METHOD FOR MANUFACTURING CEMENT

Abstract

The present invention pertains to a method for manufacturing cement, wherein the gypsum is first calcined separately before being inter-grinded with the clinker so as to minimize the release of water of crystallization of during the inter-grinding stage. The method produces cement of high strength at all ages, better rheology, enables higher use of fly ash, and reduces CO.sub.2 emission during manufacturing.

Claims

1. Method of manufacturing cement, the method comprising: (a) determining or fixing the highest temperature T C. that the working mix is expected to reach inside the mill during inter-grinding gypsum (or a dehydrated form thereof) with clinker; (b) calcining the gypsum at a temperature W C., such that W>=0.9 T; and (c) inter-grinding the pre-calcined gypsum with the clinker inside mill such that the highest temperature of working mix inside the mill does not exceed T C., wherein that the change in water of crystallization of gypsum (or a dehydrated form thereof) during inter-grinding with clinker in step (c) is minimal.

2. Method of manufacturing cement as claimed in claim 1, wherein the gypsum is precalcined at a temperature such that more than 50% of gypsum is dehydrated to hemihydrate form [CaSO.sub.4.H.sub.2O].

3. Method of manufacturing cement as claimed in claim 1, wherein the gypsum is precalcined at a temperature such that more than 80% of gypsum is dehydrated to hemihydrate form [CaSO.sub.4.H.sub.2O].

4. Method of manufacturing cement as claimed in claim 2, wherein W is about 100 C. to about 120 C.

5. Method of manufacturing cement as claimed in claim 2, wherein T is about 110 C.

6. Method of manufacturing cement as claimed in claim 1, wherein the gypsum is precalcined at a temperature such that more than 50% of gypsum is dehydrated to a form of calcium sulphate with water of crystallization less than 0.5 [CaSO4.nH2O, where 0.5>n>0].

7. Method of manufacturing cement as claimed in claim 1, wherein the gypsum is precalcined at a temperature such that more than 80% of gypsum is dehydrated to a form with water of crystallization less than 0.5 [CaSO4.nH2O, where 0.5>n>0].

8. Method of manufacturing cement as claimed in claim 6, wherein W is about 120 C. to about 160 C.

9. Method of manufacturing cement as claimed in claim 6, wherein T is about 140 C.

10. Method of manufacturing cement as clamed in claim 1, wherein the gypsum is precalcined at a temperature such that more than 50% of gypsum is dehydrated to soluble anhydrite form [CaSO4.nH2O, where 0.05>n>=0].

11. Method of manufacturing cement as claimed in claim 1, wherein the gypsum is precalcined at a temperature such that more than 80% of gypsum is dehydrated to soluble anhydrite form [CaSO4.nH2O, where 0.05>n>=0].

12. Method of manufacturing cement as claimed in claim 10, wherein W is about 160 C. to about 200 C.

13. Method of manufacturing cement as claimed in claim 10, wherein T is about 180 C.

14. Method of manufacturing cement as claimed in claim 1, wherein the gypsum is first ground or pulverized to a size of less than about 75 microns, and preferably to a size 25 less than about 45 microns before being calcined.

15. Method of manufacturing cement as claimed in claim 1, wherein the said pre-calcined gypsum is ground or pulverized to a size of less than about 75 microns, and preferably to a size less than about 45 microns before being inter-grinded with the clinker.

16. Method of manufacturing cement as claimed in claim 1, wherein the inter-grinding of pre-calcined gypsum with clinker is carried out in presence of raw materials selected from the group consisting of fly ash, slag, volcanic ash, rice husk ash, meta kaolin, silica fume, and limestone.

17. Method of manufacturing cement as claimed in claim 16, wherein the fly ash is present in an amount which is more than 25% w/w of the total mix, and preferably 35% w/w of the total mix.

Description

DESCRIPTION OF THE DRAWINGS

[0059] The foregoing and other objects of the invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which:

[0060] FIG. 1 is a graphical illustration comparing the compressive strengths of Cement I (OPC 53 G with Gypsum); Cement II (OPC 53 G with Hemihydrate); and Cement III (OPC 53 G with Soluble Anhydrite);

[0061] FIG. 2 is a graphical illustration comparing the normal consistencies of Cement I (OPC 53 G with Gypsum); Cement II (OPC 53 G with Hemihydrate); and Cement III (OPC 53 G with Soluble Anhydrite);

[0062] FIG. 3 is a graphical illustration comparing the initial and final setting time of Cement I (OPC 53 G with Gypsum); Cement II (OPC 53 G with Hemihydrate); and Cement III (OPC 53 G with Soluble Anhydrite);

