DESC:FIELD OF THE INVENTION
The present invention relates to a cement composition. More particularly, the invention relates to a high performance cement composition comprising fly ash.
BACKGROUND OF THE INVENTION
Electricity generation is one of the key drivers for the growth of any economy. Coal is a major source of fuel for production of electricity in many countries around the world, including India. Due to rapid economic growth, there has been a significant increase in electricity generation, wherein a major proportion of the generation is attributed to coal-based power plants. In the process of electricity generation, significant quantity of fly ash is produced, which varies according to the ash content of the coal being burnt. Hence, fly ash is one of the major byproducts of coal-based power stations.
Fly ash material solidifies while suspended in the exhaust gases and is collected by electrostatic precipitators or filter bags. Since the particles solidify rapidly while suspended in the exhaust gases, fly ash particles are generally spherical in shape and range in size from 0.5 µm to 300 µm. The major consequence of the rapid cooling is that few minerals have time to crystallize, and that mainly amorphous, quenched glass remains. Nevertheless, some refractory phases in the pulverized coal do not melt (entirely), and remain crystalline. In consequence, fly ash is a heterogeneous material. SiO2, Al2O3, Fe2O3 and occasionally CaO are the main chemical components present in fly ashes.
The mineralogy of fly ashes is very diverse. The main phases encountered are a glass phase, together with quartz, mullite and the iron oxides hematite, magnetite and or maghemite. Other phases often identified are cristobalite, anhydrite, freelime, periclase, calcite, sylvite, halite, portlandite, rutile and anatase. The Ca-bearing minerals anorthite, gehlenite, akermanite and various calcium silicates and calcium aluminates identical to those found in Portland cement can be identified in Ca-rich fly ashes. The mercury content can reach 1 ppm, but is generally included in the range 0.01 - 1 ppm for bituminous coal. The concentrations of other trace elements vary as well according to the kind of coal combusted to form it.
Two classes of fly ash are defined by ASTM C618: Class F fly ash and Class C fly ash. The chief difference between these classes is the amount of calcium, silica, alumina, and iron content in the ash. The chemical properties of the fly ash are largely influenced by the chemical content of the coal burned (i.e., anthracite, bituminous, and lignite).
Disposal of fly ash is one major concern for coal-based power generators, more so for Indian coal-based power stations, as the coal has high ash content. Hence, it is imperative to search for alternative avenues for the productive utilization of fly ash. In recent years efforts have been made, to utilize fly ash in different cementitious compositions. For example, United States Patent No. US 5,573,588 A discloses a cementitious mixture comprising a Class C fly ash, Portland cement clinker and gypsum. When this cementitious mixture is used to produce a hardened concrete, and the concrete is exposed to a sulfate environment, the hardened concrete is substantially free of the formation of volume-expanding compositions, such as ettringite, that cause concrete failure. The disclosed composition comprises preferably 25 to about 70 wt.% fly ash, about 70 to about 25 wt. % Portland cement clinker and from about 5 to 10 wt.% gypsum.
PCT publication number WO1996027564 discloses a cement admixture composition capable of causing combined effects of inhibiting drying shrinkage while providing enhanced workability. The admixture comprises a synthetic mixture of oxyalkylene ether adduct primarily consisting of napthalene sulphonate formaldehyde condensate or melamine suphonate formaldehyde condensate.
European Patent No. EP1511699 discloses additives for hydraulically setting systems based on modified polycarboxylates and water soluble ethers of high polymeric polysaccharides that leads to improvement in rheological profile in hydraulically setting systems.
United States Patent No 5,484,480 discloses a cementitious mixture comprising hydraulic cement, fly ash, and an effective amount of unfired nature finely divided material, such as a clay, containing at least about 35% alumina, to accelerate the early strength of a mix.
United States patent 6,332,921 discloses an aluminous cement composition comprising aluminate cement, class F fly ash and water for cementing high temperature wells containing carbon dioxide.
United States patent US 9,169,159 discloses the composition of a dry cementitious blend comprising aggregate comprising less than 3 wt. % calcium, based on the total weight of the aggregate; from about 75 wt. % to 82 wt. % pozzolonic material comprising improved ash comprising particles meeting the ASTM C 989-2010 testing protocol for grade 100 slag quality or higher, the improved ash being selected from the group consisting of fly ash, calcined or uncalcined volcanic ash, rice hull ash, and combinations thereof, a catalytically effective quantity of catalyst selected from the group consisting of alkali-containing zeolite, alkali-containing feldspathoid, and combinations thereof; and, an amount of water reducing component.
United States Patent 5,573,588 discloses a concrete mix composition using cementitious mixture containing Class C fly ash that are resistant to sulfate containing environments.
The functional demands of modern infrastructure projects, such as tunnels, bridges, dams, skyscrapers, airports, sea ports, include the use of high performance cement. High performance cement, as the name suggests exceeds the performance of ordinary Portland cement with respect to its desirable properties. Ingredients used in high performance cements may include clinker, fly ash, gypsum and a range of cement modifiers.
PCT publication WO2010126457 discloses the production of High Performance Cement (HPC) where the clinker is ground through a special grinding technology by adding a modifier for improving mechanical-chemical properties of the cement particles, resulting production of high performance cements such as HPC 62.5 with improved properties of concrete such as early strength up to 300 kg/cm2 in 24 hours, and 500 kg/cm2 in 48 hours; high strength up to 1200 kg/cm2 in 28 days; extended life time due to high performance; early removal of formwork without any steam cure application; high abrasion resistance along with other improvements mentioned in the invension.
Clinker is one of the most important ingredients in a high performance cement composition. Clinker consists of various calcium silicates including alite and belite. Tricalcium aluminate and calcium aluminoferrite are other common components. These components are often generated in situ by heating various clays and limestone. Portland cement clinker is made by heating a homogeneous mixture of raw materials in a rotary kiln at high temperature.
