Cement clinker containing both alite and active belite phases exhibiting hydraulic activation

Abstract

This invention is related to a cement clinker formed by firing raw meal prepared with new and improved raw meal minerals. This new cement clinker is a hydraulically activated cement clinker which can contain alite (tricalcium silicate) and aH' dicalcium silicate phase together with boron and fluorine doping and can be fired at lower temperatures and has lower carbon dioxide emission.

Description

[0001] DESCRIPTION

[0002] CEMENT CLINKER CONTAINING BOTH ALITE AND ACTIVE BELITE PHASES EXHIBITING HYDRAULIC ACTIVATION

[0003] Technical Field

[0004] The invention is related to cement clinker, formed as a result of firing raw meals prepared with new and improved raw meal minerals. This new cement clinker is about boron doped cement clinker that can contain alite (tricalcium silicate) and aH’ dicalcium silicate phase together, can be fired at lower temperatures, has lower carbon dioxide emissions, and shows hydraulic activation.

[0005] State of the Art

[0006] Portland Cement is the most used hydraulic binder in the world. The composition of cement consists of a mixture of clinker, gypsum and mineral additives, it is mainly clinker which gives hydraulic activity to the cement.

[0007] Clinkers are produced in an energy-intensive process by mixing the main raw materials such as limestone, clay / marl and corrective components such as iron ore, bauxite and silicon source according to the need in appropriate proportions, drying the mixture, grinding it and making it ready for firing, and then firing it at high temperatures. The grinding energy requirement used during the drying and grinding of the materials before firing, combustion emissions resulting from the use of fuel during the firing process, and emissions resulting from the chemical reactions of the raw materials during firing are the emissions released by production. During the production of 1 ton of cement, = 970 kg of CO2 is released.

[0008] Clinkers give hydraulic binder capacity to the cement. Clinkers contain 4 main minerals that give ultimate strength to the concrete or mortar. Those minerals are alite (C3S), belite (C2S), tricalcium aluminate (C3A) and tetra-calcium aluminoferrite (C4AF).

[0009] Table 1

[0010] These basic compounds can be composed of the same elements, which we call polymorphs, but different in terms of both crystal structure and hydraulic effect, depending on the temperature, minor element effect and other conditions of the process (such as the fuel used, heat profile, technology of the system, temperature, pressure, cooling and efficiency). This polymorph structure is effective on the quality properties of the product.

[0011] Table 2

[0012] When clinker compounds are evaluated in terms of hydraulic properties.

[0013] C3S (Alite); is a compound with high active hydraulic properties.

[0014] C2S (Belite); has 5 polymorphs in terms of crystal structure. These are a (alpha), aH' (alpha prime high), aL' (alpha prime low), P (beta) and y (gamma). The y-C2S gamma polymorph does not have hydraulic properties of these crystal structures.

[0015] The -C2S beta form is found in Portland cement and is considered a metastable phase and is formed during cooling.

[0016] The a' alpha prime phases of C2S polymorphs are the structures that will be focused on within the scope of this invention. This phase is the phase with high hydraulic properties among other polymorphs of C2S. a' phases are obtained at high temperatures and by using B2O3 in the raw material, B2O3 is doped to the clinker structure in the chemical reaction stage, thus ensuring both the formation and stabilization of the a' phase and allowing the active belite phases to be obtained when the clinker reaches room temperature. Therefore, it improves the clinker properties.

[0017] If we look at the early and late strength properties of 4 basic clinker phases, C3S and C2S phases are highly effective in strength development.

[0018] Table 3

[0019] Although the active form of the C2S compound obtained in the mineral structure of the clinker after the production of clinker at low temperature by doping B2O3 is obtained, the early strength properties cannot be enough at a level that is preferable for the cement and concrete sector. For this reason, while the active C2S phase is formed in the clinker content planned to be obtained at low temperatures, it is also mandatory to have a C3S phase.

