RO128292B1 - Portland cement preparation process - Google Patents

Abstract

The invention relates to a process for preparing a Portland cement. According to the invention, the process consists in grinding a raw mixture consisting of 74.43% limestone, 18.11% marl, 6.46% metaconglomerates and 1.01% pyrite ash, until reaching a fineness of 15% expressed as residue on the 90 μ m sieve, after which the ground mixture is thermally treated at a temperature of 1450°C with quick air cooling, to result in a clinker which is ground with 5% gypsum as a setting regulator, wherefrom there is obtained a Portland cement having a setting initiation of at least 60 min, a compression resistance of at least 10 MPa for 2 days and at least 42.5 MPa for 28 days.

Description

The present invention relates to a process for obtaining Portland cement by using metaconglomerates as a raw material in the crude mixture.

The main natural raw materials commonly used to obtain clinker are carbonated rocks (limestone, chalk) and silico-alumina rocks (clay, marl). To these can be added, in small quantities, different natural or artificial raw materials, for adjusting the content of Fe ₂ O ₃ from the clinker (pyrite ash, iron ore, furnace dust, etc.), SiO ₂ (sand - natural or used) or AI ₂ O ₃ (bauxite, red mud).

For the partial or total substitution of the silico-alumina component, furnace slag and ash from the power plant can be used as alternative raw materials. Worldwide, there is great concern from cement manufacturers for sustainable development of this industry and the supply of high quality products. The general tendency is to rationally use the natural and alternative resources for the production of Portland clinker and cement, given that cement is one of the indispensable materials used in the preparation of concrete used in the construction of housing and infrastructure, where large amounts of energy are consumed and raw materials.

Occasionally, during the exploitation of the limestone (the basic raw material for obtaining the Portland cement clinker) a layer of metaconglomerate may be encountered which must be removed. Separate storage of this layer implies the creation of a dump in the vicinity of the limestone quarry, occupying land surfaces and costs with the transport and handling of these metaconglomerates.

In order to make efficient use of natural resources and to protect the environment, but also to improve the quality of the clinker, the present invention proposes the use of metaconglomerates in the process of manufacturing the Portland cement clinker for silica module growth. The metaconglomerate is an ash-gray, slightly greenish rock, with a shale texture and cataclastic structure, which has fine cracks, slight limonitizations and has no magnetic properties. This rock underwent cataclastic deformation under stress conditions, observing the deformation of the component crystalloblasts in the rock, the formation of cracks and the fragmentation of the rock along the cracks, which were accompanied by recrystallization processes. The mineral components are: 40 ... 60% quartz, feldspar, 30 ... 40% biotite, desired, muscovite, 8 ... 12% lemonade, 2 ... 5% opaque minerals and 3 ... 10% calcite . The mineralogical-petrographic determinations showed that this rock is of sedimentary, psamo-psephitic origin, which has undergone a process of metamorphosis.

A process for preparing Portland cement is known from the patent document RO 95983 by grinding a mixture of limestone, granulated slag of furnace and ash of pyrite, to an appropriate fineness, homogenization of the raw flour obtained, clinking and grinding, finally, of the clinker obtained.

Patent document RU2138457 C1 describes a process for the preparation of Portland cement by mixing, in the presence of water, together with clay, the clay components, obtaining a mixture of 70 ... 90% limestone and 10 ... 30 % clay and / or ash from the power plant, which is baked until the clinker is obtained, which is then cooled and divided in the presence of specific additives, in order to obtain the desired product.

The technical problem that the invention solves is to obtain a Portland cement with superior mechanical performance than the reference cement.

The process of obtaining Portland cement by mixing the clinker with calcium sulphate dihydrate removes the mentioned disadvantages by obtaining, in a first step, the cement clinker by grinding a crude mixture, obtained from 72.90 ... 75.09% limestone, 11.43 ... 17.20% a silicoaluminous component in the form of clay or marl,

7.95 ... 12.67% metaconglomerates and 0.89 ... 1.52% pyrite ash, to a fineness expressed as a residue on the 90 pm (R _oog ) _sieve of 15 ... 20%, respectively, as a residue on the 200 µm sieve (R ₀₂ ) of maximum 2.5%, then sintered at a temperature of 145 ° C and rapid cooling in air, the clinker thus obtained, milled to a thickness of 3500 cm ² / g, mix in a proportion of 95% with an addition of a maximum of 5% socket retardant (calcium sulphate dihydrate).