[0063] FIG. 4 is a graphical illustration comparing the compressive strengths between Cement IV (PPC with Gypsum and 25% Fly Ash); and Cement V (PPC with Hemihydrate and 25% Fly Ash);

[0064] FIG. 5 is a graphical illustration comparing the compressive strengths between Cement VI (PPC with Gypsum and 35% Fly Ash); and Cement VII (PPC with Hemihydrate and 35% Fly Ash);

[0065] FIG. 6 is a graphical illustration comparing the normal consistencies of Cement IV (PPC with Gypsum and 25% Fly Ash); and Cement V (PPC with Hemihydrate and 25% Fly Ash); Cement VI (PPC with Gypsum and 35% Fly Ash); and Cement VII (PPC with Hemihydrate and 35% Fly Ash);

[0066] FIG. 7 is a graphical illustration comparing the initial and final setting time among Cement IV (PPC with Gypsum and 25% Fly Ash); and Cement V (PPC with Hemihydrate and 25% Fly Ash); Cement VI (PPC with Gypsum and 35% Fly Ash); and Cement VII (PPC with Hemihydrate and 35% Fly Ash); and

[0067] FIG. 8 shows a graphical representation on the amount of CO.sub.2 emitted during the conventional method, and the present method of production of cement.

DETAILED DESCRIPTION OF THE INVENTION

[0068] It must be understood that the specific processes illustrated in the drawings and described in the following specifications are simply exemplary embodiments of the inventive concept defined and claimed in the appended claims. Hence, the specific figures, physical properties, parameters, and characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless claims expressly state otherwise. Also, it will be understood by one having ordinary skill in the art that construction of the described disclosure is not limited to a specific method. Other exemplary embodiments of the disclosure herein may be formed from a wide range of possible variations, unless described otherwise herein. Unless the context clearly dictates otherwise, the singular forms (including a, an, and the) in the specification and appended claims shall mean and include the plural reference as well.

[0069] Unless the context clearly dictates otherwise, it is understood that when a range of value is provided, the tenth of the unit of the lower limit as well as other stated or intervening values in that range shall be deemed to be encompassed within the disclosure. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure.

[0070] It is to be noted that the construction and arrangement of parameters for method as described in the exemplary embodiments is illustrative only. Although only a few embodiments of the present invention have been described in the detail in this disclosure, those skilled in the art will readily appreciate that many modifications and variations are possible (such as variation of temperatures, dimension of particles, type of raw material, proportions of various elements, values of parameters, use of additional materials, etc.) without materially departing from the novel and innovative teachings and essence of the invention with the advantages of the subject matter recited. The method of manufacturing cement as described and claimed in the present specification may not include all the details of all the standardized procedures and functions with respect to cement manufacturing which are known in the industry. For example, the present invention may not describe the methods or machines/tools employed for inter-grinding of the clinker or gypsum or their inter-grinding, and how to maintain/regulate the mill temperature, and the source of raw material to be used. Conventionally, many practical alternatives are available in the industry with respect to these features and parameters, and it is also possible that the variation in these external parameters/procedures may also result in the variation in output of the method and the quality of cement manufactured. It is, however, submitted that the mere variations or modifications of these external parameters does not take away, circumvent or deviate from the scope of the present invention as long as the features of the present invention are also employed in the method for manufacturing cement. Accordingly, all such modifications are intended to be included within the scope of the present invention. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions, and arrangement of the desired and other exemplary embodiments without departing from the spirit of the present invention.

[0071] The exemplary and/or preferred embodiments of the method disclosed below are for illustrative purposes only and are not to be construed as limiting.

[0072] Accordingly, the present invention provides an improved method of manufacturing cement which is devoid of the drawbacks/problems in the existing methods of manufacturing cement, as identified above. According to a preferred embodiment of the present invention, the method of manufacturing cement comprise the following steps: [0073] a. Gypsum is first ground in a separate mill to a desired fineness. [0074] b. Gypsum is calcined (at a pre-determined temperature range) to synthesize dehydrated form(s) thereofCaSO.sub.4.nH.sub.2O (where 2>n>0.5); CaSO.sub.4.H.sub.2O (Hemihydrate); CaSO.sub.4.nH.sub.2O (where 0.5>n>0); and/or CaSO.sub.4 (Soluble Anhydrite). [0075] c. The ground and calcined gypsum [or dehydrated form(s) thereof] is then intergrinded with clinker such that the highest temperature while inter-grinding does not exceed a pre-determined maximum temperature range.

