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 method of preparation of composite clinker.
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 method of preparation of a composite clinker. More particularly, the present invention relates to a method of preparing a composite clinker that has 20% to 45% of belite content and shows an increased compressive strength in the cement made out of it.
BACKGROUND OF THE INVENTION
[002] Compressive strength of cement is defined as the resistance of failure under the action of compressive forces. In other words, it refers to the capacity of the structure made out of such cement to withstand load. Compressive strength of hardened cement is the most important parameter to determine the performance of the cement. Various mineralogical phases in cement contribute to the strength of the cement for instance the alite phase, which is the most reactive cement mineral, contributes significantly to early strength (1-day strength), aluminate phase (C3A) is known for its rapid hardening property and the belite phase contributes to the late strength (28 days’ strength). A balance is therefore required between the main clinker minerals, particularly alite, belite and aluminate phase.
[003] Compressive strength of cement can vary depending on a variety of factors, variation in the clinker being one of them. Cement manufacturers face the variation in clinker raw material owing to the geological distribution in the limestone mine. This sometime leads to inconsistent one day as well as ultimate strength of the resulting cement. However, this inconsistency is not accepted in the market place. Typical variation in 1-day strength is in the range of 12±0.5 MPa while that of 28-day strength is 48±0.5 MPa. Current practice to resolve this problem is by employing expensive grinding aids for performance enhancement.

There is a need to enhance 28-day strength by up to 4±0.5 MPa without using expensive grinding aids.
[004] Therefore, there is a need for composite clinker that shows enhanced compressive strength along with a simple method of its preparation that solves some of the problems present in the prior art.
SUMMARY OF THE INVENTION
[005] According to an embodiment of the present invention, there is provided a method of preparing composite clinker having 20% - 45% of belite content, comprising the steps of preparing belite rich clinker using limestone having 4% - 8% alumina and 14% - 20% silica content; preparing portland clinker having 15% - 25% belite content; and blending 1%-15% of belite rich clinker with the portland clinker to obtain the composite clinker.
[006] According to an embodiment of the present invention, there is provided a composite clinker having 20% - 45% of belite content comprising 1% - 15% of belite rich clinker having 4% - 8% alumina and 14% - 20% silica content and portland clinker having up to 15% - 25% of belite content.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[007] According to an embodiment of the present invention there is provided a method of preparing a composite clinker that has 20% to 45% of belite content and shows a high compressive strength in the cement made out of it. According to the present invention, the method comprises the steps of preparing belite rich clinker using limestone having 4% - 8% alumina and 14% - 20% silica content; preparing portland clinker having 15% - 25% belite

content; and blending 1% -15% of belite rich clinker with the portland clinker to obtain the composite clinker.
[008] In an embodiment, rejected limestone having 30% - 50% calcium content 4% - 12% alumina and 14% - 22% silica content is used in making the belite rich clinker.
[009] In another embodiment, the composite clinker is further grinded with gypsum to make ordinary portland cement (OPC) that shows an increased late strength (28 days’ strength) as well as a slightly increased early strength thereby showing an increase in overall compressive strength by 4+/- 0.5 MPa.
[010] In an embodiment, the composite clinker is further grinded with gypsum and other supplementary cementitious material to make portland pozzolana cement (PPC) that shows an increased late strength (28 days’ strength) as well as a slightly increased early strength thereby showing an increased in overall compressive strength by 4+/- 0.5 MPa.
[011] In an embodiment, the cement prepared from the composite clinker has a compressive strength of 53 MPa.
[012] In an embodiment, the present invention provides a composite clinker having 20% -45% of belite content comprising 1% -15% of belite rich clinker having 3% - 12 % alumina and 15% - 25% silica content and portland clinker having 15% - 25% of belite content.
[013] In an embodiment, the present invention depicts a synergistic effect by using rejected limestone, which has a low calcium content, to synthesize belite rich clinker that is added to portland clinker, in pre-determined quantity, in order to make composite clinker. The composite clinker is prepared such that the overall compressive strength is increased by 4+/-0.5 MPa. In case of a normal portland clinker, it is not possible to get high concentration of

desire clinker phases (C3S, C2S and C3A phases) due to formation of significant quantity of unwanted C4AF phase that has no contribution to cement strength. However, separate synthesis of belite rich clinker by using rejected limestone that is rich in C2S and C3A phases and optimum blending of such belite rich clinker with normal portland clinker enhances the compressive strength of OPC and PPC by the combined effect of enriched C2S and C3A phases in the composite clinker.
[014] In an embodiment, the composite clinker is used to prepare OPC and/or PPC cement without the use of any expensive grinding aid that results in reduced cost of the cement.
[015] Advantages and benefits of composite clinker, 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:
[016] A comparative study of phase analysis of three types of clinker was carried out where normal portland clinker, belite rich clinker (using standard quality limestone) and belite rich clinker (using rejected limestone) were taken. The belite rich clinker was synthesized using rejected limestone at different temperatures and it was observed that the Belite (C2S) and aluminate phase (C3A) phase were comparatively high at 1350°C. The results were compared and the same are provided in the tables below.
Table 1: Phase Analysis of normal portland clinker:

Clinkerization temp. Hatrurite (C3S) Larnite (C2S) Brownmillerite (C4AF) Ca
Aluminate
(C3A) Free Lime
1450°C 56.63 21.85 17.68 2.32 1.52

Table 2: Phase Analysis of Belite rich Clinker (using standard quality limestone):

Clinkerization temp. Hatrurite (C3S) Larnite (C2S) Brownmillerite (C4AF) Ca
Aluminate
(C3A) Free Lime
1350°C 37.37 44.78 11.73 3.20 2.99
Table 3: Phase Analysis of Belite rich Clinker (using rejected limestone):

