can be used up to a temperature of 7000C in areas not experiencing direct contact with molten metal or slag, hot corrosive gases and mechanical abrasion.