FORM 2
THE PATENT ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
A composition for sintered lightweight aggregate and a method of preparing the same.
APPLICANTS
Aditya Birla Science and Technology Company Private Limited, Aditya Birla Center, 2nd Floor, ‘C’ wing, S. K. Ahire Marg, Worli, Mumbai- 400025, Maharashtra, India.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes this invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
[001] The present invention relates to a composition for sintered lightweight aggregate used in producing lightweight concrete. The invention also relates to an efficient method for preparing the said lightweight aggregate.
BACKGROUND OF THE INVENTION
[002] Lightweight aggregates have been manufactured by sintering fly ash, red mud and molasses and crushing the product into suitable sizes. These aggregates possess unique characteristics that make them suitable for high-strength and high-performance concrete. Structural-grade lightweight concrete prepared using these lightweight aggregates has an in-place density of 1440 to 1840 kg/m3 compared to normal concrete with a density in the range of 2240 to 2400 kg/m3 implying that structural lightweight concrete is 25% to 35% lighter than normal concrete yet with strength comparable to normal concrete. Drying shrinkage is much less than that of normal weight concrete.
[003] Moreover, the aggregates possess high durability characteristics required in high performance structures. The importance of the lightweight aggregates lies mostly in the fact that superior qualities are achieved without having to increase the cement content.
[004] Structural lightweight concrete is usually made with lightweight aggregate replacing natural coarse aggregate. Lightweight aggregates can either be natural or artificial. Generally used natural aggregates include pumice, scoria, tuff, expanded perlite, expanded vermiculite etc. However, utilization of these aggregates may not yield concrete with the optimum properties.

[005] Structural-grade lightweight aggregates can be either manufactured by pyro-processing method or sintering process. In case of pyro-processing method, raw materials such as suitable shales, clays, slates, fly ashes, blast-furnace slags etc. are used. Pyro-processing method includes a rotary kiln process where raw materials pass through a long, slowly rotating, slightly inclined cylinder lined with refractory materials. In case of sintering process, a bed of raw materials, including fuel, is carried by a traveling grate under an ignition hood followed by the rapid agitation of molten slag with controlled amounts of air or water.
[006] Lightweight aggregates can be produced from a wide variety of raw materials, and their production conditions also vary. Therefore, the characteristics of lightweight aggregates such as particle shape, density, compressive strength, surface texture, and pore structure are often found to vary within wide limits. As most of the pores in the aggregate are open, the aggregate is susceptible to water absorption. The pore sizes are also found to vary considerably. Commercially available aggregates often have low crushing strength and high water absorption (> 10%) and, hence, are unsuitable to produce lightweight concrete with high strength.
[007] Furthermore, the method of preparation of these lightweight aggregates involves the steps of mixing of raw materials, pressing, drying at 100 oC for 24 hours, sintering at a temperature of 1100 oC for 24 hours followed by crushing. This method is not only takes a long time but is also energy consuming.
[008] Therefore, there is a need for lightweight aggregate along with an efficient method of its preparation that solves some of the problems present in the prior art.

SUMMARY OF THE INVENTION
[009] According to an embodiment of the present invention, there is provided a lightweight aggregate composition compromising, by weight of the composition, 60 – 90 % of fly ash; 8 – 30 % of red mud; 0.1 – 10 % of clay; and 0.1 – 1 % of solid carbonaceous material.
[010] According to an embodiment of the present invention, there is provided a method of preparing lightweight aggregate comprising the steps of homogenously mixing, by weight of the composition, 60 – 90 % of fly ash, 8 – 30 % of red mud, 0.1 – 10 % of clay and 0.1 – 1 % of solid carbonaceous material; granulating the mixture into pellets; drying the pellets at 80-100 degrees for 60-70 minutes; and sintering the pellets at 1100-1200 degrees for 5-20 minutes.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[011] According to an embodiment of the present invention there is provided a composition for sintered lightweight aggregate comprising, by weight of the composition, 60 to 90% of fly ash, 8 to 30% of red mud, 0.1 to 10% of clay and 0.1 to 1% of solid carbonaceous material.
[012] According to an embodiment of the present invention, fly ash is present in the range of 80-90 %, by weight of the composition.
[013] According to an embodiment of the present invention, red mud is present in the range of 8-15 %, by weight of the composition.
[014] According to an embodiment of the present invention, clay increases the strength of the aggregate and is present in the range of 0.1-5 %, by weight of the composition.

Preferably, the clay is bentonite. Usage of alternatives of clay are considered to be within the scope of the present invention.
[015] Preferably, the solid carbonaceous material is selected from the group comprising of coal, wood, graphite, carbon foam and a combination thereof. Usage of alternatives of solid carbonaceous material are considered to be within the scope of the present invention. The use of solid carbonaceous material in the composition makes the aggregates porous and harder and, therefore, stronger.
[016] In another preferred embodiment of the present invention, 60 to 90% of fly ash, 8 to 30% of red mud, 0.1 to 10% of clay and 0.1 to 1% of solid carbonaceous material, by weight of the composition, are mixed thoroughly in a blender. The resulting homogenous mixture is then transferred to a granulator for producing pellets of size 5mm to 40mm, preferably 10mm to 15mm. Preferably, the granulator is a pan granulator. Thereafter, the pellets are dried at 80-100 °C for 60-70 minutes and then sintered at 1100 to 1200 °C with a retention time of less than 10 minutes.
[017] According to an embodiment of the present invention, the fly ash is present in the range of 80-90 %, red mud is present in the range of 8-15 %, and clay is present in the range of 0.1-5 %, by weight of the composition.
[018] The lightweight aggregate prepared herein is used to produce structural lightweight concrete with higher strength. In another embodiment the lightweight aggregate prepared is used produce a lightweight concrete with lower densities. The compressive Strength (MPa) of the concrete is in the range of 45-60 MPa. The density is in the range of 1700-1900 Kg/m3. Aggregate produced from the above method was shown to have better strength and