[0020] Cement clinker is a material that gains binding properties as a result of hydration of C3S, C2S, C3A and C4AF phases. As a result of this reaction with water, C-S-H gel is formed from C3S and C2S phases and shows binding properties. Bogue and Lerch [1] compared the compressive strength of pure cement phases in their studies. When 10 and 14-day compressive strengths were observed, they determined that C3S was the phase that had the highest effect on the compressive strength in a short time. For 10 and 14 days results;

[0021] C3S >C2S>C3A>C4AF

[0022] When 1-year compressive strengths are compared, the results are as follows.

[0023] C3S=C2S>C3A>C4AF

[0024] The C3S phase, which shows fast hydration, is the phase that should be obtained the most in the clinker structure since it has high early strength.

[0025] C2S in the clinker structure has 5 polymorphs. All these polymorphs have different hydration properties and their contribution to compressive strength is different. Industrially produced clinker contains P phase, -C2S, and is formed during cooling. Jelenic and Bezjak [2] investigated the hydration properties of a' and -C2S polymorphs and determined that the reaction rate of the a' phase was faster and showed more active hydraulic properties.

[0026] Among the known applications in the art, Fletcher et al. [3] studied the CaO^CL-SiCL system and observed that boron is incorporated into the structure of dicalcium silicate (C2S) and depending on the amount of boron doped a, a' and P-C2S polymorphs are stabilized. In this solid solution state, they suggested that the Can SiCLMBCh structure formed during the heating process forms 6(a, a', P)-Ca2- o.5(Si04)i-x(B03)xdicalcium silicate by solid solution mechanism (x=B2C>3 amount, the amount determines the polymorph). Another data they found in their studies is that if B2O3 is included in the system, the thermal stability of tricalcium silicate (C3S) deteriorates and C3S becomes unstable and decomposes to C2S and CaO. Thus, the stabilization of C3S cannot be achieved with boron and the excess CaO in the designed system causes volume expansion and does not meet the requirements of TS EN 196-3 standard.

[0027] Tran et al [4] studied the solid solution mechanism of CaF2 in calcium silicate systems. They determined that the interstitial oxygen in C3S, where the Si-0 bond is absent, can be replaced by the F" anion in the crystal structure, since C2S is only containing Si-0 bond and F" anion only doped into the C3S structures. In this case, it was thought that the C3S phase could be stabilized in the presence of B2O3 in the solid solution formed by a new doping of C3S.

[0028] It was determined that CaF2 and ZnO compounds were used for the C3 S phase to doped in the structure, and these compounds are the compounds that enable the formation of the C3S phase in the clinker at low temperatures by doping as F" and Zn2+ions into the crystal lattice as a result of the research carried out in this context.

[0029] Summary of the Invention

[0030] In the light of all this information, it has been observed that the formation of both alite and active be lite phases is possible at low temperatures in the studies carried out with the use of B2O3 and CaF2 together. Due to the presence of both alite and active belite phases of the designed clinker, it has been observed that early strength and late strength properties can be suitable by optimization.

[0031] This invention related to cement clinker fired with improved raw meal minerals. The clinker formed, as a result of firing raw meal by adding CaF2 and B2O3, has superior properties compared to Portland Cement.

[0032] The C3S mineral, which was shown to be unstable in the presence of B2O3 in the prior art, was stabilized with this invention. By obtaining the active belite form with stabilized C3S and B2O3 as a result of mineralization, the clinker is chemically optimized in terms of hydration and shows a faster hydration reaction. Thanks to these properties, higher compressive strength can be obtained per unit time. The clinker obtained from this raw meal has a lower specific heat consumption compared to the raw meal without CaF2 and B2O3. It has higher compressive strength in the same unit time compared to the clinker without CaF2 and B2O3. The lower specific heat consumption and higher ultimate strength helps to reduce CO2 emission due to lower energy requirement and clinker binder factor. Clinker obtained with this raw meal has lower CO2 emissions.