[0076] Other raw materials like fly ash, slag etc. are added optionally based on type of cement and other requirements, at final inter-grinding stage to produce cement. This method activates fly ash or slag (if present in any particular cement) and accelerates hydration rate of C.sub.3S, C.sub.2S, fly ash or slag in the cement while reducing water demand and improving rheology of the cement, thereby enhancing the strength and durability of cement with less carbon emissions during manufacturing.

[0077] Thus, according to the present invention and improved process of manufacturing cement, at final grinding stage, gypsum is replaced by specially synthesized calcined gypsum [CaSO.nH.sub.2O (where 2>n>0.5) or CaSO.sub.4.H.sub.2O (Hemihydrate) or CaSO.sub.4.nH.sub.2O (where 0.5>n>0) or CaSO.sub.4 (Soluble Anhydrite)] which is inter-ground with clinker and other raw materials, which are added optionally based on type of cement and other requirements, to produce any particular kind of cement. This is in contrast to the conventional method of producing cement wherein the clinker is directly inter-grinded with gypsum. In the conventional methods, as the temperature of mill rise, gypsum loses its water of crystallization and transform into dehydrated forms [CaSO.sub.4.nH.sub.2O (where 2>n>0.5) or CaSO.sub.4.H.sub.2O (Hemihydrate) or CaSO.sub.4.nH.sub.2O (where 0.5>n>0) or CaSO.sub.4 (Soluble Anhydrite)] in the mill. As explained earlier, too much dehydration of gypsum in cement production is highly undesirable and causes problems in cement and degrades its quality.

[0078] According to the present invention, it has been observed and surprisingly found by the inventor that by replacing gypsum with pre-calcined (dehydrated form) of gypsum during inter-grinding stage with clinker minimizes the change in water of crystallization of gypsum during inter-grinding, and thus minimizes the release of water vapors of high temperature or steam. The problem arise in cement if we use gypsum at inter-grinding stage with clinker and let the gypsum to dehydrate and convert into hemihydrate or other dehydrated forms of gypsum while generating water vapors of high temperature or steam. Thus, replacing gypsum with a pre-calcined gypsum and then inter-grind it with raw clinker along with other raw materials (which are optionally added to produce any particular kind of cement) gives results which are surprising and in complete contradiction with current understanding and belief. It has been observed that, for a cement with optimum % of SO.sub.3 content, high dissolution rate of hemihydrate or other dehydrated forms of gypsum is not a problem especially when they are present as the complete source of calcium sulfate, added 10 externally replacing gypsum, in any cement.

[0079] If no hydration occurs on surface of clinker particle during inter-grinding, there is no barrier between clinker particle and calcium sulfate particles [CaSO.sub.4.nH.sub.2O (where 2>n>0.5) or CaSO.sub.4.H.sub.2O (Hemihydrate) or CaSO.sub.4.nH.sub.2O (where 0.5>n>0) or CaSO.sub.4 (Soluble Anhydrite)] and both particles are tightly packed. When the particles of dehydrated form of gypsum attach to the best possible site on clinker particle, the dissolution rate of the dehydrated form of gypsum particles and the rate of reaction between C.sub.3A and CaSO.sub.4.nH.sub.2O (where 2>n>0.5) or CaSO.sub.4.H.sub.2O (Hemihydrate) or CaSO.sub.4.nH.sub.2O (where 0.5>n>0) or CaSO.sub.4 (Soluble Anhydrite) was found to be in equilibrium, thereby reducing the probability of precipitating gypsum out of pore solution. The optimum SO.sub.3% for cements was found to be around 2%2.2% including SO.sub.3 inbound in clinker and other raw materials.

[0080] According to the literature, articles, journals and books in the prior art on cement manufacturing technology, its mentioned everywhere and always been feared that if hemihydrate is present in excess quantity (say more than 30% of gypsum or total calcium sulfate source added externally), then strength, quality and compatibility of cement will be poor and have issues. And if somehow good amount of soluble anhydrite gets generated during cement production then that cement will be practically of no use. Surprisingly, as per present invention, it is found that 100% hemihydrate or soluble anhydrite as the source of calcium sulfate added externally while replacing gypsum in any cement is not only not a problem, but it is advantageous in terms of strength, cost effectiveness and durability. The prior art, therefore, teaches away from the present invention. As per present invention when CaSO.sub.4.nH.sub.2O (where 2>n>0.5) or CaSO.sub.4.H.sub.2O (Hemihydrate) or CaSO.sub.4.nH.sub.2O (where 0.5>n>0) or CaSO.sub.4 (Soluble Anhydrite) is inter-grinded with clinker (irrespective of the clinker temperature), the particle of dehydrated form of gypsum will be tightly packed with clinker particle during inter-grinding. The surface charge on clinker particle and on dehydrated form of gypsum particle plays favorable role to attach the latter on the best possible site on clinker particle where it reacts immediately with C.sub.3A of clinker rather than precipitating gypsum out of solution when water is mixed with cement.