lower water absorption compared to the commercially available aggregates. Also, pelletized aggregate prepared from the above method required significantly less drying time as compared to conventionally prepared brick shaped aggregate and this results in substantial energy savings during production on a commercial scale.
[019] Advantages and benefits of the sintered lightweight aggregates and a method of its preparation thereof, according to the embodiments of the present invention, would become more apparent from the below experimental details to a person skilled in the art.
Example 1:
[020] (Prior art composition) 55-70% of fly ash, 30-45% red mud and 1-5% binder
molasses were mixed thoroughly and pressed. Thereafter, it was dried for 100 °C for 24 hours followed by sintering at 1100 °C for 24 hours. It was finally crushed to provide light weight aggregates.
Separately, 62.3 gms of fly ash, 26.7 gms of red mud, 10 gms of bentonite clay and 1 gm of fine coal powder were mixed thoroughly in a blender and then transferred to a pan granulator for producing pellets of size 10mm to 15mm. Thereafter, the pellets were dried at 100oC for about an hour and then sintered at 1100 to 1200°C for less than 9 minutes. The sintered lightweight aggregate thus obtained was further characterized.
Example 2:
[021] The prior art aggregates and sintered lightweight aggregates of present invention
prepared in Example 1 were characterized and found to exhibit the following properties as shown in the comparative Table 1:

Sr. No. Properties Present invention Prior art composition ISO142 Standard
1. Bulk Density (kg/m3) 780 900 <950
2. Water absorption (%) 8 11 <15
3. Crushing value (%) 39 35-42 <45
4. Impact value (%) 34 35-40 <40
Table 1
[022] Since the present invention uses lightweight material to prepare the aggregate, bulk density is low and also specific gravity is low, which is highly desirable. Further, water absorption is also low. Structurally, the aggregate has a hard, external shell and porous internal structure and, hence, it absorbs less water. Impact value refers to sudden weight bearing capacity, while crushing value refers to static weight bearing capacity. Crushing value and impact value of the aggregate of Example 1 are higher than other known lightweight aggregates due to the physical structure of the aggregate i.e. its external hard shell with internal porous structure. Therefore, it was proved that the properties of the present composition are far superior that those of the prior art composition.
Example 3:
[023] 87 gms of fly ash, 10 gms of red mud, 2 gms of bentonite clay and 1 gm of fine coal
powder were mixed thoroughly in a blender and then transferred to a pan granulator for producing pellets of size 10mm to 15mm. Thereafter, the pellets were dried at 100oC for about an hour and then sintered at 1100 to 1200°C for less than 9 minutes. The sintered lightweight aggregate thus obtained was further used to prepare concrete.

Example 4:
[024] The sintered lightweight aggregate prepared in Example 3 was mixed with cement, manufactured sand and water to prepared concretes with different mix designs and the properties of the concrete were determined at 28 days from preparing the concrete. The concretes designed with 60-65% of aggregates exhibited strengths of 45-60 MPa while the concrete with 45-50% of aggregates resulted in densities of 1700 to 1900 kg/m3. The concrete prepared using the sintered lightweight aggregate of Example 3 clearly shows that the concretes with high strength as well as lower densities can be obtained.

Sr. No. Properties Present invention Prior art composition
1. Compressive strength 48 35
2. Density (kg/m3) <1800 2312
Table 2
[025] The concrete prepared using the sintered lightweight aggregate of Example 3 clearly shows superior quality which is due to its high strength to weight ratio.
[026] The foregoing description of specific embodiments of the present invention has been presented for purposes of description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obvious modifications and variations are possible in light of the above teaching.

We claim:
1. A composition for sintered lightweight aggregate compromising, by weight of the
composition:
- 60 – 90 % of fly ash;
- 8 – 30 % of red mud;
- 0.1 – 10 % of clay; and
- 0.1 – 1 % of solid carbonaceous material.

2. The composition as claimed in claim 1, wherein the fly ash is in the range of 80-90 %, by weight of the composition.
3. The composition as claimed in claim 1, wherein the red mud is in the range of 8-15 %, by weight of the composition.
4. The composition as claimed in claim 1, wherein the clay is in the range of 0.1-5 %, by weight of the composition.
5. The composition as claimed in claim 1, wherein the clay is bentonite.
6. The composition as claimed in claim 1, wherein the solid carbonaceous material is selected form the group comprising of coal, wood, graphite, carbon foam and a combination thereof.
7. A method of preparing lightweight aggregate comprising the steps of:

a) homogenously mixing, by weight of the composition, 60 – 90 % of fly ash, 8 – 30 % of red mud, 0.1 – 10 % of clay and 0.1 – 1 % of solid carbonaceous material;
b) granulating the mixture into pellets;
c) drying the pellets at 80-100 degrees for 60-70 minutes; and
d) sintering the pellets at 1100-1200 degrees for 5-20 minutes.

8. The method as claimed in claim 7, wherein the fly ash is in the range of 80-90%, by weight of the composition.
9. The method as claimed in claim 7, wherein the red mud is in the range of 8-15%, by weight of the composition.
10. The method as claimed in claim 7, wherein the clay is in the range of 0.1-5%, by weight of the composition.
11. The method as claimed in claim 7, wherein the clay is bentonite.
12. The method as claimed in claim 7, wherein the solid carbonaceous material is selected form the group comprising of coal, wood, graphite, carbon foam and a combination thereof.