Another important constituent in high performance cement is Gypsum, which is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4.2H2O. Gypsum plays a very important role in controlling the rate of hardening of the cement. During the cement manufacturing process, upon the cooling of clinker, a small amount of gypsum is introduced during the final grinding process. Gypsum is added to control the “setting of cement”. If not added, the cement will set immediately after mixing of water leaving no time for concrete placing.
When cement reacts with water, the silicates and aluminates of calcium gets converted to the hydrated colloidal gels and following reactions take place:
1. 2CaO.SiO2 + x H2O?2CaO.SiO2 .xH2O (hydrated colloidal gel of C3S)
2. 3CaO. Al2O3 + 6 H2O?3CaO. Al2O3 .6 H2O (hydrated colloidal gel of C3A)
3. 3CaO.SiO2?2CaO.SiO2 + Ca (OH)2
4. 3CaO. Al2O3 .6 H2O?3 Ca(OH)2 + 2 Al(OH)3
In the above reactions we see that finally we have three products: (a) Calcium Hydroxide (b) Aluminium Hydroxide (c) Dicalcium silicate
Calcium Hydroxide binds the silicate participles together, while Aluminum Hydroxide fills the space in the lattice. When Gypsum is added to the Cement it binds with Tricalcium aluminates to make a colloidal gel and the above reaction don’t take place. So it slows the process of fastening.
3CaO. Al2O3 + 3CaSO4+ 2H2O?3CaO. Al2O3 .3CaSO4.2H2O
If not added, the cement will set immediately after mixing of water leaving no time for concrete placing.
Surface modifiers are used to modify the surface of particles present in the hydraulically setting systems such as OPC, PPC, PSC, PAC etc. to improve workability and enhance physical as well as chemical properties. Therefore, suitable use of organic polymeric material (known as cement modifier) plays an important role as far as composition of high performance cement is concerned. The cement modifier has ionic and steric functionality to assist cement particle dispersion, thereby significantly reducing the water demand and resulting in a denser microstructure.
United States Patent 8.993,656 discloses compositions and methods of producing a cementitious material containing portland cement, cement clinker, fly ash, ground granulated blast furnace slag, limestone and natural pozzolans wherein polycarboxylate comb polymer containing a carbon backbone and pendant polyoxyalkylene groups with linkage groups comprising at least one ether group, are used as grinding additives for resisting degradation during grinding and retaining workability and strength enhancing properties of the hydratable cementitious materials.
Cement is one of the important constituents of any concrete mix design which contributes to the overall performance of the concrete. Currently, in order to prepare high performance concrete, different kinds of expensive additives, such as reinforcing fibers, silica fume, water proofing compounds, various admixtures etc. are added along with ordinary Portland cement or blended cement. However, it is an object of the present invention to provide a cement composition that achieves comparable or better performing concretes without or with sparing use of the aforestated additives and hence provides hassle-free and reliable solution to the end users.
The strength of concrete is inversely proportional to the amount of water added or water-cement (w/c) ratio. In order to produce stronger concrete, less water is added, which makes the concrete mixture less workable and difficult to mix, necessitating the use of plasticizers, water reducers, superplasticizers or dispersants. It is also an object of the present invention to prepare a high performance cement composition having reduced water demand compared to ordinary Portland cement. It is a further object of the present invention to formulate a high performance cement composition affording a flowability that is comparable to ordinary Portland cement.
Drying shrinkage is defined as the contracting of a hardened concrete mixture due to the loss of capillary water. This shrinkage causes an increase in tensile stress, which may lead to cracking, internal warping, and external deflection, before the concrete is subjected to any kind of loading. Hence, it is an object of the present invention to formulate a high performance cement composition that affords less drying shrinkage compared to ordinary Portland cement.
When concrete is permeable to water, it can cause corrosion in reinforcement in presence of dissolved oxygen, SO3-, Cl– etc. This formation of rust due to corrosion results in cracking and spalling of reinforced concrete. Hence, it is another object of the invention to formulate a high performance cement composition that exhibits superior impermeability to water ingress.
A higher heat of hydration causes higher temperature in concrete structure and that increases the risk of cracking. Hence, it is an object of the present invention to formulate a high performance cement composition that affords lower heat of hydration as compared to ordinary Portland cement.
It is essential that cement set neither too rapidly nor too slowly. In the first case there might be insufficient time to transport and place the concrete before it becomes too rigid. In the second case too long a setting period tends to slow up the work unduly, also it might postpone the actual use of the structure because of inadequate strength at the desired age. Hence, it is yet another object of the present invention to formulate a cement composition that affords optimum initial and final setting times.
The structural design of modern infrastructure projects, such as dams, tunnels, bridges and skyscrapers necessitates the use of concrete with high compressive strength at an affordable cost. Hence, it is an object of the present invention to formulate a high performance cement composition that affords high compressive strength compared to ordinary Portland cement.
Flexural strength is a measure of the tensile strength of concrete beams or slabs. Flexural strength identifies the amount of stress and force an unreinforced concrete slab, beam or other structure can withstand such that it resists any bending failures. Flexural strength is also known as bend strength or modulus of rupture or fracture strength. Hence, it is another objective to the present invention to formulate a high performance cement composition that achieves comparable or better flexural strength compared to ordinary Portland cement.
The inventors of the present invention have developed a synergistic skim coat composition comprising Fillers, Ordinary Portland cement, Organic polymeric binder, and Organic polymer, wherein, fillers are by-product of cement manufacturing to overcome problems mentioned above.
SUMMARY OF THE PRESENT INVENTION