[0081] As per present invention one important thing has been observed that blending of separately ground gypsum or dehydrated form thereof and separately ground clinker is unfavorable. In this case surface chemistry plays important role, when clinker is separately ground, its particle gets agglomerated and hence when one try to blend separately ground gypsum or dehydrated form thereof with separately ground clinker then the clinker particles and gypsum particles gets loosely packed as a result when water is mixed with cement, rather than completely reacting with C.sub.3A, it precipitates gypsum out of pore solution in huge quantity, which gives a serious problem of false set, poor strength, and compatibility issues with water reducing admixtures, poor rheology etc.

[0082] In another preferred embodiment of the present invention, first the highest temperature T C. that the working mix is expected to reach inside the mill during intergrinding gypsum (or a dehydrated form thereof) with clinker the gypsum is determined, and then the gypsum is pre-calcined at a temperature which is at least equal to or higher than the said identified maximum temperature.

[0083] According to one of the most preferred embodiments of the present invention, the gypsum is pre-calcined at a temperature which is at least more than 90% the maximum temperature which is expected to reach inside the mill during inter-grinding of gypsum (or a dehydrated form thereof) with clinker.

[0084] In accordance with another preferred embodiment of the present invention, gypsum is pre-calcined at a temperature such that more than 50% of gypsum is dehydrated to hemihydrate form [CaSO.sub.4.H.sub.2O]. In accordance with another preferred embodiment of the present invention, gypsum is pre-calcined at a temperature such that more than 80% of gypsum is dehydrated to hemihydrate form [CaSO.sub.4.H.sub.2O].

[0085] In accordance with another preferred embodiment of the present invention, gypsum is pre-calcined at a temperature such that more than 50% of gypsum is dehydrated to a form of calcium sulphate with water of crystallization less than 0.5 [CaSO.sub.4.nH.sub.2O, where 0.5>n>=0]. In accordance with another preferred embodiment of the present invention, gypsum is pre-calcined at a temperature such that more than 80% of gypsum is dehydrated to a form of calcium sulphate with water of crystallization less than 0.5 [CaSO.sub.4.nH.sub.2O, where 0.5>n>=0]. In accordance with another preferred embodiment of the present invention, gypsum is pre-calcined at a temperature such that more than 50% of gypsum is dehydrated to soluble anhydrite form [CaSO.sub.4.nH.sub.2O, where 0.05>n>=0]. In accordance with another preferred embodiment of the present invention, gypsum is pre-calcined at a temperature such that more than 80% of gypsum is dehydrated to soluble anhydrite form [CaSO.sub.4.nH.sub.2O, where 0.05>n>=0]. In accordance with another preferred embodiment of the present invention, gypsum is first ground or pulverized to a size of less than about 75 20 microns, and preferably to a size less than about 45 microns before being calcined.

[0086] In accordance with another preferred embodiment of the present invention, wherein the inter-grinding of pre-calcined gypsum with clinker is carried out in presence of raw materials selected from the group consisting of fly ash, slag, volcanic ash, rice husk ash, meta kaolin, silica fume, and limestone. The method of manufacturing cement in accordance with the present invention also enables higher use of fly ash (in the range of up to 35%) without compromising the early strength (or day one strength) of the cement.