Clinkerization temp. Hatrurite (C3S) Larnite (C2S) Brownmillerite (C4AF) Ca
Aluminate
(C3A) Free Lime
1350°C 5.14 66.13 8.54 18.59 1.60
[017] It was observed that a general purpose clinker has a high alite phase but a low belite phase resulting in a high early strength but a low late strength (28 days’ strength) of the cement made out of it. It was also observed that if belite rich clinker is synthesized using rejected limestone, then the belite phase of such clinker is higher than a belite rich clinker synthesized using standard quality limestone and therefore the compressive strength of belite rich clinker using rejected limestone will be higher.
Example 2:
[018] The chemical analysis of rejected limestone was carried out to study the various chemicals present in it. It was observed that the as the calcium level is low and SiO2 is high in rejected limestone, it helped in achieving the desired belite phase.
Table 4: Chemical Analysis of rejected limestone used for the synthesis of belite rich clinker

SiO2 Al2O3 Fe2O3 CaO MgO K2O 1.01 Na2O SO3
0.01 TiO2 P2O5 LOI 35.7 LSF 69 SM 2.19 AM 2.66
16.35 5.43 2.04 37.05 1.60
0.50
0.26 0.01

[019] Additionally, the chemical phase analysis of normal portland clinker, belite rich clinker
(prepared by using rejected limestone) and composite clinker were carried out. The table
below illustrates the results.
Table 5: Chemical analysis of normal portland clinker, belite rich clinker and composite clinker

Comp Normal Portland Clinker Belite Rich Clinker Composite clinker
with 99% normal
portland clinker
and 1% belite rich
clinker Composite clinker with 85% normal portland clinker and 15% belite rich clinker
SiO2 20.88 25.43 20.93 21.56
Al2O3 5.38 8.44 5.41 5.84
Fe2O3 3.92 3.17 3.91 3.81
CaO 63.78 57.62 63.72 62.86
MgO 1.86 2.49 1.87 1.95
K2O 1.27 1.57 1.27 1.32
Na2O 0.48 0.78 0.48 0.53
SO3 1.72 0.02 1.70 1.47
Total 99.29 99.52 99.29 99.33
[020] It was observed that as the content of SiO2 and Al2O3 is higher and CaO is lower, the C2S and C3S phases are also higher in composite clinker compare to normal clinker.
Example 3:
[021] The phase analysis of composite clinker was carried out by changing the quantity of belite rich clinker blended with the normal portland clinker and it was found to exhibit the following percentage of phases contributing to compressive strength.
Table 6: Phase Analysis of composite clinker:

Percentage of Belite rich clinker Percentage of normal portland clinker Hatrurite (C3S) Larnite (C2S) Brownmillerite (C4AF) Ca
Aluminate
(C3A) Free Lime
0.50 99.5 56.38 22.09 17.64 2.41 1.52

1.50 98.5 55.89 22.57 17.55 2.58 1.53
15.00 85 49.25 29.10 16.39 4.93 1.64
[022] It was observed that C2S and C3A phase are high in composite clinker and these two phases are increasing with increase in the blending percentage of belite rich clinker. However, optimum blending of these belite rich clinker with normal clinker leads to the enhancement of later compressive strength as well as early compressive strength in both OPC and PPC.
Example 4:
[023] The composite clinker was further grinded with gypsum to make ordinary portland cement that showed an increased compressive strength by up to 4±0.5 MPa than cement prepared by using portland clinker. Further, the composite clinker was grinded with gypsum and supplementary cementitious material to prepare pozzolanic portland cement that also showed an increased compressive strength by up to 4±0.5 MPa than cement prepared by using portland clinker. In both the cements prepared by using composite clinker, there was no need to use an expensive grinding aid.
Tables 7: Compressive strength of PPC synthesized by normal portland clinker and composite clinker:

Compressive Strength Test Result of PPC Cement
Normal Portland Clinker Composite Clinker
Strength (Mpa) 1D 28D 1D 28D
Average 12.80 48.81 12.99 53.10

Tables 8: Compressive strength of OPC synthesized by normal portland clinker and composite clinker:

Compressive Strength Test Result of OPC Cement
Normal Portland Clinker Composite Clinker
Strength (Mpa) 1D 28D 1D 28D
Average 13.11 48.91 13.17 53.24
[024] 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 method of preparing composite clinker having 20% - 45% of belite content,
comprising the steps of:
a) preparing belite rich clinker using limestone having 4% - 8% alumina and 14% -20% silica content;
b) preparing portland clinker having 15% - 25% belite content; and
c) blending 1-15% of belite rich clinker with the portland clinker to obtain the composite clinker.

2. The method as claimed in claim 1, wherein rejected limestone having 30% - 50% calcium content, 4% - 12% alumina and 14% - 22% silica content is used.
3. The method as claimed in claim 1, wherein the composite clinker is further grinded with gypsum to make ordinary portland cement showing an increased compressive strength by 4+/- 0.5 MPa.
4. The method as claimed in claim 1, wherein the composite clinker is further grinded with gypsum and other supplementary cementitious material to make portland pozzolana cement showing an increased compressive strength by 4+/- 0.5 MPa.
5. A composite clinker having 20% -45% of belite content comprising 1% -15% of belite rich clinker having 4% - 8% alumina and 14% - 20% silica content and portland clinker having up to 15% - 25% of belite content.

6. A cement prepared from the composite clinker of claim 5 wherein the cement has a compressive strength of 53 MPa.
Dated this 26th day of March, 2019