[0033] Brief Description of Drawings

[0034] Figure 1: Industrial Process Steps

[0035] Figure 2: X-Ray Diffraction and Rietveld Analysis of OPC Clinker

[0036] Figure 3: X-Ray Diffraction and Rietveld Analysis of Boron Doped Clinker

[0037] Figure 4: X-Ray Diffraction and Rietveld Analysis of Fluorine Doped Clinker

[0038] Figure 5: X-Ray Diffraction and Rietveld Analysis of Boron and Flurorine Doped Clinker Detailed Description of the Invention

[0039] This invention, cement clinker, is produced as clinker after crushing and proportioning of raw materials, mixing of raw materials, grinding of raw materials and firing of raw materials (Figure 1). For this clinker, alkali waste, aragonite, calcite, cement flue dust, cement stone, chalk, limestone, marble, marl, clay, mud, shale, iron ore, bauxite, fluorite, colemanite, ulexite, borax (pentahydrate, decahydrate) can be used as raw materials.

[0040] That cement clinker may include about %64-66.5 CaO, about %20.5-21.5 SiCh, about %5.3-5.8 AI2O3, about %3.4-3.8 Fe2C>3, about %1.4-1.8 MgO, about %0.5-l .5 SO3, about %0.5-l .5 K2O, about %0. 1-0.5 Na2O about %0.2-l CaF2, about %0.2-l B2O3 by weight.

[0041] The recommended and preferred oxide percentages, Lime Saturation Factor (LSF), Aluminum Modulus (ALM), CaF2 / B2C>3 ratio in the clinker and Sodium Equivalence (Na2Oeq) for industrial production of the cement clinker are shown in Table 4.

[0042] Na20eq= Na20 + 0.658 * K2O

[0043] Table 4: Oxide percentage of clinker (recommended, preffered)

[0044] That cement clinker may include about %52-65 C3S, %2-10 P-C2S, %5-25 a’-C2S, %2-8 C3A, %7-l 5 C4AF, %0.1-3 lime, %0. 1-3 periclase and about %0. 1-5 minor phases by weight.

[0045] X-ray diffraction and Rietveld analysis were performed to determine the phases and their weight percentages in Portland cement and the results are shown in Table 5. Portland cement contains 7.63% P-C2S phase and 70.56% Alite (C3S) phase. The P-C2S phase is formed during cooling and is present in Portland cement without doping. a'-C2S phase was not found in the clinker. Table 5: Rietveld Analysis of OPC Clinker

[0046] The Rietveld analysis of the clinker fired by adding only boron into the raw meal is shown in Table 6.

[0047] It was determined that the alite (C3S) phase was not formed in the clinker obtained by boron doping only, and that the belite phase only a'-C2S phase was present.

[0048] Tablo 6: Rietveld Analysis of Boron Doped Clinker The Rietveld analysis after X-Ray Diffraction of the clinker fired by adding only fluorine into the raw meal is shown in Table 7. It is observed that the P-C2S phase can be stabilized in the fluorine doped clinker like Portland Cement, but since fluorine can change the eutectic point of the raw meal, the liquid phase formation can occur at earlier temperatures and consequently reduce the specific heat consumption.

[0049] Table 7: Rietveld Analysis of Fluorine Doped Clinker

[0050] The Rietveld analysis of the clinker doped with boron and fluorine is shown in Table 8. It is observed that the a'-C2S phase can be stabilized in the clinker doped with boron and fluorine and in this case the C3S phase is also stabilized.

[0051] Table 8: Rietveld Analysis of Fluorine and Boron Doped Clinker

[0052] Tests were performed according to TS-EN 196-1 to compare the compressive strengths of the clinkers obtained, and the results are shown in Table 9. The specific surface area experiment was performed according to TS EN 196-6. The experiments were repeated in the range of specific surface area of 3100- 3200 cm2 / gr. Table 9 shows the result of one of the samples. All clinkers were grinded by sulfate with a maximum SO3 content of 3.5% in accordance with TS EN 197-1.