[0087] The cement manufactured in accordance with the present invention has the following characteristics: [0088] 1. During the inter-grinding process of Clinker with specially synthesized CaSO.sub.4.nH.sub.2O where 1>n>0.5 or hemihydrate (CaSO.sub.4.H.sub.2O) or CaSO.sub.4.nH2O where 0.5>n>0 or soluble anhydrite (CaSO4) along with other raw materials like fly ash, slag etc., which are added optionally based on type of cement and other requirements, at elevated temperatures of grinding mill around 90 C.150 C. no water vapors of high temperature or steam generates from CaSO4.nH2O where 1>n>0.5 or hemihydrate (CaSO.sub.4.H.sub.2O) or CaSO.sub.4.nH.sub.2O where 0.5>n>0 or soluble anhydrite(CaSO4) hence no hydration reaction takes place on the surface of clinker particle. [0089] 2. The CaSO4.nH2O where 1>n>0.5 particle or hemihydrate(CaSO4.H2O) particle or CaSO4.nH2O where 0.5>n>0 particle or soluble anhydrite(CaSO4) particle and clinker particle have very high affinity towards each other and both are packed in perfect manner to each other in any particular kind of manufactured cement like, OPC, PPC, PSC etc. [0090] 3. After addition of water to cement the specially synthesized CaSO4.nH2O where 1>n>0.5 or hemihydrate(CaSO.sub.4.H.sub.2O) or CaSO4.nH2O where 0.5>n>0 or soluble anhydrite (CaSO4) dissolves and rapidly release sulfate ions in pore solution and reacts immediately with C3A at the very initial moments after water is mixed with cement, 20 minimizing the formation of calcium aluminate hydrate. [0091] 4. The equilibrium of dissolving CaSO4.nH2O where 1>n>0.5 or hemihydrate (CaSO.sub.4.H.sub.2O) or CaSO4.nH2O where 0.5>n>0 or soluble anhydrite(CaSO.sub.4) into pore solution and their immediate reaction with C3A is in perfect manner. [0092] 5. The rapid reaction between CaSO4.nH2O where 1>n>0.5 or hemihydrate (CaSO.sub.4.H.sub.2O) or CaSO4.nH2O where 0.5>n>0 or soluble anhydrite (CaSO.sub.4) and C.sub.3A, immediately controls and slow down C.sub.3A hydration and hence cement hydration for some time. [0093] 6. There is nil tendency of dissolved CaSO4.nH2O where 1>n>0.5 or hemihydrate (CaSO.sub.4.H.sub.2O) or CaSO4.nH2O where 0.5>n>0 or soluble anhydrite (CaSO.sub.4) to precipitate gypsum out of pore solution rather than immediately reacting with C3A. [0094] 7. There are, therefore, nil chances of false set in cement because of external and controlled addition of SO3 in form of CaSO4.nH2O where 1>n>0.5 or hemihydrate (CaSO.sub.4.H.sub.2O) or CaSO4.nH2O where 0.5>n>0 or soluble anhydrite (CaSO.sub.4). [0095] 8. The water requirement or N/C of cement produced with the method of present invention is less than the conventional method giving more compact cement paste with low porosity hence enhancing strength of cement at all ages. [0096] 9. Depending on type of cement produced by the method of present invention like OPC, PPC, or PSC, the fly ash or slag or other pozzolans are better activated. Also the 15 hydration rate of C3S, C2S, fly ash, slag or other pozzolans of cement is accelerated. [0097] 10. The rheology of cement is improved a lot providing huge benefits in production of mortar, concrete etc. made from the cement produced by the method of present invention. [0098] 11. All these positive changes result in better strength and durability of cement and products produced from the cement like mortar, concrete etc. at all ages.

EXAMPLES

[0099] The inventor of the present invention carried out large number of experiments to establish and confirm the finding of the present invention. The results of some of these experiments is provided herein below by way of examples. It is to be noted that these examples are by way of illustration only, and does not limit the scope of the present invention in any manner.

[0100] ClinkerThe clinker used in producing cement in accordance with the preferred embodiments of the present invention is one of the commercially available clinkers in market with following chemical composition: [0101] SiO.sub.2 21.55% Al.sub.2O.sub.3 5.54% [0102] Fe.sub.2O.sub.3 4.45% [0103] CaO 64.48% [0104] MgO 1.07% [0105] SO.sub.3 1.13% [0106] K.sub.2O 0.51% [0107] Na.sub.2O 0.20% [0108] LOI 0.31% [0109] IR 0.25% [0110] Free Lime 1.22% [0111] LSF 0.90 [0112] C.sub.3S 50.12 [0113] C.sub.2S 24.0 [0114] C.sub.3A 7.15 [0115] C.sub.4AF 13.54

[0116] The clinker used in all cements have moderate level of C.sub.3S and LSF (lime saturation factor). There are, however, companies which are producing clinkers with high percentage content of C.sub.3S (around 55% to 60%) and LSF (of about 0.95 to 0.98) in order to produce high strength cement, but high C.sub.3S clinkers need more energy, High Grade Limestone Mines, and are costlier to produce. Also, the cement produced with high percentage content of C.sub.3S clinkers have high shrinkage, cracking problems and are less durable. If high strength, especially early age strength, can be achieved with clinkers having lower % of C.sub.3S then, then more durable cements can be produced.