In accordance with an embodiment of the invention, there is provided a high performance cement composition comprising, (a) Clinker; (b) Gypsum; (c) Fly Ash; and (d) Cement modifier.
In accordance with an embodiment of the invention, there is provided a high performance cement composition comprising, comprising, Clinker present in the range from 70 to 83%;
In accordance with an embodiment of the invention, there is provided a high performance cement composition comprising, Gypsum present in range from 1.8 to 5%
In accordance with an embodiment of the invention, there is provided a high performance cement composition comprising, Fly Ash present in the range of 15 to 20%.
In accordance with an embodiment of the invention, there is provided a high performance cement composition comprising, Cement modifier present in range of 0.1 to 1.5%.
In accordance with an embodiment of the invention, there is provided a high performance cement composition comprising, wherein one or more cement modifier selected from group comprising, a comb shaped polycarboxylate composed of anionic backbone (main chain) and holding polyoxyalkylene pendant groups where the main chain is linked via ester, ether, imide and/or amide groups with polyoxyalkylene side chains.
In accordance with an embodiment of the invention, there is provided a process for preparation of high performance cement composition; comprising steps of:
a. Grinding clinker, gypsum and fly ash;
b. Adding cement modifier to the mixture of step (a) to obtain the high performance cement composition of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
It is to be noted that, as used in the specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a composition containing “a compound” includes a mixture of two or more compounds. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
The expression of various quantities in terms of “%” or “% w/w” means the percentage by weight, relative to the weight of the total solution or composition unless otherwise specified. The term “water” used herein refers to demineralized water unless otherwise specified.
The term “clinker” used in reference is one of the important ingredients in a high performance cement composition. Clinker consists of various calcium silicates including alite and belite. Tricalcium aluminate and calcium aluminoferrite are other common components. These components are often generated in situ by heating various clays and limestone.
The term “gypsum” used in reference is soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4.2H2O; Gypsum plays a very important role in controlling the rate of hardening of the cement. Gypsum is added to control the setting of cement.
The term “Fly Ash” used in reference is Fly ash material solidifies while suspended in the exhaust gases and is collected by electrostatic precipitators or filter bags. Fly ash is a heterogeneous material. SiO2, Al2O3, Fe2O3 and occasionally CaO are the main chemical components present in fly ashes.
The term “cement modifier” used in reference are used to modify the surface of particles present in the hydraulically setting systems such as OPC, PPC, PSC, PAC etc. to improve workability and enhance physical as well as chemical properties.
In accordance with an embodiment of the invention, there is provided a high performance cement composition comprising, (a) Clinker; (b) Gypsum; (c) Fly Ash; and (d) Cement modifier.