[0053] OPC, fluorine doped, boron and fluorine doped clinker, grinding process was performed with the same specific surface area in order to make comparisons. Boron doped clinker did not show compressive strength on the first day even with higher specific surface area, while it showed a compressive strength of 26.6 MPa at 28 days. The volume expansion was found to be 40 mm due to the high CaO content. The low strength and high-volume expansion showed insufficient properties according to TS EN 196-3 standards. Some improvement was observed in only fluorine doped clinker compared to OPC clinker. The low strength properties of boron doped clinker were improved with the boron and fluorine doped clinker and the 28-day strength increased by about 20% compared to OPC clinker and ranged between 48-54 MPa. This value is 53.0 MPa in Table 9. This increase is due to the simultaneous presence of C3S and a'-C2S phases in the clinker thanks to the invention. The two phases with higher degree of hydration showed faster hydraulic binder properties, allowing higher strength to be obtained in 28 days. However, since the tests were carried out according to TS EN 196-1, no chemical or mineral additives were used in the clinkers. Improvements in product performance can be realized by using chemical or mineral additives, so it is possible to achieve higher values in all strength classes. The same is true forthe specific surface area. Since the interaction between molecules will increase as the specific surface area increases, it is possible to obtain higher strength in all strength classes at higher specific surface values.

[0054] While the volume expansion of 40 mm in boron doped clinker according to TS EN 196-3 has invalid values in the standard, this problem has been eliminated in boron and fluorine doped clinker and it has been brought into compliance with TS EN 196-3 standard. In addition, boron and fluorine doped clinker provides energy savings between 2-6% compared to Portland cement clinker in terms of specific heat consumption. It provides a reduction in CO2 emissions during its production due to the fact that it reduces the heat required for firing by having lower heat consumption and reduces the clinker binding factor by showing more compressive strength in 28 days. Although the start of setting is shown as 230 minutes and the end of setting as 360 minutes in the example given in Table 9 in the composition of boron and fluorine doped clinker, it was observed that these values were 175 minutes and 320 minutes on average, respectively.

[0055] Bl: 1stday compressive strength, B2: 2ndday compressive strength, B7: 7thday compressive strength, B28: 28thday compressive strength, P.Beginning: Setting start, P.End: Setting End, Volume Expansion, mm.: Volume expansion, millimeter

[0056] References

[0057] [1] Rogue, R.H. and Lerch, William. (1934) ‘Hydration of Portland cement compounds’, Industrial and Engineering Chemistry, 26(8), pp. 837-847. doi: 10.1021 / ie50296a007. [2] I. Jelenic, A. Bezjak, On the hydration kinetics of a'- and - modifications of dicalcium silicate, 1981

[0058] [3] Fletcher, J.G. and Glasser, F.P. (1993) ‘Phase relations in the system CaO-B2O3-SiO2’, Journal of

[0059] Materials Science, 28(10), pp. 2677-2686. doi: 10.1007 / bf00356203.

[0060] [4] Thuan T. Tran, Duncan Herfort, Hans J. Jakobsen, And Jorgen Skibsted Site preferences of fluoride guest ions in the calcium silicate phases of Portland cement from29Si{19F} CP-REDOR NMR spectroscopy, 2009

Claims

CLAIMS1. A cement clinker, comprising; %64-66.5 CaO, %20.5-21.5 SiO2, %5.3-5.8 AI2O3, %3.4-3.8 Fe2O3, %1.4-1.8 MgO, %0.5-1.5 SO3, %0.5-1.5 K2O, %0.1-0.5 Na2O, %0.2-l CaF2, %0.2-l E Chby weight, and mineral phases of %52-65 C3S, %2-10 P-C2S, %5-25 a’-C2S, %2-8 C3A, %7-15 C4AF, %0. 1-3 Lime ve %0. 1-3 periclase, by weight.

2. The production method of cement clinker according to claim 1, wherein the CaF2 / B2O3 ratio used during production is between 0.8-1.7.

3. The production method of cement clinker according to claim 2, wherein the CaF2 / B2O3 ratio used during production is preferably between 0.9-1.5.

4. The cement clinker according to claim 1 , characterized in having a specific surface area of 3100- 3200 cm2 / gr and a compressive strength of 48-54 MPa on day 28.

5. The cement clinker, according to claim 1, characterized in having a specific surface area of 3100-3200 cm2 / gr and an average start of the setting is 175 minutes.

6. The cement clinker, according to claim 1, characterized in having a specific surface area of 3100-3200 cm2 / gr and an average end of setting is 320 minutes.

7. A cement, produced by using the clinker according to claim 1.

8. The cement according to claim 7, wherein it is Portland cement.

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