[0117] GypsumFor the purposes of better illustration, the below-mentioned two kind of dehydrated forms of gypsum [i.e., hemihydrate (CaSO.sub.4.H.sub.2O) or CaSO.sub.4.nH.sub.2O where 0.5>n>0 or soluble anhydrite (CaSO.sub.4)] were tested. [0118] 1. Beta formwherein the dehydrated form [i.e., hemihydrate (CaSO.sub.4.H.sub.2O) or CaSO.sub.4.nH.sub.2O where 0.5>n>0 or soluble anhydrite(CaSO.sub.4)] was prepared by grinding/pulverizing mineral gypsum (gypsum from other sources can also be used like marine gypsum or synthetic gypsum etc.) and calcining it at temperature ranging from about 115 C. to about 170 C.; and [0119] 2. Alpha formwherein dehydrated form [i.e., hemihydrate (CaSO.sub.4.H.sub.2O) or CaSO.sub.4.nH.sub.2O where 0.5>n>0 or soluble anhydrite (CaSO.sub.4)] was prepared from selenite gypsum by the process of autoclaving and calcining already known. Alpha product is very high in cost, so its use in cement industry is usually avoided. Moreover, large machinery is required to produce alpha form of gypsum as well. It is also observed that if alpha form is used then it reduces the grinding efficiency of clinker/cement in ball mill, whereas beta form increases the grinding efficiency of clinker/cement with respect to gypsum.

[0120] For the purposes of illustrating the present invention by way of examples, three sets of cements were produced namely first set OPC, second and third set PPC with 25% fly ash and 35% fly ash, which makes a total of 7 kinds of cements wherein 3 types of cements with conventional method using gypsum at inter-grinding stage along with clinker and fly ash; and 4 types of cements, in which gypsum was replaced with hemihydrate and soluble anhydrite, by inter-grinding clinker and fly ash with specially synthesized hemihydrate and soluble anhydrite from gypsum. Gypsum was first ground around 45 microns and then: [0121] a. was calcined at about 115 C. to remove its th water of crystallization to produce hemihydrate with water of crystallization around H.sub.2O; or [0122] b. was calcined at about 170 C. to remove its both molecules of water of crystallization to produce soluble anhydrite (CaSO.sub.4).

[0123] The gypsum used in reference mix and to synthesize hemihydrate and soluble anhydrite was mineral gypsum of 90% purity.

[0124] First Set: Three cements of OPC 53 Grade were produced by inter-grinding clinker with: [0125] a. Gypsum using conventional method of manufacturing (Cement 1, Reference Mix); [0126] b. Synthesized hemihydrate (Cement 2); and [0127] c. Soluble anhydrite (Cement 3) in Ball Mill.

[0128] No grinding aid was used. The temperature of mill discharge product was maintained around 110130 centigrade.

Example I:

[0129] Cement I (Reference Mix, conventional method using gypsum): This reference mix produced by the conventional method comprises of 95.8% of clinker; and 2.2% of gypsum; and 2% of fly-ash. Cement 1 is tested for its properties and the observed physical and chemical properties are tabulated in Table 1.

TABLE-US-00001 TABLE 1 S. No Properties Units 1. Compressive Strength: 1 Day 24.4 MPa 3 Days 40.2 MPa 7 Days 51.7 MPa 28 Days 73.4 MPa 2. Fineness 297 (m.sup.2/kg) 3. Normal Consistency 28.50% 4. Sulphuric Anhydrite 2.0% by mass 5. Setting Time: Initial 150 Minutes Final 220 minutes 6. Soundness: Le Chatelier 1.0 mm Autoclave 0.06%

Example II:

[0130] Cement II (with hemihydrate as per present invention): This mix produced by new method comprises of 96.1% of clinker; 1.9% of hemihydrate; and 2% of fly-ash. Cement II is tested for its properties and the observed physical and chemical properties are tabulated in Table 2.

TABLE-US-00002 TABLE 2 S. No Properties Units 1. Compressive Strength: 1 Day 30.5 MPa 3 Days 49.6 MPa 7 Days 63.2 MPa 28 Days 88.1 MPa 2. Fineness 294 (m.sup.2/kg) 3. Normal Consistency 24.25% 4. Sulphuric Anhydrite 2.03% by mass 5. Setting Time: Initial 130 Minutes Final 180 minutes 6. Soundness: Le Chatelier 1.0 mm Autoclave 0.06%

Example III:

[0131] Cement III (with soluble anhydrite as per present invention): This mix produced by new method comprises of 96.2% of clinker; 1.8% of soluble anhydrite; and 2% of flyash. Cement III is tested for its properties and the observed physical and chemical properties are tabulated in Table 3.