RO 128292 Β1

The clinker thus obtained is characterized by the sum of the content of tricalcium silicate 1 (3CaO.SiO ₂ ) and dicalcium silicate (2CaO.SiO ₂ ) of at least 67%, with a MgO content of maximum 5% and a calcination loss of maximum 5 %. 3

The CEM I Portland cement, obtained by grinding the clinker (95% proportion) with an addition of 5% retarder (calcium sulfate dihydrate - gypsum) up to a fineness of about 3500 cm ² / g, is characterized starting from the outlet of a minimum of 60 min, stability determined with Le Chatelier rings of maximumIO mm, compressive strength 7 to 2 days of 10MPa min, and at 28 days - of minimum 42.5 MPa. The mechanical performances of the cement obtained from clichés with higher silica modulus (2.35-2.45) are superior to the reference cement 9. In addition, the increase of the silica module contributes to the drilling of a smaller amount of liquid phase, an important fact during the lifetime of the refractory lining of the 11 clinker furnace.

By using metaconglomerates in the manufacture of Portland cement clinker, a waste resulted in the discovery of limestone quarries, which also allows the growth of the M _Si silica module at 2.35-2.45, implicitly the calcium silicate content, which makes them more valuable. 15 confers superior mechanical strength to the cement. In addition, the increase of the silica module compared to the reference mixture based on limestone, silico-alumina component (type: 17 clay, marl, furnace slag, ash power plant) and pyrite ash, contributes to the formation of a smaller amount of liquid phase during sintering, with positive implications in 19 regarding the lifetime of the refractory lining of the clinker oven.

The following is an example of the application of the invention. 21

Example 1

A crude mixture, containing 74.55% limestone, 15.63% marble, 8.58% metaconglomerates 23 and 1.24% pyrite ash, characterized by degree of saturation in limestone, Sk 0.98, M _Si 2.35 and M _Ai 1.40, is ground to a fineness expressed as a residue on a 90 µm 15% sieve, and 25 is heat treated at 1450 ° C, resulting in a clinker with calcium silicate content (C ₃ S + C ₂ S) of 80%.

The chemical composition of the raw materials is shown in table 1. 27

Table 1 29

Oxidical composition of raw materials

Oxidical composition of raw materials

Raw material P.C. (%) As a (%) SiO ₂ (%) AI ₂ O ₃ (%) F © 2 ^ 3 (%) MgO (%) Na ₂ O (%) K ₂ O (%) SO ₃ (%) chalk 4312 5211 114 35 32 2.29 9 15 4 Marl 1391 1351 4728 1378 539 170 123 246 0 Metaconglomerate 1155 1021 5960 1049 340 114 181 113 15 Pyrite ash 1025 nc. nc. nc. 7996 nc. 44 25 489

By grinding the clinker obtained previously with the addition of a regulating outlet (5% gypsum) to a fineness of 3500 cm ² / g, a CEM type I cement (according to EN 197-1: 2000) is obtained, having 39 the physical-mechanical characteristics presented in table 2 Physical-mechanical testing of the cement was performed according to the standards EN 196-1,3: 2005. 41

Table 2

Physical-mechanical characteristics of the cement

Water of standard consistency (%) Take time Stability, mm Bending resistance, MPa Compressive strength, MPa beginning (minutes) end (hours-minutes) 2 days 7 days 28 days 2 days 7 days 28 days 24.2 two hundred 4-15 o, o 30 666 852 179 373 568

RO 128292 Β1

Claims (2)

3 1. Process for obtaining Portland cement by mixing clinker with calcium sulphate dihydrate, characterized in that the clinker is obtained in a first step. 5 cement by grinding a crude mixture obtained from 72.90 ... 75.09% limestone, 11.43 ... 17.20% a silicoaluminous component in the form of clay or marble, 7.95 ... 12.67 % metaconglo7 merate and 0.89 ... 1.52% pyrite ash, to a fineness expressed as a residue on the 90 pm (R _oog ) _sieve of 15 ... 20%, respectively, as a residue on the 200 sieve pm (R ₀₂ ) not more than 2.5%, 9 is then sintered at a temperature of 1450 ° C, followed by rapid cooling in the air, the clinker thus obtained, ground to a thickness of 3500 cm ² / g, is mixed 95% with 11 a maximum of 5% outlet delay (calcium sulphate dihydrate). Portland cement, obtained by the process defined in claim 1, characterized in 13 that it is made of milled clinker and gypsum, and has a minimum starting time of 60 min, stability - determined with Le Chatelier rings - of maximum 10 mm, resistance to compression at 2 days of minimum 10 MPa, and at 28 days - at least 42.5 MPa.