In accordance with an embodiment of the invention, there is provided a high performance cement composition comprising, comprising, Clinker present in the range from 75 to 90%;

In accordance with an embodiment of the invention, there is provided a high performance cement composition comprising, Gypsum present in range from 2 to 5%

In accordance with an embodiment of the invention, there is provided a high performance cement composition comprising, Fly Ash in an amount present in the range of 15 to 20%.
In accordance with an embodiment of the invention, there is provided a high performance cement composition comprising, Cement modifier present in range of 0.1 to 1.5%.

In accordance with an embodiment of the invention, there is provided a high performance cement composition comprising, wherein one or more cement modifier selected from group comprising, a comb shaped polycarboxylate composed of anionic backbone (main chain) and holding polyoxyalkylene pendant groups where the main chain is linked via ester, ether, imide and/or amide groups with polyoxyalkylene side chains.
In accordance with an embodiment of the invention, there is provided a process for the preparation of the high performance cement composition; comprising the steps of:
a. Grinding clinker, gypsum and fly ash; and
b. Adding cement modifier to the mixture of step (a) to obtain the high performance cement composition of the present invention.
In accordance with another embodiment of the invention, the mixture of step (a) is ground to achieve a specific surface area (Blaine) in the range of 350 to 400.
Please note that the Test Samples belong to high performance cement named as Dalmia INFRAGREEN in the present invention.
The general compositional ranges (example 1) of the constituent materials of the present invention along with four preferred compositions (example 2 to 5) are tabulated below.
Example 1
Constituents %
Clinker 70-83
Gypsum 1.8-5.0
Fly Ash 15-25
Cement modifier 0.1-1.5

Example 2
Constituents %
Clinker 81.75
Gypsum 2
Fly Ash 16
Cement modifier 0.25

Example 3
Constituents %
Clinker 74
Gypsum 3
Fly Ash 22
Cement modifier 1

Example 4
Constituents %
Clinker 71
Gypsum 4.5
Fly Ash 24.25
Cement modifier 0.25

Example 5
Constituents %
Clinker 83
Gypsum 1.85
Fly Ash 15
Cement modifier 0.15

Example 6
A comparison between regular fly ash based cement (PPC) and the present invention (high performance cement, already BIS approved) on the basis of physical characteristics are tabulated below (Table 1-4; Example 7-10). The results show an overall performance enhancement in the current invention. This high performance cement can be considered as a 53 grade cement in 7 days based on the compressive strength value as opposed to 28 days for a normal cement based on PPC or OPC.
Composition for Control Sample is given in table below:
Constituents %
Clinker 79
Gypsum 2.5
Fly Ash 18.5
Example 7
Table 1: Consistency and Setting Time
Characteristics As per IS 1489, part 1:2015 Test Sample Control Sample
CONSISTENCY Not Specified 21% 29%
SETTING TIME
a) INITIAL SETTING TIME Shall not be Less than 30 Minutes 110 minutes 155 minutes
b) FINAL SETTING TIME Shall not be More than 600 Minutes 170 minutes 210 minutes