TABLE-US-00003 TABLE 3 S. No Properties Units 1. Compressive Strength: 1 Day 32.6 MPa 3 Days 51.5 MPa 7 Days 65.9 MPa 28 Days 93.3 MPa 2. Fineness 293 (m.sup.2/kg) 3. Normal Consistency 23.00% 4. Sulphuric Anhydrite 2.04% by mass 5. Setting Time: Initial 140 Minutes Final 190 minutes 6. Soundness: Le Chatelier 1.0 mm Autoclave 0.06%

[0132] FIG. 1 shows a graphical illustration comparing the compressive strengths of the above three varieties of cements (viz. Cement I, Cement II and Cement III). It is observed that Cement III has the highest compressive strength than the other two varieties. It is also observed that Cement II and Cement III have similar normal consistency (24.25% and 23%) in comparison to Cement I as illustrated in FIG. 2. Further, the initial and final time taken for setting is lesser in Cement II and Cement II in comparison to Cement I as illustrated in the graphical representation of FIG. 3.

[0133] Second Set: Two cements of PPC grade were produced by inter-grinding clinker 10 with [0134] a. Gypsum and 25% fly ash; and [0135] b. Specially synthesized hemihydrate and 25% fly ash in ball mill.

[0136] No grinding aid was used. The temperature of mill discharge product was maintained around 100 C.110 C.

Example IV:

[0137] Cement IV (Reference Mix, conventional method with Gypsum): This reference mix comprises of 72% of clinker; 3% of gypsum; and 25% of fly ash. Cement IV is tested for its properties and the observed physical and chemical properties are tabulated in Table 4.

TABLE-US-00004 TABLE 4 S. No Properties Units 1. Compressive Strength: 1 Day 15.5 MPa 3 Days 28.2 MPa 7 Days 38.1 MPa 28 Days 58.4 MPa 2. Fineness 382 (m.sup.2/kg) 3. Normal Consistency 31.75% 4. Sulphuric Anhydrite 2.07% by mass 5. Setting Time: Initial 160 Minutes Final 220 minutes 6. Soundness: Le Chatelier 0.6 mm Autoclave 0.03%

Example V:

[0138] Cement V (with Hemihydrate as per the present invention): The mix produced by new method comprises of 72% of Clinker; 2.7% of Hemihydrate; and 25.3% of Fly Ash. Cement V is tested for its properties and the observed physical and chemical properties are tabulated in Table 5.

TABLE-US-00005 TABLE 5 S. No Properties Units 1. Compressive Strength: 1 Day 22.4 MPa 3 Days 37.3 MPa 7 Days 49.5 MPa 28 Days 73 MPa 2. Fineness 384 (m.sup.2/kg) 3. Normal Consistency 26.50% 4. Sulphuric Anhydrite 2.15% by mass 5. Setting Time: Initial 145 Minutes Final 190 minutes 6. Soundness: Le Chatelier 0.6 mm Autoclave 0.03%

[0139] It is observed that the compressive strength of Cement V (with Hemihydrate and 25%

[0140] Fly Ash) is higher than Cement IV (with gypsum and 25% Fly Ash) as shown in 5 FIG. 4.

[0141] Third Set: Two cements were produced with 35% fly ash with: [0142] a. Gypsum; and [0143] b. synthesized Hemihydrate.

[0144] No grinding aid was used. The temperature of mill discharge product was around 100 C.

Example VI:

[0145] Cement VI (Reference Mix, conventional method with Gypsum): This reference mix produced by conventional method comprises of 62% of Clinker; 3.3% of Gypsum; and 34.7% of Fly Ash. Cement VI is tested for its properties and the observed physical and chemical properties are tabulated in Table 6.

TABLE-US-00006 TABLE 6 S. No Properties Units 1. Compressive Strength: 1 Day 11.8 MPa 3 Days 22.1 MPa 7 Days 31.5 MPa 28 Days 49.3 MPa 2. Fineness 394 (m.sup.2/kg) 3. Normal Consistency 33.50% 4. Sulphuric Anhydrite 2.08% by mass 5. Setting Time: Initial 175 Minutes Final 250 minutes 6. Soundness: Le Chatelier 0.5 mm Autoclave 0.025%

Example VII:

[0146] Cement VII (with Hemihydrate according to the present invention): This reference mix produced by the method disclosed in the present invention comprises of 62% of Clinker; 3% of Hemihydrate; and 35% of Fly Ash. Cement VII is tested for its properties and the observed physical and chemical properties are tabulated in Table 7.

TABLE-US-00007 TABLE 7 S. No Properties Units 1. Compressive Strength: 1 Day 18.8 MPa 3 Days 30.9 MPa 7 Days 44.1 MPa 28 Days 67.2 MPa 2. Fineness 390 (m.sup.2/kg) 3. Normal Consistency 27.50% 4. Sulphuric Anhydrite 2.19% by mass 5. Setting Time: Initial 150 Minutes Final 200 minutes 6. Soundness: Le Chatelier 0.5 mm Autoclave 0.025%

[0147] FIG. 5 shows a graphical illustration comparing the compressive strengths of the above two varieties of cement (viz. Cement VI, and Cement VII). It is observed that the compressive strength of Cement VII prepared by the method disclosed in the present invention with the hemihydrate increases with number of days, and has the highest compressive strength.

[0148] As shown in FIG. 6, Cement V and VII has the preferred normal consistency viz. 26.5% and 27.5% respectively in comparison to Cement IV and Cement VI (viz. 31.75 and 33.5%). Further, the initial and final time taken for setting is also lesser in Cement V (viz. 145 and 190 mins respectively) and Cement VII (viz. 150 and 200 mins respectively) as illustrated in the graphical representation of FIG. 7.

[0149] The below table (Table 8) lists the physical and chemical properties of all the seven different types of cements namely Cement I (OPC 53G with gypsum); Cement II (OPC 53G with hemihydrate); Cement III (OPC 53G with soluble anhydrite); Cement IV (PPC with gypsum and 35% FA); Cement V (PPC with hemihydrate and 35% FA); Cement VI (PPC with gypsum and 25% FA); and Cement VII (PPC with hemihydrate and 25% FA) as 20 observed for ease of reference.

TABLE-US-00008 TABLE 8 Blaine Cement % Fly % % % % Soluble % Fineness Sr. No. Type Ash Clinker Gypsum Hemihydrate Anhydride Limestone m2/Kg 1 OPC 53G with Gypsum 2 95.8 2.2 0.0 0.0 0.0 297 2 OPC 53G with Hemihydrate 2 96.1 0 1.9 0.0 0.0 294 3 OPC 53G with Soluble 2 96.2 0 0.0 1.8 0.0 293 Anhydrite 4 PPC with Gypsum, 35% FA 34.7 62 3.3 0.0 0.0 0.0 394 5 PPC with Gypsum, 25% FA 25 72 3 0.0 0.0 0.0 382 6 PPC with Hemihydrate, 35 52 0 3 0 0.0 390 35% FA 7 PPC with Hemihydrate, 25.3 72 0 2.7 0.0 0.0 384 25% FA Initial Final Compressive Strength Normal setting setting (Mpa) Sulphuric Consistency time time 1 3 7 28 Anhydride Sr. No. % (minutes) (minutes) Day Day's Day's Day's (%) 1 28.50 150 220 24.4 40.2 51.7 73.4 2.0 2 24.25 130 180 30.5 49.6 63.2 88.1 2.03 3 23.00 140 190 32.6 51.5 65.9 93.3 2.04 4 33.50 175 250 11.8 22.1 31.5 49.3 2.08 5 31.75 160 220 15.5 28.2 38.1 58.4 2.07 6 27.50 150 200 18.8 30.9 44.1 67.2 2.19 7 26.50 145 190 22.4 37.3 49.5 73 2.15

[0150] The below table (Table 9) illustrates the data of different types of cement production in India in 2017 including projected increased production of cement and amount of CO.sub.2 emission during manufacturing of such cements.

TABLE-US-00009 TABLE 9 Indian cement production data for year 2017 Increment in Current Projected increased cement production Production production of cement capacity based on Average Average Fly Ash, per annum in with same quantity of same clinker Clinker Slag or other Million clinker production per production capacity Sr. No. Cement Type (%) used fillers (%) Used tonnes annum in million tonnes (in %) 1 OPC 43G & 53G old 95 3 100 0 technology 2 OPC 43G & 53G new 93 5 0 102 2 technology 3 PPC with 27% Fly Ash 70 27 270 0 manufactured with Gypsum, old technology 4 PPC with 35% Fly Ash 62 35 0 305 13 manufactured according to new invention 5 PSC old technology 50 47 30 0 6 PSC new technology 40 57 0 37.5 25 7 Old Technology 8 New Technology CO2 emission per Mt of cement production (only based on clinker % in cement, i.e 860 Kg of CO2 Comparative Total CO2 emission per Mt of clinker emission, based on production, without projected increased Total CO2 emission consideration of emission production of cement, to produce clinker for involved to produce final per annum in million manufacturing 445 Sr. No. cement product) (Unit Mt) tonnes million tonne of cement 1 0.817 83.33 2 0.800 81.6 3 0.602 183.6 4 0.533 162.5 5 0.430 16.1 6 0.344 12.9 7 283 8 257

[0151] It is observed that the amount of carbon dioxide produced during the manufacturing of cement according to the present invention is much lesser viz. 257 million tonnes in comparison to the amount produced during the conventional method of cement production viz. 283 million tonnes, clearly showing that the present method is greener and environment friendly (refer FIG. 8), in addition to the surprising physical and chemical properties of cement produced as illustrated in other figures.