Example 8
Table 2: Compressive Strength
Characteristics As per IS 1489, part 1:2015 Test Sample Control Sample
COMPRESSIVE STRENGTH
a) 24h (average of three results) Not Specified 21.1 MPa 13.4 MPa
b) 72±1h (average of three results) Shall not be Less than 16 MPa 39.1 MPa 23.60 MPa
c) 168±2h (average of three results) Shall not be Less than 22 MPa 54.5 MPa 39.80 MPa
d) 672±4h (average of three results) Shall not be Less than 33 MPa 74.7 MPa 59.70 MPa

Example 9
Table 3: Flexural Strength
Characteristics As per IS 1489, part 1:2015 Test Sample Control Sample
FLEXURAL STRENGTH
a) 24h (average of three results) The cement shall show a progressive increase in Strength from the strength at 72 hours 3.86 MPa 3.51 MPa
b) 72±1h (average of three results) 4.80 MPa 4.75 MPa
c) 168±2h (average of three results) 7.40 MPa 7.00 MPa
d) 672±4h (average of three results) 8.65 MPa 8.15 MPa
Example 10
Table 4: Drying Shrinkage
Characteristics As per IS 1489, part 1:2015 Test Sample Control Sample
DRYING SHRINKAGE
c) 7 Days Not Specified 0.022% 0.025%
d) 28 Days 0.035% 0.046%

Example 11
In accordance with another aspect of the present invention, there is provided a high performance structural concrete mix design (M70with initial slump, approx.. 600mm) to compare, evaluate and establish the superior properties (compressive strength, particularly in 3 and 7 days) imparted by using high performance cement over ordinary Portland cement. Please note that there is a substantial decrease in the cement and cementitious materials along with decrease in water content and admixture dosage in the concrete composition using the high performance cement (Dalmia INFRAGREEN).
a. The high performance cement or ordinary Portland cement;
b. Water;
c. Aggregates; and
d. Plasticizers/additives
Table 5: Typical M70 Concrete Mix design
Basic Materials Mix-Design with OPC 53 Mix design with Dalmia INFRAGEEN
Cement 460 450
FLYASH 120 0
Micro silica 40 0
W / C Ratio 0.24 0.28
Water 149 128
AGG 40mm 0 0
AGG 20mm 531 310
AGG 10mm 436 680
Coarse Sand 746 880
Admixture doses 1.10% 0.50%
Example 12
Table 6: Comparison of Compressive Strength M70 Grade (N/mm2)
Compressive Strength M70 Grade (N/mm2)
Mix design with OPC 53 Mix design with Dalmia INFRAGREEN
3 days 28 48
7 days 42 61
28 days 79 82
,CLAIMS:We claim:
1. A high performance cement composition comprising ,
(a) Clinker;
(b) Gypsum;
(c) Fly Ash; and
(d) Cement modifier.
2. The high performance cement composition as claimed in claim 1 comprising , Clinker present in the range from 70 to 83%;

3. The high performance cement composition as claimed in claim 1 comprising Gypsum present in range from 1.8 to 5%;

4. The high performance cement composition as claimed in claim 1 comprising Fly Ash present in the range of 15 to 25%.

5. The high performance cement composition as claimed in claim 1 comprising Cement modifier present in range of 0.1 to 1.5%.

6. The high performance cement composition as claimed in claim 1 comprising, wherein one or more cement modifier selected from group comprising, a comb shaped polycarboxylate composed of anionic backbone (main chain) and holding polyoxyalkylene pendant groups where the main chain is linked via ester, ether, imide and/or amide groups with polyoxyalkylene side chains.

7. A process for preparation of high performance cement composition; comprising steps of:
a. Grinding clinker, gypsum and fly ash;
b. Adding cement modifier to the mixture of step (a) to obtain the high performance cement composition of the present invention.